U.S. patent application number 12/426383 was filed with the patent office on 2009-10-08 for electronic data communication systems.
This patent application is currently assigned to KING'S LONDON COLLEGE. Invention is credited to Abdol Hamid Aghvami, Mischa Dohler, Seyed Ali Ghorashi, Fatin Said.
Application Number | 20090252200 12/426383 |
Document ID | / |
Family ID | 27256208 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090252200 |
Kind Code |
A1 |
Dohler; Mischa ; et
al. |
October 8, 2009 |
ELECTRONIC DATA COMMUNICATION SYSTEMS
Abstract
A method of transmitting data across an electronic data
communication system comprising a plurality of terminals that can
send and receive data in the form of electromagnetic waves to and
from at least one of the terminals, which method comprises the
steps of: (a) identifying at least one control terminal, at least
one target terminal and at least two relaying terminals from the
plurality of terminals; and (b) using the control terminal to
instruct the at least two relaying terminals to receive and relay
data intended for the at least one target terminal, so that the at
least one target terminal can receive data directly from at least
one terminal and from the at least two relaying terminals, thereby
increasing capacity of the system.
Inventors: |
Dohler; Mischa; (London,
GB) ; Aghvami; Abdol Hamid; (London, GB) ;
Said; Fatin; (London, GB) ; Ghorashi; Seyed Ali;
(London, GB) |
Correspondence
Address: |
BARKUME & ASSOCIATES, P.C.
20 GATEWAY LANE
MANORVILLE
NY
11949
US
|
Assignee: |
KING'S LONDON COLLEGE
London
GB
|
Family ID: |
27256208 |
Appl. No.: |
12/426383 |
Filed: |
April 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10481950 |
Dec 23, 2003 |
|
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PCT/GB02/03010 |
Jun 28, 2002 |
|
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12426383 |
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Current U.S.
Class: |
375/141 ;
375/211; 375/267; 375/E1.002; 455/7 |
Current CPC
Class: |
H04L 5/0032 20130101;
H04L 5/0037 20130101; H04L 27/2655 20130101; H04W 84/22 20130101;
H04B 7/2606 20130101; H04L 5/0048 20130101; H04L 41/0893 20130101;
H04W 52/46 20130101; H04L 5/0007 20130101 |
Class at
Publication: |
375/141 ; 455/7;
375/211; 375/267; 375/E01.002 |
International
Class: |
H04B 7/02 20060101
H04B007/02; H04B 7/14 20060101 H04B007/14; H04B 1/707 20060101
H04B001/707 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2001 |
GB |
0115799.9 |
Jun 28, 2001 |
GB |
0115804.7 |
Jun 28, 2001 |
GB |
0115807.0 |
Claims
1-73. (canceled)
74. A method of transmitting data across an electronic data
communication system comprising a plurality of terminals that can
send and receive data in the form of electromagnetic waves to and
from at least one of the terminals, which method comprises the
steps of: (a) identifying at least one control terminal, at least
one target terminal and at least one relaying terminal from the
plurality of terminals; (b) using the control terminal to instruct
the at least one relaying terminal to receive and relay data
intended for the at least one target terminal, so that the at least
one target terminal can receive data directly from at least one of
said plurality of terminals, and from the at least one relaying
terminal; and (c) applying a multiple-input multiple-output
communication technique to transfer data to the target terminal
from the at least one terminal and at least one relaying terminal
thereby increasing capacity of the system.
75. The method as claimed in claim 74, further comprising the steps
of: (d) estimating the physical position of the at least one target
terminal; and (e) assigning the at least one relaying terminal by
searching for a terminal that is within a range of the at least one
target terminal such that relaying data from that terminal is
deemed unlikely to reduce the capacity of the system.
76. The method as claimed in claim 75, said method further
comprising the steps of grouping said relaying and target terminals
together by the criteria in step (e) to form a group, and
instructing the relaying terminals in the group to relay data to
the at least one target mobile terminal in that group.
77. The method as claimed in claim 76, further comprising the steps
of controlling the relaying power of said at least one relaying
terminal so as to reduce effects of interference in the system.
78. The method as claimed in claim 77, wherein the relaying power
is controlled so that each relaying terminal has a relaying range
of between approximately 2 m and 100 m in any environment, and
preferably between approximately 10 m and 20 m.
79. The method as claimed in claim 74, further comprising the step
of instructing the at least one relaying terminal to relay said
data intended for the at least one target terminal by one of the
following methods: (1) relaying the entire part of the
electromagnetic signal received including data for other terminals;
(2) relaying only that part of the electromagnetic signal
containing data intended for the at least one target terminal; or
(3) if the data is in packet form, storing said packets in a buffer
for a predetermined time for transmission to the at least one
target terminal if requested thereby.
80. The method as claimed in claim 74, further comprising the step
of instructing the at least one relaying terminal to relay data to
at least two other relaying terminals for onward transmission to a
target terminal.
81. The method as claimed in claim 80, wherein said at least two
other relaying terminals form a group and said at least one target
terminal lies outside said group, said method further comprising
the step of instructing said group to relay data for the at least
one target terminal to another group of relaying terminals nearer
to the target terminal.
82. The method as claimed in claim 74, wherein data for each
terminal has been multiplied by a different spreading code each
having a chip rate allowing each terminal to extract its data using
a copy of the spreading code, the method further comprising the
steps of scrambling data intended for the at least one relaying
terminal with a first scrambling code and instructing the at least
one relaying terminal to de-scramble any data received under the
first scrambling code.
83. The method as claimed in claim 82, wherein there are at least
two relaying terminals forming a group, the method further
comprising the step of instructing each relaying terminal in the
group to relay data for the at least one target terminal so that
the path difference of each signal from each relaying terminal
and/or control terminal at the at least one target terminal is out
of synchronisation by an amount greater than the duration of one
chip of the spreading code of the target terminal.
84. The method as claimed in claim 83, wherein said synchronisation
is imposed by the data communication system, by natural delay or by
organising each group of relaying terminals within a range of at
least one other terminal such that data relayed from that terminal
does not reduce the capacity of the system
85. The method as claimed in claim 82, wherein there are at least
two relaying terminals forming a group, the method further
comprising the step of instructing each relaying terminal in the
group to relay data for the at least one target terminal so that
the path difference of each signal from each relaying mobile
terminal at the at least one target terminal is in synchronisation
by an amount less than the duration of one chip of the spreading
code of the target terminal.
86. The method as claimed in claim 85, wherein said at least one
target terminal lies within said group, said method further
comprising the step of instructing said group to relay data for the
at least one target terminal to said at least one target
terminal.
87. The method as claimed in claim 84, wherein said synchronisation
is imposed by the data communication system, by natural delay or by
organising each group of relaying terminals within a range of at
least one other terminal such that data relayed from that terminal
does not reduce the capacity of the system.
88. The method as claimed in claim 82, further comprising the steps
of identifying a first group of relaying terminals that lie within
chip range of one another whereby the path difference of each
signal from each relaying terminal at each other relaying terminal
is in synchronisation by an amount less than or equal to the
duration of one chip of each spreading code, and identifying a
second group of relaying terminals that lie within chip range of
one another whereby the path difference of each signal from each
relaying terminal at each other relaying terminal is in
synchronisation by an amount less than or equal to the duration of
one chip of each spreading code, said first and second groups being
organised so that they are out of chip range of one another.
89. The method as claimed in claim 74, the method further
comprising the steps of instructing the data for each terminal to
be transmitted during a first time slot, and instructing the at
least one relaying terminal to relay data for the at least one
target terminal in a second time slot different to said first.
90. The method as claimed in claim 82, further comprising the steps
of instructing the at least one relaying terminal to de-spread the
data for the at least one target terminal and to relay that data
thereto.
91. The method as claimed in claim 74, further comprising the steps
of instructing the at least one relaying terminal to relay data to
the at least one target terminal during a number of time slots
and/or over at least two sub-carrier frequencies, each of which are
orthogonal to one another, and to utilise said at least two
sub-carrier frequencies in a frequency band different to that over
which the data was transmitted to the at least one relaying
terminal.
92. The method as claimed in claim 82, further comprising the steps
of instructing the at least one relaying terminal to relay data to
the at least one target terminal according to the relaying step of
claim 92.
93. The method as claimed in claim 74, wherein data intended for
the target terminal is encoded with space-time codes and
transmitted from a plurality of antenna elements, the method
further comprising the step of using the different signals from the
at least one relaying terminal and from the plurality of antenna
elements to take advantage of the space-time coding, the at least
one relaying terminal effectively acting as an antenna element for
the target terminal, such that a communication channel between the
plurality of antenna elements and the target terminal is similar to
a multiple input multiple output channel.
94. The method as claimed in claim 93, wherein the plurality of
antennae comprises a plurality of separate and distinct terminals,
each having an antenna element.
95. The method as claimed in claim 74, further comprising the step
of instructing the at least one relaying terminal to relay data
intended for the at least one target terminal using wire, power
line communication or another transmission standard for example
Bluetooth, infrared, ultra wideband or HiperLAN2.
96. An apparatus for transmitting electromagnetic waves comprising
a transmitter, means for controlling emission of electromagnetic
waves therefrom for wireless communication with at least one
terminal, said means for controlling being able to issue
instructions to said at least one terminal remote from said
transmitter for performing the method as claimed in claim 74 to
increase capacity of said wireless communication.
97. The apparatus as claimed in claim 96, said means for
controlling transmission of said instructions to a terminal for
storage thereon so that it can operate the method on request of the
means for controlling.
98. The apparatus as claimed in claim 96, wherein the apparatus is
a base station controller, a radio network controller, a central
controller or a portable terminal such as a mobile telephone, a
portable computer or a personal digital assistant in a
telecommunication system.
99. The apparatus as claimed in claim 96, wherein there is a
plurality of said apparatus that can communicate with the at least
one relaying terminal.
100. A computer readable storage medium comprising a computer
program comprising computer executable instructions for carrying
out a method as claimed in claim 74.
101. A subscriber identity module card comprising a computer
readable storage medium storing computer readable instructions for
performing the method as claimed in claim 74.
Description
FIELD OF THE FIRST INVENTION
[0001] The present invention relates to a method, computer program
and apparatus for improving the capacity of an electronic data
communication system. There is also provided a terminal that can be
operated in accordance with the method, and a subscriber identity
module card provided with computer executable instructions for
carrying out the method.
BACKGROUND TO THE INVENTION
[0002] Portable electronic devices having the ability to
communicate with external networks have become increasingly popular
and relatively inexpensive in recent years. Examples of such
devices are mobile telephones, notebook computers, pagers and
personal digital assistants. Such devices often have the capability
of sending and/or receiving data over a wireless link that enables
the user to exchange information with other users and/or networks
whilst the user remains relatively free to move around. The data
can be voice data, text and numerical data, for example, which have
been put into digital format. This allows the user to hold
telephone conversations, access the Internet and/or private
computer networks for example. Due to their portability, notebook
computers are frequently brought to meetings, conferences and
hotels for example, where increasingly the opportunity of accessing
a local network or the Internet is given to the user. Such a
situation generates a "hot-spot" where a number of users that are
physically close to one another (typically 5 m to 200 m) require
delivery of data across a wireless link. The nature of conferences
and meetings means that the users very frequently demand data a
substantially the same time.
[0003] Frequently, the wireless link is between a base station
transceiver and a mobile transceiver, both capable of sending and
receiving data via the electromagnetic spectrum. The ultra-high
frequency (UHF) part of the electromagnetic spectrum is most
frequently used for this kind of data transmission, which has a
wavelength in the range of approximately 1 m to 0.1 m (and
frequency of 300 MHz to 3000 MHz), although higher bands (microwave
and infrared) can be used for example 17 GHz and 60 GHz. The
International Telecommunication Union (ITU), which manages the
international allocation of radio spectrum, allocated the bands
890-915 MHz for the uplink (mobile station to base station) and
935-960 MHz for the downlink (base station to mobile station) for
mobile telecommunications networks in Europe. The base station is
usually mounted high on a stationary object such as a building
where it can broadcast a signal for the surrounding area. The
demand by users for smaller portable electronic devices as
described above means that the base station usually comprises a
much larger transceiver, whereas the mobile transceiver is much
smaller.
[0004] There are many difficulties associated with successfully
transmitting and receiving data to users over a wireless link. One
problem is that of "multipath". Radio waves emitted from a base
station and from a mobile terminal are repeatedly reflected and
scattered on their way to the mobile terminal or base station. Thus
when they reach the destination the waves will interfere either
constructively or destructively, resulting in a signal that can be
heavily attenuated. When the mobile terminal starts to move, the
received signal begins to vary rapidly with time causing an effect
known as "fast fading". If the mobile terminal stops or is
positioned in a fade the signal can be of extremely poor quality,
known as "slow fading". This problem can be particularly acute with
laptops and notebooks placed randomly by the user. Multipath
dominates over a scale of approximately one wavelength to one half
a wavelength. A relatively simple solution is to construct a series
of antennae, for example two, each spaced more than this distance
apart. Thus, if one antenna receives a signal in a fade, there is a
good chance that the signal at the other antenna will not be in a
fade. The signals from each antenna can be combined to provide a
better output signal. Spacing antennae in this manner is known as
using "diversity" to improve signal quality. In the example
described the base station usually has antennae arranged in this
manner to achieve "receive" diversity since it receives the signal
from the mobile terminal (also known as "uplink"). If the base
station uses physically separate antennae to transmit to a mobile
terminal this is known as "transmit diversity". A useful example of
a method for achieving transmit diversity has been devised by S.
Alamouti and is discussed in his paper "A Simple Transmit Diversity
Technique for Wireless Communications" IEEE Journal on Select Areas
in Communications, Vol. 16, No. 8, October 1998.
[0005] Achieving receive diversity at the mobile terminal by
spatial separation of antennae is difficult as, particularly with
mobile telephones, there is not sufficient room to space them by
the required range of one wavelength to one half wavelength.
Furthermore, this would add cost to the mobile terminal that would
not be welcomed by users.
[0006] More recently, with the increase in the popularity of mobile
electronic communications devices and the demand for higher
bandwidths in terms of data transfer, the scarcity of the spectrum
has become a problem. In many countries including USA, Japan and
the members of the European Community, the UHF part of the spectrum
is allocated by governments for data transmission of this nature.
That allocated portion is then further divided into smaller
portions and distributed amongst telecommunication suppliers, very
frequently to the highest bidder. Thus each supplier must try to
obtain the greatest efficiency from their part of the spectrum that
is possible, and a wide variety of complicated algorithms have been
developed to do this. A further problem is that an increasing
number of users results in a greater amount of interference that
must also be overcome technically. Thus it is apparent that there
is a need for increased capacity on wireless communications
networks in terms transferring greater amounts of data over the
available frequency bandwidth, improving signal quality at the
receiver and accommodating a larger number of users at any one time
on a network having a wireless link.
[0007] In attempting to achieve greater efficiency from the
electromagnetic spectrum there are two main parameters available to
the designer: frequency and time. Referring to FIG. 1 the spectrum
can be divided by frequency so that each user sends and receives
data with a given frequency band all of the time. Such schemes are
known as Frequency Division Multiple Access (FDMA) and allow
multiple users to use the same base station simultaneously.
Alternatively each user is allocated a specific time window or
"slot" in which to send or receive data over the entire available
frequency band, also shown in FIG. 1. This scheme is known as Time
Division Multiple Access (TDMA) and also allows multiple users to
use the same base station, effectively simultaneously as far as the
user can perceive. Another possibility is to permit all users to
use the entire available frequency band all of the time. However,
the data of each user is multiplied with a spreading code to ensure
that each user receives only the data intended for them. This
scheme is know as Code Division Multiple Access and is also shown
in FIG. 1. The spreading code is designed to provide uniqueness to
enable identification of the data by the mobile terminal. One
example of the code used in a CDMA scheme is Gold code. The exact
code that is used depends upon the intended function. For example
Walsh and Gold codes can be used to enable a mobile terminal to
locate and synchronise with the correct data, whereas orthogonal
variable spreading factor codes are intended to ensure that each
user's allocated channel is kept separate and distinct. The code
"spreads" the data over larger frequency bandwidth enabling power
per unit frequency (W/Hz) to be reduced, achieving the same
bandwidth in bits per second whilst lowering interference.
[0008] One area where the aforementioned problems have been
extensively addressed is in the mobile telecommunications industry.
The mobile telecommunications industry started major expansion in
the early 1980s, although mobile telecommunications were
investigated before that. Generally the development of the system
has been in "generations" (G) that can be summarised as follows:
[0009] 1G networks (e.g. Nordic Mobile Telephony (NMT), Advanced
Mobile Phone System (AMPS), TACS) are considered to be the first
analogue cellular systems, which started early 1980s. [0010] 2G
networks (e.g. Global System for Mobile Communications (GSM)),
cdmaOne based on the EIA Interim Stand 95 (IS-95), Digital Advanced
Mobile Phone System (DAMPS)) are the first digital cellular systems
launched early 1990s. [0011] 2.5G networks (e.g. General Packet
Radio Service (GPRS), cdma2000 based on the EIA Interim Standard
2000 that provides an evolutionary path to 3G) are the enhanced
versions of 2G networks with data rates up to about 144 kbit/s.
[0012] 3G networks (e.g. Universal Mobile Telecommunications
Service (UMTS) Frequency Division Duplex (FDD) and Time Division
Duplex (TDD), cdma2000 1.times.EVDO, cdma2000 3.times., Time
Division Space Code Multiple Access (TD-SCDMA), Association of
Radio Industries and Business (Japan) (ARIB) Wideband CDMA (WCDMA),
Enhanced Data for Global Evolution (EDGE), International Mobile
Telecommunication 2000 (IMT-2000), Digital European Cordless
Telecommunications (DECT)) are the latest cellular networks that
have data rates 384 kbit/s and more. [0013] 4G is predominantly
conceptual at the moment. Some basic 4G research is being done, but
no frequencies have been allocated. The Fourth Generation could be
ready for implementation around 2012.
[0014] For example, UMTS is a third generation (3G)
telecommunications system based on wideband CDMA direct sequence
(W-CDMA DS). W-CDMA is similar to CDMA except that the data is
spread over a larger frequency bandwidth. FIG. 2 shows examples of
the types of code in W-CDMA and their function.
[0015] The solution reached for dealing with a large number of
users wanting to use a comparatively small part of the available
spectrum has been to geographically divide a network into cells. In
this way, by keeping the emitted power of base stations and mobile
terminals low, together with use of coding schemes as mentioned
above, it is possible to distribute frequencies amongst cells so
that the same combination of frequencies can re-used in the
network, providing those cells are sufficiently distant. It also
permits the terminals carried by the user to be made smaller.
However, the demand for increased data transfer rates and improved
signal quality still persist.
[0016] Another more recent technique that has achieved an increase
in capacity utilises multiple-input multiple-output transmission
techniques (MIMO) in which a multi antenna transmitter sends data
to a multi-element receiver. The signal at each receive antenna is
different due to the effects of multipath as described above, from
which the original signal can be re-assembled. Coding and sending
the signal spaced in time has been found to be particularly
beneficial in achieving increased capacity in MIMO channels. Thus
space, time and coding are used to enhance system capacity which is
known as "space-time coding". As the name suggests space-time
encoding involves splitting the signal and transmitting it over a
number of antennae that are spatially separate and by sending the
signal from each antenna at a different time. This achieves a
double diversity effect. One piece of software that has achieved
good results was designed by Bell Labs and is known is Bell Labs
Layered Space-Time code (BLAST--see
www.bell-labs.com/project/blast) that uses space-time coding to
encode data at the transmitter and re-assemble data at the
receiver. However, MIMO techniques rely upon there being
multi-element antennae at the receiver that is not practical for
many applications, such as mobile phones and PDAs where the space
is not normally available to accommodate a number of antenna
elements the required distance apart.
[0017] One solution that has been proposed is to provide the mobile
terminal with one active antenna and several tuneable passive
antennae that together form an array
(www.signal.uu.se/Publications/pdf/c0114.pdf). This system is known
as switched parasitic antennae (SPA). Although the results of the
computer simulation were encouraging in terms of replicating full
MIMO capacity, the applicant believes that the difficulty of
implementing SPA in practice, bearing in mind the likely tuning
difficulties due to interaction between the antennae, the mobile
terminal and the user, will make costs prohibitive. Furthermore,
the fact that several antennae are still necessary in SPA inhibits
the mobile terminal from being made smaller.
SUMMARY OF THE FIRST INVENTION
[0018] It is apparent that there is a need for improved method and
apparatus that can increase the capacity of an electronic data
communication system, particularly in the downlink direction where
data bandwidths are high. Terminals in such systems can be nomadic
where terminals can move but generally only communicate whilst
stationary, ad-hoc where the number of terminals fluctuates with
time (i.e. temporary) networks are formed, or fixed. Such apparatus
should also be able to take advantage of space-time codes used over
a MIMO or MIMO-like channel, but which does not necessarily
increase the size and weight of mobile or remote terminals.
[0019] There is also a need for a method and apparatus that can
reduce the effects of terminals in bad channel conditions, and
particularly when those terminals are unlikely to move from that
position for some time.
[0020] The present invention is based on an insight that the
capacity of an electronic data communication system as
aforementioned can be enhanced by using the mobile or remote
terminals served by one or more control terminals to provide a
relaying function of data to other terminals. The terminals that
perform relaying are known as "relaying terminals" and the
terminals that are the recipients of the relayed data are known as
"target terminals". In some embodiments a terminal can be both a
relaying and target terminal simultaneously. Preferably the
relaying terminals can be grouped together into groups known as
"virtual antenna arrays". The groups are organised so that there is
little or no additional interference in the system. There can be
one or more control terminal comprising a mobile terminal (e.g.
mobile telephone, portable computer), a base station controller or
a radio network controller for example. The invention is
particularly advantageous for use in ad-hoc networks where the
control terminal is a portable device to which appropriate
instructions can be downloaded on request or pre-stored
thereon.
[0021] The present invention is also based on the insight that the
benefits of MIMO channels can be obtained without requiring more
than one antenna in the target terminal.
[0022] According to the present invention there is provided a
method of transmitting data across an electronic data communication
system comprising a plurality of terminals that can send and
receive data in the form of electromagnetic waves to and from at
least one of the terminals, which method comprises the steps
of:
[0023] (a) identifying at least one control terminal, at least one
target terminal and at least two relaying terminals from the
plurality of terminals; and
[0024] (b) using the control terminal to instruct the at least two
relaying terminals to receive and relay data intended for the at
least one target terminal, so that the at least one target terminal
can receive data directly from at least one terminal and from the
at least two relaying terminals, thereby increasing capacity of the
system. In one embodiment data is relayed via the at least two
relaying terminals substantially simultaneously, thereby providing
at least two paths for data to reach the target terminal via the
relaying terminals.
[0025] The present invention is set out in more detail in the
appended claims to which attention is hereby directed.
[0026] The following communications standards currently available
or under investigation and standardisation are applicable to this
invention: Global System for Mobile Communications (GSM) and
derivatives of it (GPRS, EDGE, 3GSM), Universal Mobile
Telecommunications Standard (UMTS), Code Division Multiple Access
2000 (CDMA2000), IEEE802.11, High Performance Local Area Network
Type 2 (HiperLAN2), Bluetooth (BT), Power Line Communications
(PLC), Ultra Wide Band (UWB), Infrared Communications and any
future systems based on either of the following access schemes:
Code Division Multiple Access (CDMA), Time Division Multiple Access
(TDMA), Frequency Division Multiple Access (FDMA) or Orthogonal
Frequency Division Multiple Access (OFDMA).
[0027] In one embodiment, the main link interface from the control
terminal to the mobile terminals is based on either of the
following access schemes: W-CDMA (UMTS, CDMA2000), TDMA/FDMA (GSM
& derivatives) or TDMA/OFDMA (IEEE802.11, HiperLAN2). The
relaying link from the relaying mobile terminals to the target
mobile terminals is preferably based on either of the following
access schemes: W-CDMA (UMTS, CDMA2000, UWB), TDMA/FDMA (GSM &
derivatives, Bluetooth) or TDMA/OFDMA (IEEE802.11, HiperLAN2,
PLC).
[0028] According to another aspect of the first invention there is
provided a system for transmitting and receiving electromagnetic
signals in which there is at least one base station comprised of at
least one antenna element, which sends out signals to a group of
target receivers or terminals, each receiver or terminal within
this group of target receivers or terminal receives the signal
stream, extracts its own dedicated signal and, after possible
processing, relays the signals dedicated to the other users within
the group.
[0029] Preferably, the process of relaying is accomplished by
retransmission through a wireless, wired, infrared or UWB
interface.
[0030] Advantageously, in which each receiver can act as a virtual
transmitter or a virtual receiver for at least one other receiver
in the group.
[0031] Preferably, the distinction between a virtual transmitter
and virtual receiver is achieved through appropriate orthogonality
of physical channels between the main link between base station and
target group and the relaying links between the terminals within
the target group.
[0032] Advantageously, the system is a CDMA based system and
orthogonality is achieved through delay, codes or frequency.
[0033] Preferably, the data stream for the users is spread with a
distinct spreading code with given chip-rate for each user, each of
the users receives the incoming data streams, from the other users
optionally processes at least some of the data streams and relays
the possibly processed data streams to the remaining users within
the group of users and each of the users then finally processes the
signal streams.
