U.S. patent application number 12/648995 was filed with the patent office on 2010-04-29 for communication systems.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Michael John Beems Hart, Yuefeng Zhou.
Application Number | 20100103991 12/648995 |
Document ID | / |
Family ID | 37081243 |
Filed Date | 2010-04-29 |
United States Patent
Application |
20100103991 |
Kind Code |
A1 |
Hart; Michael John Beems ;
et al. |
April 29, 2010 |
Communication Systems
Abstract
A transmission method for use in a multi-hop wireless
communication system is provided. Furthermore, the system has
access to a time-frequency format for use in assigning available
transmission frequency bandwidth during a discrete transmission
interval. The format defines a plurality of transmission windows
within such an interval, where each window occupies a different
part of that interval and has a frequency bandwidth profile within
the available transmission frequency bandwidth over its part of
that interval. Furthermore, each window being assignable for such a
transmission interval to one of said apparatuses for use in
transmission. The transmission method for use in this system
includes employing said format for one or more such transmission
intervals to transmit data and control information together along
at least two consecutive said links as a set of successive
transmission signals, link by link. Each said signal is transmitted
in an available transmission window of said interval(s) and at
least two of said signals are transmitted during the same said
transmission interval such that said information is transmitted
along said consecutive links in fewer transmission intervals than
said number of consecutive links.
Inventors: |
Hart; Michael John Beems;
(London, GB) ; Zhou; Yuefeng; (Haywards Heath,
GB) |
Correspondence
Address: |
BAKER BOTTS L.L.P.
2001 ROSS AVENUE, SUITE 600
DALLAS
TX
75201-2980
US
|
Assignee: |
Fujitsu Limited
Kawasaki-shi
JP
|
Family ID: |
37081243 |
Appl. No.: |
12/648995 |
Filed: |
December 29, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11840546 |
Aug 17, 2007 |
|
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12648995 |
|
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Current U.S.
Class: |
375/211 |
Current CPC
Class: |
H04W 28/06 20130101;
H04B 7/2606 20130101; H04W 88/04 20130101; H04B 7/155 20130101;
H04W 72/0453 20130101; H04W 40/02 20130101; H04W 16/26
20130101 |
Class at
Publication: |
375/211 |
International
Class: |
H04B 3/36 20060101
H04B003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 2006 |
GB |
GB 0616481.8 |
Claims
1. A communication method used in a multi-hop radio communication
system including a base station apparatus, intermediate apparatuses
and a user equipment, said communication method comprising:
providing a first transmission window and a second transmission
window in a radio frame; transmitting data from an intermediate
apparatus which is an odd number of hops from said base station
apparatus using said second transmission window and transmitting
data from an intermediate apparatus which is an even number of hops
from said base station apparatus using said first transmission
window.
2. The communication method according to claim 1, wherein said user
equipment receives data from an intermediate apparatus
corresponding to the last hop.
3. The communication method according to claim 1, wherein said base
station apparatus transmits data to an intermediate apparatus in
the first hop of a downlink transmission using said first
transmission window.
4. The communication method according to claim 1, wherein said user
equipment transmits data to an intermediate apparatus in the first
hop of an uplink transmission.
5. The communication method according to claim 1, wherein said base
station apparatus receives data from an intermediate apparatus
using said first transmission window in the last hop of an uplink
transmission.
6. The communication method according to claim 1, wherein said base
station apparatus and said intermediate apparatuses except for an
intermediate apparatus corresponding to the last hop of a downlink
transmission transmit preamble, frame structure information or
relay amble using corresponding transmission windows.
7. The communication method according to claim 1, wherein an
intermediate apparatus which is the furthest intermediate apparatus
from the base station apparatus receives a downlink transmission
using said first transmission window or said second transmission
window but does not use said first transmission window and second
transmission window for transmission to said user equipment.
8. The communication method according to claim 1, wherein an
intermediate apparatus which is the furthest intermediate apparatus
from the base station apparatus does not transmit any relay
amble.
