U.S. patent application number 14/088823 was filed with the patent office on 2014-03-27 for radio channel allocation and link adaptation in cellular telecommunication system.
This patent application is currently assigned to Core Wireless Licensing S.A.R.L.. The applicant listed for this patent is Core Wireless Licensing S.A.R.L.. Invention is credited to Jari HULKKONEN, Olli PIIRAINEN.
Application Number | 20140087746 14/088823 |
Document ID | / |
Family ID | 35510765 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140087746 |
Kind Code |
A1 |
HULKKONEN; Jari ; et
al. |
March 27, 2014 |
RADIO CHANNEL ALLOCATION AND LINK ADAPTATION IN CELLULAR
TELECOMMUNICATION SYSTEM
Abstract
Methods, apparatuses, controllers, systems, and terminals can,
in certain embodiments, determine a number and properties of
potential interferers in a plurality of available radio channels.
The properties of the potential interferers can include modulation
methods used by the potential interferers. A network element
responsible for channel allocation can perform channel allocation
for a terminal and select a modulation method for the allocated
channel on the basis of the determination.
Inventors: |
HULKKONEN; Jari; (Oulu,
FI) ; PIIRAINEN; Olli; (Oulu, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Core Wireless Licensing S.A.R.L. |
Luxembourg |
|
LU |
|
|
Assignee: |
Core Wireless Licensing
S.A.R.L.
Luxembourg
LU
|
Family ID: |
35510765 |
Appl. No.: |
14/088823 |
Filed: |
November 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13659149 |
Oct 24, 2012 |
8600419 |
|
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14088823 |
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|
11642551 |
Dec 21, 2006 |
8320947 |
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13659149 |
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Current U.S.
Class: |
455/452.1 |
Current CPC
Class: |
H04L 27/2601 20130101;
H04W 72/082 20130101; H04L 27/3488 20130101; H04B 1/1027
20130101 |
Class at
Publication: |
455/452.1 |
International
Class: |
H04W 72/08 20060101
H04W072/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2005 |
FI |
20055687 |
Claims
1. A method comprising: receiving, by a network element responsible
for radio resource allocation, interference-related information
associated with one or more base stations surrounding a terminal;
determining, by the network element responsible for radio resource
allocation, potential interferers in a plurality of available radio
resources based on the received interference-related information
associated with the one or more base stations surrounding the
terminal; performing, by the network element responsible for radio
resource allocation, radio resource allocation for the terminal on
the basis of the determination; and selecting, by the network
element responsible for radio resource allocation, a modulation
method for the radio resource allocation.
2. The method of claim 1, wherein the radio resource allocation is
radio channel allocation.
3. The method of claim 1, wherein the interference-related
information comprises signal strength measurements of base station
signals.
4. The method of claim 3, wherein the base station signals are
downlink signals.
5. The method of claim 3, wherein the interference-related
information is received from the terminal.
6. The method of claim 3, wherein the signal strength measurements
are made by the terminal.
7. The method of claim 1, wherein determining the potential
interferers includes determining a number and properties of the
potential interferers.
8. The method of claim 7, wherein the properties of the potential
interferers comprise at least one of a signal level of the
interferer, modulation method used by the interferer, and signal
bandwidth of the interferer.
9. The method of claim 1, wherein determining includes determining
interference caused to surrounding one or more base stations in the
plurality of available radio resources based on the received
interference-related information associated with the one or more
base stations surrounding the terminal.
10. The method of claim 1, further comprising: receiving, by the
network element responsible for radio resource allocation, a radio
resource allocation request from the terminal.
11. A method comprising: receiving, by a network element
responsible for radio resource allocation, interference-related
information associated with one or more base stations surrounding a
terminal; determining, by the network element responsible for radio
resource allocation, interference caused to the surrounding one or
more base stations in a plurality of available radio resources
based on the received interference-related information associated
with the one or more base stations surrounding the terminal;
performing, by the network element responsible for radio resource
allocation, radio resource allocation for the terminal on the basis
of the determination; and selecting, by the network element
responsible for radio resource allocation, a modulation method for
the radio resource allocation.