[0034] Advantageously, if user in is addressed then n users form
the virtual transmitting array and m-1=u-n-1 users the virtual
receiving array where u-1 is the number of data streams processed,
the virtual transmitting array of n users is formed through
synchronous transmission within chip-length and the virtual
receiving array of m-1 users is formed through retransmission out
of chip-length.
[0035] Preferably, the retransmission out of chip length is
achieved through network imposed or natural delay.
[0036] Advantageously the required synchronisation for the virtual
transmitting array is achieved through external network
synchronisation.
[0037] Preferably, the required synchronisation for the virtual
transmitting array is achieved by letting spatially close mobile
terminals form the virtual transmitting array.
[0038] Advantageously, retransmission without interrupting the
ongoing transmission between base station and mobile terminal is
accomplished by introducing a third oscillator for the relaying
transmission in a separate frequency band.
[0039] Preferably, retransmission without interrupting the ongoing
transmission between base station and mobile terminal is
accomplished, in case of rather static terminals, by cutting the
uplink and reprogramming the uplink oscillator onto the relaying
frequency band.
[0040] Advantageously, the information of u users is first spread
by u distinct spreading codes and then by one scrambling code, the
scrambling code being unique for the group of u users and differs
from other used scrambling codes within the same geographical
area.
[0041] Preferably, there are groups of users formed of individual
users, which are close together so they act as a group and act as
transparent relays to send to the signal to the target receiver,
the users in each group being in chip-range so they act as a
one-signal receiver, each group being out of chip-range to the
other groups and so each group is distinguishable from the other
groups and so the signal from each group can be considered as one
signal received by one finger of the Rake receiver, depending on
the number of Rake fingers in the target receiver, the target
receiver detects the strongest signals, combines them and retrieves
the initial symbols.
[0042] Advantageously, the system is a TDMA base system and
orthogonality is achieved through frequency and appropriate time
slot scheduling.
[0043] Preferably, the data stream for u users is sent through
burst within u dedicated time slots at the same frequency band
f.sub.1, each of the u users receives all u data bursts and each
user i retransmits the other users' ji received bursts at the
appropriate time-slot for each user j at another frequency f.sub.2
and at its own time slot, each user i receives the u-1
retransmitted bursts at frequency f.sub.2.
[0044] Advantageously, retransmission without interrupting the
ongoing transmission between base station and mobile terminal is
accomplished by introducing a third oscillator for the relaying
transmission in a separate frequency band.
[0045] Preferably, retransmission without interrupting the ongoing
transmission between base station and mobile terminal is
accomplished, in case of rather static terminals, by cutting the
uplink and reprogramming the uplink oscillator onto the relaying
frequency band.
[0046] Advantageously, the relaying frequency f.sub.2 is reserved
by the network.
[0047] Preferably, (n,m) space-time codes are applied for future
software defined ratios and the bursts for u users are transmitted
simultaneously at u different frequency bands.
[0048] Advantageously, the system is an OFDMA based system and
orthogonality is achieved through frequency, sub-carrier frequency
and appropriate time slot scheduling.
[0049] Preferably, the data stream for u users is sent through
burst within u dedicated time slots at the same frequency band
f.sub.1, each of the u users receives all u data bursts and each
user i retransmits the other users' u.noteq.i received bursts at
the appropriate time-slot for each user u.noteq.i at another
frequency f.sub.2 and at its own time slot each user i receives the
u-1 retransmitted bursts at frequency f.sub.2.
[0050] Advantageously, retransmission without interrupting the
ongoing transmission between base station and mobile terminal is
accomplished by introducing a third oscillator for the relaying
transmission in a separate frequency band.
[0051] Preferably, retransmission without interrupting the ongoing
transmission between base station and mobile terminal is
accomplished, in case of rather static terminals, by cutting the
uplink and reprogramming the uplink oscillator onto the relaying
frequency band.
[0052] Advantageously, the relaying frequency f.sub.2 is reserved
by the network.
[0053] Preferably, (n,m) space-time codes are applied for future
software defined radios and the bursts for u users are transmitted
simultaneously at u different frequency bands.
[0054] Advantageously, each transceiver is a mobile terminal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] For a better understanding of the present invention
reference will now be made by way of example to the accompanying
drawings in which:
[0056] FIG. 1 shows schematically the schemes of FDMA, TDMA and
CDMA used in wireless communication;
[0057] FIG. 2 is a table showing, by way of example, the codes that
can be used in a W-CDMA access scheme;
[0058] FIG. 3 is a schematic view of part of a first embodiment of
a data communication system in accordance with the present
invention in which two virtual antenna arrays have been defined,
shown employed in a downlink mode of operation;
[0059] FIG. 3A is a schematic view of a RAKE receiver used in a
mobile terminal;
[0060] FIG. 4 is a schematic view of part of a second embodiment of
a data communication system in accordance with the present
invention in which two virtual antenna arrays have been defined,
shown employed in a downlink and uplink mode of operation;
[0061] FIG. 5 is a flowchart showing the stages of set-up of a
virtual antenna array as used in a in accordance with the present
invention;
[0062] FIG. 6 is a flowchart showing the stages of operation of a
data communication system in accordance with the present invention
based on a CDMA access scheme;
[0063] FIG. 7 is a flowchart showing the stages of operation of a
data communication system in accordance with the present invention
based on a TDMA and/or OFDMA access scheme;
[0064] FIG. 8 is a schematic view of part of a third embodiment of
a data communication system in accordance with the present
invention in which one virtual antenna array has been defined,
shown employed in a downlink mode of operation;
[0065] FIG. 9 is a schematic view of part of a fourth embodiment of
a data communication system in accordance with the present
invention in which one virtual antenna array has been defined,
shown employed in a receiving mode of operation;
[0066] FIG. 10 is a schematic view of part of a fifth embodiment of
a data communication system in accordance with the present
invention in which two virtual antenna arrays have been defined,
the first employed in a transmitting mode of operation and the
second employed in a receiving mode of operation;
[0067] FIG. 11 is a schematic view of a sixth embodiment of a data
communication system in accordance with the present invention
showing a plurality of virtual antenna arrays employed therein;
[0068] FIG. 12 is a schematic view of a part of a seventh
embodiment of a data communication system in accordance with the
present invention;
[0069] FIG. 13 is a schematic view of part of a eighth embodiment
of a data communication system in accordance with the present
invention;
[0070] FIG. 14 is a schematic view of a ninth embodiment of a data
communication system in accordance with the present invention;
[0071] FIG. 15 is a graphical representation of bit error rate
(y-axis) against signal to noise ratio (x-axis) for the data
communication system of FIG. 11;
[0072] FIG. 16 is a schematic view of a tenth embodiment of a data
communication system in accordance with the present invention;
[0073] FIG. 17 is a graphical representation of the bit error rate
(y-axis) against the number of users in the virtual antenna arrays
of FIG. 13;
[0074] FIG. 18 is a schematic illustration of an eleventh
embodiment of a data communication system in accordance with the
present invention, utilising two frequencies and two scrambling
codes;
[0075] FIG. 19 is a graphical representation of bit error rate
(y-axis) against signal to noise ratio (x-axis) for the system of
FIG. 15;
[0076] FIG. 20 is a schematic illustration of a twelfth embodiment
of a data communication system in accordance with the present
invention;
[0077] FIG. 21 is a schematic view of a thirteenth embodiment of a
data communication system in accordance with the present invention
that is based on a TDMA access scheme;
[0078] FIG. 22 is a graphical representation of blocking rate
(y-axis) against number of users (x-axis) for a W-CDMA data
communication system in accordance with the present invention and
for such a system in which virtual antenna arrays have not been
used; and
[0079] FIG. 23 is a graphical representation of the ratio of number
of users being served to total number of users demanding service
(y-axis) against total number of users (x-axis) for a data
communication system in accordance with the present invention and
for such a system in which virtual antenna arrays have not been
used;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0080] Referring to FIG. 3 a first embodiment of a data
communication system is generally identified by reference numeral
10 that comprises a control terminal 11 having m antenna elements
12. The control terminal may be a base station for example. The
control terminal 11 is part of a larger network of control
terminals (not shown) through which data can be passed. The control
terminals serve to divide an area into a number of cells (not
shown), as described in the introduction above, permitting inter
alia frequency re-use between the cells. There are
n.sub.1+n.sub.2+n.sub.v mobile terminals 13 in the cell served by
control terminal 11. Referring to FIG. 3A each mobile terminal 13
comprises a RAKE receiver 14a having a plurality of antenna
elements 15a, each of which acts as a "finger" that can lock on to
uncorrelated copies of the signal created by multipath. The first
finger locks on to the strongest signal, the second finger the next
strongest and so on. The signal from each finger can be combined by
the diversity combiner 16a to improve signal quality, effectively
taking advantage of time diversity to do this. Very frequently the
first component is a line-of-sight part of the transmitted power
and the remaining components are those caused by multipath.
However, it is not important that the terminals have RAKE receivers
as a single antenna in each terminal will suffice. The remaining
components are normally very much more attenuated than the
line-of-sight component. Each mobile terminal is free to move in
the cell.
[0081] Electronic digital data 14 is sent from higher layers of the
network to the control terminal intended for those mobile terminals
13 in the cell that are demanding data. Other mobile terminals 13
are inactive or active in terms of receiving data. The data 14 is
in the form of digital (binary) data that can carry a wide variety
of information, for example text, voice and images. At the control
terminal 11 the digital data must be modulated onto an
electromagnetic wave carrier in order to convey the data wirelessly
from the control terminal 11 to the mobile terminals 13. There are
various schemes that do this so as to allow multiple users to send
and receive data simultaneously from the control terminal 11. These
schemes will be described in the context of the invention in
greater detail below.
[0082] The control terminal 11 sends the data 14 for the mobile
terminals 13 from the antenna elements 12 ("downlink"). Each mobile
terminal 13 receives the signal from the control terminal and
extracts its own data. The control terminal 11 monitors the
capacity of the network serving the mobile terminals 13. The
measurement of capacity can include any of the following: the
availability of power, codes, time slots, frequency bands or
frequency sub-carriers to either the control terminal 11 or any of
the mobile terminals 13. When the control terminal determines that
the network has breached a threshold in terms of the availability
of any of theses resources it performs the set up of a group or
groups of r-MTs 13 that relay some or all of the data stream that
they receive with the aim of improving capacity. These groups are
referred to herein as Virtual Antenna Arrays. Such a situation may
arise for example when a large number of users attempt to access
the network in a short space of time, if a few users place large
data bandwidth demands on the network, if users demand a higher
Quality of Service (QoS) (meaning that a better signal quality is
required) or if interference conditions change as a result of
fluctuation in propagation characteristics of the wireless path
between control terminal 11 and mobile terminals 13. The detailed
steps of formation of the virtual antenna arrays will be described
in greater detail hereafter.
[0083] Virtual antenna arrays 15, 16 and 17 (hereinafter VAAs) are
formed under control of the control terminal 11. Within the virtual
antenna array 17 there is a target mobile terminal 18 (hereinafter
"t-MT"). The t-MT 18 may be a mobile terminal that is in an area of
poor reception, may require a higher data bandwidth etc. There may
be more than one t-MT in the VAA 17 or the VAAs 15 and 16. The t-MT
18 may be surrounded by a number of active or inactive mobile
terminals 13; inactive mobile terminals are not sending or
receiving data themselves but are nonetheless in an "on" state.
Data 14 is now received from the network and is encoded in an
encoder 19a. Details of the appropriate coding are given below. The
data 14 is sent from the antenna elements 12 of the control
terminal. In the embodiment shown there are now a much greater
number of paths by which the data can reach the t-MT 18. For
example, the data can be received directly by the t-MT 18 via the
path 19. Secondly, data can pass from the control terminal to the
VAA 15 via path 19'. On being received by each of the n.sub.1
mobile terminals 13, the data is relayed on to the VAA 16 via path
19''. The method of relaying will be described in greater detail
hereafter. In the VAA 16 each of the n.sub.2 mobile terminals
receives the relayed signal from VAA 15 and directly from the
control terminal 11. These signals are relayed on to the next VAA
(not shown) and the process is repeated until the signals reach the
vth VAA 17 via path 19''' whereat data for the t-MT 18 is relayed
by the n.sub.v-1 mobile terminals in that VAA. The t-MT 18 also
receives data directly from some of the other VAA provided that
they are spatially close enough. Once at the t-MT 18 the data can
be decoded by decoder 19' to retrieve the data 14.
[0084] In this way the quality of the signal at the t-MT 18 is
greatly improved since there are a large number of signals reaching
the fingers of the RAKE receiver in the t-MT 18 i.e. the signal is
relayed by a number of terminals substantially simultaneously to
the t-MT. Furthermore, due to the relaying process in the VAA 15,
16 and 17 the signals will be uncorrelated so as to combat the
effects of any signal that might be in a fade. This is particularly
important where the channel is slow fading for example where a
portable computer (e.g. laptop, notebook) has been positioned in a
fade, but is unlikely to move from that fade for sometime. The same
problem also exists in fast fading channels, for example where a
mobile telephone passes in and out of fades comparatively quickly
if the user is walking or driving. This method reduces the effect
of both types of fading and improves the bit error rate on the
channel for the same signal to noise ratio, allowing the data
bandwidth of the channel and QoS to be increased and thereby
improving network capacity.
[0085] Referring to FIG. 4 a second embodiment of a data
communication system is generally identified by reference numeral
20 that is similar to the data communication system 10 with like
numerals indicating like parts. The main difference between the two
embodiments is that the data communications system 20 operates in
both a downlink and an uplink (mobile terminal to control terminal)
mode. One advantage of this is that the power of the t-MT 28 can be
reduced leading to less interference in the cell. Another advantage
is that whilst the t-MT 28 might be in a fade with respect to the
control terminal 21, it is unlikely to be in a fade with respect to
the other mobile terminals 13 in the VAAs 25, 26 and 27 such that
it can both send and receive data at an improved bit error rate to
and from the control terminal 21.
[0086] Referring to FIG. 5 a flowchart showing the main functional
requirements of the algorithms required to run a data communication
system in the manner described above is generally identified by
reference numeral 30. The data communication system is controlled
by a central controller (CC) that can be a radio network controller
(RNC), a control terminal or a "master" mobile terminal for
example. At step 31 the CC is determined for the system. At step 32
the CC obtains information from the mobile terminals in the cell,
for example VAA membership settings, relaying capability, awareness
of other mobile terminals, location (obtained by a Global
Positioning System for example). At step 33 data transfer takes
place across the system in the usual fashion under one or a
combination of access schemes. At step 34 the CC monitors the
network capacity. If capacity is not running low the algorithm
returns to step 33 and data transfer continues normally. If
however, the capacity of the network is or has been degraded due to
changing interference conditions for example, then the algorithm
proceeds to step 35 where a VAA is set up. The rules by which a VAA
should be set up are as follows. A VAA shall be formed if (1) the
network capacity is already saturated or if mobile terminal's data
request would saturate the network capacity; (2) all potential VAA
users have agreed to participate in a VAA when so requested by the
CC; (3) the additional interference produced does not deteriorate
communication of other mobile terminals in the network or does not
increase the overall system interference above a given threshold
such that the total system capacity decreases.
[0087] At step 36 the CC designates the mobile terminal that will
be the first member of the VAA. This is done by determining the
mobile terminal with the maximum capacity in terms of the
aforementioned resources and which is spatially close to the target
mobile(s). A mobile terminal can be utilised in a VAA if (1) its
agreement has been obtained to participate in a VAA; (2) the mobile
terminal would benefit from the induced capacity increase; (3) (if
applicable) the existing VAA would obtain an increase in capacity;
and/or (4) the entire network would receive an increase in
capacity.
[0088] Whether a mobile terminal has given its agreement to join a
VAA if so requested can be done as follows. (1) a mobile terminal
agrees to form or be part of a VAA without any prior notification
and under any conditions; (2) a mobile terminal agrees to form or
be part of a VAA only with appropriate confirmation of the owner
(request required); (3) a mobile terminal agrees to form or be part
of a VAA only if it would gain any capacity benefits in form of
better QoS or higher data rates; (4) a mobile terminal agrees to
form or be part of a VAA only if the other VAA members belong to a
set of prior defined mobile terminals and (5) a mobile terminal
agrees to form or be part of a VAA under any conditions, but
automatically releases from a VAA group when a predefined set of
conditions are violated.
[0089] Target mobile(s) are defined as those terminals can be any
terminal(s) that wishes to send or receive data over the network. A
second mobile terminal is then assigned to the VAA and the CC
informs the two mobiles about the conditions of relay for example
what power, frequency and/or codes are to be used, and the
mechanism of synchronisation if applicable. The assigning of the
second mobile can either be done by the CC or under control of the
CC by the first mobile terminal. Together the first and second
mobile terminals of the VAA begin to relay the necessary signal to
the target mobile(s) at stage 36 whilst the normal wireless
communication continues for the rest of the system. At stage 37 the
CC monitors the result of implementation of a VAA in the network to
determine whether capacity has been increased or reduced as a
result. If the capacity remains the same or improves the system
keeps running with the VAA deployed. If the capacity worsens then
the VAA is dissolved and the algorithm returns to step 35 forming
another VAA using different mobile terminals. If the capacity is
enhanced by formation of the first VAA, but has not reached the
increase required by the CC, then the CC determines at step 38
whether the addition of a further mobile terminal to the VAA would
increase capacity of the system. If yes a further mobile terminal
is added to the VAA and the algorithm returns to step 36 and steps
36 to 38 are repeated in a loop. If no, the central controller
determines whether the formation of a separate VAA would be of
benefit in terms of capacity. If yes, the algorithm returns to step
35, whereas if no the algorithm returns to step 36.
[0090] It is important that the mobile terminals in a VAA remain
synchronised with one another. The synchronisation control can be
done by the CC, a RNC or a master mobile terminal in the VAA. This
can be accomplished in accordance with the method described in
below in connection with the second invention. The method of the
third invention described below is also applicable to this first
invention.
[0091] At some point it will become necessary to dissolve a VAA,
all VAAs or release one or mobile terminals from any number of
VAAs. The central controller monitors the condition of each mobile
terminal. If a mobile terminal indicates that its battery is
running low then the CC will detach that mobile terminal from the
VAA and possible attach another mobile terminal (if available)
depending on the effect that the removal has on capacity of the
system. Alternatively, if the formation of one or more VAA has
increased the system capacity beyond that needed by the CC then
mobile terminals can be released in order of priority based on
battery life, additional signalling load or interference for
example, until the capacity required by the CC its reached.
[0092] In order for a mobile terminal to join a VAA it must be
"spatially close" to at least one other member of the VAA.
Furthermore all members of a VAA must be spatially close to at
least one other member of the VAA in order for capacity gain to be
realised. The actual distance in each case will be dependent on a
number of factors including the control terminal transmitter power,
the interference in the system, the transmission power of the r-MTs
in the VAAs and the additional noise generated thereby, the noise
sensitivity of the mobile terminals, the distance to the next VAA
utilising the same resources and the propagation environment. In a
computer simulation carried out by the applicant the following
assumptions were made: the relaying process does not generate any
interference at the control terminal and each mobile terminal has a
relaying power of 30 dBm. It was found that "spatially close" could
be interpreted as 20-50 m in a typical indoor environment. In
practice in such an environment "spatially close" is between 2 m
and 100 m, with 10-20 m being ideal. The power of the mobile
terminals can be controlled, for example, by the CC in the range 0
dBW to 10 dBW at a power of 10 mW or less, depending on the relay
distance.
Relay Schemes
[0093] The signals from the control terminal may by relayed from
the mobile terminals in the VAA in the following ways:
[0094] (1) transparent relaying;
[0095] (2) regenerative relaying; or
[0096] (3) IP (Internet Protocol) based relaying.
[0097] In transparent relaying the entire part of the
electromagnetic signal received by each mobile terminal is
amplified, possibly frequency translated (i.e. shifted in
frequency) and re-transmitted. In regenerative relaying the entire
part of the electromagnetic signal received by each mobile terminal
is amplified, de-coded and then re-encoded with the same or a
different code, possibly frequency translated (i.e. shifted in
frequency) and re-transmitted. In IP based relaying the packets
received at each mobile terminal are stored in a buffer and only
re-transmitted if a target mobile requests them, so as to minimise
power consumption and preserve bandwidth. For example, when
web-browsing packets could be held in a buffer for approximately 30
s. Up to approximately 100 radio packets might be held in a
1-megabyte buffer.
Transmission Schemes
[0098] The table below sets out examples of transmit and relay
schemes that can be utilised in the present invention:
TABLE-US-00001 Main Link (Control Relay Link (from Mobile terminal
to VAA(s)) Terminals to t-MT) A CDMA CDMA B CDMA TDMA C CDMA OFDMA
D TDMA TDMA E TDMA OFDMA F OFDMA OFDMA
A: CDMA/CDMA
[0099] In this scheme the main and relaying links both utilise
CDMA, as shown in FIG. 6, in which data 40 for each mobile terminal
is spread with a respective spreading code 41 to make each set of
data unique so that each terminal can identify the correct data
from the signal comprising all of the data for all n mobile
terminals. In the example shown in FIG. 6 there are u sets of data
spread with u spreading codes for u mobile terminals that together
form one VAA. Each set of data then is then multiplied by the same
scrambling code 42. The CC informs each mobile terminal in each VAA
of the relevant scrambling code. By locking on to each scrambling
code each mobile terminal can determine the data to be relayed
amongst the members of the VAA.
[0100] At stage 43 the encoded data for mobile terminals outside
the VAA, which may be encoded with different scrambling and
spreading codes, is added to data for the u mobile terminals. At
stage 44 all of the data is transmitted from the control terminal
antenna elements (not shown); the electromagnetic waves are as
aforementioned. The signal reaches the first mobile terminal,
designated MT#1 in FIG. 6. This mobile terminal uses its RAKE
receiver (see FIG. 3A) at stage 45 to lock on to the scrambling
code 42 and the relevant spreading code. The mobile terminal MT#1
simply relays all of the data under scrambling code 42 at stage 46,
thereby not interfering with that data, nor having to process it,
which would otherwise use up processing power and battery power.
The mobile terminal MT#1 may also receive signals relayed from the
other members of VAA at stage 47 and so it also locks on to the
scrambling and spreading codes of these signals. All of the signals
are combined and decoded in the mobile terminal MT#1 for use by the
user. The fact that the mobile terminal MT#1 receives relayed
signals from the other members of the VAA means that its overall
signal quality is much better than if the RAKE receiver were to
lock on to the line of sight component and then on to the
attenuated multipath signals. In this way the capacity of the
system is enhanced as the bit error rate is lowered for a given
signal to noise ratio for example.
[0101] As a first specific example of a CDMA/CDMA scheme, VAAs
could be deployed in a Universal Mobile Telecommunications Service
Frequency Division Duplex (UMTS FDD), as well as cdma2000, as
follows. Such a scenario is likely to arise where the mobile
terminals are relatively stationary, for example, notebook
computers or personal digital assistants at a conference, as
compared to mobile telephones for example which often need data
whilst moving. Such a situation will also mean that a relatively
large number of users, for example between 20 and 100, will require
delivery of data at approximately the same time. This places strain
on the network in terms of capacity. As the mobile terminals are
relatively stationary, the environment for transmission of data can
be assumed to be slow fading. One or a group of mobile terminals
may be experience bad channel conditions for a period of time
whereas another mobile terminal or group of mobile terminals may
experience good channel conditions for the same period of time. As
described above the CC receives information from the mobile
terminals on channel conditions, and the CC determines whether a
VAA should be formed if the capacity of the system deteriorates.
The CC utilises those mobile terminals in the good channel
conditions in the VAA to relay data to those mobile terminals in
the bad channel conditions. In this embodiment there should be at
least one relaying mobile terminal (hereinafter "r-MT") in the VAA
for each t-MT to achieve the best results. If the channel
conditions deteriorate for a r-MT in the VAA then this should
become a target mobile, assuming that there is another mobile
terminal available to join the VAA. If channel conditions improve
for a t-MT then it should join the VAA. This association and
disassociation of mobile terminals from the VAA can be accomplished
for example through interference measurement or a take back
function where a mobile terminal is detached from a VAA, which can
be optimised for battery life, interference level etc. In this
embodiment the relaying can be accomplished using a variety of
standards that utilise CDMA for example IEEE802.11, HiperLAN2,
Bluetooth, Infrared, PLC. The transmission rates of data sent from
the control terminal to the mobile terminals can be regulated by
changing the spreading factor of the spreading code, the coding
rate or rate matching attributes. Several encoding, transmission,
relaying and detection schemes are possible as outlined below:
(1) It is assumed that a VAA group(s) is already formed and that a
terminal within a VAA cell can act either as an r-MT or t-MT only.
In this configuration a MT cannot be t-MT and r-MT at the same
time. The data stream for each user within the serving sector or
cell is appropriately encoded for m antenna elements of the control
terminal. Each user is assigned a unique spreading code, which is
the same for each control terminal antenna element. All data
streams are then scrambled by the sector/cell specific scrambling
code and sent out from all antenna elements in the same frequency
downlink band f.sub.1DL. Note that UMTS has three downlink
("DL"--control terminal to mobile terminal) frequency bands
f.sub.1DL, f.sub.2DL and f.sub.3DL, and three uplink ("UL"--mobile
terminal to control terminal) frequency bands, f.sub.1UL, f.sub.2UL
and f.sub.3UL, available. First, each mobile terminal extracts its
own data stream by locking to the appropriate spreading sequence.
It is appropriately de-scrambled and de-spread until the narrowband
signal is obtained. Note that no hard decision is to be performed.