9. A multi-hop radio communication system comprising: a base
station apparatus; intermediate apparatuses; a user equipment,
wherein a first transmission window and a second transmission
window are provided in a radio frame and an intermediate apparatus,
which is an odd number of hops from said base station apparatus is
configured to transmit data using said second transmission window
and an intermediate apparatus, which is an even number of hops from
said base station apparatus is configured to transmit data using
said first transmission window.
10. A base station apparatus used in a multi-hop radio
communication system including intermediate apparatuses, said base
station apparatus comprising: a transmitting unit configured to
transmit data to an intermediate apparatus in a first hop using a
first transmission window in a radio frame wherein an intermediate
apparatus, which is an odd number of hops from said base station
apparatus, transmits data using a second transmission window in
said radio frame and an intermediate apparatus, which is an even
number of hops from said base station apparatus transmits data
using said first transmission window in said radio frame.
11. An intermediate apparatus used in a multi-hop radio
communication system including intermediate apparatuses, said
intermediate apparatus comprising: a transmitting unit configured
to transmit data using either a first transmission window or a
second transmission window in a radio frame in accordance with a
hop number from a base station apparatus to said intermediate
apparatus wherein an intermediate apparatus, which is an odd number
of hops from said base station apparatus transmits data using said
second transmission window in said radio frame and an intermediate
apparatus, which is an even number of hops from said base station
apparatus, transmits data using said first transmission window in
said radio frame.
12. A user equipment used in a multi-hop radio communication system
including intermediate apparatuses, said user equipment comprising:
a receiving unit configured to receive data from either an
intermediate apparatus which is an odd number of hops from a base
station and transmits data to the next intermediate apparatus using
a second transmission window in a radio frame or an intermediate
apparatus which is an even number of hops from a base station and
transmits data to the next intermediate using a first transmission
window in said radio frame, the intermediate apparatus transmitting
said data to be received by said receiving unit being the furthest
intermediate apparatus from the base station and transmitting to
the user equipment in a further transmission window of said radio
frame.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application of pending
U.S. patent application Ser. No. 11/840,546 filed Aug. 17, 2007;
which claims foreign priority benefits under 35 U.S.C. .sctn.119 of
United Kingdom Application No. GB 0616481.8, filed on Aug. 18,
2006, entitled "Communication Systems".
TECHNICAL FIELD
[0002] This invention relates in general to communication systems,
and more particularly to a frame structure for a multihop
communication system.
OVERVIEW
[0003] Currently there exists interest in the use of multihop
techniques in packet based radio and other communication systems,
where it is purported that such techniques will enable both
extension in coverage range and increase in system capacity
(throughput).
[0004] In a multi-hop communication system, communication signals
are sent in a communication direction along a communication path
(C) from a source apparatus to a destination apparatus via one or
more intermediate apparatuses. FIG. 3 illustrates a single-cell
two-hop wireless communication system comprising a base station BS
(known in the context of 3G communication systems as "node-B" NB) a
relay node RN (also known as a relay station RS) and a user
equipment UE (also known as mobile station MS). In the case where
signals are being transmitted on the downlink (DL) from a base
station to a destination user equipment (UE) via the relay node
(RN), the base station comprises the source station (S) and the
user equipment comprises the destination station (D). In the case
where communication signals are being transmitted on the uplink
(UL) from a user equipment (UE), via the relay node, to the base
station, the user equipment comprises the source station and the
base station comprises the destination station. The relay node is
an example of an intermediate apparatus (I) and comprises: a
receiver, operable to receive data from the source apparatus; and a
transmitter, operable to transmit this data, or a derivative
thereof, to the destination apparatus.
[0005] Simple analogue repeaters or digital repeaters have been
used as relays to improve or provide coverage in dead spots. They
can either operate in a different transmission frequency band from
the source station to prevent interference between the source
transmission and the repeater transmission, or they can operate at
a time when there is no transmission from the source station.
[0006] FIGS. 4a and 4b illustrate a number of applications for
relay stations. For fixed infrastructure, the coverage provided by
a relay station may be "in-fill" to allow access to the
communication network for mobile stations which may otherwise be in
the shadow of other objects or otherwise unable to receive a signal
of sufficient strength from the base station despite being within
the normal range of the base station. "Range extension" is also
shown, in which a relay station allows access when a mobile station
is outside the normal data transmission range of a base station.