12. The method of claim 11, wherein the radio resource allocation
is radio channel allocation.
13. The method of claim 11, wherein the interference-related
information comprises signal strength measurements of base station
signals.
14. The method of claim 13, wherein the base station signals are
downlink signals.
15. The method of claim 13, wherein the interference-related
information is received from the terminal.
16. The method of claim 13, wherein the signal strength
measurements are made by the terminal.
17. The method of claim 11, wherein the determining includes
determining a number and properties of potential interferers.
18. The method of claim 17, wherein properties of the potential
interferers comprise at least one of a signal level of the
interferer, modulation method used by the interferer, and signal
bandwidth of the interferer.
19. The method of claim 11, wherein the determining includes
determining potential interferers in the plurality of available
radio resources based on the received interference-related
information associated with the one or more base stations
surrounding the terminal.
20. The method of claim 11, further comprising: receiving, by the
network element responsible for radio resource allocation, a radio
resource allocation request from the terminal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/659,149, filed on Oct. 24, 2012. U.S.
patent application Ser. No. 13/659,149 is a continuation of U.S.
patent application Ser. No. 11/642,551, filed on Dec. 21, 2006 and
which is now U.S. Pat. No. 8,320,947. U.S. patent application Ser.
No. 11/642,551 claims priority from Finnish Patent Application No.
20055687, filed on Dec. 21, 2005. U.S. patent application Ser. No.
13/659,149, U.S. Pat. No. 8,320,947, and Finnish Patent Application
No. 20055687 are incorporated herein by reference.
FIELD
[0002] Exemplary embodiments relate to radio channel allocation and
link adaptation in a cellular telecommunication system.
BACKGROUND
[0003] One of the key problems in constructing and maintaining
cellular radio networks is the limited scope of available radio
spectrum. Careful planning of the use of radio frequencies aims at
utilizing the available frequencies as efficiently as possible but
simultaneously at minimizing co-channel interference and adjacent
channel interference. By means of various models, available
frequencies are divided into different cells so as to minimize the
interference occurring in radio connections and thus maximize the
network capacity. In a cell repeat pattern, the same or adjacent
frequencies must not be too close to one another, because this
causes excessive interference in the system. On the other hand, the
tighter the repeat pattern, the more efficient the usage of the
frequencies.
[0004] In known mobile systems, the allocation of a radio channel
to a given subscriber terminal generally depends on whether or not
a radio cell has an available traffic channel at that instant. In
the simplest case, if said radio cell has a free radio channel, it
is allocated to the subscriber terminal when necessary. More
sophisticated channel allocation methods have also been developed.
The quality of an idle radio channel may be taken into account. For
example in a GSM system (Global System for Mobile
Telecommunications), when allocating an uplink radio channel, the
interference power level of idle radio channels is measured and a
channel with the lowest interference level is allocated to a
terminal. Since the GSM system is time-divisional, a traffic
channel which comprises a time slot on a given frequency channel is
allocated to the subscriber terminal.
[0005] U.S. Pat. No. 6,799,044 discloses a dynamic channel
allocation method where a carrier-to-interference ratio of
available channels is evaluated. In the solution, a channel and a
frequency are dynamically selected on the basis of the evaluated
ratio. However, the proposed solution does not take possible
interference rejection into account and it cannot be used in
systems employing fixed frequency planning.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Various embodiments provide an improved solution for channel
allocation and link adaptation. According to an exemplary
embodiment, there is provided a method of allocating a radio
channel to a connection between a terminal and a base station in a
telecommunication system, the method comprises determining the
number and properties of potential interferers in a plurality of
available radio channels, and performing channel allocation on the
basis of the determination.