A r-MT is assumed to be in good channel conditions and therefore it
is assumed that at least one r-MT transparently relays the entire
received signal stream to at least one t-MT on frequency band
f.sub.2DL or f.sub.3DL. In this configuration the utilised
frequency band f.sub.1DL is reserved for VAA only and power control
is applied to the relaying links so as to reduce mutual
interference in between the relaying links (for example the entire
signal can be multiplied by a power control factor that can be
controlled by the CC). Furthermore the VAA is organised by the CC
so that synchronisation between members of the VAA is "inline".
Inline synchronisation is achieved where the mutual difference in
path distance is less than one chip duration, an approximate
estimate of which can be calculated as [1/(number of chips per
second)].times.speed of light. For example, referring to FIG. 2 the
Gold synchronisation code has a chip rate of 3.84 million bits per
second, giving a single chip duration of 2.6.times.10.sup.-7 s and
a separation of approximately 78 m between mobile terminals to keep
synchronisation inline. The t-MTs lock on to the strongest signal
with their first fingers and with their remaining fingers on to the
next strongest signal components, perform channel compensation and
soft-combining with the direct signal component. Finally, the
signal is decoded. (2) The same encoding, modulation and
transmission process is assumed as in (1). However, synchronisation
is assumed to be staggered i.e. the mobile terminals have a
separation of greater than one chip length. This allows the
creation of stronger diversity paths at the t-MTs. (3) The same
encoding, modulation and transmission process is assumed as in (1).
However, each r-MT compensates the main link channel before
transparently relaying the signal stream to the t-MTs (i.e. channel
estimation coefficients are used to compensate for phase shift in
the control terminal to relaying mobile terminals). (4) The same
encoding and modulation process is assumed as in (1). However, the
data stream is sent on the downlink frequency band f.sub.1DL to the
r-MTs within a VAA or VAAs. The r-MTs then transparently relay the
data to the t-MTs on frequency band f.sub.2DL. Power control has to
be applied to the relaying links such as to minimise mutual
interference between the relaying links and between the relaying
and main links. No frequency bands are reserved for VAA only. (5)
The same encoding, modulation and transmission process is assumed
as in (1) and (4). However, relaying is accomplished on any of the
remaining frequency bands f.sub.2DL, f.sub.3DL, f.sub.1UL,
f.sub.2UL or f.sub.3UL, where the prevailing and generated
interference is reduced. Note that possibly an uplink link might be
cut and utilised for relaying purposes. (6) The same deployments as
in (1) to (5) are assumed. However, every mobile terminal of the
VAA is simultaneously a r-MT and t-MT under control of the CC. This
is particularly advantageous in fast fading channels, where channel
conditions change rapidly, for example with mobile telephones. (7)
The same deployments as in (1) to (5) are assumed. However, each
r-MT in the VAA retrieves the information for the t-MTs,
regenerates it as describes above under "relay schemes" and relays
it to the t-MTs. (8) The same deployments as in (1) to (5) are
assumed. However, each r-MT retrieves the information for the
t-MTs, decodes it and stores the obtained packets (for example IP
or physical layer) in a buffer for a given. These packets are then
relayed only if requested by a t-MT. (9) The same deployment as in
(8) is assumed, however, the IP-packets are relayed through another
interface such as mentioned above.
[0102] A second specific example is a TDD TDMA scheme employing
CDMA, VAAs can be deployed in a Universal Mobile Telecommunications
Service Time Division Duplex (UMTS TDD) as follows. Such a scheme
is could be used in conference rooms and airport lounges where use
of notebook computers and PDAs requiring access to external data
networks is likely. The deployment of VAA(s) will increase capacity
of the UMTS TDD system. Again, a group of VAA users are sent data
with a user specific spreading sequence at a given time slot over a
given duration of time slots. Once a VAA is setup then the mobile
terminals with good channel conditions serve as r-MTs for all
remaining t-MTs. There should be at least one for each t-MT and at
least one t-MT for at least one r-MT. When channel conditions
deteriorate for a r-MT then it should become a t-MT. When channel
conditions improve for a t-MT then it should become a r-MT. With
appropriate convergence layers (convergence of IP data to any
wireless network), relaying can be accomplished by using any
current or future access scheme or any of the following standards:
IEEE802.11, HiperLAN2, Bluetooth, Infrared, PLC. Advantageously, IP
packets are relayed by the r-MTs to the t-MTs. The relaying links
could be utilised on a FAIL/ACKNOWLEDGEMENT basis or through a
`reserved` link during a pre-specified duration of time. The
transmission rates of the data sent from the BS to the MTs can be
regulated by changing spreading factors, coding rate and rate
matching attributes. The same deployment configurations (1) to (9)
as for the UMTS FDD case are possible.
B: CDMA/TDMA
[0103] In this scheme the main link uses CDMA, for example UMTS,
and the relaying link uses TDMA, for example Global System for
Mobile Communication (GSM) or derivatives. The first part of the
CDMA/CDMA scheme as described above is applicable.
[0104] Once the data has been transmitted it reaches the mobile
terminals, including those that are members of the VAA. Those
relaying terminals of the VAA relay the data stream for the t-MTs.
Referring to "relay schemes" above, the first method of transparent
relaying is not feasible for this scheme as CDMA and TDMA operate
in fundamentally different ways such that the relay mobile cannot
pass on CDMA encoded data to a terminal configured for TDMA. In the
second method of regenerative relaying each r-MT extracts, decodes,
re-encodes and re-assembles the signal stream for the remaining
n-u-1 t-MTs (remembering that there are a total of n mobile
terminals out of which there are u mobile terminals in the VAA).
Re-assembly allows a continuous signal stream, typical to CDMA
based systems, to be split into a discontinuous signal stream,
typical to TDMA based systems. At least one relay terminal then
retransmits the re-assembled data streams to associated t-MTs
during a specified time slot at a specified frequency. Note that
time and frequency slots are controlled either by the network or a
MT within a VAA acting as a CC. The third method of IP-relaying is
the preferred embodiment of any hybrid access scheme, such as CDMA
in the main link and TDMA in the relaying links. In such
deployment, each r-MT retransmits only IP packets which were not
received properly by a t-MT Note that incremental redundancy
schemes (Page: 26 for example 1/3rate encoders where one bit goes
in and three come out. Thus, a packet of length n will become 3n.
Firstly n bits are transmitted, and if the packet is not decoded
properly, the next n are sent such that 2n are available at the
receiver) could equally be deployed, where additional packet
redundancy is provided by the relay mobile terminals at each
unsuccessful decoding of a packet at the t-MT.
C: CDMA/OFDMA
[0105] In this scheme the main link uses CDMA, for example UMTS,
and the relaying link uses OFDMA, for example Global System for
Mobile Communication (GSM) or derivatives. The first part of the
CDMA/CDMA scheme as described above is applicable.
[0106] Once the data has been transmitted it reaches the mobile
terminals, including those that are members of the VAA. Those r-MTs
of the VAA relay the data stream for the t-MTs. Referring to "relay
schemes" above, the first method of transparent relaying is not
feasible for such embodiment as CDMA and OFDMA operate in
fundamentally different ways such that the relay mobile cannot pass
on CDMA encoded data to a terminal configured for OFDMA. In the
second method of regenerative relaying each r-MT extracts, decodes,
re-encodes and re-assembles the signal stream for the remaining
n-u-1 t-MTs (remembering that there are a total of n mobile
terminals out of which there are u mobile terminals in the VAA). At
least one r-MT then retransmits the re-assembled data streams to
associated t-MTs during a specified time slot at a specified
frequency utilising a specified number of sub-carrier frequency
bands. Time, frequency slots and sub-carrier bands are controlled
either by the network or a MT within a VAA acting as a CC. The
third case of IP-relaying is the preferred embodiment of such
deployment. Each r-MT retransmits only IP packets that were not
received properly by the target mobile, utilising OFDMA as the
relaying access scheme.
D: TDMA/TDMA
[0107] In this scheme the main and relaying links are based on
TDMA, as shown in FIG. 7, in which data 50 for u mobile terminals
forming a VAA is appropriately encoded at stage 51 for transmission
from in antenna elements of a control terminal (not shown). This
data is to be transmitted over k time slots and l frequency bands,
where u=kl. This is in accordance with known schemes for example
GSM. At stage 52 the remaining data that has been encoded for the
remaining n-u mobile terminals in the cell or sector is added to
the data for the u mobile terminals and is transmitted from the
control terminal at stage 53. The electromagnetic waves are
attenuated and de-correlated as aforementioned.
[0108] Each of the u mobile terminals of the VAA receives its own
data at a given time slot and frequency band at stage 54 and
relayed data at stage 55. It also receives data for one or more
t-MTs at another time slot(s) and frequency band(s). The r-MTs
relay the data for the target mobile at stage 56 at a different
time slot and frequency band to that it was received on. This is to
ensure that the interference between the main and relaying links is
reduced. The CC determines which time slots and frequency bands are
to be used using radio resource management. Because the relaying
frequency bands are used comparatively locally i.e. within or just
outside a VAA the same time slots and frequencies can be re-used
within adjacent VAAs without degrading system capacity. This means
that a number of frequency bands can be reserved for VAA use by the
CC. The maximum number of time slots r needed so that each of the u
r-MTs can relay data to the u-1 possible t-MTs is given by
r=u(u-1)(u-2) . . . 21=u!. The occupation of less time slots is
possible if more frequency bands are Used simultaneously or not all
r-MTs relay information, or if some r-MTs relay at the same time
slot and same frequency band due to inline synchronisation, as
described above.
[0109] Referring to "relay schemes" above, the first method of
transparent relaying each r-MT simply frequency-translates and
relays the entire data frame, either with staggered or inline
synchronisation. At least one t-MT receives the relayed signal and
extracts its own signal. Finally, within each t-MT all extracted
signal streams are (soft) combined and decoded. In the second
method of regenerative relaying each r-MT extracts, decodes,
re-encodes and re-assembles the signal stream for the t-MTs. At
least one r-MT then retransmits the data to associated target
mobiles during a specified time slot at a specified frequency. In
the third method of IP-relaying a r-MT retransmits only IP packets,
which were not received properly by the t-MT, utilising TDMA at a
pre-specified time slot and frequency band.
[0110] A first specific example of a TDMA/TDMA transmission scheme
a VAA(s) can be employed in a GSM network for example GPRS or EDGE
as follows. If technology allows the mobile terminals shall be
devised so as to relay the information transparently, otherwise
regenerative relaying should be deployed. For the setup and release
of VAA cells the control terminal has to have information on the
each mobile terminal's VAA membership settings. The main resource
of this system is the available channel capacity in form of
frequency bands and time slots. A take-back function can be
deployed that is optimised for the mobile terminal battery-power or
generated co-channel or adjacent channel interference. Several
encoding, transmission, relaying and detection schemes are possible
as outlined below:
(1) The data stream for each user within the serving sector/cell is
appropriately encoded for m antenna elements of the control
terminal. Each mobile terminal is assigned a unique time slot and
frequency band, which is the same for each antenna element. All
data streams are then sent out from all m antenna elements in the
frequency downlink bands. Note that GSM has 124 downlink (DL) and
124 uplink (UL) frequency bands available. The assignment of time
slots and frequency bands is such that all mobile terminals
belonging to the same VAA group are served in consecutive time
slots, but possibly on different frequency bands. However, for
simplicity the frequency band should be the same. If the number of
VAA r-MTs exceeds the number of time slots in a frame (8 in GSM))
or if interference becomes predominant then more than one frequency
band can be deployed. The number of reserved frequency bands
utilised for relaying should be one less than the number of r-MTs
within a VAA group i.e. u-1. Since the reserved frequencies bands
are used only very locally they can be re-used by other adjacent
VAA groups, increasing capacity. If u r-MTs form a VAA group then
u-1 receives the data intended for r-MT #1 at time slot #1 and
frequency band #1. Each amplifies the data stream and frequency
translates it onto one of the locally reserved VAA frequency bands,
where each r-MT utilises a different band. Thus a t-MT #1 receives
on frequency band #1 the direct link information and on frequency
bands #1.sub.VAA-#(u-1).sub.VAA the remaining relayed information.
This happens at the same time slot #1 where the relayed streams are
slightly delayed due to additional propagation and
processing/translation time. The delay in the relaying links should
not exceed the guard times in between the time slots. If it does
then the either the guard time has to be increased or only half of
the r-MTs can participate in a VAA group since one time slot must
be left unused if the relayed time slot generates too much
interference. The process is repeated for the remaining u-1
r-MTs.
[0111] In this scenario it will be most likely that the channel
will appear to be fast fading due to low data rates. Accordingly,
every r-MT participating in a VAA group should be simultaneously a
r-MT and a t-MT. With increased transceiver complexity in the
control terminal more than one frequency band could be relayed. It
is not mandatory for frequency bands to be reserved for VAA
relaying. Alternatively an interference measurement can be
performed within a VAA and relaying can take place in only those
bands with low interference.
(2) The same encoding, modulation, transmission and relaying
process as in (1). However, if the CC detects a slow fading channel
then only those mobile terminals in good channel conditions should
act as relaying terminals. (3) The same encoding, modulation and
transmission process as in (1) and all channels involved are slow
fading and thus assumed to be known. For certain encoding
techniques, such as space-time trellis codes, the data can be
relayed at the same frequency band and same time-slot (inline
synchronisation). The addition of all signal streams, which is
usually done in the receiver, is thus performed in the air
interface. Such system is advantageously deployed for strong
line-of-sight (LOS) relaying links, which obey Rician statistics
and thus approach a Gaussian channel. Note that either
synchronisation is necessary such that the relaying carrier
frequencies do not cancel each other, or a CSI of the relaying
links. The decoding process follows the one in (1). (4) The same
encoding, modulation and transmission process as in (1). However,
each r-MT regenerates the data streams and relays it as deployed in
(1)-(3) utilising either inline or staggered synchronisation. (5)
The same deployments as in (1)-(4) are assumed. However, each r-MT
retrieves the information for the other t-MTs, decodes it and
stores the obtained packets in a buffer for a given time. These
packets are then relayed only if requested by a t-MT. (6) The same
deployment as in (5) is assumed. However, the IP-packets are
relayed through another interface such as mentioned above.
E: TDMA/OFDMA
[0112] In this transmission scheme the main link is based on TDMA
and the relaying link is based on OFDMA. Accordingly the first part
of the TDMA/TDMA scheme described above is relevant for this
scheme.
[0113] At least one r-MT of the VAA group receives the data stream
for at least one other t-MT within the VAA group at given time
slot(s) or frequency band(s). Referring to the "relay scheme"
section above, the first method of transparent relaying is not
feasible in such deployment since TDMA and OFDMA operate on
fundamentally different principles. In the second method of
regenerative relaying each r-MT extracts, decodes, re-encodes and
re-assembles the data stream for the t-MTs. At least one r-MT then
retransmits the data to associated t-MTs during a specified time
slot at a specified frequency utilising a specified number of
sub-carrier frequency bands. In the third method of IP-relaying a
r-MT retransmits only IP packets, which were not received properly
by a t-MT, utilising OFDMA at a pre-specified time slot, frequency
band and number of sub-carriers.
[0114] In a specific example of such a system, the VAA is deployed
within an IEEE802.11 or HiperLAN2 network as follows. Since both
standards rely on an OFDMA/TDMA/TDD system, the same as for the
TDMA/TDMA embodiment above holds with the only difference that the
modulation is based on OFDMA and uplink and downlink frequency
bands are shared in time (TDD). A further difference is that the
slot length may vary from user to user due to varying PDU train
length.
F: OFDMA/OFDMA
[0115] In this transmission scheme the both the main link and
relaying link are based on OFDMA. OFDMA based systems are usually
hybrids of TDMA based systems. In such an embodiment the data
streams for u r-MTs forming a VAA are appropriately encoded for m
antenna elements of the control terminal, modulated onto
appropriate sub-carrier frequency bands and transmitted. Each of
the u r-MTs receives its own data stream at given sub-carrier
frequency bands. At least one r-MT in the VAA further receives the
signal for at least one t-MT in the VAA. Referring to the "relay
scheme" section above, in the first method of transparent relaying
the r-MT simply frequency-translates and relays all necessary
sub-carrier frequency bands, either with staggered or inline
synchronisation. At least one t-MT receives the relayed signal and
extracts its own signal. Finally, within each t-MT all extracted
signal streams are (soft) combined and decoded. In the second
method of regenerative relaying each r-MT extracts, decodes,
re-encodes and re-assembles the signal stream for the t-MTs. At
least one r-MT then retransmits the data to associated t-MTs
utilising a specified number of sub-carrier frequency bands. In the
third method of IP-relaying a r-MT retransmits only those IP
packets that were not received properly by the t-MT, utilising
OFDMA at a number of given sub-carriers.
[0116] In another embodiment the main and relaying links are based
on any combination of transmission schemes described above or on
any combination of current or future access schemes. In such
deployment at least two VAA groups have to communicate with each
other, where one VAA group acts as a virtual transmitter (TX-VAA)
and the other as a virtual receiver (RX-VAA). The RX-VAA can be
deployed as in the previous embodiments of the invention with the
only difference that the signal stream does not stem from a control
terminal but from another VAA. The TX-VAA receives the data stream
intended for the t-MTs of the RX-VAA either from a control terminal
or from another TX-VAA. In the former case, the RX-VAA is served
straight from the control terminal. In the latter case, the RX-VAA
is served through a multi-hop ad-hoc VAA network. The originator of
the information stream, which could be a control terminal with a
single antenna, a control terminal with an antenna array or any
mobile terminal with single antenna or antenna array, transmits the
data stream to a VAA, which acts as a TX-VAA. The data could be
encoded using any of the aforementioned encoding methods and could
be transmitted using any of the aforementioned transmission
schemes. Each MT of the TX-VAA receives the data stream,
appropriately decodes it and re-encodes it with any of the
aforementioned encoding schemes assuming an m-element antenna array
is available, where m denotes the number of antenna elements
available within the TX-VAA, and relays the encoded data stream to
the RX-VAA. In use, the network would only benefit if the distances
between the all receivers and transmitters using weak or no coding
is very low, so as to guarantee a good signal quality even for high
data rate streams. Again, a BS or CC initiated staggered or inline
synchronisation can be achieved for each TX-VAA.
[0117] In another embodiment of the invention the VAA is deployed
within a Bluetooth (BT) network as follows. Current and future BT
standards rely on either TDMA or CDMA based technology. Therefore,
the same as for the UMTS FDD and GSM embodiment of the invention
hold.
[0118] For all aforementioned embodiments of the invention the
transceivers of the mobile terminals can be based on Software
Defined Radio (SDR). This gives VAA the flexibility to perform all
necessary algorithms such as relaying, decoding, frequency
translating, etc. under the control of software. Thus filters,
centre frequencies, etc. can be adapted dynamically. Furthermore,
the software to setup and maintain a VAA group can be downloaded
using SDR download mechanisms.
[0119] In another embodiment of the invention the VAA groups can
also form ad-hoc single frequency networks with obvious
implications for capacity and routing algorithms, as only one
frequency needs to be used.
[0120] Where the invention is utilised in a cellular data
communication system, for example a telecommunications network, a
VAA group can be served by more than one control terminal. Such
situation might arise if at least one mobile terminal of the VAA is
in a soft-handover between to or more case stations. The data
stream from both control terminals could be encoded appropriately
so as to make use of the additional antenna elements. For example,
if both control terminals have six antenna elements and the data
stream was encoded assuming a six-antenna element array, then in
soft-handover the data shall be encoded as if a twelve-element TX
array was available, resulting in greater capacity.
[0121] It is preferable, although not essential that the number of
mobile terminals within a VAA should equal or exceed the number of
transmit antenna elements of the control terminal or RX-VAA.
Maximum coding gain is achieved if the number of MTs equals the
number of transmit antenna elements. Additional MTs yield diversity
gain.
[0122] Referring to FIG. 8 a third embodiment of a data
communication system is generally identified by reference numeral
60 that comprises a control terminal 61 comprising m antenna
elements. There is a plurality of mobile terminals 62 that are part
of a VAA 63 that has been set up in accordance with the rules
described above. Each mobile terminal 62 is free to move within the
cell served by the control terminal 61. The number of mobile
terminals 62 is greater than the number of antenna elements of the
control terminal. If a mobile terminal 62 moves out of the cell,
another control terminal (not shown) will serve it. Each mobile
terminal comprises a plurality of antenna 64. In use, data 65 is
received from higher layers of the network at the control terminal
61 and appropriately encoded for the transmission scheme in use.
The data 65 is transmitted from the control terminal 61 and the
mobile terminals receives it and all bar a t-MT 66 re-transmit the
data 65 for the benefit of the target mobile 66. The target mobile
66 receives the data 65 directly from the control terminal 61 and
also from each of the other r-MTs 62 in the VAA 63. Using its
plurality of antenna 64 the t-MT 66 locks on to the strongest
signal (likely to be the line of sight component) and then on to
the next strongest signals with its remaining antennae (most likely
to be the relayed signals from the r-MTs 62). In this way the t-MT
66 obtains a much better signal quality, resulting in higher system
capacity. It will be noted that in this embodiment the VAA 63 acts
as a receiver for the t-MT 66, the link between the VAA 63 and the
control terminal 61 being a single hop.
[0123] Referring to FIG. 9 a fourth embodiment of a data
communication system is generally identified by reference numeral
70 that is similar to the data communication system 60 with like
numerals indicating like parts. The main difference is that each
mobile terminal has only one antenna 74, which is the case for
mobile telephones for example.
[0124] Referring to FIG. 10 a fifth embodiment of a data
communication system is generally identified by reference numeral
80 that comprises a control terminal 81 having m antenna elements.
A plurality of mobile terminals 84 in the cell have been divided
into to two VAAs, VAA#1 and VAA#2 each have n.sub.1 and n.sub.2
mobile terminals respectively. Each mobile terminal 84 of VAA#1 has
k.sub.i,1 antenna elements and each mobile terminal 82 of VAA#2 has
k.sub.i,2 antenna elements where i is the number of each terminal
in the VAA In use data 82 is received from the backbone of the
network and is appropriately encoded in an encoder 83. The
proximity of VAA#1 to the control terminal may allow for little or
no coding of the data (since there is likely to be a strong signal
with little or no fading). It is transmitted from the control
terminal 81, the number of wireless links being given by
m.times..SIGMA.k.sub.i,1. VAA#1 receives the data and each terminal
84 extracts its own data and relays on either all of the data 82 or
part of the data 82 depending on the relay transmission scheme
used. The relayed data is received by the mobile terminals 84 in
VAA#2 who also extract their data and then relay on the appropriate
data to a target mobile terminal 85, the number of wireless links
now being given by .SIGMA.k.sub.i,1.times..SIGMA.k.sub.i,2. The
target mobile 85 then receives a number of copies of the signal,
each of which is usually of better quality than the multipath
signals, and is able to extract and decode the relevant data.
[0125] Referring to FIG. 11 a sixth embodiment of a data
communication network is generally identified by reference numeral
90 that illustrates schematically how several VAAs 91, 92 and 93
can be set up in a cell 94 around a control terminal 95. It will be
noted that not all of the mobile terminals in the cell have been
utilised in the VAAs. This is because the VAAs have been set up in
"hot-spot" areas where a large number of mobile terminals are
closely arranged, as might happen at a conference or hotel for
example.
[0126] Referring to FIG. 12 a seventh embodiment of a data
communication network is generally identified by reference numeral
100 that comprises a wireless local area network formed from a
plurality of notebook computers 101. Each notebook computer 101
sends and receives data to and from a control terminal 102 via a
mobile telephone 103 or PCMCIA card. The notebook computers have
been formed into a VAA under control of the control terminal 102.
This mitigates the effects on the network of one or more of the
notebook computers 101 being in a fade. This is particularly useful
with portable computers as users randomly position their terminal
with respect to the control terminal.
[0127] Referring to FIG. 13 a eighth embodiment of a data
communication network is generally identified by reference numeral
110 that comprises a wireless local area network formed from a
plurality of notebook computers 111. The embodiment is similar to
that shown in FIG. 12 except that the relaying link between
notebooks in the VAA is accomplished via the power supply network
104.
[0128] Referring to FIG. 14 an ninth embodiment of a data
communication system is generally identified by reference numeral
120 that comprises two control terminals 121 and 122, and two
mobile terminals 123 and 124. Data received at the control
terminals 120 and 121 is encoded accordingly to a (2,2) Alamouti
scheme (see paper mentioned in introduction). However, in
accordance with the invention one mobile terminal 124 relays data
to the other mobile terminal 123. This may happen under control of
one of the control terminals 121 and 122 if one of the mobile
terminals moves into a fade or if channel conditions worsen. FIG.
15 shows the results graphically with a non-perfectly operating
power control routine on the relaying link for the scheme of FIG.
2, if the relaying link is stronger or weaker than the original
data stream. The deviation from the perfect power control (ppc)
case was assumed to be .+-.2 dB.