One example of in-fill shown at the top right of FIGS. 4a and 4b is
positioning of a nomadic relay station to allow penetration of
coverage within a building that could be above, at, or below ground
level.
[0007] Other applications are nomadic relay stations which are
brought into effect for temporary cover, providing access during
events or emergencies/disasters. A final application shown in the
bottom right of FIGS. 4a and 4b provide access to a network using a
relay positioned on a vehicle.
[0008] Relays may also be used in conjunction with advanced
transmission techniques to enhance gain of the communications
system as explained below.
[0009] It is known that the occurrence of propagation loss, or
"pathloss", due to the scattering or absorption of a radio
communication as it travels through space, causes the strength of a
signal to diminish. Factors which influence the pathloss between a
transmitter and a receiver include: transmitter antenna height,
receiver antenna height, carrier frequency, clutter type (urban,
sub-urban, rural), details of morphology such as height, density,
separation, terrain type (hilly, flat). The pathloss L (dB) between
a transmitter and a receiver can be modeled by:
L=b+10n log d (A)
Where d (meters) is the transmitter-receiver separation, b(db) and
n are the pathloss parameters and the absolute pathloss is given by
l=10.sup.(L/10). The sum of the absolute path losses experienced
over the indirect link SI+ID may be less than the pathloss
experienced over the direct link SD. In other words it is possible
for:
L(SI)+L(ID)<L(SD) (B)
[0010] Splitting a single transmission link into two shorter
transmission segments therefore exploits the non-linear
relationship between pathloss verses distance. From a simple
theoretical analysis of the pathloss using equation (A), it can be
appreciated that a reduction in the overall pathloss (and therefore
an improvement, or gain, in signal strength and thus data
throughput) can be achieved if a signal is sent from a source
apparatus to a destination apparatus via an intermediate apparatus
(e.g. relay node), rather than being sent directly from the source
apparatus to the destination apparatus. If implemented
appropriately, multi-hop communication systems can allow for a
reduction in the transmit power of transmitters which facilitate
wireless transmissions, leading to a reduction in interference
levels as well as decreasing exposure to electromagnetic emissions.
Alternatively, the reduction in overall pathloss can be exploited
to improve the received signal quality at the receiver without an
increase in the overall radiated transmission power required to
convey the signal.
[0011] Multi-hop systems are suitable for use with multi-carrier
transmission. In a multi-carrier transmission system, such as FDM
(frequency division multiplex), OFDM (orthogonal frequency division
multiplex) or DMT (discrete multi-tone), a single data stream is
modulated onto N parallel sub-carriers, each sub-carrier signal
having its own frequency range. This allows the total bandwidth
(i.e. the amount of data to be sent in a given time interval) to be
divided over a plurality of sub-carriers thereby increasing the
duration of each data symbol. Since each sub-carrier has a lower
information rate, multi-carrier systems benefit from enhanced
immunity to channel induced distortion compared with single carrier
systems. This is made possible by ensuring that the transmission
rate and hence bandwidth of each subcarrier is less than the
coherence bandwidth of the channel. As a result, the channel
distortion experienced on a signal subcarrier is frequency
independent and can hence be corrected by a simple phase and
amplitude correction factor. Thus the channel distortion correction
entity within a multicarrier receiver can be of significantly lower
complexity of its counterpart within a single carrier receiver when
the system bandwidth is in excess of the coherence bandwidth of the
channel.
[0012] Orthogonal frequency division multiplexing (OFDM) is a
modulation technique that is based on FDM. An OFDM system uses a
plurality of sub-carrier frequencies which are orthogonal in a
mathematical sense so that the sub-carriers' spectra may overlap
without interference due to the fact they are mutually independent.