[0007] According to another exemplary embodiment, there is provided
a method of allocating a radio channel to a terminal in a cellular
telecommunication system, comprising at least a base station and
terminals, the method comprising: measuring, in the terminals
signal strengths of base stations surrounding each terminal;
calculating base station coverage areas which would be interfered
with by uplink transmission of a terminal to which the radio
channel is to be allocated, calculating the number of interferers
interfering with the uplink transmission of the terminal to which
the radio channel is to be allocated and the properties of the
interfering signals, performing channel allocation on a terminal on
the basis of the calculations.
[0008] According to an exemplary embodiment, there is provided a
method of performing link adaptation on a connection between a
terminal and a base station in a telecommunication system, the
method comprising: determining the number and properties of
potential interferers in a plurality of available radio channels,
and performing link adaptation on a connection on the basis of the
determination.
[0009] According to an exemplary embodiment, there is provided a
network element of a telecommunication system, configured to
allocate radio channels to connections between terminals and base
stations of the telecommunication system. The network element is
configured to determine the number and properties of potential
interferers in a plurality of available radio channels, and perform
channel allocation on a connection on the basis of the
determination.
[0010] According to an exemplary embodiment, there is provided a
network element of a telecommunication system, configured to
allocate radio channels to terminals of the telecommunication
system and to receive from terminals of the telecommunication
system measurement results relating to signal strength of a signal
received by each terminal from base stations surrounding the
terminal. The network element is configured to calculate base
station coverage areas which would be interfered with by uplink
transmission of a terminal to which the radio channel is to be
allocated, calculate the number of interferers interfering with the
uplink transmission of the terminal to which the radio channel is
to be allocated, perform channel allocation on a terminal on the
basis of the calculations.
[0011] According to an exemplary embodiment, there is provided a
base station controller of a telecommunication system, controlling
a number of base stations connected to the base station controller,
configured to allocate radio channels to terminals of the
telecommunication system for communicating with at least one base
station. The base station controller is configured to determine the
number and properties of potential interferers in a plurality of
radio channels, and perform channel allocation on a terminal on the
basis of the determination.
[0012] According to an exemplary embodiment, there is provided a
telecommunication system, comprising a network element for
allocating radio channels to connections between terminals and base
stations of the telecommunication system. The system comprises a
network element for determining the number and properties of
potential interferers in a plurality of available radio channels,
and performing channel allocation on a connection on the basis of
the determination.
[0013] According to an exemplary embodiment, there is provided a
network element of a telecommunication system, configured to
perform link adaptation on connections between terminals and base
stations of the telecommunication system. The network element is
configured to determine the number and properties of potential
interferers in a plurality of available radio channels, and perform
link adaptation on a connection on the basis of the
determination.
[0014] According to an exemplary embodiment, there is provided a
terminal of a telecommunication system, configured to allocate
radio channels to connections between the terminal and base
stations of the telecommunication system. The terminal is
configured to determine the number and properties of potential
interferers in a plurality of available radio channels, and perform
channel allocation on a connection on the basis of the
determination.
[0015] According to an exemplary embodiment, there is provided a
computer program product encoding a computer program of
instructions for executing a computer process for allocating a
radio channel to a connection between a terminal and a base station
in a telecommunication system, the process comprising: determining
the number and properties of potential interferers in a plurality
of available radio channels, and performing channel allocation on
the basis of the determination.
[0016] According to an exemplary embodiment, there is provided a
computer program distribution medium readable by a computer and
encoding a computer program of instructions for executing a
computer process for allocating a radio channel to a connection
between a terminal and a base station in a telecommunication
system, the process comprising: determining the number and
properties of potential interferers in a plurality of available
radio channels, and performing channel allocation on the basis of
the determination.
[0017] According to an exemplary embodiment, there is provided a
computer program distribution medium readable by a computer and
encoding a computer program of instructions for executing a
computer process for performing link adaptation to a connection
between a terminal and a base station in a telecommunication
system, the process comprising: determining the number and
properties of potential interferers in a plurality of available
radio channels, and performing link adaptation on the basis of the
determination.