[0129] Referring to FIG. 16, tenth embodiment of a data
communication system is generally identified by reference numeral
130 that is a CDMA based transmission scheme and that comprises two
control terminal transmitters 131 and 132. The control terminals
have defined VAAs 133, 134 and 135 in which the individual mobile
terminals 133', 134' and 135' receivers are close enough together
so that each mobile terminal is in chip-range of all the others in
that VAA and t-MT Furthermore each VAA 133, 134 and 135 are far
enough apart to be outside chip-range (i.e. the duration of one
chip) of each other VAA. In this way interference and power
consumption are minimised as well as permitting the same spreading
codes or scrambling codes to be used in each VAA. Each of the
mobile terminals 133', 134' and 135' receives a signal from each of
the control terminals 131 and 132 and each of the VAAs 133, 134 and
135 retransmits the signal to the target mobile in that VAA. Each
group is out of chip-range of the other groups and so each group is
to distinguishable from the other groups through an appropriate
RAKE receiver. The target mobile detects the strongest signals,
combines them and retrieves the initial signal. The scheme was
found to operate at its best for R-1 VAAs, where R is the number of
fingers of the RAKE receiver in the target mobile.
[0130] FIG. 17 shows the dynamic behaviour of the scheme presented
in FIG. 16. The performance of two users in a group is the same as
for more than two users in a group and does not deteriorate, which
applies to the case of two control terminal antennas, one receiver
antenna within the handset and the appropriate number of supporting
users to emulate the (n,m) transceiver structure case. A SNR of 6
dB was fixed and the BER analysed with respect to a dynamic number
of helping users in the virtual antenna array group and a changing
number of uncorrelated paths. The labelling shows the number of
terminals that are out of and within chip length.
[0131] Referring to FIG. 18 a eleventh embodiment of a data
communication system is generally identified by reference numeral
140 that comprises a control terminal 145 and four mobile terminals
141, 142, 143 and 144. The system is a (2,2) forced synchronised
VAA Trellis encoded CDMA transmission scheme. The control terminal
145 transmits the signal for mobile terminals 142 and 143 to mobile
terminals 141 and 144 on frequency f.sub.1, and the signal for the
mobile terminals 141 and 144 to the mobile terminals 142 and 143 on
frequency and f.sub.2 as shown. The symbols for the `right` group
142 and 143 are sent to the `left` group 141 and 144 and vice
versa. The signals are Trellis encoded and retransmitted to the
other group. The scheme is advantageous for more than two relays
per group.
[0132] Referring to FIG. 19 the results of a computer simulation
assuming a normalised Rayleigh channel of the system of FIG. 18 are
shown compared with various other transmission schemes. Curve 150
shows the results of the system of FIG. 18. Curve 151 shows the
results of the system of FIG. 18 with participation of an extra
control terminal. Curve 152 shows the results obtained with a
single link i.e. each mobile terminal receives data directly from
the control terminal with no relaying. Curve 153 shows the results
of "classic" receive diversity. Curve 154 shows the results
obtained using one direct link and one relayed link. As can be seen
with only one control terminal the bit error rate is not much
improved over the single link scenario. However, the introduction
of a second control terminal results in a large improvement that is
nearly as good as the classic receive diversity set up.
[0133] Referring to FIG. 20 an twelfth embodiment of a CDMA based
data communication system is generally identified by reference
numeral 160 that comprises 4 mobile terminals 161, 162, 163 and 164
forming a VAA are used in a (1,3) MRRC (maximal ratio receive
combining) receive diversity scheme. The labelling of the signals
is (frequency, scrambling code and spreading code). Each mobile
terminal has been assigned a respective spreading code as follows:
161--#1, 162--#2, 163--#3 and 164--#4. A control terminal (not
shown) sends data as shown by arrows 165, 166. 167 and 168. Mobile
terminals 161 and 164 are informed by the control terminal that
they should receive data on frequency bands f.sub.1 only and that
mobile terminals 162 and 163 should receive data on frequency band
f.sub.2 only. All mobile terminals are instructed that any data
under scrambling code 1 can be de-scrambled, each mobile terminal
then being able to extract their respective data via their assigned
spreading code. Any data that is scrambled under scrambling code 2
should be relayed as follows. The data should be de-scrambled using
the mobile terminal's copy of scrambling code 2, re-scrambled using
scrambling code 1, frequency translated to other of the two
frequency bands that it was received on and then broadcast on that
frequency. For example, mobile terminal 161 receives the following
pattern of data: (f.sub.1,1,#1), (f.sub.1,2,#2), and
(f.sub.1,2,#3). That data intended for mobile terminal 161 under
scrambling code 1 can be de-scrambled and the data obtained by
multiplying the signal stream with spreading code #1. The mobile
terminal 161 detects the scrambling code 2, de-scrambles that data
and then re-scrambles it using scrambling code 1. The data is then
frequency translated onto frequency band f.sub.2 and broadcast from
mobile terminal 161 as shown by arrows 169 and 169'. The mobile
terminals 162 and 163 receive these signals and can obtain their
data as aforementioned. An analogous process happens at each of the
remaining mobile terminals 162, 163 and 164. It will be noted that,
using this method, each mobile terminal receives several copies of
the data it is intended to receive. Since the mobile terminals are
spaced apart, the copies of the signal at each mobile terminal are
likely to be much stronger than those created by multipath directly
from the control terminal. Accordingly each mobile terminal can
lock onto a number of much better quality signals, ultimately
reducing the bit error rate and enabling the system capacity to be
increased.
[0134] Referring to FIG. 21 a thirteenth embodiment of a TDMA based
data communication system is generally identified by reference
numeral 170 that comprises a control terminal 171 and eight mobile
terminals 172.sub.0 to 172.sub.7 that together form a VAA. The data
communication system 170 operates on a GSM burst structure. The
control terminal addresses each of the eight mobile terminals
during designated time slots t0, t1 . . . t7 on the downlink
frequency band f.sub.1 although it is to be noted that the mobile
terminals do no have to be addressed in numerical order. The mobile
terminals 172.sub.0 to 172.sub.7 communicate with the control
terminal during allocated time slots on uplink frequency band
f.sub.2. The mobile terminals 172.sub.0 to 172.sub.7 relay data to
one another at appropriate time slots on frequency band f.sub.3.
One out of the 120 available frequency bands may be used for this
purpose. The relaying power of each mobile terminal is dynamically
controlled by the control terminal so that it reduces interference
with an adjacent VAA that will be using frequency band f.sub.3 for
the same purpose. One possible solution is to fix the relaying
output power so that transmission takes place over a radius of
approximately 10 m to 20 m.
[0135] Referring to FIG. 22 the blocking rate (i.e. number of user
connections refused or dropped due to network overload) against
number of users in a computer simulation of a wideband CDMA
(W-CDMA) network is shown in two states. The simulation assumed 3
terminals per VAA, no interference and no mobility of users. Curve
180 shows the blocking rate when VAAs are used. Curve 181 shows the
same network in which no VAAs are used. The VAA groups consist of 3
mobile terminals. As can be seen the blocking rate decreases by a
factor of 3 when VAAs are utilised.
[0136] Referring to FIG. 23 this illustrates the ratio of satisfied
mobile terminals against number of users in a computer simulation
of a W-CDMA network with VAAs (curve 182) and without VAAs (curve
183). The simulation assumed 3 terminals per VAA, no interference
and no mobility of users. The VAA groups are assumed to consist of
3 mobile terminals. As can be seen the ratio of satisfied users
increases by a factor of 3 when VAAs are used.
Hardware and Software
[0137] (1) Control Terminal
[0138] Provided that the control terminal can address or is
connected to an antenna having a plurality of antenna elements then
no hardware changes are necessary at the control terminal.
[0139] The following software changes should be made within a
control terminal or any logical unit controlling the control
terminal antenna array, for example a central controller or radio
network controller. Primarily the software should be written to
perform the functional steps described in connection with FIG. 5
and the rules mentioned therein. The (software) algorithms have to
allow appropriate data encoding (e.g. space-time, BLAST etc.) at
the BS antenna array; control the setup and release of VAA groups
as described above; inform adjacent mobile terminals about the
possibility of constructing a VAA; control the association and
disassociation of mobile terminals to and from a VAA, respectively;
control synchronisation and power for the VAA. For the main and
relaying links, the software should control the appropriate choice
of scrambling and spreading codes for CDMA based systems, the
appropriate choice of frequency bands and time slots for TDMA based
systems and the appropriate choice of frequency bands, time slots
and frequency sub-carriers for OFDMA based systems. The software
should assist appropriate security, identification and
authorisation of potential and existing VAA members; control an
appropriate billing mechanism; control a possible software update
within the mobile terminals to support certain VAA features; inform
the backbone about the increase in transmission capacity and
reliability.
[0140] (2) Mobile Terminals
[0141] The following hardware changes should be made within a
mobile terminal. If the relaying scheme is chosen so that the main
and relaying links do not communicate at the same time over the
same air interface and no transparent relaying is performed, then
no hardware changes need to be made. However, algorithms in the
mobile terminal have to ensure that data is appropriately relayed
over the air interface, i.e. either as a regenerated data stream or
IP-packets. If the relaying scheme is chosen to be such that
another interface is used for relaying, then the hardware has to
provide this interface, e.g. PLC (power line communication) or
Bluetooth. If transparent relaying is deployed then hardware has to
be provided which allows amplification, frequency translation and
retransmission. This may pose requirements on additional
oscillators and filter design. If the r-MT is operated in duplex
mode, i.e. simultaneous communication with the control terminal and
the t-MT, then appropriate filters have to separate the used
frequency bands sufficiently such as not to cause any adjacent
channel interference. In case of SDR the appropriate hardware has
to be provided and specifically tailored to support the
requirements for a VAA.
[0142] It is a feature of the present invention that the following
software changes should be made within a mobile terminal. If a
mobile terminal is to be used to act as a Central Controller (CC)
for an ad-hoc VAA, then appropriate control algorithms have to be
provided (see FIG. 5 and associated description). Furthermore,
algorithms have to inform the control terminal about the relaying
capabilities and VAA membership settings of the mobile terminal.
The algorithms have to understand messages from the control
terminal informing the MT about surrounding mobile terminals, their
relaying capabilities and VAA membership settings. They have to
perform negotiation with the control terminal for formation of a
VAA or an association of a mobile terminal to an existing VAA. They
have to be able to influence the data streams such as to comply
with the requirements needed to allow for relaying and thus
formation of a VAA group. They have to be able to control
synchronisation and power control, either autonomously or imposed
by the master mobile terminal, control terminal or central
controller. They have to guarantee appropriate security for the
relaying signal stream and t-MTs.
[0143] The required software could be provided to the mobile
terminals in any of the following ways: (1) it could be
manufacturer loaded, e.g. already available on the notebook or SIM
card or mobile phone as supplied; (2) it could be downloaded via
the air interface and automatically installed by the control
terminal, e.g. SDR; (3) it could be received from any surrounding
mobile terminal; (4) it could be downloaded from special service
points which provide the necessary software; and (5) it could be
downloaded e.g. onto a notebook from the Internet, floppy disk,
CD-ROM or any other computer readable storage medium.
[0144] It is a feature of the present invention that it lowers the
bit error rate (BER) or packet error rate (PER) or frame error rate
(FER) for a given signal-to-noise ratio (SNR) with increasing
number of VAA members and groups. It therefore enables to control
and enhance the network capacity by allowing remoter users to
attain data rates with required quality-of-service (QoS) or
decrease the transmission power of the TX or to increase the data
rates for existing MTs or to increase the number of served MTs (for
CDMA based systems only).
[0145] It is a feature of the present invention that it enables
several sufficiently close MTs to cooperate with each other and so
enhance the overall system capacity.
[0146] The present invention relates to a system useful for use in
operating networks such as those in mobile, fixed or nomadic
wireless networks.
[0147] Conventional mobile terminals have one (or very few)
receiving antenna(s) through which the signals are received and
transmitted. Recently Multiple-Input-Multiple-Output (MIMO) channel
transmission techniques in form of e.g. BLAST-like or Space-Time
encoded systems have emerged which allow a significant increase in
capacity. Having only one (or few) antenna(s) per mobile terminal
significantly limits the potential capacity increase promised by
MIMO communications techniques.
[0148] A procedure that has been proposed to overcome the specific
problem of having only one receiving antenna in a mobile handset is
using Switched Parasitic Antennas (SPA). In SPA there is one active
and several tuneable passive antenna elements close to each other
forming an antenna array. However, there are severe interactions
between the antenna elements, the actual handset and the human body
and it is very difficult to tune the passive elements. Also, the
additional passive antenna elements require significant space
within the handset so making it bigger and bulkier.
[0149] Another approach has been to use TDMA-based relaying along a
plurality of mobile handsets, however Space-Time Codes or
BLAST-like techniques are not applicable to such a system and also
this gives rise to problems of billing as the relaying handset
would incur the charges which were generated for the target
handset. The system was called Opportunity Driven Multiple Access
(ODMA).
[0150] We have now invented a system, which enables several
sufficiently close mobile terminals (MTs) to cooperate with each
other and so enhance the overall system capacity, i.e. increase the
received signal quality and the total data throughput.
[0151] According to the invention there is provided a system for
transmitting and receiving signals in which there is at least one
transmitter (TX) comprised of at least one antenna element, which
sends out signals to a group of MTs each of which is comprised of
at least one antenna element. Each MT within this group receives at
least part of all signals, if necessary extracts its own dedicated
signal and, after possible processing, relays the signals dedicated
to the other MTs within the group or to MTs of other groups. The
process of relaying can be accomplished by retransmission through a
wireless or wired interface.
[0152] In use, the TX appropriately encodes the signals for the MTs
in dependency of channel state information (CSI) available and
prevailing complexity issues, and transmits it via the air
interface to the appropriate group(s) of MTs. In a preferred,
although not restricted to, embodiment of the invention two
operational modes are possible. First, signals are relayed within
one group only. In this case, each MT within such group can be
considered to act as a relaying receiver (r-RX) and thus as a
virtual receiver for at least one other target MT (t-MT) within the
same group. Second, signals are relayed from one group to another
group of MTs. In this case, MTs of one group can be considered to
act as a relaying transmitter (r-TX) and thus as a virtual
transmitter for at least one other t-MT within another group. A MT
acting either as r-RX or r-TX is termed relaying MT (r-MT). For
either case the relaying is accomplished by using either the same
air interface as from the TX to the MTs or a different interface,
which could be wireless or wired. The retransmitted signals
transmitted over the relaying link among the MTs have to be
separable from the original signals sent over the main link from
the TX to the MTs. The separation is achieved through appropriate
orthogonality of physical or logical channels between the main link
and the relaying links. Orthogonality can be achieved through
frequency or path delay combined with spreading codes in a CDMA
based system; through frequency and appropriate time slot
scheduling in a TDMA based system; through frequency, sub-carrier
frequency and appropriate time slot scheduling in an OFDMA based
system; or through a different access scheme in any system.
[0153] Such system enables a group of users in a spatially close
area to communicate with each other and so to increase capacity. As
a result the group of users forms a spatially distributed antenna
array to which MIMO capacity enhancing techniques can be applied.
This overcomes the limitations of having only one (or few) antenna
element(s) per MT without increasing the actual size of each
receiver.
[0154] The system is referred to as a Virtual Antenna Array
(VAA).
[0155] The system is applicable to mobile telephones in which each
transceiver is a mobile handset. The system is applicable to any
ad-hoc or meshed, centralised or decentralised network in which
each MT is mobile, fixed or nomadic.
[0156] The following communications standards currently available
or under investigation and standardisation are applicable to VAA:
Global System for Mobile Communications (GSM) and derivatives of it
(GPRS, EDGE, 3GSM), Universal Mobile Telecommunications Standard
(UMTS), Code Division Multiple Access 2000 (CDMA2000), IEEE802.11,
High Performance Local Area Network Type 2 (HiperLAN2), Bluetooth
(BT), Power Line Communications (PLC), Ultra Wide Band (UWB),
Infrared Communications and any future systems based on either of
the following access schemes: Code Division Multiple Access (CDMA),
Time Division Multiple Access (TDMA), Frequency Division Multiple
Access (FDMA) or Orthogonal Frequency Division Multiple Access
(OFDMA).
[0157] In a preferred, although not restricted to, embodiment of
the invention the main link interface from the TX to the MTs is
based on either of the following access schemes: W-CDMA (UMTS,
CDMA2000), TDMA/FDMA (GSM & derivatives) or TDMA/OFDMA
(IEEE802.11, HiperLAN2). The relaying link from the r-MT to the
t-MT is preferably based on either of the following access schemes:
W-CDMA (UMTS, CDMA2000, UWB), TDMA/FDMA (GSM & derivatives, BT)
or TDMA/OFDMA (IEEE802.11, HiperLAN2, PLC).
[0158] In a preferred, although not restricted to, embodiment of
the invention the signals for the t-MTs are encoded at the TX array
using either of the following schemes: BLAST-like techniques,
Space-Time Coding or no coding. In the case of BLAST-like
techniques, the entire CSI has to be available at the TX. In the
case of Space-Time Coding (STC), the signals are encoding utilising
either Block or Trellis codes which are optimised for the number of
transmit antennas only and the channel to conditions. In the case
of no coding, only receive diversity is provided at the t-MTs.
[0159] In a preferred, although not restricted to, embodiment of
the invention the signals for the t-MT are retransmitted via the
r-MT using either of the following relaying methods: transparent
relaying, regenerative relaying or IP-based relaying. In the case
of transparent relaying, the entire or part of the
(electromagnetic) signal is received by the r-MT, amplified,
possibly frequency translated and retransmitted to the t-MT. In the
case of regenerative relaying, the entire or part of the
(electromagnetic) signal is received by the r-MT, amplified,
processed (decoded, encoded with the same or a different code),
possibly frequency translated and retransmitted to the t-MT. In the
case of IP-based relaying, IP packets are only retransmitted by the
r-MT to the t-MT if the t-MT does request IP packets that were not
received properly.
[0160] The relaying IP-based scheme is referred to as IP-Diversity
(IP-D).
[0161] In a preferred, although not restricted to, embodiment of
the invention the r-MT operates in full duplex, i.e. it retransmits
signals to the t-MT while communicating with the TX. This can be
accomplished either by introducing a third oscillator for the
relaying transmission in a separate frequency band or, in case of
rather static terminals, by cutting the uplink and reprogramming
the uplink oscillator onto the relaying frequency band. Note that
relaying frequency bands are used only locally within a VAA
operating as a virtual receive antenna array.
[0162] The relaying scheme using a third oscillator or the
reprogrammed uplink oscillator is referred to as Frequency Relaying
(FR).
[0163] In a preferred, although not restricted to, embodiment of
the invention the rules for the formation and destruction of a
single or several VAA groups within a wireless network are as
follows. A VAA group shall be formed if the network capacity is
already saturated or if the user's data request would saturate the
network capacity and all potential VAA users prior agreed to a VAA
group membership. A VAA group should be formed only if the
additional interference produced does not deteriorate communication
of other users in the network or does not increase the overall
system interference above a given threshold such that the total
system capacity decreases. If these conditions cannot be met then
the VAA group should be resolved. Note that generally the formation
of VAA groups should decrease the overall system interference
level.
[0164] In a preferred, although not restricted to, embodiment of
the invention the rules for the attachment and detachment of a user
to and from a VAA group are as follows. A user shall be attached if
the prior agreed to a VAA group membership and he would benefit
from the induced capacity increase. A user shall also be attached
if he prior agreed to a VAA group membership and an existing VAA
group would benefit from the induced capacity increase. A user
shall also be attached if he prior agreed to a VAA group membership
and the entire network would benefit from the induced capacity
increase. If any of the aforementioned conditions cannot be met
then the user should be detached from the VAA group.
[0165] In a preferred, although not restricted to, embodiment of
the invention the VAA groups operate in downlink, the main
envisaged data bottleneck. An uplink or ad-hoc direct link
deployment is equally feasible where all mentioned and depicted
signal streams apply in reverse or ad-hoc direction,
respectively.
[0166] In a preferred, although not restricted to, embodiment of
the invention the network with deployed VAA regulates its capacity
as follows. First, user remoter from the serving TX can be served
maintaining the same data rates and interference level. Second,
maintaining the same cell radius the TX transmission power can be
decreased leading to a decreased interference scenario, which is
vital for CDMA based networks. Third, maintaining cell radius and
TX transmission power the data rate can be increased. This can be
achieved e.g. by increasing the modulation level, e.g. from QPSK to
16QAM, or by applying puncturing to the encoded data stream at the
transmitter, or by deploying incremental redundancy techniques.
[0167] In a preferred, although not restricted to, embodiment of
the invention not all MTs associated to a VAA necessarily have to
be involved in the process of relaying. In reality each MT will
experience a different direct link quality; therefore only MTs with
good direct link quality could act as r-MTs for all t-MTs within a
VAA group.
[0168] In a preferred, although not restricted to, embodiment of
the invention the required tight synchronisation within a VAA can
either be achieved through external network synchronisation and/or
by letting only spatially close MTs form the VAA. Synchronisation
forces the r-MTs to retransmit the signals to the t-MT such that
they arrive at the t-MT either in staggered time moments or at the
same time instant. This allows controlling the separability of the
relayed signal streams from the main signal stream and from each
other. For the first case of staggered delays (staggered
synchronisation), the mutual path delay has to be at least one chip
duration for a CDMA based network (such that the t-MT Rake receiver
may lock onto the respectively delayed signal streams) or one
time-slot duration for a TDMA based network. For the second case of
no delay (inline synchronisation), the mutual path delay must not
exceed one chip duration for a CDMA based network or one symbol
duration for a TDMA based network. Since the processing delay
within the r-MTs is assumed to be the same, synchronisation is
mainly dictated by the natural position of the MTs of a VAA and
network imposed delays. Generally, although not restricted to, the
staggered synchronisation method should be deployed if the
demodulation/detection algorithms require a separate processing at
each virtual receive antenna element. Generally, although not
restricted to, the inline synchronisation method should be deployed
if the demodulation/detection algorithms do not require a separate
processing at each virtual receive antenna element but can deal
with the sum of all relayed signal streams. Both types of
synchronisation are applicable to any aforementioned relaying
methods, such as transparent, etc.
[0169] The synchronisation scheme, as a result of the natural
position of MTs, is referred to as Forced Synchronisation (FS).
[0170] In a first embodiment of the invention the VAA is deployed
as a virtual RX and the main and relaying links are based on CDMA,
e.g. UMTS. In such embodiment the data streams for u MTs forming a
VAA group are appropriately encoded for an m element TX antenna
array. Prior to transmission the encoded data is spread with s
distinct spreading codes each with given chip-rate, where
s.gtoreq.u. Each of the u MTs receives the entire data stream and
extracts its own dedicated signal. Extraction is possible if a
Rake-like receiver locks to the appropriate spreading code(s). In
the first case of transparent relaying each r-MT simply
frequency-translates and relays the entire data stream, either with
staggered or inline synchronisation. All t-MTs receive the relayed
signal and extract their own signal. Finally, within each t-MT all
extracted signal streams are (soft) combined and decoded. In the
second case of regenerative relaying each r-MT extracts, decodes
and re-encodes the signal stream for the remaining u-1 t-MTs. Note
that the re-encoding can be performed utilising the original
spreading/scrambling sequences or different spreading/scrambling
sequences. The data stream is then frequency translated and
retransmitted. Each t-MT then processes all received signal
streams. In the third case of IP-relaying the decision upon
relaying is drawn at network layer or above. Note that in general
the number of MTs forming a VAA group should exceed the number of
TX antenna elements as to give maximum performance, i.e.
u.gtoreq.m.
[0171] In such embodiment of the invention, a simplified relaying
decision can be achieved if the information of the u MTs is first
spread by s distinct spreading codes and then by one scrambling
code. The scrambling code should be unique for the group of u MTs
and should differ from other scrambling codes used within the same
geographical area. For example, the secondary scrambling code
within one sector could be used for UMTS systems. Each of the u MTs
within the group locks onto the common scrambling code and relays
all information, which lies beneath this scrambling code. The
relaying procedure thus does not analyse or interfere with the
actual signal contents under this group common scrambling code.
[0172] The concept using a common scrambling code for a group of u
MTs forming a VAA is referred to as Group Code (GC).
[0173] In a second embodiment of the invention the VAA is deployed
as a virtual RX and the main link is based on CDMA, e.g. UMTS, and
the relaying links on TDMA, e.g. GSM or derivatives. In such
embodiment the data streams for u MTs forming a VAA group are
appropriately encoded for an m element TX antenna array. Prior to
transmission the encoded data is spread with s distinct spreading
codes each with given chip-rate, where s.gtoreq.u. Each of the u
MTs receives the entire data stream and extracts its own dedicated
signal. Extraction is possible if a Rake-like receiver locks to the
appropriate spreading code(s). The first case of transparent
relaying is not feasible for such embodiment. In the second case of
regenerative relaying each r-MT extracts, decodes, re-encodes and
re-assembles the signal stream for the remaining u-1 t-MTs.
Re-assembling allows a continues signal stream, typical to CDMA
based systems, to be split into a discontinuous signal stream,
typical to TDMA based systems. At least one r-MT then retransmits
the re-assembled data streams to associated t-MTs during a
specified time slot at a specified frequency. Note that time and
frequency slots are controlled either by the network or a MT within
a VAA acting as a central controller. The third case of IP-relaying
is the preferred embodiment of any hybrid access scheme, such as
CDMA in the main link and TDMA in the relaying links. In such
deployment, each r-MT retransmits only IP packets which were not
received properly by a t-MT. Note that incremental redundancy
schemes could equally be deployed, where additional packet
redundancy is provided by the r-MTs at each unsuccessful decoding
of a packet at the t-MT.