The orthogonality of OFDM systems removes the need for guard band
frequencies and thereby increases the spectral efficiency of the
system. OFDM has been proposed and adopted for many wireless
systems. It is currently used in Asymmetric Digital Subscriber Line
(ADSL) connections, in some wireless LAN applications (such as WiFi
devices based on the IEEE 802.11a/g standard), and in wireless MAN
applications such as WiMAX (based on the IEEE 802.16 standard).
OFDM is often used in conjunction with channel coding, an error
correction technique, to create coded orthogonal FDM or COFDM.
COFDM is now widely used in digital telecommunications systems to
improve the performance of an OFDM based system in a multipath
environment where variations in the channel distortion can be seen
across both subcarriers in the frequency domain and symbols in the
time domain. The system has found use in video and audio
broadcasting, such as DVB and DAB, as well as certain types of
computer networking technology.
[0013] In an OFDM system, a block of N modulated parallel data
source signals is mapped to N orthogonal parallel sub-carriers by
using an Inverse Discrete or Fast Fourier Transform algorithm
(IDFT/IFFT) to form a signal known as an "OFDM symbol" in the time
domain at the transmitter. Thus, an "OFDM symbol" is the composite
signal of all N sub-carrier signals. An OFDM symbol can be
represented mathematically as:
x ( t ) = 1 N n = 0 N - 1 c n j2.pi. n .DELTA. ft , 0 .ltoreq. t
.ltoreq. T s ( 1 ) ##EQU00001##
where .DELTA.f is the sub-carrier separation in Hz, Ts=1/.DELTA.f
is symbol time interval in seconds, and c.sub.n are the modulated
source signals. The sub-carrier vector in (1) onto which each of
the source signals is modulated c .di-elect cons. C.sub.n,
c=(c.sub.0, c.sub.1 . . . c.sub.N-1) is a vector of N constellation
symbols from a finite constellation. At the receiver, the received
time-domain signal is transformed back to frequency domain by
applying Discrete Fourier Transform (DFT) or Fast Fourier Transform
(FFT) algorithm.
[0014] OFDMA (Orthogonal Frequency Division Multiple Access) is a
multiple access variant of OFDM. It works by assigning a subset of
sub-carriers, to an individual user. This allows simultaneous
transmission from several users leading to better spectral
efficiency. However, there is still the issue of allowing
bi-directional communication, that is, in the uplink and download
directions, without interference.
[0015] In order to enable bi-directional communication between two
nodes, two well known different approaches exist for duplexing the
two (forward or download and reverse or uplink) communication links
to overcome the physical limitation that a device cannot
simultaneously transmit and receive on the same resource medium.
The first, frequency division duplexing (FDD), involves operating
the two links simultaneously but on different frequency bands by
subdividing the transmission medium into two distinct bands, one
for forward link and the other for reverse link communications. The
second, time division duplexing (TDD), involves operating the two
links on the same frequency band, but subdividing the access to the
medium in time so that only the forward or the reverse link will be
utilizing the medium at any one point in time. Both approaches (TDD
& FDD) have their relative merits and are both well used
techniques for single hop wired and wireless communication systems.
For example the IEEE 802.16 standard incorporates both an FDD and
TDD mode. As an example, FIG. 5 illustrates the single hop TDD
frame structure used in the OFDMA physical layer mode of the IEEE
802.16 standard (WiMAX).
[0016] Each frame is divided into DL and UL subframes, each being a
discrete transmission interval. They are separated by
Transmit/Receive and Receive/Transmit Transition Guard interval
(TTG and RTG respectively). Each DL subframe starts with a preamble
followed by the Frame Control Header (FCH), the DL-MAP, and the
UL-MAP.
[0017] The FCH contains the DL Frame Prefix (DLFP) to specify the
burst profile and the length of the DL-MAP. The DLFP is a data
structure transmitted at the beginning of each frame and contains
information regarding the current frame; it is mapped to the
FCH.
[0018] Simultaneous DL allocations can be broadcast, multicast and
unicast and they can also include an allocation for another BS
rather than a serving BS. Simultaneous ULs can be data allocations
and ranging or bandwidth requests.