[0018] Various embodiments provide several advantages. The solution
according to various embodiments takes an interference situation
into account in a more detailed manner compared to idle radio
channel measurements. The solution does not need dynamic frequency
allocation and is thus simpler to implement compared to the
solution of U.S. Pat. No. 6,799,044, for example. Furthermore, the
solution is especially suitable to be used in connection with
interference cancellation methods. Interference cancellation
methods are able to enhance reception quality when the number of
interfering signals is low, or when one or few interfering signal
levels are higher compared to the rest of the interfering signal
levels. When there are only few interferers, preferably only one,
the interference rejection procedures can cancel the interference
even at a high power level of the interference.
[0019] In addition, various embodiments are suitable to be used in
a system where more than one modulation method is used. For
example, various embodiments may be used in systems where it is
possible to allocate time slot specifically wide-band carriers
which overlap with adjacent carriers and thus cause interference to
other users and in the same time suffer from interference more than
users with narrower bandwidth.
[0020] In an embodiment, a solution disclosed herein is applied to
the uplink direction. In another embodiment, the solution is
applied to the downlink direction.
[0021] In an exemplary embodiment, terminals of a telecommunication
system measure signal strength of base stations signals they are
receiving. These measurement results are transmitted to a network
element, such as a base station controller, for example. The
network element calculates the number and properties of potential
interferers of idle radio channels. The number and properties of
potential interferers of idle radio channels are compared with each
other. Idle radio channels are prioritized on the basis of the
comparison.
[0022] In an embodiment, when a terminal requires a radio channel,
the network element allocates a radio channel which provides
sufficient quality to the terminal.
LIST OF DRAWINGS
[0023] In the following, exemplary embodiments will be described in
greater detail with reference to the embodiments and the
accompanying drawings, in which
[0024] FIG. 1A shows an example of a cellular telecommunication
system;
[0025] FIG. 1B illustrates an example of a structure of a base
station controller;
[0026] FIG. 2 illustrates an example of terminals carrying out
downlink measurements of base station signals;
[0027] FIG. 3 illustrates an exemplary flow chart;
[0028] FIG. 4 illustrates another example of terminals carrying out
downlink measurements;
[0029] FIGS. 5A and 5B illustrate examples of a group of carrier
waves in a GSM/EDGE based system;
[0030] FIG. 6 illustrates an example of a structure of a wide-band
carrier wave generator;
[0031] FIG. 7 illustrates an example of a structure of a base
station; and
[0032] FIG. 8 illustrates an exemplary flow chart; and
[0033] FIG. 9 illustrates an example of the structure of a
terminal.
DESCRIPTION OF EMBODIMENTS
[0034] Exemplary embodiments are applicable in various
telecommunication systems, in which terminals are provided with
different radio path properties. In the exemplary embodiments, the
users are typically separated from each other in time domain and
several frequency carriers are in use. Typical examples of a system
in which various embodiments can be applied are cellular
telecommunication systems such as GSM and GSM/EDGE based systems
and evolutions of third generation systems such as 3.9G, also
called LTE (Long Term Evolution) or EUTRAN (Enhanced UMTS
Terrestrial Radio Access Network).
[0035] Let us take a closer look at FIG. 1A, which illustrates an
example of the structure of a cellular telecommunication system.
FIG. 1A is a simplified block diagram describing the most important
cellular telecommunication system parts at network element level
and the interfaces between them. The structure and operation of the
network elements are not described in detail, since they are
commonly known.
[0036] The cellular telecommunication system may be divided into a
core network (CN) 100, a GSM/EDGE radio access network (GERAN) 102
and a mobile station (MS) 104.
[0037] The GERAN 102 includes a base station system (BSS) 106,
which includes a base station controller (BSC) 108 and base
stations (BTS) 110, 112 and 114.