[0174] In a third embodiment of the invention the VAA is deployed
as a virtual RX and the main link is based on CDMA, e.g. UMTS, and
the relaying links on OFDMA. In such embodiment the data streams
for u MTs forming a VAA group are appropriately encoded for an m
element TX antenna array. Prior to transmission the encoded data is
spread with s distinct spreading codes each with given chip-rate,
where s.gtoreq.u. Each of the u MTs receives the entire data stream
and extracts its own dedicated signal. Extraction is possible if a
Rake-like receiver locks to the appropriate spreading code(s). The
first case of transparent relaying is not feasible for such
embodiment. In the second case of regenerative relaying each r-MT
extracts, decodes, re-encodes and re-assembles the signal stream
for the remaining u-1 t-MTs. At least one r-MT then retransmits the
re-assembled data streams to associated t-MTs during a specified
time slot at a specified frequency utilising a specified number of
sub-carrier frequency bands. Note that time, frequency slots and
sub-carrier bands are controlled either by the network or a MT
within a VAA acting as a central controller. The third case of
IP-relaying is the preferred embodiment of such deployment. Each
r-MT retransmits only IP packets which were not received properly
by the t-MT utilising OFDMA as the relaying access scheme.
[0175] In a fourth embodiment of the invention the VAA is deployed
as a virtual RX and the main and relaying links are based on TDMA,
e.g. GSM and derivatives. In such embodiment the data streams for u
MTs forming a VAA group are appropriately encoded for an m element
TX antenna array and transmitted at k time slots and l frequency
bands, where u=kl. Each of the u MTs receives its own data stream
at a given time slot and frequency band. At least one r-MT of the
VAA group further receives the information for at least one other
t-MT within the VAA group at given time slot(s) or frequency
band(s). It retransmits the signal stream(s) to the t-MT(s) using
different time slot(s) and frequency band(s). The main and relaying
links must not interfere as not to degrade the system performance.
Therefore, the relaying time slots and frequency bands have to
differ from the main link time slots and frequency bands. Which
time slots and frequency bands to use within the VAA should be
determined, although it is not restricted to, by the network or a
MT within a VAA acting as a central controller. Note that the
relaying frequency bands are used only highly locally such as not
to interfere with other MTs or VAA groups within the network. Thus
certain frequency bands can be reserved a priori for VAA and they
can be reused from VAA group to VAA group. Note further that the
maximum number of relaying time slots r needed such that each of
the u MTs can relay the information of the remaining u-1 t-MTs is
r.ltoreq.u(u-1)(u-2) . . . 21=u!. The occupation of less time slots
is possible if more frequency bands are used simultaneously or not
all MTs relay information or some MTs relay at the same time slot
and same frequency band due to inline synchronisation. In general,
three relaying cases are possible. In the first case of transparent
relaying each r-MT simply frequency-translates and relays the
entire data frame, either with staggered or inline synchronisation.
At least one t-MT receives the relayed signal and extracts its own
signal. Finally, within each t-MT all extracted signal streams are
(soft) combined and decoded. In the second case of regenerative
relaying each r-MT extracts, decodes, re-encodes and re-assembles
the signal stream for the t-MTs. At least one r-MT then retransmits
the data to associated t-MTs during a specified time slot at a
specified frequency. In the third case of IP-relaying an r-MT
retransmits only IP packets, which were not received properly by
the t-MT, utilising TDMA at a pre-specified time slot and frequency
band.
[0176] The concept of locally reserving a specific number of
frequency bands and time slots for relaying within a VAA group
utilising TDMA is referred to as VAA Femto Cell (VAA-FC).
[0177] In a fifth embodiment of the invention the VAA is deployed
as a virtual RX and the main link is based on TDMA, e.g. GSM and
derivatives, and the relaying links on OFDMA. In such embodiment
the data streams for u MTs forming a VAA group are appropriately
encoded for an m element TX antenna array and transmitted at k time
slots and l frequency bands, where u=kl. Each of the u MTs receives
its own data stream at a given time slot and frequency band. At
least one r-MT of the VAA group further receives the information
for at least one other t-MT within the VAA group at given time
slot(s) or frequency band(s). The first case of transparent
relaying is not feasible in such deployment. In the second case of
regenerative relaying each r-MT extracts, decodes, re-encodes and
re-assembles the signal stream for the t-MTs. At least one r-MT
then retransmits the data to associated t-MTs during a specified
time slot at a specified frequency utilising a specified number of
sub-carrier frequency bands. In the third case of IP-relaying an
r-MT retransmits only IP packets, which were not received properly
by the t-MT, utilising OFDMA at a pre-specified time slot,
frequency band and number of sub-carriers.
[0178] In a sixth embodiment of the invention the VAA is deployed
as a virtual RX and the main and relaying links are based on OFDMA.
Note that OFDMA bases systems are usually hybrids with TDMA. In
such embodiment the data streams for u MTs forming a VAA group are
appropriately encoded for an m element TX antenna array, modulated
onto appropriate sub-carrier frequency bands and transmitted. Each
of the u MTs receives its own data stream at given sub-carrier
bands. At least one r-MT of the VAA group further receives the
signal for at least one other t-MT in the VAA. In the first case of
transparent relaying the r-MT simply frequency-translates and
relays all necessary sub-carrier frequency bands, either with
staggered or inline synchronisation. At least one t-MT receives the
relayed signal and extracts its own signal. Finally, within each
t-MT all extracted signal streams are (soft) combined and decoded.
In the second case of regenerative relaying each r-MT extracts,
decodes, re-encodes and re-assembles the signal stream for the
t-MTs. At least one r-MT then retransmits the data to associated
t-MTs utilising a specified number of sub-carrier frequency bands.
In the third case of IP-relaying an r-MT retransmits only IP
packets, which were not received properly by the t-MT, utilising
OFDMA at a number of given sub-carriers.
[0179] In a seventh embodiment of the invention the VAA is deployed
as a virtual TX and the main and relaying links are based on any
combination of access schemes described in the previous embodiments
of the invention or on any combination of current or future access
schemes. In such deployment at least two VAA groups have to
communicate with each other, where one VAA group acts as a virtual
TX (TX-VAA) and the other as a virtual RX (RX-VAA). The RX-VAA can
be deployed as in the previous embodiments of the invention with
the only difference that the signal stream does not stem from a
real TX antenna array but from a VAA group. The TX-VAA receives the
data stream intended for the t-MTs of the RX-VAA either from a real
TX antenna array or from another TX-VAA. In the former case, the
RX-VAA is served through a single-hop ad-hoc VAA network. In the
later case, the RX-VAA is served through a multi-hop ad-hoc VAA
network. The originator of the information stream, which could be a
base station (BS) with a single antenna, a BS with an antenna array
or any MT with single antenna or antenna array, transmits the data
stream to a VAA group, which acts as a TX-VAA. The data could be
encoded using any of the aforementioned encoding methods and could
be transmitted using any of the aforementioned access schemes. Each
MT of the TX-VAA receives the data stream, appropriately decodes it
and re-encodes it with any of the aforementioned encoding schemes
assuming an m-element antenna array was available, where m denotes
the number of antenna elements available within the TX-VAA, and
relays the encoded data stream to the RX-VAA. In use, the network
would only benefit if the distances between the all RXs and TXs
using weak or no coding is very low, as to guarantee a good signal
quality even for high data rate streams. Again, a BS or central
controller initiated staggered or inline synchronisation can be
achieved for each TX-VAA.
[0180] In a first specific embodiment of the invention the VAA
could be deployed within a UMTS FDD network (as well as CDMA2000)
as follows. First, discovery mechanisms guarantee that the RNC and
MTs within the network are aware of their mutual proximity, their
VAA membership agreements and their communications standards
supported. This allows the formation of VAA groups whenever deemed
necessary by the RNC and a fast setup of relaying connections
within a VAA group. Most likely, although not restricted to,
additional redundancy will be requested from rather stationary MTs
in form of notebooks or PDAs in hot-spot areas, such as conference
or meeting rooms. Due to the stationary environment the channel can
be assumed slow fading. This implies that one single MT could be in
bad channel conditions for a rather long time, whereas another MT
could be in good channel conditions for approximately the same
amount of time. The channel conditions of each main link from Node
B to the MT are reported to the RNC. The RNC decides whether a VAA
should be formed among the hot-spot MTs, which relaying method to
deploy and which interface to use for the relaying process. Once a
VAA is setup then the MTs with good channel conditions serve as
r-MTs for all remaining t-MTs. There should be maximum one r-MT for
each t-MT and at least one t-MT for at least one r-MT. When channel
conditions deteriorate for a r-MT then it should become a t-MT.
When channel conditions improve for a t-MT then it should become a
r-MT. With appropriate convergence layers, relaying can be
accomplished by using any current or future access scheme or any of
the following standards: IEEE802.11, HiperLAN2, Bluetooth,
Infrared, PLC. The transmission rates of the data sent from Node B
to the MTs can be regulated by changing spreading factors, coding
rate and rate matching attributes. The association and
disassociation procedure can be controlled either through
interference measurement or through any take-back function, which
could be optimised for battery life, interference level, etc.
Several encoding, transmission, relaying and detection schemes are
possible.
a) The information stream for each user within the serving
sector/cell is appropriately encoded for an m-element TX array.
Each user is assigned a unique spreading code, which is the same
for each TX array element. All data streams are then scrambled by
the sector/cell specific scrambling code and sent out from all TX
antenna elements in the same frequency downlink band f.sub.1. Note
that UMTS has three downlink (DL), f.sub.1, DL/f.sub.2, DL/f.sub.3,
DL, and three uplink (UL) frequency bands, f.sub.1, UL/f.sub.2,
UL/f.sub.3, UL, available. First, each user extracts its own data
stream by locking to the appropriate spreading sequence. It is
appropriately de-scrambled and de-spread until the narrowband
signal is obtained. Note that no hard decision is to be performed.
Further, it is assumed that VAA groups are already formed and that
a terminal within a VAA cell can act either as an r-MT or t-MT
only. In this configuration a MT cannot be t-MT and r-MT at the
same time. A r-MT is assumed to be in good channel conditions and
therefore it is assumed that at least one r-MT transparently relays
the entire received signal stream to at least one t-MT on frequency
band f.sub.2, DL or f.sub.3, DL. Note that in this configuration
the utilised frequency band is reserved for VAA only. Note further
that power control is applied to the relaying links such as to
minimise mutual interference in between the relaying links. An
inline synchronisation is assumed where the mutual difference in
path distance is less than one chip duration (around 80 m). The
target receiver then locks with its remaining fingers to the
strongest signal components, performs channel compensation and
soft-combining with the direct signal component. Finally, the
signal is decoded. b) The same encoding, modulation and
transmission process is assumed as in a), however, the
synchronisation is assumed to be staggered. This allows the
creation of more strong diversity paths at the t-MT. c) The same
encoding, modulation and transmission process is assumed as in a),
however, each r-MT compensates the main link channel before
transparently relaying the signal stream to the t-MTs. d) The same
encoding and modulation process is assumed as in a), however, to
the r-MTs within a VAA the information is sent on the downlink
frequency band f.sub.1, DL and to the t-MTs on frequency band
f.sub.2, DL. The r-MTs then transparently relay the information on
frequency band f.sub.2, DL. Note that power control has to be
applied to the relaying links such as to minimise mutual
interference in between the relaying links and between the relaying
and main links. Note further that no frequency bands are reserved
for VAA only. e) The same encoding, modulation and transmission
process is assumed as in a), however, relaying is accomplished on
any of the remaining frequency bands f.sub.2, DL/f.sub.3, DL, or
f.sub.1, UL/f.sub.2, UL/f.sub.3, UL, where the prevailing and
generated interference is minimised. Note that possibly an uplink
link might be cut and utilised for relaying purposes. f) The same
deployments as in a)-e) are assumed, however, every MT is r-MT and
t-MT. This is advantageously applied to fast fading channels, where
channel conditions change rapidly. g) The same deployments as in
a)-e) are assumed, however, each r-MT retrieves the information of
the other t-MTs, regenerates it and relays it to the t-MTs. h) The
same deployments as in a)-e) are assumed, however, each r-MT
retrieves the information of the other t-MTs, decodes it and stores
the obtained packets in a buffer for a given time. These packets
are then relayed only if requested by a t-MT. i) The same
deployment as in h) is assumed, however, the IP-packets are relayed
through another interface such as mentioned above.
[0181] In a second specific embodiment of the invention the VAA is
deployed within a UMTS TDD network as follows. A TDD network will
be setup most likely, but not restricted to, in a hotspot area such
as conference rooms or airport lounges. Target MTs are most likely,
but not restricted to, notebooks, laptops, portable computers or
PDAs. The deployment of VAA will boost capacity of the UMTS TDD
system. Again, a group of VAA users are sent data with a user
specific spreading sequence at a given time slot over a given
duration of time slots. Once a VAA is setup then the MTs with good
channel conditions serve as r-MTs for all remaining t-MTs. There
should be maximum one r-MT for each t-MT and at least one t-MT for
at least one r-MT. When channel conditions deteriorate for a r-MT
then it should become a t-MT. When channel conditions improve for a
t-MT then it should become a r-MT. With appropriate convergence
layers, relaying can be accomplished by using any current or future
access scheme or any of the following standards: IEEE802.11,
HiperLAN2, Bluetooth, Infrared, PLC. Advantageously, although not
restricted to, IP packets are relayed by the r-MTs to the t-MTs.
The relaying links could be utilised on a FAIL/ACKNOWLEDGEMENT
basis or as a `reserved` link during a pre-specified duration of
time. The transmission rates of the data sent from the BS to the
MTs can be regulated by changing spreading factors, coding rate and
rate matching attributes. The same deployment configurations as for
the UMTS FDD case are possible.
[0182] In a third specific embodiment of the invention the VAA is
deployed within a GSM network or derivatives (GPRS, EDGE) as
follows. If technology allows the MTs shall be devised such as to
relay the information transparently, otherwise regenerative
relaying shall be deployed. For the setup and release of VAA cells
the BS has to have information on the MT's VAA membership settings.
Further, main figure of merit will be the available channel
capacity in form of frequency bands and time slots. A take-back
function can be deployed which could be optimised for the MT
battery-power or generated co-channel or adjacent channel
interference. Several encoding, transmission, relaying and
detection schemes are possible.
a) The information stream for each user within the serving
sector/cell is appropriately encoded for an m-element TX array.
Each MT is assigned a unique time slot and frequency band, which is
the same for each TX array element. All data streams are then sent
out from all TX antenna elements in the frequency downlink bands.
Note that GSM has 124 downlink (DL) and 124 uplink (UL) frequency
bands available. The assignment of time slots and frequency bands
shall be such that all MTs belonging to the same VAA group are
served in consecutive time slots and possibly on different
frequency bands. Note that for simplicity the frequency band should
be the same. However, if the number of VAA MTs exceeds the number
of time slots in a frame or if interference becomes predominant
then more than one frequency band can be deployed. The number of
reserved frequency bands utilised for relaying should be one less
than the number of MTs within a VAA group. Note that the reserved
relaying bands can be utilised locally by other VAA groups, which
justifies the increase in capacity. If u MTs are forming a VAA
group then each of the u MTs receives the data intended for MT #1
at time slot #1 and frequency band #1. Each of the remaining u-1
r-MTs amplifies the data stream and frequency translates it onto
one of the locally reserved VAA frequency bands, where each r-MT
utilises another band. The t-MT #1 receives thus on frequency band
#1 the direct link information and on frequency bands
#1.sub.VAA-#(u-1).sub.VAA the remaining relayed information. This
happens at the same time slot #1 where the relayed streams are
slightly delayed due to additional propagation and
processing/translation time. Note that the delayed occurred in the
relaying links should not exceed the guard times in between the
time slots. If it does then the either the guard time has to be
increased or only half of the MTs can participate in a VAA group.
Then, the process is repeated for the remaining u-1 MTs. Note that
most likely the channel will appear to be fast fading due to the
low data rates. Therefore, every MT participating in a VAA group
should be r-MT and t-MT at the same time. Note further that with
increased complexity more than one frequency band could be relayed.
Note further that not necessarily frequency bands have to be
reserved for VAA relaying, but an interference measurement can be
performed within a VAA to relay in the bands with low interference.
b) The same encoding, modulation, transmission and relaying process
is assumed as in a), however, a slow fading channel could allow
that not all MTs act as r-MT but only those in good channel
conditions. c) The same encoding, modulation and transmission
process is assumed as in a) and all channels involved are slow
fading and thus assumed to be known. For certain encoding
techniques, such as Space Time Trellis Codes, the data can be
relayed at the same frequency band and same time-slot (inline
synchronisation). The addition of all signal streams, which is
usually done in the receiver, is thus performed in the air
interface. Such system is advantageously deployed for strong
line-of-sight (LOS) relaying links, which obey Ricean statistics
and thus approach a Gaussian channel. Note that either
synchronisation is necessary such that the relaying carrier
frequencies do not cancel each other or a CSI of the relaying
links. The decoding process follows the one in a).
[0183] The scheme utilising the addition of all signal streams in
the air interface is referred to as Natural Combining (NC).
d) The same encoding, modulation and transmission process is
assumed as in a), however, each MT regenerates the data streams and
relays' it as deployed in a)-c) utilising either inline or
staggered synchronisation. e) The same deployments as in a)-d) are
assumed, however, each r-MT retrieves the information of the other
t-MTs, decodes it and stores the obtained packets in a buffer for a
given time. These packets are then relayed only if requested by a
t-MT. f) The same deployment as in e) is assumed, however, the
IP-packets are relayed through another interface such as mentioned
above.
[0184] In a fourth specific embodiment of the invention the VAA is
deployed within an IEEE802.11 or HiperLAN2 network as follows.
Since both standards rely on an OFDM/TDMA/TDD system, the same as
for the GSM and derivative embodiment holds with the only
difference that the modulation is based on OFDM and uplink and
downlink frequency bands are shared (TDD). A further difference is
that the slot length may vary from user to user due to varying PDU
train length.
[0185] In a fifth specific embodiment of the invention the VAA is
deployed within a Bluetooth (BT) network as follows. Current and
future BT standards rely on either TDMA or CDMA based technology.
Therefore, the same as for the UMTS FDD and GSM embodiment of the
invention hold with minor differences in realisation.
[0186] For all aforementioned embodiments of the invention the
transceivers of the MTs involved can be based on Software Defined
Radios (SDR). This gives VAA the flexibility to perform all
necessary algorithms such as relaying, decoding, frequency
translating, etc. under the control of software. Thus filters,
centre frequencies, etc. can be adapted dynamically. Furthermore,
the software to setup and maintain a VAA group can be downloaded
using SDR download mechanisms.
[0187] In a possible embodiment of the invention the VAA groups can
also form ad-hoc single frequency networks with obvious
implications for capacity and routing algorithms.
[0188] In a preferred embodiment of the invention a VAA group can
be served by more than one TX array. Such situation could arise if
at least one MT of the VAA group is in a soft-handover. In a
preferred embodiment the signal stream from both TX antenna arrays
shall be encoded appropriately as to make use of the additional
antenna elements. For example, if both TX antenna elements have six
antenna elements and the data stream was encoded assuming a six
element TX array, then in soft-handover the data shall be encoded
as if a twelve element TX array was available.
[0189] In a preferred, although not restricted to, embodiment of
the invention the number of MTs within a VAA group should be equal
to or exceed the number of transmit antenna elements used. Maximum
coding gain is achieved if the number of MTs equals the number of
transmit antenna elements. Additional MTs yield diversity gain.
[0190] In a preferred, although not restricted to, embodiment of
the invention each MT has a specific VAA membership. Although not
restricted to, the membership options could be as follows. First a
MT agrees to form or be part of a VAA without any prior
notification and under any conditions. Second, a MT agrees to form
or be part of a VAA only with appropriate confirmation of the owner
(request required). Third, a MT agrees to form or be part of a VAA
only if it would gain any capacity benefits in form of better QoS
or higher data rates. Fourth, a MT agrees to form or be part of a
VAA only if the other VAA members belong to a set of prior defined
MTs. Fifth, a MT agrees to form or be part of a VAA under any
conditions, however, automatically releases from a VAA group when a
predefined set of conditions are violated.
[0191] In a preferred, although not restricted to, embodiment of
the invention a VAA group within any type of network is formed as
follows. It assumed that a VAA setup is required and that all
aforementioned requirements, e.g. interference or capacity
requirements, to form a VAA are met. The VAA group is built up
consecutively, i.e. MT by MT, where at least two MTs have to be
available. The VAA group setup is initiated when the network is
running out of (or low in) capacity in terms of available power,
codes, time slots, frequency bands or frequency sub-carriers. This
may happen if the number of MTs requesting a connection exceeds the
given network capacity threshold, or remote MTs have to be served,
or certain MTs require higher data rates or a better link QoS, or
interference conditions change due to temporal changes in
propagation characteristics. The network is assumed to be
supervised by a CC, which could be a RNC, a BS or a master MT. The
CC is informed first by all MTs about their VAA membership
agreements, relaying capabilities and possibly already about their
mutual awareness. The CC then extracts those MTs within the network
which cause the system capacity to run out. This is achieved by
directly monitoring the transmission to each MT, or by receiving
information of the MTs involved, or by any other means informing
the CC about the MTs causing the network capacity congestion. If
this information cannot be achieved then a blind formation of VAA
groups shall be initiated by the CC until the capacity congestion
is reduced or no other VAA groups can be formed. The CC is assumed
to know the spatial positions of those MTs potentially forming VAA
groups. This can be achieved by GPS or any location determining
algorithms. If the location is not available to the CC then either
a blind formation of VAA groups shall be initiated with constant
surveillance of the interference level or a beacon signal has to be
exchanged between the MTs. For the latter case the CC controls the
exchange of beacon signals along the relaying links for MTs with
the same relaying capabilities, e.g. first all MTs with HiperLAN2
capability exchange their beacons, then all Bluetooth devices, etc.
The CC is thus finally informed about the entire status of the
network. Then, in dependency of VAA membership agreements, relaying
capabilities, capacity bottlenecks and other figures of merit, the
CC assigns a first member of a first VAA group. In dependency of
the network deployment or signalling load invoked, the CC either
automatically assigns the second member of the same VAA group or it
informs the first member to search for a second member. The CC then
informs both members about the exact resources to be used for the
main links in terms of power, code, frequency band, time slot or
frequency sub-carrier. If not already provided by the relaying
mechanism/standard, the CC informs both members about the exact
resources to be used for the relaying links, as well as the
synchronisation method used and other details necessary to
accomplish data relaying. Note that the exact order of resource
allocation and member assignment could be different as long as an
appropriate functioning of the forming VAA group is guaranteed.
Then, the data transmission is initiated and the system capacity
monitored. If the system capacity deteriorates then the VAA shall
be resolved and another group shall be formed. If the system
capacity enhances and the system capacity requirements are met then
no further VAA group formations are initiated. If it enhances and
the system capacity requirements are not met then another MT is
assigned to join the VAA by any method mentioned above. Possibly,
resources have to be reallocated for each new MT. Again, the
capacity is monitored and aforementioned decisions taken. This
formation loop is continued until the capacity gains level out or
the number of potential VAA MTs runs out. If the system capacity
requirements are still not met then the formation of a second VAA
group shall be initiated according to the steps provided above.
This procedure is continued until the capacity requirements are met
or all potential VAA users belong to a VAA group.
[0192] In a preferred, although not restricted to, embodiment of
the invention a VAA group within any type of network is
administered as follows. Of major importance is to maintain
synchronisation between the MTs of a VAA group. This could be
controlled either by a CC, or by a master MT within a VAA group, or
by each MT within the group. Furthermore, the CC has to monitor
continuously the interference and resource situation. Interference
can be estimated either directly from the CC or via feedback from
the MTs. In accordance with interference and resource availability,
the CC either does not initiate any changes to the network, or it
extends current VAA groups or forms new VAA groups according to the
steps provided above, or it releases MTs from VAA groups or
dissolves VAA groups according to the steps provided below.
[0193] In a preferred, although not restricted to, embodiment of
the invention a VAA group within any type of network is resolved as
follows. In dependency of the VAA membership settings of the MTs,
the general interference scenario and resource availability, the CC
may initiate the detachment of a MT from a VAA group. If the
membership settings of some MTs require a detachment of highest
priority (e.g. due to battery life restrictions, etc.), then the CC
chooses the VAA group which would suffer least capacity degradation
due to the detachment. If generally the interference scenario and
resource availability generates sufficient additional capacity,
then the CC chooses MTs with highest detachment priority or any MT
out of a VAA group which would suffer least capacity degradation
due to the detachment. This process is repeated until a given
interference and resource availability threshold is achieved.
[0194] In a preferred, although not restricted to, embodiment of
the invention the distance between the MTs within a VAA group is
dictated by the deployment scenario of VAA, the TX transmission
power, the interference susceptibility of the system, the
transmission power of the r-MTs, the additional noise introduced in
the r-MTs, the noise sensitivity of the MTs, the distance to the
next VAA group utilising the same resources and the propagation
environment. For instance, if the relaying process does not produce
any interference to the main link system and the r-MT has a
transmission power of 30 dBm, then the operational distance is in
the magnitude of 20-50 m within a typical indoor environment. The
distance between each MT in the VAA is ideally between 2 m and 100
m, with 10-20 m being preferable. The transmission power of the MTs
can be controlled, although not restricted to, by the CC in steps
from 0 dBW to 10 dBW.
[0195] It is a feature of the present invention that no hardware
changes have to be performed within a BS antenna array, as long as
each antenna element can be accessed separately.
[0196] It is a feature of the present invention that the following
software changes have to be performed within a BS or any logical
unit controlling the BS antenna array. The (software) algorithms
have to allow an appropriate data encoding at the BS antenna array.