SUMMARY OF EXAMPLE EMBODIMENTS
[0019] In accordance with one embodiment of the present invention,
a transmission method for use in a multi-hop wireless communication
system is provided. The system includes a source apparatus, a
destination apparatus and one or more intermediate apparatuses. The
source apparatus is operable to transmit information along a series
of links forming a communication path extending from the source
apparatus to the destination apparatus via the intermediate
apparatus. Each intermediate apparatus is operable to receive
information from a previous apparatus along the path and to
transmit the received information to a subsequent apparatus along
the path. Furthermore, the system has access to a time-frequency
format for use in assigning available transmission frequency
bandwidth during a discrete transmission interval. The format
defines a plurality of transmission windows within such an
interval, where each window occupies a different part of that
interval and has a frequency bandwidth profile within the available
transmission frequency bandwidth over its part of that interval.
Furthermore, each window being assignable for such a transmission
interval to one of said apparatuses for use in transmission. The
transmission method for use in this system includes employing said
format for one or more such transmission intervals to transmit data
and control information together along at least two consecutive
said links as a set of successive transmission signals, link by
link. Each said signal is transmitted in an available transmission
window of said interval(s) and at least two of said signals are
transmitted during the same said transmission interval such that
said information is transmitted along said consecutive links in
fewer transmission intervals than said number of consecutive
links.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] For a more complete understanding of the present invention
and its advantages, reference is now made to the following
description, taken in conjunction with the accompanying drawings,
in which:
[0021] FIG. 1 shows a frame structure;
[0022] FIG. 2 shows node activity within each zone;
[0023] FIG. 3 shows a two-hop system;
[0024] FIGS. 4a and 4b show applications of relaying; and
[0025] FIG. 5 shows a TDD frame structure used in OFDMA.
DETAILED DESCRIPTION
[0026] When a node is required to support two independent links to
two different nodes, e.g. a relay station communicating with a base
station and a mobile, the existing TDD or FDD frame structures
require some modification in order to make realization of the relay
practical.
[0027] Particular embodiments provide a frame structure for a
multihop communication system that is an extension of the standard
TDD frame structure (see IEEE 802.16 standard for an example) that
provides support for any number of hops in the system. The proposed
frame structure has numerous benefits, as described later in this
description.
[0028] The proposed frame structure makes the assumption that the
MS cannot reliably receive the control information originating from
the head node or that a network that incorporates relays that will
perform some degree of local connection management and/or medium
allocation management. This local management could be based on
decisions being made at the RS independent of all other nodes in
the communication system or network, or with some degree of
co-operation between the various nodes that incorporate some
control functionality. Further, it could be that whilst the RS has
the capability to transmit control information, that all management
decisions are made at a node other than the RS from which the
signals are transmitted.
[0029] It is also assumed that the modified frame TDD structure
should provide support for legacy mobile devices that have no
knowledge of a relay station such that they can operate within the
communication system or network.
[0030] One proposed generic TDD frame structure is shown in FIG. 1.
It is composed of a number of transmission and reception zones for
both the downlink and uplink sub-frames. The zone types are either:
[0031] B Broadcast of control related information such as:
synchronization sequences, commands, information and details of the
structure or layout of the frame. [0032] C Dedicated control
information that is transmitted in a non-broadcast zone (i.e.
either to individual or a group of receivers) [0033] T Dedicated
user-data transmission The 9 different zones are described in Table
1, below.
TABLE-US-00001 [0033] Zone Number Label Description 1 P Preamble or
synchronization sequence transmissions for cell identification 2
MAP Frame format description (zone boundaries, allocations within
the zones, etc) 3 RP Relay preamble or synchronization transmission
or reception zone. 4 BS-RS/ BS to RS transmission zone & RS to
RS transmission BS-MS/ zone. Can also be used for BS to MS
transmission if RS-RS spatial division multiple access is supported
(i.e. the same transmission resource can be used to communicate
with more than one entity) 5 BS-MS/ BS to MS transmission zone
& RS to RS transmission BS-RS/ zone (including an RP zone as
described in item (3) RP above). 6 BS-MS/ RS to MS & BS to MS
transmission zone (BS ideally RS-MS transmits to MSs that will have
limited impact from simultaneous RS transmission). 7 MS-BS/ MS
control information transmission zone to an RS or MS-RS BS. Control
information can be information or requests from the MS. 8 MS-BS/ MS
to RS & MS to BS transmission zone. MS-RS 9 MS-BS/ MS to BS
& RS to RS transmission zone. RS-RS 10 RS-BS/ RS to BS & RS
to RS transmission zone. Can also be RS-RS used for MS to BS
transmission if spatial division multiple access is supported (i.e.