[0038] The structure of the core network 100 supports both
circuit-switched connections and packet-switched connections.
[0039] A Mobile Services Switching Centre MSC 116 is the centre of
the circuit-switched side of the core network 100. The functions of
the mobile services switching centre 116 include: switching,
paging, location registration of user equipment, handover
management, collecting subscriber billing information, encryption
parameter management, frequency allocation management and echo
cancellation. The number of mobile services switching centres 116
may vary: a small network operator may be provided with a single
mobile services switching centre 116, but larger core networks 100
may be provided with several.
[0040] Larger core networks 100 may comprise a separate Gateway
Mobile Services Switching Centre GMSC 118 handling the
circuit-switched connections between the core network 100 and
external networks 120. The gateway mobile services switching centre
118 is located between the mobile services switching centres 116
and the external networks 120. The external network 120 may for
instance be a Public Land Mobile Network PLMN or a Public Switched
Telephone Network PSTN.
[0041] The network elements described in FIG. 1A are operational
entities, and the physical implementation thereof may vary.
[0042] A Serving GPRS Support Node SGSN 122 is the centre of the
packet-switched side of the core network 100. The main task of the
serving GPRS support node 122 is to transmit and receive packets
with the user equipment 104 supporting packet-switched transmission
using the base station system 106. The serving GPRS support node
122 includes subscriber data and location information concerning
the user equipment 104.
[0043] A Gateway GPRS Support Node GGSN 124 is the corresponding
part on the packet-switched side to the gateway GMSC 118 on the
circuit-switched side. The gateway GPRS support node 124 must be
able to route the outgoing traffic from the core network 100 to
external networks 126. In this example, the Internet represents the
external networks 126.
[0044] The base station system 106 is composed of a Base Station
Controller BSC 108 and Base Transceiver Stations or Base Stations
BTS 110, 112 and 114. The base station controller 108 controls the
base stations 110, 112 and 114. In principle, the aim is to place
the equipment implementing the radio path and the functions
associated therewith in the base station 110, 112 and 114 and to
place the control equipment in the base station controller 108.
[0045] FIG. 1B illustrates an example of the structure of a base
station controller 108 in more detail. The radio network controller
108 comprises a group switching field 130 and a control unit 132.
The group switching field 130 is used for switching speech and data
and for combining signalling circuits. The base station system 106
comprising the base station controller 108 and the base stations
110, 112 and 114 further comprises a transcoder 134. The transcoder
134 is usually located as close to a mobile services switching
centre 116 as possible since speech can thus be transmitted in a
cellular radio network mode between the transcoder 134 and the base
station controller 108 using as little transmission capacity as
possible. The transcoder may also be located in the mobile services
switching centre 116 or in each base station.
[0046] The transcoder 134 converts the different digital speech
encoding modes used between a public switched telephone network and
a radio telephone network into compatible ones, e.g. from the fixed
network mode into another mode of the cellular radio network, and
vice versa. The control unit 132 is configured to perform radio
resource management of the base stations 110, 112 and 114,
inter-cell handover, frequency management, or allocation of
frequencies to the base stations 110, 112 and 114, management of
frequency hopping sequences, measurement of time delays in the
uplink direction, operation and maintenance, and power control
management, for example. The control unit 132 can be realized with
one or more processors or discrete components, such as ASICs
(Application Specific Intergrated Circuit) and associated software,
for example.
[0047] The group switching field 130 is configured to perform
switching procedures both to the public switched telephone network
PSTN 120 through the mobile services switching centre 116 and to a
packet transmission network 126.
[0048] Returning to FIG. 1A, the base station 110, 112 and 114
includes at least one transceiver implementing a carrier, or eight
time slots, or eight physical channels. Typically, one base station
serves one cell, but such a solution is also possible, in which one
base station 110, 112 or 114 serves several sectorized cells. The
base station 110, 112 and 114 has following functions: calculations
of timing advance, measurements in the uplink direction, channel
coding, encryption, decryption and frequency hopping, for
example.