They further have to control the setup and release of VAA groups.
They have to inform adjacent MTs about the possibility to setup a
VAA group. They have to control the association and disassociation
of MTs to and from a VAA group, respectively. They have to control
synchronisation and power control for the VAA group. For the main
and relaying links, they have to control the appropriate choice of
scrambling and spreading codes for CDMA based systems, the
appropriate choice of frequency bands and time slots for TDMA based
systems and the appropriate choice of frequency bands, time slots
and frequency sub-carriers for OFDMA based systems. They have to
guarantee appropriate security, identification and authorisation of
potential and existing VAA members. They have to control an
appropriate billing mechanism. They have to control a possible
software update within the MTs such as to support certain VAA
features. They have to inform the backbone about the increase in
transmission capacity and reliability.
[0197] It is a feature of the present invention that the following
hardware changes have to be performed within a MT. First, if the
relaying scheme is chosen to be such that main and relaying links
do not communicate at the same time over the same air interface and
no transparent relaying is performed, then no hardware changes have
to be performed. Note, however, that receiving algorithms have to
take care that the information is appropriately relayed over the
air interface, i.e. either a regenerated stream or IP-packets.
Second, if the relaying scheme is chosen to be such that another
interface is used for relaying, then the hardware has to provide
this interface, e.g. PLC or Bluetooth. Third, if transparent
relaying is deployed then hardware has to be provided which allows
amplification, frequency translation and retransmission. This may
pose requirements on additional oscillators and filter design.
Fourth, if the r-MT is operated in duplex mode, i.e. simultaneous
communication with the TX and the t-MT, then appropriate filters
have to separate the used frequency bands sufficiently such as not
to cause any adjacent channel interference. Fifth, in case of SDR
the appropriate hardware has to be provided and specifically
tailored to support the requirements for a VAA.
[0198] It is a feature of the present invention that the following
software changes have to be performed within a MT. If a MT is to be
used to act as a Central Controller (CC) for an ad-hoc VAA group,
then appropriate control algorithms have to be provided.
Furthermore, algorithms have to inform the TX about the relaying
capabilities and VAA membership settings of the MT. They have to
understand messages from the TX informing the MT about surrounding
MTs, their relaying capabilities and VAA membership settings. They
have to perform negotiation with the TX in case of a formation of
or an association to a VAA group. They have to be able to influence
the data streams such as to comply with the requirements needed to
allow for relaying and thus formation of a VAA group. They have to
be able to control synchronisation and power control, either
autonomously or imposed by the TX/BS/CC. They have to guarantee
appropriate security for the relaying signal stream and t-MTs. The
required software could be provided to the MTs in one of the
following ways: First, it could be in-built, e.g. already available
on the notebook or SIM card or mobile phone. Second, it could be
downloaded via the air interface and automatically installed, e.g.
SDR. Third, it could be received from any surrounding MT. Fourth,
it could be downloaded from special service points which provide
the necessary software. Fifth, it could be downloaded from the
Internet or floppy disk or CD-ROM, e.g. onto a notebook.
[0199] It is a feature of the present invention that it lowers the
bit error rate (BER) or packet error rate (PER) or frame error rate
(FER) for a given signal-to-noise ratio (SNR) with increasing
number of VAA members and groups. It therefore enables to control
and enhance the network capacity by allowing remoter users to
attain data rates with required quality-of-service (QoS) or
decrease the transmission power of the TX or to; increase the data
rates for existing MTs or to increase the number of served MTs (for
CDMA based systems only).
[0200] It is a feature of the present invention that it enables
several sufficiently close MTs to cooperate with each other and so
enhance the overall system capacity.
[0201] The invention is illustrated in the accompanying drawings in
which:--
[0202] FIG. 3 shows a generic network with deployed VAA in
downlink
[0203] FIG. 4 shows a generic network with deployed VAA in
downlink, uplink or ad-hoc
[0204] FIG. 5 illustrates the setup of VAA within the network
[0205] FIG. 6 illustrates the CDMA network flowchart with deployed
VAA
[0206] FIG. 7 illustrates the TDMA/OFDMA network flowchart with
deployed VAA
[0207] FIG. 8 shows a single-hop network with deployed RX-VAA
[0208] FIG. 9 shows a typical cellular network with deployed
RX-VAA
[0209] FIG. 10 shows a typical cellular network with deployed
TX-VAA
[0210] FIG. 11 shows geographically a typical cellular network with
deployed VAA
[0211] FIG. 12 shows a typical W-LAN network with deployed VAA and
wireless relaying
[0212] FIG. 13 shows a typical W-LAN network with deployed VAA and
PLC relaying
[0213] FIG. 14 shows a simple realisation with two BS antennas
(Alamouti scheme)
[0214] FIG. 15 shows the performance of the scheme of FIG. 9
[0215] FIG. 16 illustrates a CDMA embodiment with groups of
receivers
[0216] FIG. 17 shows the performance and dynamical behaviour of the
scheme of FIG. 11
[0217] FIG. 18 illustrates a scheme using two frequencies and
scrambling codes
[0218] FIG. 19 shows an average BER vs. SNR results from the scheme
of FIG. 13
[0219] FIG. 20 illustrates a scheme with four users and two
frequencies
[0220] FIG. 21 illustrates a simple TDMA-scheme embodiment
[0221] FIG. 22 illustrates the blocking rate for a W-CDMA network
with deployed VAA
[0222] FIG. 23 illustrates the number of satisfied MTs for a W-CDMA
network
[0223] Referring to FIG. 3, it shows the most generic case of a
network with deployed VAA in downlink. Data is received for MTs
within the network from a backbone, encoded and transmitted by a TX
with m antenna elements. It is received by the first VAA group and
relayed to the next VAA. The relaying might be transparent,
regenerative or IP-relaying with appropriate
decoding/encoding/frequency translating processes. The signals are
received by the second VAA group where the same as in the first VAA
group takes place. Note that the second VAA group may as well
receive the data streams directly from the TX. This continues until
the target VAA group is reached. Within the target VAA group r-MT
act as virtual receivers for a t-MT. A t-MT is r-MT for other t-MTs
in the same VAA group. Note that each MT may consist of more than
one antenna element, where at least one is involved in the process
of relaying. Note further that a target VAA group might be as well
a relaying VAA group for another target VAA group.
[0224] Referring to FIG. 4, it shows the most generic case of a
network with deployed VAA in downlink, uplink and ad-hoc mode. The
same as for FIG. 1 applies with the only difference that the data
flows apply in either direction and that a MT might act as a
TX.
[0225] Referring to FIG. 5 this illustrates the flowchart as to
deploy VAA within a CDMA network. It explains how to encode and
transmit the data stream and finally relay it within the VAA
group.
[0226] Referring to FIG. 6 this illustrates the flowchart as to
deploy VAA within a TDMA network. It explains how to encode and
transmit the data stream and finally relay it within the VAA
group.
[0227] Referring to FIG. 7 this illustrates the flowchart as to
setup VAA within any network. Initially, the requirements and
capabilities of the network and each MT are verified. Then,
communication is initiated and capacity/interference/resources are
monitored. If a capacity congestion is observed then the formation
of a 2-member VAA group shall be initiated. If capacity congestion
still prevails then the number of VAA members shall be increased
until no gain is achieved any more. If the capacity is still
congested then another VAA group shall be formed, etc.
[0228] Referring to FIG. 8, it shows a single-hop network with
deployed VAA. The data for all MTs in the VAA group is
appropriately encoded and transmitted to the VAA group, where the
relaying and combining process takes place.
[0229] Referring to FIG. 9, it shows a typical cellular system with
deployed VAA. Each user MT is assumed to have only one transceiver
antenna element and the VAA is operated in single-hop receiving
mode.
[0230] Referring to FIG. 10, it shows a typical cellular system
with deployed VAA. The first VAA group is assumed to be close to
the BS and have more MTs than the BS antenna elements. The
proximity of the first VAA group to the BS may allow a transmission
of the data stream with no or little coding. It is received by the
first VAA group and encoded as if an antenna array was available.
The data is finally received, relayed and combined within the
target VAA group.
[0231] Referring to FIG. 11, it shows a typical cellular system
with deployed VAA. The BS is assumed to consist of an antenna
array. Users with similar mobility and VAA membership settings are
assumed to form VAA groups within geographically close areas.
[0232] Referring to FIG. 12, it shows a typical W-LAN system with
deployed VAA. A high capacity transmit array is assumed to send
data to the MTs (here in form of notebooks). They receive the data
stream and relay it via a wireless link using either inbuilt
antennas or a PCMCIA card. The data is then received and processed
by each terminal.
[0233] Referring to FIG. 13, it shows a typical W-LAN system with
deployed VAA. A high capacity transmit array is assumed to send
data to the MTs (here in form of notebooks). They receive the data
stream and relay it via the power cables (PLC) using the
traditional power plug. The data is then received and processed by
each terminal.
[0234] Referring to FIG. 14, there are two base stations BS-A1 and
BS-A2 each of which transmit a signal to the target receiver MS1.
In addition the relaying receiver MS2 receives the signals and
retransmits it to MS1. This is a (2,2) Alamouti scheme to a common
single antenna mobile terminal.
[0235] Referring to FIG. 15, it shows the results graphically with
a non-perfectly operating power control routine on the relaying
link for the scheme of FIG. 2. The deviation from the perfect power
control (ppc) case was assumed to be .+-.2 dB.
[0236] Referring to FIG. 16, it depicts a CDMA-scheme embodiment of
the virtual antenna array. There are two base station transmitters
BS-A1 and BS-A2, there are groups of receivers MS1, MS2, MS3 in
which the individual mobile receivers are close together so that
each individual receiver is in chip-range of all the others in the
group and target receiver, so each group can be considered as one
virtual transmitting array. The groups MS1, MS2 and MS3 are far
enough apart to be outside chip-range of the other groups. Each of
the receivers receives a signal from each of the base station
transmitters and each of the groups retransmits the signal to the
target mobile. Each group is out of chip-range to the other groups
and so each group is distinguishable from the other groups through
an appropriate Rake receiver. The target receiver detects the
strongest signals combines them and retrieves the initial signal.
The scheme was found to operate at its best for R-1 groups of
users, where R is the number of fingers of the Rake receiver.
[0237] Referring to FIG. 17, it depicts the dynamic behaviour of
the scheme presented in FIG. 11. The performance of two users in a
group is the same as for more than two users in a group and does
not deteriorate, which applies to the case of two base station
antennas, one receiver antenna within the handset and the
appropriate number of supporting users to emulate the (n,m)
transceiver structure case. A SNR of 6 dB was fixed and the BER
analysed with respect to a dynamic number of helping users in the
virtual antenna array group and a changing number of uncorrelated
paths.
[0238] Referring to FIG. 18 this illustrates a (2,2) forced
synchronised VAA Trellis encoded CDMA scheme. The base transmitter
BS transmits the signal to the groups of receivers MS1, MS2, MS3
and MS4 on frequencies f.sub.1 and f.sub.2 as shown. The symbols
for the `right` group MS2 and MS3 are sent to the `left` group MS1
and MS4 and vice versa. The signals are Trellis encoded and
retransmitted to the other group. The scheme is advantageous for
more than two relays per group.
[0239] Referring to FIG. 19 shows the results of the scheme
introduced in FIG. 13. It shows average BER vs. average SNR over a
normalised Rayleigh channel. The curve corresponds to the VAA.
Within the region of interest it operates worse than the classical
MRRC scheme. Introducing a 2.sup.nd BS Tx, however, gives better
performance in the region of interest, almost as good as the MRRC
scheme.
[0240] Referring to FIG. 20 this illustrates a VAA scheme occupying
2 bands and emulating the (1,3) MRRC Rx diversity scheme. The
labelling is according to (frequency, scrambling and
spreading).
[0241] Referring to FIG. 21 this illustrates a possible TDMA-scheme
embodiment of the VAA scheme based on GSM burst structure. The base
station addresses each of the eight mobile terminals during
designated time-slots at the down link frequency band f.sub.1. The
mobile terminals communicate with the base station at appropriate
time slots at up link frequency f.sub.2. In a preferred embodiment
of the TDMA scheme the group of mobile terminals, which forms a VAA
group, communicates among each other at the remaining time-slots at
a third frequency f.sub.3. In GSM one out of 120 frequency bands
could be reserved for this purpose. The direct communication is
power controlled in the sense that the transmission should not
interfere with another group of VAA. A preferable solution is to
fix the relaying output power such that the transmission radius
does not exceed 10-20 m.
[0242] Referring to FIG. 22 this illustrates the blocking rate of a
W-CDMA network with deployed VAA. The VAA groups are assumed to
consist of 3 MTs. As can be seen the blocking rate decreases by a
factor of 3.
[0243] Referring to FIG. 23 this illustrates the ratio of satisfied
MTs of a W-CDMA network with deployed VAA. The VAA groups are
assumed to consist of 3 MTs. As can be seen the ratio increases by
a factor of 3.
FIELD OF THE SECOND INVENTION
[0244] The second invention relates to a method and apparatus for
synchronising an electronic data communication system, a computer
program comprising instructions for performing the method, a
computer readable storage medium provided with the program and a
subscriber identity module card provided with computer executable
instructions.
BACKGROUND TO THE SECOND INVENTION
[0245] Synchronisation of wireless electronic data communication
systems is necessary for a number of reasons, for example ensuring
orthoganility (i.e. the ability to distinguish) between
communication channels and increasing received signal quality.
Synchronisation is normally defined as the temporal alignment of at
least two signals that are within a limit or limits that can be
tolerated by the system. The limits are dependent on a number of
factors including the access scheme used and the topology of the
network that in wireless networks is variable in time.
[0246] Bits of digital data to be transmitted over such a system
from a transmitter to a receiver needs to highly organised if the
data is to be received and interpreted properly by the receiver.
One method for organising digital data is to divide the bits into
various groups known as super-frame, frame and slot. In general the
super-frame comprises a plurality of frames, each of which
comprises a plurality of slots. Each slot has one or more logical
channels. Frames and super-frames usually contain some
delimitation, address and control information to enable the
transmitter and receiver to deal with the data appropriately. These
various groups must be synchronised in transmission.
[0247] Other levels on which an electronic data communication
system must be synchronised are the network and application level,
symbol, bit, chip and carrier frequency level. Symbols are
generated by various operations on the bits of data, for example
compression and encoding. A chip is one bit of a code used in a
specific access scheme in wireless data communication networks,
namely Code Division Multiple Access (CDMA). In a CDMA scheme the
data for each terminal is multiplied by a different spreading code
that spreads the data over frequency bandwidth and provides
uniqueness to the signal so that a terminal can extract its own
data from the signals for all of the other terminals. The carrier
frequency is a frequency that is modulated with the data signal,
synchronisation of carrier frequencies being necessary to reduce
interference between channels to optimise signal strength at the
receiver.
[0248] Synchronisation is often achieved on the network and
application level by the running application. It is achieved on the
super-frame, frame and slot level either automatically or by a
central controller (hereinafter "CC") that could be a
telecommunications base station or mobile switching station for
example. Synchronisation on the symbol, bit, chip and carrier
frequency level is normally achieved with the aid of tracking
loops, for example a phase locked loop.
[0249] Synchronisation usually has to be re-initiated when the
signal bearer undergoes certain changes. For example, a change of
network means that the application layer has to initiate a new
synchronisation between transmitter and receiver at application
layer. The change of a communication session at the physical layer
means that the CC has to re-initiate synchronisation at the
super-frame, frame and slot level. With a change in the propagation
environment of electromagnetic waves, the tracking loops at
transmitter and receiver have to guarantee continuous
synchronisation at symbol, bit, chip and carrier frequency
level.
[0250] Algorithms and methods for synchronising at the network and
application layers, and for synchronising super-frames, frames and
slots are well established, for example using a guard interval or
special synchronising pattern. Self-synchronising algorithms for
symbols, bits, chips and carrier frequencies are also well known,
for example phase locked loops
[0251] In sending data between a transmitter and a receiver using
electromagnetic waves, it is possible to increase the capacity (in
bits/s/Hz) of the system by using a group of terminals to relay the
data to the receiver. However, due the fact that a wireless link is
used the propagation channel of the electromagnetic waves is
continually changing, which can cause synchronisation difficulties
at the receiver. Furthermore, in some systems some of the relaying
terminals are free to move whilst relaying. It has been found that
this dynamic nature of the position of the relaying receivers can
also cause synchronisation difficulties at the receiver. This is
because the alignment of the signals from the or each relaying
terminal at the receiver is out of synchronisation by an amount
greater than can be tolerated by the system.
[0252] For example, one or a group of sources wishes to send data
to one or a group of sinks providing a synchronised
single/multi-point to single/multi-point communication link via one
or more groups of relays. Each group comprises two or more
terminals. Synchronisation at super-frame, frame and time slot
level is necessary as to reduce interference between consecutive
super-frames, frames and time slots. For instance, if one group
comprising two relays is used to relay a signal to a target
terminal then the signal has two paths to reach the target terminal
via the relays. On reaching the target terminal it is possible that
the temporal difference between the two paths might be
significantly smaller than the frame length but is of the order of
a time slot length. Accordingly the system appears synchronised at
super-frame and frame level, but unsynchronised at time slot level,
which leads to time slot interference.
[0253] Similarly, synchronisation at symbol, bit and chip level is
necessary to reduce interference between consecutive symbols, bits
and chips. For instance, if one group comprising two relays is used
as described above it is possible that the temporal difference
between the two relays is significantly smaller than the symbol
length but is of the order of the chip length. Accordingly the
system appears synchronised at symbol level, but unsynchronised at
chip level resulting in inter-chip interference.
[0254] As mentioned above synchronisation at frequency carrier
level is vital as to obtain optimum signal strength. It is assumed
for present purposes that appropriate tracking loops guarantee
(self) synchronisation at carrier level. Accordingly, the present
invention does not relate to the synchronisation of carrier
frequencies.
SUMMARY OF THE SECOND INVENTION
[0255] It is apparent that there is a need for a method an
apparatus of assisting synchronisation of signal streams over a
wireless link in which the signal is relayed from an information
source to an information sink via at least one group of relaying
terminals, the synchronisation being within tolerances acceptable
to the access scheme in use
[0256] According to one aspect of the second invention there is
provided a method of synchronising data transfer in an electronic
data communication system comprising at least one information
source and a plurality of information sinks each of which can send
and receive data in the form of electromagnetic waves to and from
the at least one at least one information source using a
transmission access scheme, which method comprises the steps
of:
[0257] (1) identifying a plurality of information relays from the
plurality of information sinks; and
[0258] (2) instructing the plurality of information relays to
receive and relay data intended for at least one of the plurality
of information sinks;
[0259] wherein at step (1) the plurality of information relays is
identified on the basis of ability to relay data such that it
remains synchronous or has a deviation that can be tolerated by the
at least one information sink.
[0260] Preferred features of the invention are set out in the
appended claims to which attention is hereby directed.
[0261] If the signals were transmitted synchronised at super-frame,
frame, time-slot, symbol, bit and chip level from the information
source and relayed by at least one group of relays which are
spatially close (such as to require a similar physical propagation
time) and inherit the same processing time, then the signals are
received by the information sink synchronised within tolerable
limits. The tolerable limits dictate the allowed difference in
propagation and processing time. At super-frame, frame and time
slot level a delay of approximately less than one percent is
usually tolerated. At symbol and bit level a delay of less than ten
percent is usually tolerated. At chip level a delay of less than
hundred percent is usually tolerated. Timing tolerances are thus
dictated by the access scheme, which may operate at symbol or chip
level. CDMA based systems require a delay difference of less than
one chip duration, whereas TDMA based systems require a delay
difference significantly less than a symbol duration. As long as
propagation and processing times do not change out of the timing
tolerances, the system remains synchronised without the necessity
of supervision by a CC; thus achieving automatic
self-synchronisation.
[0262] Applying the concept of retransmission of information
between spatially distributed but sufficiently close relays allows
the formation of virtual information sources and information sinks
which allows the deployment multiple-input-multiple-output (MIMO)
capacity measures, e.g. in form of Space-Time Codes, and thus leads
to an increase in system capacity in terms of bits/s/Hz (with
implication on the number of users served, data rates, transmission
power, interference level, etc.). The system can be applied to a
Virtual Antenna Array (VAA) as described above in connection with
the first invention.
[0263] According to another aspect of the second invention there is
provided a system for synchronisation of a network in which network
there is at least one source of information and at least one sink
of information in which the information is transmitted from the
source(s) to the sink(s) by serially or simultaneously using one or
several relaying links, the relaying links being spatially close
such that, if the information is simultaneously relayed via several
relays, the information reaches the sink(s) at the same time or
with a deviation, which can be tolerated by the sink(s). Preferably
the system is a CDMA based system.
[0264] Advantageously, the data stream for the users is spread with
a distinct spreading code with given chip-rate for each user, each
of the users receives the incoming data streams from the other
users, optionally processes at least some of the data streams and
relays the possibly processed data streams to the remaining users
within the group of users and each of the users then finally
processes the signal streams.
[0265] Preferably, if user m is addressed then n users form the
virtual transmitting array and m-1=u-n-1 users the virtual
receiving array where u-1 is the number of data streams processed,
the virtual transmitting array of n users is formed through
synchronous transmission within chip-length and the virtual
receiving array of m-1 users is formed through retransmission out
of chip-length.
[0266] Advantageously, the retransmission out of chip length is
achieved through network imposed or natural delay.
[0267] Preferably, the required synchronisation for the virtual
transmitting array is achieved through external network
synchronisation.
[0268] Advantageously the required synchronisation for the virtual
transmitting array is achieved by letting spatially close mobile
terminals form a virtual transmitting array.
BRIEF DESCRIPTION OF THE DRAWINGS
[0269] For a better understanding of the present invention,
reference will now be made by way of example to the accompanying
drawings in which:
[0270] FIG. 24 is a schematic flow diagram of an electronic data
communication system operated in accordance with the present
invention;
[0271] FIG. 25 is a flowchart of the stages of set up and operation
of a data communication system in accordance with the present
invention;
[0272] FIG. 26 is a schematic view of a first embodiment of a data
communication system being operated in accordance with the present
invention;
[0273] FIG. 27 is a schematic view of a second embodiment of a data
communication system being operated in accordance with the present
invention; and
[0274] FIG. 28 is a schematic view of a third embodiment of a data
communication system being operated in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0275] Referring to FIG. 24 a diagram of a data communication
system is generally identified by reference numeral 210 that
comprises a group of i information sources 211. Data is to be
transferred between the i information sources 211 to s information
sinks 12 via two relay groups 213 and 214 respectively. Relay group
213 comprises r information relays and relay group 214 comprises g
information relays. The information relays have been grouped
together by a central controller (not shown) according to criteria
that will be described in more detail below. In use, the data is
broadcast over a wireless link 215 from the information sources
211, is relayed by relay group 213 to relay group 214 over a
wireless link 216, and is sent from the relay group 214 to the
information sinks 212 over a wireless link 217. Due to the
organisation of each relay group 213 and 214, signals arrive at the
information sinks 212 with a temporal separation within that which
can be tolerated by the information sinks 212 i.e. the signals are
synchronised.
[0276] In order to maintain the synchronisation of the signals from
the information sources 211 whilst they pass via the relay groups
213 and 214, the central controller chooses those information
relays of each relay group so that they a "spatially close" to one
another. Spatially close can be defined as those information relays
that generate a similar propagation time between receiving a signal
and that signal being received at the next relay group or at the
information sink, such that the relative delay between the signals
is less than or equal to the delay that can be tolerated by the
system. The exact delay that can be tolerated depends on the
system, examples of which are given in more detail below.
"Propagation time" should be understood as including the processing
time at each information relay and the travel time of the
electromagnetic waves between that information relay and the next
relay group or information source. It is important to note that it
is not the absolute delay of the signal that is important, but the
relative delay imposed on copies of the signal by each information
relay. For example, all of the information relays in one relay
group may impose an absolute delay of 5 .mu.s on all copies of the
signal. On re-transmission it is possible that there is almost zero
relative delay between the copies of the signal i.e. they are still
synchronised.
[0277] Referring to FIG. 25 a flowchart showing the stages of set
up and administration of a relay group is generally identified by
reference numeral 220. The flowchart is intended as a guide for the
design of an algorithm for implementing invention. At stage 221 the
central controller (CC) is determined by a radio network controller
(not shown) for example. The central controller might be a base
station or a mobile terminal (e.g. mobile telephone or portable
computer), for example. At stage 222 the CC polls potential
information relays in its vicinity for status information including
relaying capability and physical location. At stage 223
communication continues over traditional wireless links with each
information sink (e.g. notebook computer and/or mobile telephone)
communicating directly with a base station. At stage 224 the CC
waits for a request from an information sink that it believes it
would benefit from the relay of information. Alternatively, the
request may be initiated if the system is reaching capacity in
terms of available power, frequencies, codes etc. If such a request
is received the CC determines at stage 225 whether such relaying
would be of benefit to the system, for example by calculating the
signal to interference ratio (SIR) and adding the gain expected
from the relay group. If no, the CC returns to stage 223. If yes,
the CC determines at stage 226 relay groups of those information
relays it believes are spatially close to one another that would
maintain the synchronisation of signals that they relay, and
informs those terminals that they will be so used. The CC also
determines the relaying route via one or more relay groups to the
information sink at this stage. At stage 227 the CC instructs
communication to begin between the information source and the sink,
the signals being relayed by the relay groups until they ultimately
reach the information sink. At stage 228 the CC monitors the result
of the relaying process by receiving a performance indication from
the information sink (for example the SIR in a CDMA network). If
the performance indication says that signals are arriving at the
information sink within a tolerance acceptable to the sink, then
the relaying continues until the sink informs the CC otherwise. If
the performance indication says that the signals are arriving out
of synchronisation then the CC determines at stage 229 whether it
would the situation would be improved by detaching one or more of
the relay groups and/or information relays. Alternatively the CC
may instruct employment of chip/symbol stretching as described more
fully hereafter. As a final measure the CC may terminate the link
between the information source and the information sink if it
cannot reach a solution. The necessary changes are made at stage 30
and the routine returns to stage 224.