the same transmission resource can be used to communicate with more
than one entity)
[0034] FIG. 2 illustrates the operation of the BS, RS and MS in
terms of its activity within each of the zones described in Table
1. Whilst FIG. 2 only illustrates the case of a BS-RS1-RS2-RS3-MS
link (i.e. a four hop link), it is possible to use the frame
structure to support any number of hops. As shown for the case of
RS3, the generalisation is that last relay in the hop (RSn) is not
required to transmit the RP or RSn to RSn+1 zones in the DL
sub-frame or receive the RSn+1 to RSn in the uplink. Due to the
fact that the RS transmits the MAP information after reception of
control information from the previous transmitter (i.e. BS or RS),
two hop relaying will always incur at least an extra frame
latency.
[0035] However, due to the fact it is possible to relay control
information within a frame from RS to RS, if more than two-hop
relaying is undertaken then the proposed frame structure keeps the
relaying induced latency to a minimum, where the latency is given
by:
L.sub.relay(frames)=floor(N.sub.hops/2) (1)
[0036] In order to enable implementation, the frame structure may
also need to incorporate some gap times to allow a node to turn
around (i.e. change from transmitting to receiving mode, or vice
versa). In this case, some of the zones may also incorporate a gap
region or a gap zone maybe inserted in between two adjacent zones
that require the change in operation mode of the node.
[0037] It is further preferably that in such a case that a BS is
transmitting information to the RS in the MAP zone that it
schedules transmission to the RS first, before transmission to any
MS. The BS could then indicate in the MAP zone when there is no
more information pending for the RS so that it can stop receiving
whilst the BS transmits MAP information to other receivers and use
this time as an opportunity for turn around.
[0038] In summary, the benefits of particular embodiments may
include: [0039] Enable the construction of relays that incorporate
some degree of local management of medium access [0040] Maximize
spectral efficiency by making sure that the BS does not have any
time in the frame when it is idle [0041] Minimal latency: two or
three-hop relaying incurs 1 frame latency; 4 or 5 hop relaying
incurs a 2 frame latency, 6 or 7 hop relaying incurs a 3 frame
latency, etc. [0042] Enable the relaying enabled system to provide
support to a legacy single-hop TDD user [0043] The possibility to
further improve spectral efficiency through using SDMA based
techniques to enable the same transmission resource (frequency
& time) to be used between the BS and the RSs and MSs within a
cell. [0044] Are extendable to any number of hops [0045] Define a
special synchronization interval to enable synchronization of the
relay with other relays or base stations [0046] Enable an RS to
transmit a standard preamble or synchronization sequence (similar
to that transmitted by a BS) that a legacy (non-relay aware) user
can decode.
[0047] Embodiments of the present invention may be implemented in
hardware, or as software modules running on one or more processors,
or on a combination thereof
[0048] That is, those skilled in the art will appreciate that a
microprocessor or digital signal processor (DSP) may be used in
practice to implement some or all of the functionality of a
transmitter embodying the present invention. The invention may also
be embodied as one or more device or apparatus programs (e.g.
computer programs and computer program products) for carrying out
part or all of any of the methods described herein. Such programs
embodying the present invention may be stored on computer-readable
media, or could, for example, be in the form of one or more
signals. Such signals may be data signals downloadable from an
Internet website, or provided on a carrier signal, or in any other
form.
[0049] Although the present invention has been described with
several embodiments, a myriad of changes, variations, alterations,
transformations, and modifications may be suggested to one skilled
in the art, and it is intended that the present invention encompass
such changes, variations, alterations, transformations, and
modifications as fall within the scope of the appended claims.
* * * * *