[0049] The subscriber terminal 104 includes at least one
transceiver that implements the radio connection to the radio
access network 102 or to the base station system 106. In addition,
the subscriber terminal 104 typically comprises an antenna, a
processor controlling the operation of the device and a battery.
Many kinds of subscriber terminals 104 with various properties
currently exist, for instance vehicle-mounted and portable
terminals.
[0050] A terminal requires a radio channel when it communicates
with a base station during a call, for example. A radio channel is
allocated to the terminal in a network element of the
telecommunication system responsible for channel allocation. In GSM
and GSM/EDGE based cellular telecommunication systems the network
element is base station controller (BSC).
[0051] In an exemplary embodiment, interference rejection combining
(IRC) algorithm is utilized in the system in the uplink reception.
IRC algorithms provide a well-known solution for reducing
interference. The algorithms are especially efficient in situations
where there is only one interfering signal. A receiver utilizing
IRC may tolerate an interference signal of moderate level with only
slight impact on the received signal quality. If the number of
interferers is more than one the tolerated interference level is
lower.
[0052] In an exemplary embodiment, terminals of the cellular
telecommunication system measure downlink signal strength of base
station signals they are receiving. These measurement results are
transmitted to a network element, such as a base station
controller, for example. In GSM and GSM/EDGE based cellular
telecommunication systems, each base station transmits a broadcast
control channel (BCCH) in a given time slot. Typically, this is the
first time slot of a frame on one of the frequencies the base
station is utilizing. The terminals of the system measure the
signal strength of BCCH sent by surrounding base stations. In prior
art, this information is utilized when making handover decisions,
for example.
[0053] FIG. 2 illustrates measurement of BCCH. FIG. 2 shows four
base stations 200, 202, 204 and 206 and three terminals 208, 210
and 212. Each terminal measures the BCCH signal strength of each
BCCH it is able to receive and reports the measurement results to a
network element responsible for channel allocation. Each terminal
has been informed by the network of the frequency each nearby base
station uses to transmit a BCCH. Let us assume in this example that
the network element is a base station controller. In this example,
the terminal 208 reports base stations 200 and 202. Terminal 210
reports base stations 200, 202 and 204. Terminal 212 reports base
stations 202, 204 and 206. Thus, terminals 208 and 210 report base
station 200. Because of the reciprocity of uplink and downlink
channels, terminals 208 and 210 would be potential interferers to a
terminal in the coverage area of base station 200. Whether or not
terminals 208 and 210 are actual interferers depends upon the radio
channel (time slot and frequency, for example) of the terminal in
the coverage area of base station 200. For example, traffic in the
same time slots in adjacent frequency carriers may cause
interference. Furthermore, although a time slot is allocated to a
terminal no traffic necessarily occurs all the time.
[0054] In an exemplary embodiment, when a radio channel is to be
allocated to a terminal, the base station controller is configured
to determine the available idle radio channels in the cell where
the terminal is located. The base station controller is further
configured to determine the number and properties of potential
interferers in a plurality of the available radio channels, and
perform channel allocation on a terminal on the basis of the
determination. The properties of the potential interferers comprise
the signal level of the interferer, modulation method used by the
interferer or the signal bandwidth of the interferer, for example.
By selecting a radio channel with only one interferer the
properties of IRC may be effectively utilized.
[0055] With reference to FIG. 3, an exemplary embodiment is
illustrated with a flow chart.
[0056] In step 300, a channel allocation request is received by a
network element responsible for channel allocation. Let us assume
in this example that the network element is a base station
controller. The cause for the channel allocation request may be a
mobile originating or a mobile terminating call, for example.
[0057] In step 302, the base station controller determines
available idle time slots in the cell where the terminal is
located.
[0058] In step 304, the base station controller gathers the
measurement results reported by the terminals.
[0059] In step 306, the base station controller calculates the
number and properties of potential interferers regarding the
available idle radio channels.