[0278] Referring to FIG. 26 a first embodiment of a data
communication system is generally identified by reference numeral
240 that comprises a base station 241 having m antenna elements
that serves a plurality of mobile terminals 242 (e.g. portable
computer, personal digital assistant or mobile telephones). Each
mobile terminal has a plurality of antenna elements. The base
station 241 wishes to send data from a backbone (not shown) to a
target mobile terminal 243. Under control of a CC (not shown) the
mobile terminals 242 deemed suitable to act as relays have been
grouped into two relay groups 244 and 245 as described above. Data
is broadcast from the base station 241, the signal being received
by the relay group 244, relayed to the relay group 245 and
ultimately received by the target mobile terminal 243. Note that
the target mobile terminal 243 is also part of a group 246 that
forms the information sink. Mobile terminals in the groups 246 only
relay to the target mobile terminal 243, interference being reduced
by appropriate power control. It is possible for the target mobile
terminal 243 to be an information relay for the other members of
the group 246. It is not necessary for all of the antennae of each
mobile terminal to relay the signal. Only one antenna is
needed.
[0279] Referring to FIG. 27 a second embodiment of a data
communication system is generally identified by reference numeral
250 that comprises a base station 251 having m antenna elements
that serves a four mobile terminals 252, 253, 254 and 255 (e.g.
portable computer, personal digital assistant or mobile
telephones). Each mobile terminal 252, 253, 254 and 255 has a
plurality of antenna elements. In use, data from a backbone (not
shown) is to be sent from the base station 251 to the target mobile
terminal 255 (t-MT). Under control of a CC (not shown) the mobile
terminals 252, 253 and 254 are determined to be suitable for use a
relaying mobile terminals (r-MT) by virtue of their spatial
separation. The CC has determined that relaying via these three
mobile terminals should not cause the signal to de-synchronise. The
path distance between r-MT 252 and t-MT 255 is p1, between r-MT 253
and t-MT 255 is p2 and between r-MT 254 and t-MT 255 is p3. In this
case it is assumed that an access scheme is deployed which requires
a synchronisation precision such that the maximum difference
between the path distances p1, p2 and p3 is less than 100 m. The
path distances are defined as:
.DELTA.1=p1-p2
.DELTA.2=p1-p3
.DELTA.3=p2-p3
[0280] For this example if the maximum value [max(.DELTA.1,
.DELTA.2, .DELTA.3)] between all three possible differences in path
distance shall be less than 100 m and thus the data sent from the
base station 251 via these mobile terminals will arrive
synchronised at the t-MT 255. Note that the distance between the
base station and the r-MTs was neglected in the calculation since
it was assumed that the r-MTs are far from the transmitter.
[0281] Referring to FIG. 28 a data communication system is
generally identified by reference numeral 260 that is similar to
the data communication system 250 with like numerals indicating
like parts. However, in this embodiment the r-MTs 262, 263 and 264
are in a position where their mutual path differences are more than
100 m, meaning that the signals at the t-MT arrive out of
synchronisation with one another. This may be because the r-MTs
have moved over time or if the t-MT has moved. This leads to
performance deterioration and appropriate steps have to be
initiated by the network or CC (see flowchart in FIG. 25). Note
again that the distance between the transmitter and the r-MTs was
neglected in the calculation since it was assumed that the r-MTs
are far from the transmitter. In these two embodiments if a mobile
terminal is moving with an average speed of 1 m/s the network
topology remains synchronised for roughly 2 mins. Note that for
stationary MTs or MTs moving in the same direction the
synchronisation duration is significantly higher. Once the network
becomes unsynchronised and thus the performance deteriorates, the
CC has to be informed by the t-MT to re-assign relaying terminals
or impose additional delays or to terminate the connection or to
extend the chip/symbol duration, which increases the range around
the target terminal in which terminals can act as relaying
terminals without losing synchronisation. The concept of varying
the chip/symbol duration such as to maintain forced synchronisation
is referred to as Chip/Symbol Stretching (C/SS).
[0282] In all of the above embodiments there are a number of
relaying and access (or transmission schemes that can be
employed:
Relay Schemes
[0283] The signals from the base station may by relayed from the
information relays in any of the following ways:
[0284] (1) transparent relaying; or
[0285] (2) regenerative relaying.
[0286] In transparent relaying the entire part of the
electromagnetic signal received by each mobile terminal is
amplified, possibly frequency translated (i.e. shifted in
frequency) and re-transmitted. In regenerative relaying the entire
part of the electromagnetic signal received by each mobile terminal
is amplified, de-coded and then re-encoded with the same or a
different code, possibly frequency translated (i.e. shifted in
frequency) and re-transmitted.
Transmission Schemes
[0287] For CDMA based systems, the timing deviations tolerated at
the information sink is of the order of one chip duration for CDMA
based systems. The spatial constraints for the relaying mobile
terminals or information relays with respect to the target mobile
terminal depend on the chip rate (number of chips per second),
where the maximum path difference (in m) between any relaying
mobile terminal and the target mobile terminal should not be more
than the speed of light [in m/s] divided by the chip-rate For
instance, a Universal Mobile Telecommunications Service Wideband
Code Division Multiple Access (UMTS W-CDMA) scheme has a chip rate
of 3.84 Mcps (mega chips per second), which yields a maximum path
difference of 3.times.10.sup.8/3.84.times.10.sup.6.apprxeq.80 m.
The relative path delay between relaying terminals and the target
terminal is of importance, rather than the absolute path delay
between relaying terminals and target terminal.
[0288] The invention can be employed within a CDMA network as
follows. The data stream for u t-MTs is appropriately encoded,
spread with u distinct spreading codes at given chip rate and
transmitted. A first relay group receives the signal stream, where
each MT within this group either transparently or regeneratively
relays the information stream to another relay group, until the
group of t-MTs is reached. If more than one MT forms the group of
t-MTs, then each MT may act as a further r-MT for each t-MT.
Synchronisation is achieved if the total time deviation caused by
path differences involved in the relaying process does not exceed
chip duration in the case of transparent relaying. Synchronisation
is achieved if the maximum time deviation caused by path
differences involved in the relaying process from one relaying
group to another relaying group does not exceed chip duration in
the case of regenerative relaying. Hybrid cases of transparent and
regenerative relaying are possible, where the spatial requirements
have to be adjusted appropriately.
[0289] For Time Division Multiple Access TDMA, the timing
deviations tolerated are about ten percent of the symbol duration.
The spatial constraints for the relaying terminals with respect to
the target terminals depend on the symbol rate, where the maximum
path difference (in m) between any relaying terminal and the target
terminal should not be more than the speed of light (in m/s)
divided by the symbol rate (in number per second). For instance,
Global System for Mobile Communications (GSM) TDMA has a symbol
rate of 270.8 kbps, which yields a maximum path difference of
3.times.10.sup.8/[(270.8.times.10.sup.3)10%].apprxeq.100 m. The
relative path delay is of importance, rather than the absolute path
delay.
[0290] The invention can be employed within a TDMA network as
follows. The data stream for u t-MTs is appropriately encoded and
transmitted at appropriate time slots and frequency bands. A first
relay group receives the signal stream, where each MT within this
group either transparently or regeneratively relays the information
stream to the another relaying group, until the group of t-MTs are
reached. If more than one MT forms the group of t-MTs, then each MT
may act as a further r-MT for each t-MT. Synchronisation is
achieved if the total time deviation caused by path differences
involved in the relaying process does not exceed ten percent of the
symbol duration in the case of transparent relaying.
Synchronisation is achieved if the maximum time deviation caused by
path differences involved in the relaying process from one relaying
group to another relaying group does not exceed ten percent of the
symbol duration in the case of regenerative relaying. Hybrid cases
of transparent and regenerative relaying are possible, where the
spatial requirements have to be adjusted appropriately.
[0291] For Orthogonal Frequency Division Multiple Access (OFDMA),
the timing deviations tolerated are about ten percent of the symbol
duration. The spatial constraints for the relaying terminals with
respect to the target terminal depend on the symbol rate, where the
maximum path difference (in m) between any relaying terminal and
the target terminal should not be more than the speed of light (in
m/s) divided by the symbol rate (in number per second). For
instance, HiperLAN2 OFDM has a symbol rate of 250 ksps, which
yields a maximum path difference of
3.times.10.sup.8/[(250.times.10.sup.3)10%].apprxeq.120 m. However,
the target ranges (i.e. distance between base station and terminal)
of HiperLAN2 are usually below 120 m. The relative path delay is of
importance, rather than the absolute path delay.
[0292] If transparent relaying is to be deployed then the relative
path differences along all relaying groups is of importance;
whereas, if regenerative relaying is to be deployed then only the
relative path differences from relaying group to relaying group are
of importance.
Hardware and Software
[0293] (1) Transmitter
[0294] Assuming that C/SS is not to be used then no hardware
changes are necessary in a transmitter. If C/SS is to be used then
the transmitter has to be able to adapt to the new timing/clock
requirements for the new chip/symbol durations.
[0295] The following software changes should be made in a
transmitter. Appropriate algorithms have to guarantee proper
encoding and transmission utilising the relaying network. If the
network inevitably bases on relaying, e.g. in the case of deployed
VAA, then no additional software changes have to be performed in
the transmitting information source. If C/SS is deployed then the
algorithms have to take the new chip/symbol rates into account.
[0296] (2) Relay Terminal
[0297] The following hardware changes should be made in a relay
terminal. The relay has to guarantee a proper reception,
amplification, possibly processing (decoding, encoding with the
same or different code), possibly a frequency translation and
retransmission. If the network inevitably bases on relaying, e.g.
in the case of deployed VAA, then no additional hardware changes
have to be performed in the relay. If C/SS is deployed then the
relay has to be able to adapt to the new chip/symbol rates.
[0298] The following software should be made in the relay terminal.
If transparent relaying is to be performed then no further software
changes are required. If regenerative relaying is to be deployed
then the relay has to guarantee a proper decoding and re-encoding
with the same or different code. If the network inevitably bases on
relaying, e.g. in the case of deployed VAA, then no additional
software changes have to be performed in the relay. If C/SS is
deployed then the algorithms have to take the new chip/symbol rates
into account.
[0299] (3) Target Terminal
[0300] The following hardware changes should be made in receiving
information sink or target terminal. The hardware has to guarantee
a proper reception of possibly the direct link from the source to
the sink and the synchronised relaying links within tolerable
delays. If C/SS is deployed then the receiver has to be able to
adapt to the new chip/symbol rates.
[0301] The following software changes should be made within
receiving information sink or target terminal. The algorithms have
to be able to process synchronised signal streams so as to give
optimum performance in terms of SIR and capacity (bits/s/Hz) for
example. They should be sufficiently robust to withstand some
synchronisation errors. To aid this C/SS could be deployed, where
the algorithms have to take the new chip/symbol rates into
account.
[0302] The following changes should be made in a network with in
which the present invention is operated. The network should have at
least one CC as to decide which MTs form relaying groups such as to
guarantee an information routing between source and sink with
synchronisation deviations within the tolerated limits. Note that a
proper routing without CC is also possible. The network should also
be able to detach those MTs from relaying groups or resolve
relaying groups entirely, which cause synchronisation deviations at
the receiver out of the tolerated limits. The network should also
be able to decide on a possible deployment of C/SS by finding a
trade-off between data-throughput and data rates depending on the
application.
[0303] It is a feature of the present invention that it can be
applied to any network and provides a simple means for achieving
synchronisation. Thus, envisaged network topologies can operate and
survive without major external control.
[0304] The relaying terminals are assumed to require the same
internal relaying time, thus using similar hardware with similar
internal clocks. In this case, the timing deviations tolerated by
the system solely depend on the access scheme. If the relaying
times of the relaying terminals differ then the time deviations
calculated below have to be adjusted appropriately.
[0305] The present invention relates to a system useful for use in
any mobile, fixed or nomadic, ad-hoc or meshed, centralised or
decentralised, wireless network.
[0306] In the context of this invention, synchronisation is
understood to be the temporal alignment of at least two signals at
a receiver sent by a transmitter within tolerable temporal limits.
Synchronisation is vital as to guarantee orthogonality between
communication channels and optimum received signal quality.
[0307] In general, any network needs synchronisation, which is
usually achieved by either automatic (self) synchronisation or a
Central Controller (CC). Within a wireless network, synchronisation
is necessary on application and network level, on super-frame,
frame and slot level, on symbol, bit and chip level and on carrier
frequency level. Traditionally, the application and network level
is synchronised by the running application; the super-frame, frame
and slot level is synchronised by the CC; and the symbol, bit, chip
and carrier frequency level are self synchronised at the receiver
with the aid of tracking loops, such as PLL.
[0308] Synchronisation usually has to be re-initiated when the
signal bearer undergoes certain changes. Thus, with a change of
network the application layer has to initiate a new synchronisation
between transmitter and receiver at application layer; with the
change of a communication session at physical layer the CC has to
re-initiate synchronisation of super-frame, frame and time slot;
with the change of the propagation environment the tracking loops
have to guarantee continuous synchronisation at symbol, bit, chip
and carrier frequency level.
[0309] Synchronisation algorithms at application layer and within
the CC to synchronise application, network, super-frame, frame and
time-slot are well established; such are automatic
self-synchronising algorithms for symbol, bit, chip and carrier
frequency. We have now invented a system, which enables automatic
synchronisation within a network with changing topology at
super-frame, frame and time-slot, as well as at symbol, bit and
chip level without the supervision of a CC.
[0310] According to the invention there is provided a system for
synchronisation of a network in which there is at least one source
of information and at least one sink of information in which the
information is transmitted from the source(s) to the sink(s) by
using one or several transparent or regenerative relaying links,
the relaying links being spatially close and requiring the same
relaying time such that if the information is instantaneously or
equally delayed relayed via several relays the information reaches
the sink(s) at the same time or with a deviation, which can be
tolerated by the sink(s).
[0311] In use, one or a group of sources wishes to communicate to
one or a group of sinks providing a synchronised single/multi-point
to single/multi-point communication link through a group of relays.
Synchronisation at super-frame, frame and time slot level is
necessary as to prevent interference between consecutive
super-frames, frames and time slots. For instance, if two relays
are deployed and the temporal difference between the two relays to
achieve the relaying process is significantly smaller than the
frame length but in the magnitude of the time slot length, then the
system appears synchronised at super-frame and frame level,
however, unsynchronised at time slot level, which leads to time
slot interference. Similar, synchronisation at symbol, bit and chip
level is necessary as to prevent interference between consecutive
symbols, bits and chips. For instance, if two relays are deployed
and the temporal difference between the two relays to achieve the
relaying process is significantly smaller than the symbol length
but in the magnitude of the chip length, then the system appears
synchronised at symbol level, however, unsynchronised at chip
level, which leads to inter-chip interference. Note that
synchronisation at frequency carrier level is vital as to obtain an
optimum signal strength. It is assumed that appropriate tracking
loops guarantee (self) synchronisation at carrier level; it is not
part of this invention.
[0312] If the signals were transmitted synchronised at super-frame,
frame, time-slot, symbol, bit and chip level from the information
source and relayed by at least one group of relays which are
spatially close (such as to require a similar physical propagation
time) and inherit the same processing time, then the signals are
received by the information sink synchronised within tolerable
limits. The tolerable limits dictate the allowed difference in
propagation and processing time. At super-frame, frame and time
slot level a delay of less than one percent is usually tolerated.
At symbol and bit level a delay of less than ten percent is usually
tolerated. At chip level a delay of less than hundred percent is
usually tolerated. Timing tolerances are thus dictated by the
access scheme, which may operate at symbol or chip level. CDMA
based systems require a delay difference of less than one chip
duration, whereas TDMA based systems require a delay difference
significantly less than a symbol duration. As long as propagation
and processing times do not change out of the timing tolerances,
the system remains synchronised without the necessity of
supervision by a CC; thus achieving automatic
self-synchronisation.
[0313] The concept is referred to as Forced Synchronisation
(FS).
[0314] The system is applicable to any form of wireless network
with deployed relays where synchronisation of the received signals
at the target mobile terminal (MT) is essential to an optimum
system performance. For instance, if the relaying MTs (r-MTs) are
utilised to act as a virtual transmit or receive array for a given
target MT (t-MT) and MRC is to deployed at the t-MT then the
signals relayed by the r-MTs should reach the t-MT synchronised
within tolerances.
[0315] In a preferred, although not restricted to, embodiment of
the invention the r-MT are assumed to require the same relaying
time, thus using similar hardware with similar internal clocks.
Then, the timing deviations tolerated by the system solely depend
on the access scheme. If the relaying times of the r-MTs differ
then the time deviations calculated below have to be adjusted
appropriately.
[0316] In use, the timing deviations tolerated are in the magnitude
of chip duration for CDMA based systems. The spatial constraints
for the r-MTs with respect to the t-MT depend on the chip rate,
where the maximum path difference [in m] between any r-MT and the
t-MT should not be more than the speed of light [in m/s] divided by
the chip-rate [in l/s]. For instance, UMTS W-CDMA has a chip rate
of 3.84 Mcps, which yields a maximum path difference of
3e8/3.84e6.apprxeq.80 m. Note that not the absolute path delay
between r-MTs and t-MT but the relative path delay between r-MTs
and t-MT is of importance.
[0317] In use, the timing deviations tolerated are about ten
percent of the symbol duration for TDMA based systems. The spatial
constraints for the r-MTs with respect to the t-MT depend on the
symbol rate, where the maximum path difference [in m] between any
r-MT and the t-MT should not be more than the speed of light [in
m/s] divided by the symbol rate [in l/s]. For instance, GSM TDMA
has a symbol rate of 270.8 kbps, which yields a maximum path
difference of 3e8/270.8e310%.apprxeq.100 m. Note again that not the
absolute path delay but the relative path delay is of
importance.
[0318] In use, the timing deviations tolerated are about ten
percent of the symbol duration for OFDMA based systems. The spatial
constraints for the r-MTs with respect to the t-MT depend on the
symbol rate, where the maximum path difference [in m] between any
r-MT and the t-MT should not be more than the speed of light [in
m/s] divided by the symbol rate [in 1/s]. For instance, HiperLAN2
OFDM has a symbol rate of 250 ksps, which yields a maximum path
difference of 3e8/250e310%.apprxeq.120 m. Note that the target
ranges of HiperLAN2 are usually below 120 m. Note again that not
the absolute path delay but the relative path delay is of
importance.
[0319] Note that if transparent relaying is to be deployed then the
relative path differences along all relaying groups is of
importance; whereas, if regenerative relaying was to be deployed
then only the relative path differences from relaying group to
relaying group are of importance.
[0320] In a preferred, although not restricted to, embodiment of
the invention forced synchronisation is achieved and maintained as
follows. First, it is assumed that a CC has setup a transmission
path between an information source and information sink via at
least one group of relays. The relays in each group should have
such spatial constrains as to guarantee relaying with total timing
deviations tolerated by the information sink. The CC thus has
knowledge of the spatial distribution of the MTs within the
network. Note that the CC not necessarily has to be the information
source or sink. Then, the information source transmits the signal
to the first group of relays, which receive the signal and possibly
retransmit the signal to another group of relays, etc., until the
last group of relays retransmits the signal to the information
sink. Note that the process of relaying may involve, but is not
restricted to, transparent and regenerative relaying. Regenerative
relaying may involve decoding and re-encoding with the same or a
different code. The receiver receives the signal and performs the
appropriate detection/demodulation/decoding, where performance in
terms of bit or packet error rate is maximised if all relayed
signal streams are received synchronised with deviations tolerated.
If during the operation of such network the network topology
changes e.g. due to moving r-MTs or a time variant propagation
environment, then the signal stream will remain synchronised at the
t-MT as long as the topological changes do not cause any delays
exceeding the deviations tolerated by the system. For typical
networks in deployment the total mutual path differences should not
exceed roughly 100 m. Assuming, for instance, MTs moving with an
average speed of 1 m/s the network topology remains synchronised
for roughly 2 mins. Note that for stationary MTs or MTs moving in
the same direction the synchronisation duration is significantly
higher. Once the network becomes unsynchronised and thus the
performance deteriorates, the CC has to be informed by to the t-MT
to re-assign relaying terminals or impose additional delays or to
terminate the connection or to extend the chip/symbol duration.
[0321] The concept of varying the chip/symbol duration such as to
maintain forced synchronisation is referred to as Chip/Symbol
Stretching (C/SS).
[0322] Applying the concept of retransmission of information
between spatially distributed but sufficiently close relays allows
the formation of virtual information sources and information sinks
which allows the deployment multiple-input-multiple-output (MIMO)
capacity measures, e.g. in form of Space-Time Codes, and thus leads
to an increase in system capacity in terms of bits/s/Hz (with
implication on the number of users served, data rates, transmission
power, interference level, etc.). The system can be applied to a
Virtual Antenna Array (VAA) as described in above.
[0323] In a preferred, although not restricted to, embodiment of
the invention forced synchronisation is achieved within a CDMA
network as follows. The data stream for u t-MTs is appropriately
encoded, spread with u distinct spreading codes at given chip rate
and transmitted. The first relaying group receives the signal
stream, where each MT within this group either transparently or
regeneratively relays the information stream to the next relaying
group, until the group of t-MTs are reached. If more than one MT
forms the group of t-MTs, then each MT may act as a further r-MT
for each t-MT. Synchronisation is achieved if the total time
deviation caused by path differences involved in the relaying
process does not exceed chip duration in the case of transparent
relaying. Synchronisation is achieved if the maximum time deviation
caused by path differences involved in the relaying process from
one relaying group to another relaying group does not exceed chip
duration in the case of regenerative relaying. Note that hybrid
cases of transparent and regenerative relaying are possible, where
the spatial requirements have to be adjusted appropriately.
[0324] In a preferred, although not restricted to, embodiment of
the invention forced synchronisation is achieved within a TDMA
network as follows. The data stream for u t-MTs is appropriately
encoded and transmitted at appropriate time slots and frequency
bands. The first relaying group receives the signal stream, where
each MT within this group either transparently or regeneratively
relays the information stream to the next relaying group, until the
group of t-MTs are reached. If more than one MT forms the group of
t-MTs, then each MT may act as a further r-MT for each t-MT.
Synchronisation is achieved if the total time deviation caused by
path differences involved in the relaying process does not exceed
ten percent of the symbol duration in the case of transparent
relaying. Synchronisation is achieved if the maximum time deviation
caused by path differences involved in the relaying process from
one relaying group to another relaying group does not exceed ten
percent of the symbol duration in the case of regenerative
relaying. Note that hybrid cases of transparent and regenerative
relaying are possible, where the spatial requirements have to be
adjusted appropriately.
[0325] It is a feature of the present invention that no hardware
changes have to be performed within a transmitting information
source if no C/SS is to be deployed. If C/SS is deployed then the
transmitter has to be able to adapt to the new timing/clock
requirements for the new chip/symbol durations.
[0326] It is a feature of the present invention that the following
software changes have to be performed within a transmitting
information source. Appropriate algorithms have to guarantee proper
encoding and transmission utilising the relaying network. If the
network inevitably bases on relaying, e.g. in the case of deployed
VAA, then no additional software changes have to be performed in
the transmitting information source. If C/SS is deployed then the
algorithms have to take the new chip/symbol rates into account.
[0327] It is a feature of the present invention that the following
hardware changes have to be performed within a relay. The relay has
to guarantee a proper reception, amplification, possibly processing
(decoding, encoding with the same or different code), possibly a
frequency translation and retransmission. If the network inevitably
bases on relaying, e.g. in the case of deployed VAA, then no
additional hardware changes have to be performed in the relay. If
C/SS is deployed then the relay has to be able to adapt to the new
chip/symbol rates.
[0328] It is a feature of the present invention that the following
software changes have to be performed within a relay. If
transparent relaying is to be performed then no further software
changes are required. If regenerative relaying is to be deployed
then the relay has to guarantee a proper decoding and re-encoding
with the same or different code. If the network inevitably bases on
relaying, e.g. in the case of deployed VAA, then no additional
software changes have to be performed in the relay. If C/SS is
deployed then the algorithms have to take the new chip/symbol rates
into account.
[0329] It is a feature of the present invention that the following
hardware changes have to be performed within a receiving
information sink. The hardware has to guarantee a proper reception
of possibly the direct link from the source to the sink and the
synchronised relaying links within tolerable delays. If C/SS is
deployed then the receiver has to be able to adapt to the new
chip/symbol rates.
[0330] It is a feature of the present invention that the following
software changes have to be performed within a receiving
information sink. The algorithms have to be able to process
synchronised signal streams such as to give optimum performance.
They should be sufficiently robust to guarantee some
synchronisation errors. To aid this C/SS could be deployed, where
the algorithms have to take the new chip/symbol rates into
account.
[0331] It is a feature of the present invention that the following
changes have to be performed within a network with forced
synchronisation. The network should have at least one CC as to
decide which MTs form relaying groups such as to guarantee an
information routing between source and sink with synchronisation
deviations within the tolerated limits. Note that a proper routing
without CC is also possible. The network should also be able to
detach those MTs from relaying groups or resolve relaying groups
entirely, which cause synchronisation deviations at the receiver
out of the tolerated limits. The network should also be able to
decide on a possible deployment of C/SS by finding a trade-off
between data-throughput and data rates.
[0332] It is a feature of the present invention that it can be
applied to any network and provides a simple means for achieving
synchronisation. Thus, envisaged network topologies can operate and
survive without major external control.
[0333] The invention is illustrated in the accompanying drawings in
which:--
[0334] FIG. 24 shows a generic information flow for FS schemes
[0335] FIG. 25 illustrates the flowchart to guarantee forced
synchronisation in the network
[0336] FIG. 26 illustrates a generic FS scheme applied to a
wireless system
[0337] FIG. 27 illustrates a FS scheme where the r-MTs guarantee
synchronisation
[0338] FIG. 28 illustrates a FS scheme where the r-MTs do not
guarantee synchronisation
[0339] Referring to FIG. 24, a group of information sources i
communicates to a group of information sinks s via at least one
group of relays r. Only relays that are spatially close together
are used to accomplish the forced synchronisation. There might be
several groups of spatially close relays. There might be several
information sinks and information sources, which not necessarily
have to be linked in a unique and unambiguous manner.
[0340] Referring to FIG. 26, it shows the most generic case of a
network with deployed FS in downlink. Data is received for MTs
within the network from a backbone, encoded and transmitted by a TX
with m antenna elements. It is received by the first relaying group
and relayed to the next relaying group. The relaying might be
transparent or regenerative with appropriate
decoding/encoding/frequency translating processes. The signals are
received by the second relaying group where the same as in the
first relaying group takes place. This continues until the target
receiver or relaying group is reached. A t-MT is r-MT for other
t-MTs in the same target relaying group. Note that each MT may
consist of more than one antenna element, where at least one is
involved in the process of relaying.
[0341] Referring to FIG. 27, it shows an illustrative case of a
network with deployed FS. The transmitter consisting of an in
element antenna array transmits the signal for the t-MT via three
r-MTs. Note that each of the MTs may have more than one antenna
element. The path distance between r-MT#1 and t-MT#4 is p1, between
r-MT#2 and t-MT#4 is p2 and between r-MT#3 and t-MT#4 is p3. In
this case it is assumed that an access scheme is deployed which
requires a synchronisation precision such that the maximum
difference between the path distances is less than 100 m. For the
given example the maximum value between all three possible
differences in path distance shall be less than 100 m and thus the
signals arrive synchronised at the t-MT. Note that the distance
between the transmitter and the r-MTs was neglected in the
calculation since it was assumed that the r-MTs are far from the
transmitter.
[0342] Referring to FIG. 28, it shows an illustrative case of a
network with deployed FS. The transmitter consisting of an m
element antenna array transmits the signal for the t-MT via three
r-MTs. Note that each of the MTs may have more than one antenna
element. The path distance between r-MT#1 and t-MT#4 is p1, between
r-MT#2 and t-MT#4 is p2 and between r-MT#3 and t-MT#4 is p3. In
this case it is assumed that an access scheme is deployed which
requires a synchronisation precision such that the maximum
difference between the path distances is less than 100 m. For the
given example the maximum value between all three possible
differences in path distance shall exceed 100 m and thus the
signals arrive unsynchronised at the t-MT. This leads to
performance deterioration and appropriate steps have to be
initiated by the network or CC. Note again that the distance
between the transmitter and the r-MTs was neglected in the
calculation since it was assumed that the r-MTs are far from the
transmitter.
[0343] Referring to FIG. 25, it depicts the flowchart describing a
suggested procedure as to guarantee forced synchronisation within a
wireless network. Note that the CC has to have knowledge about the
locations of the MTs.
FIELD OF THE THIRD INVENTION
[0344] The third invention relates to a method of transmitting data
between at least one information source and at least one
information sink using electromagnetic waves, to a computer program
for performing such a method, to a computer readable storage
medium, to a transmitter for use in the method and to a subscriber
identity module card.
BACKGROUND TO THE THIRD INVENTION
[0345] The envisaged scenario of wireless networks beyond 3G
focuses on network topologies that support all current and future
developed networks. Such topologies will rely more and more on a
direct and ad-hoc (i.e. temporary) mode of communication such that
there will not be a significant difference between a base station
(BS) and mobile terminal (MT). Each MT can be seen as an
information source, a relaying hop or/and a terminating information
sink. Such network topology inevitably requires a direct mode of
communication between at least one source MT (s-MT) and at least
one target MT (t-MT) via at least one relaying MT (r-MT).
[0346] A procedure that has been proposed to allow such direct
communication utilises TDMA-based relaying along a plurality of
mobile handsets. The system is known as Opportunity Driven Multiple
Access (ODMA). The main problem occurred with such deployment is
that the r-MT could not communicate with both, the s-MT and the
t-MT, at the same time and thus interrupting the session between
both. Therefore, a TDMA based approach was adopted where the r-MT
receives the signal stream during one time slot and retransmits it
during the consecutive time slot. It thus diminishes the system
capacity measured in bits/s/Hz. It further prevents the application
of multiple-input-multiple-output (MIMO) capacity measures in form
of e.g. Space-Time Codes or BLAST-like techniques and also gives
rise to problems of billing as the r-MT would incur the charges
which were generated for the t-MT.
[0347] A traditional approach has been to use frequency duplex
systems where the MTs communicate with the BS simultaneously in up
and downlink frequency, e.g. Universal Mobile Telecommunication
Service (UMTS). Such approach is not applicable to ad-hoc networks
where a clear up- and downlink does not exist as such and where
more than two simultaneous links are required.
SUMMARY OF THE THIRD INVENTION
[0348] It is apparent that there is a need for a MT to be a r-MT
for at least one s-MT or BS and a t-MT for at least one s-MT, r-MT
or BS at the same time. There is also a need for a simultaneous
wireless connection between at least one s-MT or BS and at least
one t-MT via at least one r-MT.
[0349] According to the third invention there is provided a method
of transmitting data between at least one information source and at
least one information sink using electromagnetic waves, which
method comprises the steps of:
[0350] (a) identifying at least one information relay; and
[0351] (b) instructing the at least one information relay to relay
data received from the information source intended for the
information sink on an unused frequency band such that simultaneous
communication can take place between the information source and
sink whilst said information relay relays data to the information
sink.
[0352] Preferred features of the invention are set out in the
attached claims to which attention is hereby directed.
[0353] As mentioned above the first and second inventions can be
advantageously employed together or individually in the third
invention.
[0354] In use, one or a group of sources wishes to communicate to
one or a group of sinks providing a single/multi-point to
single/multi-point communication link through a group of relays,
which themselves could be information sources or sinks. Then the
r-MTs have to be able to receive the to-be-relayed information
within at least one frequency-band and the relaying is accomplished
by retransmission within at least one different frequency band.
[0355] The concept is referred to as Frequency Relaying (FR).
[0356] According to another aspect of the third invention there is
provided a system for transmitting and receiving signals in which
there is a wireless connection between an information source and
information sink in which a relaying procedure is accomplished
using an unused frequency band such that there can be simultaneous
communication between the source and the sink and each source and
sink can function as a source, sink or relay.
[0357] Preferably, the relayed signal is re-transmitted at another
frequency.
[0358] Advantageously, at least one source communicates with at
least one sink by providing a single/multi-point to
single/multi-point communication link through at least one relay,
which relay is an information source or sink and in which the relay
is able to receive the to-be-relayed information and the relaying
is accomplished by retransmission by the relay at a different
frequency band.
[0359] Preferably, the relay transceiver has another programmable
oscillator besides its uplink and downlink oscillators which
another programmable oscillator retransmits the relayed signal at a
different frequency.
[0360] Advantageously, the controlling program of the receiver can
cut the uplink connection and reprogram the re-programmable uplink
oscillator to the relaying or re-transmitting frequency.
[0361] Preferably, the system is a CDMA-scheme.
[0362] Advantageously, the data stream for u users is spread with u
distinct spreading codes with given chip-rate, each of the u users
receives the u incoming data streams at frequency f.sub.1,
optionally processes u-1 data streams and relays the possibly
processed u-1 data streams at assigned frequencies f.sub.2,
f.sub.3, etc. to the remaining users within the group of u users,
each of the u users then receives its information at frequency
f.sub.1 and f.sub.x and processes u signal streams.
BRIEF DESCRIPTION OF THE DRAWINGS
[0363] FIG. 29 is a schematic view of a first embodiment of a data
communication system operating in accordance with the present
invention; and
[0364] FIG. 30 is a schematic view of a second embodiment of a data
communication system operating in accordance with the present
invention;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0365] Referring to FIG. 29 a data communication system is
generally identified by reference numeral 310 that comprises i
information sources 311, r information relays 312 and s information
sinks 313. The information sources, relays and sinks can be base
stations and/or mobile terminals (for example portable computers,
mobile telephones). In use data is to be sent from one or more of
the information sources 11 to one or more of the information sinks
313, via one or more information relays 312, each of which
communicates via electromagnetic waves ("wireless" link). The
information relays 312 are chosen such that data relayed therefrom
remains synchronised as described above. Data is sent from the
information sources 311 on frequencies f.sub.1 to f.sub.n
respectively and is received by all of the information relays 12.
Each information relay 312 receives data on frequencies f.sub.1 to
f.sub.n and has been instructed to relay the data on frequencies
f.sub.n+1 to f.sub.m respectively, where f.sub.n+1 to f.sub.m, are
unused frequency bands different to f.sub.1 to f.sub.n. In this way
the information relays 312 can communicate simultaneously with the
information sources 311 and the information sinks 313, and
communication directly between the information sources 311 and the
information sinks 313 does not have to be interrupted.
[0366] Referring to FIG. 30 a second embodiment of a data
communication system is generally identified by reference numeral
320 that comprises a base station 321 and four mobile terminals
322, 323, 324 and 325. The base station transmits the signal to the
mobile terminals 322, 323, 324 and 325 on frequencies f.sub.1 and
f.sub.2 as shown. The symbols for the `right` terminals 323 and 324
are sent to the `left` terminals 322 and 325 and vice versa. The
signals could be, but are not restricted to, Trellis encoded and
retransmitted on different frequency bands respectively to the
other group.
[0367] The embodiments described above can be implemented via any
or any combination of the access schemes described below.
[0368] In one embodiment of the invention simultaneous
communication between a base station (BS), relaying mobile terminal
(r-MT) and a target mobile terminal (t-MT) is assumed. In this
case, (1) the BS has to communicate with the r-MT and the t-MT in
up and downlink, (2) the r-MT has to communicate with the BS in up
and downlink and with the t-MT in forward and backward link, and
(3) the t-MT has to communicate with the BS in up and downlink and
with the r-MT in forward and backward link. Thus each terminal
involved requires four communication channels. Since a terminal
cannot transmit and receive at the same time at the same frequency,
it is necessary either to (a) use two frequency bands and two time
slots and one code, (b) two frequency bands, one time slot and two
codes, (c) one frequency band, two time slots and two codes, (d)
four frequency bands, one time slot and one code, (e) one frequency
band, four time slots and one code, or (f) one frequency band, one
time slot and four codes, or other hybrid solutions. Since system
efficiency or capacity is measured in bits/s/Hz, the number of time
slots and frequency bands utilised should be minimised. However, to
deploy four codes raises problems with power control inherent to
all code division multiple access (CDMA) based systems. Various
deployments in accordance with the invention are feasible. Firstly,
the BS maintains communication with the t-MT and r-MT on two
frequencies, traditionally up and downlink. The r-MT communicates
simultaneously with the t-MT on a third frequency, where
orthogonality (i.e. separability of communication channels) is
maintained either through time slot or code. Second, the r-MT stops
communicating with the BS in the uplink and reprograms the uplink
oscillator on the direct link frequency, which could be
advantageously deployed where terminals are substantially static
where an uplink communication with the BS is not vital, for example
in a packet switched network where traffic flow is asymmetric.
Third, a fourth oscillator is deployed to communicate in forward
and backward link between the r-MT and t-MT. Fourth, the BS
communicates with the r-MT and the t-MT in two different frequency
bands for up and downlink. Then, relaying is accomplished in the
appropriate downlink frequency band of the other MT. Further hybrid
combinations are possible.
[0369] In another embodiment of the invention simultaneous
communication between at least one r-MT, at least one t-MT and
possibly at least on BS is assumed. Such embodiment requires the
provision of an appropriate amount of frequency bands, and thus
sufficient oscillators within the MTs, to be able to support the
simultaneous multi-point-to-multi-point communication scenario.
[0370] In one embodiment, a CDMA-scheme is employed and the data
stream for u users is spread with u distinct spreading codes with
given chip rate. Each of the u users receives the u incoming data
streams at frequency f.sub.1, possibly processes u-1 data streams
and relays the possibly processed u-1 data streams at assigned
frequencies f.sub.2, f.sub.3, etc. to the remaining users within
the group of u users. Each of the u users then receives its
information at the relaying frequencies f.sub.2, f.sub.3, etc. and
thus processes u signal streams
[0371] In another embodiment, a TDMA-scheme is employed and the
data stream for u users is transmitted at appropriate time slots
and frequency bands. Each of the u users receives the u incoming
data streams at the specific time slot and specific frequency band,
possibly processes u-1 data streams and relays the possibly
processed u-1 data streams at least one of the assigned frequencies
f.sub.2, f.sub.3, etc. to the t-MT within the group of u users.
Each of the u users then receives its information at frequency
f.sub.1 and at least one frequency f.sub.x and thus processes at
least two signal streams.
[0372] It is not necessary to make any hardware changes in a
transmitter operating in accordance with the invention.
[0373] The following software changes should be in transmitter or
any logical unit controlling the transmitter antenna array. The
(software) algorithms have to control the setup and release of
relaying frequency oscillators in use. They have to inform adjacent
MTs about the possibility to setup a relaying connection. They have
to control the association and disassociation of MTs to and from a
relaying routing path. They have possibly to control
synchronisation and power control for the relaying MT. For the main
and relaying links, they have to control the appropriate choice of
scrambling and spreading codes for CDMA based systems, the
appropriate choice of frequency bands and time slots for TDMA based
systems and the appropriate choice of frequency bands, time slots
and frequency sub-carriers for OFDMA based systems. They have to
guarantee appropriate security, identification and authorisation of
potential and existing r-MTs. They have to control an appropriate
billing mechanism. They have to control a possible software update
within the MTs such as to support certain relaying features.
[0374] The following hardware changes should be performed within a
MT. Firstly, if the relaying scheme is chosen to be such that
another interface is used for relaying, then the hardware has to
provide this interface, e.g. PLC (Power Line Communications) or
Bluetooth. Secondly, if transparent relaying is deployed then
hardware has to be provided which allows amplification, frequency
translation and retransmission. This may pose requirements on
additional oscillators and filter design. Thirdly, if the r-MT is
operated in duplex mode or higher (e.g. triplex), i.e. simultaneous
communication with the TX and at least one t-MT, then appropriate
filters have to separate the used frequency bands sufficiently such
as not to cause any adjacent channel interference.
[0375] The following software changes have to be performed within a
MT. If a MT is to be used to act as a Central Controller (CC) for
an ad-hoc relay, then appropriate control algorithms have to be
provided. They have to perform negotiation with the CC in case of a
formation of or an association to a new relaying path. They have to
be able to influence the data streams such as to comply with the
requirements needed to allow for relaying. They have to be able to
control synchronisation and power control, either autonomously or
imposed by the TX/BS/CC. They have to guarantee appropriate
security for the relaying signal stream and t-MTs. The required
software could be provided to the MTs in one of the following ways:
Firstly, it could be in-built, e.g. already available on the
notebook or SIM (subscriber identity module) card or mobile phone.
Secondly, it could be downloaded via the air interface and
automatically installed, e.g. SDR (software defined radio).
Thirdly, it could be received from any surrounding MT. Fourthly, it
could be downloaded from special service points that provide the
necessary software. Fifthly, it could be downloaded from the
Internet, floppy disk or CD-ROM, e.g. onto a notebook.
[0376] The present invention relates to a system useful for use in
any mobile, fixed or nomadic, ad-hoc or meshed, centralised or
decentralised, wireless network.
[0377] The envisaged scenario of wireless networks beyond 3G
focuses on network topologies that support all current and future
developed networks. Such topologies will rely more and more on a
direct and ad-hoc mode of communication such that there will not be
a significant difference between a base station (BS) and mobile
terminal (MT). Each MT can be seen as an information source, a
relaying hop or/and a terminating information sink. Such network
topology inevitably requires a direct mode of communication between
at least one source MT (s-MT) and at least one target MT (t-MT) via
at least one relaying MT (r-MT).
[0378] A procedure that has been proposed to allow such direct
communication is utilising TDMA-based relaying along a plurality of
mobile handsets. The system was called Opportunity Driven Multiple
Access (ODMA). The main problem occurred with such deployment is
that the r-MT could not communicate with both, the s-MT and the
t-MT, at the same time and thus interrupting the session between
both. Therefore, a TDMA based approach was adopted where the r-MT
receives the signal stream during one time slot and retransmits it
during the consecutive time slot. It thus diminishes the system
capacity measured in bits/s/Hz. It further prevents the application
of multiple-input-multiple-output (MIMO) capacity measures in form
of e.g. Space-Time Codes or BLAST-like techniques and also gives
rise to problems of billing as the r-MT would incur the charges
which were generated for the t-MT.
[0379] A traditional approach has been to use frequency duplex
systems where the MTs communicate with the BS simultaneously in up-
and downlink frequency, e.g. UMTS. Such approach is not applicable
to ad-hoc networks where a clear up- and downlink does not exist as
such and where more than two simultaneous links are required.
[0380] We have now invented a system, which enables a MT to be an
s-MT, r-MT for at least one s-MT or BS and a t-MT for at least one
s-MT, r-MT or BS at the same time. According to the invention there
is provided a simultaneous wireless connection between at least one
s-MT or BS and at least one t-MT via at least one r-MT.
[0381] In use, one or a group of sources wishes to communicate to
one or a group of sinks providing a single/multi-point to
single/multi-point communication link through a group of relays,
which themselves could be information sources or sinks. Then the
r-MTs have to be able to receive the to-be-relayed information
within at least one frequency band and the relaying is accomplished
by retransmission within at least one different frequency band.
[0382] The concept is referred to as Frequency Relaying (FR).
[0383] In a preferred, although not restricted to, embodiment of
the invention simultaneous communication between a BS, r-MT and a
t-MT is assumed. Then, the BS has to communicate with the r-MT and
the t-MT in up- and downlink, the r-MT with the BS in up- and
downlink and with the t-MT in forward and backward link, and the
t-MT with the BS in up- and downlink and with the r-MT in forward
and backward link. Thus each terminal involved requires four
communication channels. Since a terminal cannot transmit and
receive at the same time at the same frequency, it is necessary to
use two frequency bands and two time slots and one code, or two
frequency bands and one time slot and two codes, or one frequency
band and two time slots and two codes, or four frequency bands and
one time slot and one code, or one frequency band and four time
slots and one code, or one frequency band and one time slot and
four codes, or other hybrid solutions. Since the system efficiency
is measured in bits/s/Hz, the number of time slots and frequency
bands utilised should be minimised. However, to deploy four codes
rises problems with power control inherent to all CDMA based
systems. Various deployments are feasible. First, the BS maintains
communication with the MTs on two frequencies, traditionally up-
and downlink. The r-MT communicates simultaneously with the t-MT on
a third frequency, where orthogonality is maintained either through
time slot or code. Second the r-MT stops communicating with the BS
in the uplink and reprograms the uplink oscillator on the direct
link frequency, which could be deployed in a rather static
environment where an uplink communication with the BS is not vital.
Third, a fourth oscillator is deployed to communicate in forward
and backward link between the r-MT and t-MT. Fourth, the BS
communicates with the r-MT and the t-MT in two different frequency
bands for up- and downlink. Then, relaying is accomplished in the
appropriate downlink frequency band of the other MT. Further hybrid
combinations are possible.
[0384] In a preferred, although not restricted to, embodiment of
the invention simultaneous communication between at least one r-MT,
at least one t-MT and possibly at least on BS is assumed. Such
embodiment requires the provision of an appropriate amount of
frequency bands, and thus sufficient oscillators within the MTs, to
be able to support the simultaneous multi-point-to-multi-point
communication scenario.
[0385] In a preferred, although not restricted to, CDMA-scheme
embodiment of the invention the data stream for u users is spread
with u distinct spreading codes with given chip rate. Each of the u
users receives the u incoming data streams at frequency f.sub.1,
possibly processes u-1 data streams and relays the possibly
processed u-1 data streams at assigned frequencies f.sub.2,
f.sub.3, etc. to the remaining users within the group of u users.
Each of the u users then receives its information at frequency
f.sub.1, and f.sub.x and thus processes u signal streams
[0386] In a preferred, although not restricted to, TDMA-scheme
embodiment of the invention the data stream for u users is
transmitted at appropriate time slots and frequency bands. Each of
the u users receives the u incoming data streams at the specific
time slot and specific frequency band, possibly processes u-1 data
streams and relays the possibly processed u-1 data streams at least
one of the assigned frequencies f.sub.2, f.sub.3, etc. to the t-MT
within the group of u users. Each of the u users then receives its
information at frequency f.sub.1 and at least one frequency f.sub.x
and thus processes at least two signal streams.
[0387] It is a feature of the present invention that no hardware
changes have to be performed within a BS antenna array.
[0388] It is a feature of the present invention that the following
software changes have to be performed within a BS or any logical
unit controlling the BS antenna array. The (software) algorithms
have to control the setup and release of relaying frequency
oscillators in use. They have to inform adjacent MTs about the
possibility to setup a relaying connection. They have to control
the association and disassociation of MTs to and from a relaying
routing path. They have possibly to control synchronisation and
power control for the relaying MT. For the main and relaying links,
they have to control the appropriate choice of scrambling and
spreading codes for CDMA based systems, the appropriate choice of
frequency bands and time slots for TDMA based systems and the
appropriate choice of frequency bands, time slots and frequency
sub-carriers for OFDMA based systems. They have to guarantee
appropriate security, identification and authorisation of potential
and existing r-MTs. They have to control an appropriate billing
mechanism. They have to control a possible software update within
the MTs such as to support certain relaying features.
[0389] It is a feature of the present invention that the following
hardware changes have to be performed within a MT. First, if the
relaying scheme is chosen to be such that another interface is used
for relaying, then the hardware has to provide this interface, e.g.
PLC or Bluetooth. Second, if transparent relaying is deployed then
hardware has to be provided which allows amplification, frequency
translation and retransmission. This may pose requirements on
additional oscillators and filter design. Third, if the r-MT is
operated in duplex mode or higher, i.e. simultaneous communication
with the TX and at least one t-MT, then appropriate filters have to
separate the used frequency bands sufficiently such as not to cause
any adjacent channel interference.
[0390] It is a feature of the present invention that the following
software changes have to be performed within a MT. If a MT is to be
used to act as a Central Controller (CC) for an ad-hoc relay, then
appropriate control algorithms have to be provided. They have to
perform negotiation with the CC in case of a formation of or an
association to a new relaying path. They have to be able to
influence the data streams such as to comply with the requirements
needed to allow for relaying. They have to be able to control
synchronisation and power control, either autonomously or imposed
by the TX/BS/CC. They have to guarantee appropriate security for
the relaying signal stream and t-MTs. The required software could
be provided to the MTs in one of the following ways: First, it
could be in-built, e.g. already available on the notebook or SIM
card or mobile phone. Second, it could be downloaded via the air
interface and automatically installed, e.g. SDR. Third, it could be
received from any surrounding MT. Fourth, it could be downloaded
from special service points which provide the necessary software.
Fifth, it could be downloaded from the Internet or floppy disk or
CD-ROM, e.g. onto a notebook.
[0391] It is a feature of the present invention that highly dynamic
ad-hoc networks can be operated in a decentralised direct mode
between terminals at various frequencies within given network
topologies.
[0392] The system can be applied to a Virtual Antenna Array (VAA)
as described above.
[0393] The invention is illustrated in the accompanying drawings in
which:--
[0394] FIG. 29 shows a generic information flow for forced
synchronised schemes FIG. 30 illustrates a CDMA embodiment with
groups of receivers
[0395] Referring to FIG. 29, a group of information sources i
communicates to a group of information sinks s via a group of
relays r. Those relays that are spatially close together are used
to accomplish forced synchronisation. There might be several groups
of spatially close relays. There might be several information sinks
and information sources, which not necessarily have to be linked in
a unique and unambiguous manner, which communicate via the relays
in at least one frequency band.
[0396] Referring to FIG. 30 this illustrates the frequency relaying
concept realizing a (2,2) Alamouti scheme. The base transmitter BS
transmits the signal to the groups of receivers MS1, MS2, MS3 and
MS4 on frequencies f.sub.1 and f.sub.2 as shown. The symbols for
the `right` group MS2 and MS3 are sent to the `left` group MS1 and
MS4 and vice versa. The signals could be, but are not restricted
to, Trellis encoded and retransmitted on respective differing
frequency bands to the other group.
[0397] The first, second and third inventions described herein can
be used in any desired combination.
* * * * *
References