[0060] In step 308, the base station controller compares the number
and properties of potential interferers of a plurality of radio
channels with each other and prioritizes the channels. In an
embodiment, the base station prioritizes available radio channels
according to the number of potential interferers. In an embodiment,
the base station prioritizes available radio channels according to
the properties of potential interferers.
[0061] In step 310, the base station controller allocates a radio
channel to the terminal on the basis of the determination and
priorisation.
[0062] In an exemplary embodiment, the amount of interference the
radio channel to be allocated would cause to surrounding cells is
also taken into account in the channel allocation.
[0063] In FIG. 4, a base station 200 serves a terminal 208. Thus,
the terminal transmits an uplink signal 400 to the base station 200
and receives a downlink signal 402 from the base station. The
system also comprises other base stations 202, 204, 206, near the
area where the terminal is located. The terminal measures the BCCH
signal strength of each BCCH it is able to receive. In the example
of FIG. 4, the terminal 208 receives four BCCH signals 402, 404,
406 and 408. Of these signals, let us assume that signals 402, 404,
406 from base stations 200, 202 and 204, respectively, are the
strongest ones. The terminal reports these signals to the base
station controller. On the basis of this, it is possible for the
base station controller to determine that the signal strength of
the uplink signal transmitted by the terminal 208 is strongest in
the cells served by base stations 200, 202 and 204.
[0064] In an exemplary embodiment, frame based transmission is
utilized in the uplink direction of the cellular telecommunication
system. The frames comprise time slots. In the above described
GSM/EDGE based system, each frame comprises eight time slots. In an
embodiment, different modulation methods may be used in different
time slots. Different modulation methods may lead to different
bandwidths.
[0065] With reference to FIGS. 5A and 5B, let us consider the
carrier wave structure of the GSM/EDGE system. The x-axis 502 and
y-axis 504 show frequency and signal power, respectively, in
arbitrary units.
[0066] FIG. 5A shows a group of carrier waves 500A comprising
narrow-band carrier waves 506A, 506B, 506C, 506D. FIG. 5A shows the
carrier wave structure according to the present GSM/EDGE system,
whereas FIG. 5B illustrate the carrier wave structure of an
enhanced GSM/EDGE system. In this context, the term "narrow band"
refers to a narrow bandwidth 512 obtained with a first modulation
symbol rate. A typical first modulation symbol rate of 13/48 MHz,
also approximated with 270.833 kHz, results in the narrow bandwidth
512 of about 200 kHz.
[0067] The narrow-band carrier waves 506A-506D are separated by a
predefined carrier spacing 510, which is typically defined as a
separation of the band origins 508A, 508B, 508C, 508D of the
narrow-band carrier waves 506A-506D. According to a GSM/EDGE
specification, the predefined carrier spacing 510 is 200 kHz.
[0068] In FIG. 5B, a wide-band carrier 514 is generated into the
group of the carrier waves 500B by applying linear modulation at a
second modulation symbol rate that is a multiple of the first
modulation symbol rate applied to the narrow-band carrier waves
506A-506D. In this case, the narrow-band carrier wave 506B is
replaced with the wide-band carrier wave 514 while the structure of
the rest of the group of the carrier waves 500A remains unaltered.
The predefined carrier spacing 510 is preserved and the wide-band
carrier wave 514 is allowed to overlap with adjacent carrier waves
506A, 506C.
[0069] In an exemplary embodiment, the second modulation symbol
rate is twice the first modulation symbol rate. For example, when
the first modulation symbol rate is 13/48 MHz, the second
modulation symbol rate of 26/48 MHz, also approximated with 641.666
kHz, is obtained.
[0070] The linear modulation at the second modulation symbol rate
results in a wide bandwidth 516 of the wide-band carrier wave 514.
The second modulation symbol rate of 26/48 MHz results in the wide
bandwidth 516 of about 600 kHz.
[0071] In the transmission of the wide-band carrier wave 514, the
burst structure of the GSM/EDGE burst is preserved in the
conventional structure, i.e. in the structure applied when
transmitting signals at the first symbol rate.
[0072] As a consequence of the introduction of the wide-band
carrier and preservation of the carrier spacing, the data transfer
capacity of individual carriers and the overall data transfer
capacity of the group of carriers increase.
[0073] FIG. 6 illustrates a section of a transmitter utilizing
wide-band carriers. The wide-band carrier wave generator 600 of a
transmitter typically includes an I-modulator 604A and a
Q-modulator 604B. The digital signal 602 is converted from a serial
format into a parallel format in a serial-to-parallel converter
(S/P) 626, and parallel components of the digital signal 602 are
fed into the I-modulator 604A and the Q-modulator 604B.
[0074] The I-modulator 604A is provided with a first analog signal
waveform 624A which encodes the bits of the digital signal 602
according to the applied linear modulation at the second modulation
symbol rate.
[0075] The Q-modulator 604B is provided with a second analog signal
waveform 624B which encodes the bits of the digital signal 602
according to the applied linear modulation at the second modulation
symbol rate.
[0076] The first analog waveform 624A and the second analog
waveform 624B may be generated in a frequency generator (FG) 606
which adjusts signal characteristics of the first analog waveform
624A and those of the second analog waveform 624B so that the
applied modulation is realized. Such signal characteristics may be
the relative phase and/or amplitude of the first analog waveform
624A and the second analog waveform 624B.
[0077] The frequency generator 606 may be provided with a control
signal 614 including, for example, instructions on the applied
modulation scheme and a clock signal. The timing information
carried by the clock signal may be used to synchronize the feeding
of the digital signal 602 into the wide-band carrier wave generator
600.
[0078] The I-modulator 604A outputs an I-branch waveform 608A into
a combiner 610.
[0079] The Q-modulator 604B outputs a Q-branch waveform 608B into
the combiner 610.
[0080] The combiner 610 combines the I-branch waveform 608A and the
Q-branch waveform 608B and outputs a combined waveform 612.
[0081] The I-modulator 604A and the Q-modulator 604B may be
implemented with a digital signal processor and software. In some
applications, the I-modulator 604A and the Q-modulator 604B are
implemented with ASICs (Application-Specific Integrated
Circuit).
[0082] The combined waveform 612 is fed into an up-converter 616
which converts the combined waveform 612 into the wide-band carrier
wave 622. The up-converter 616 is typically coupled to a local
oscillator 620 which provides a local oscillator frequency 618 for
the up-converter 616.
[0083] The wide-band carrier wave generator 600 may apply an M-ary
phase shift keying (M-PSK), where M=2, 4, 8, 16, for encoding the
bits of the digital signal 602 into the wide-band carrier wave 622
at the second symbol rate. In an exemplary embodiment, the
wide-band carrier wave generator 600 applies an octal phase shift
keying (8-PSK).
[0084] The wide-band carrier wave generator 600 may also apply an
M-ary quadrature amplitude modulation (M-QAM), where M=2, 4, 8, 16,
32 or 64, for encoding the bits of the digital signal 602 into the
wide-band carrier wave 622 at the second symbol rate.
[0085] When applying an M-ary modulation rate, the tail bits,
training sequence bits, and the data bits are encoded at the M-ary
modulation rate.
[0086] The wide-band carrier wave generator 600 is further capable
of implementing narrow-band carrier waves 506A-506D.
[0087] The wide-band carrier radio channels described above may be
allocated for terminals requiring high transmission capability. The
drawback is that adjacent carriers overlap, thus creating
interference. The overlapping carriers cause more interference to
other users in the system. Also the users utilizing wide-band
carriers suffer from the overlapping.
[0088] FIG. 7 illustrates an example of the structure of a base
station 700 of an enhanced GSM/EDGE system and capable of receiving
and processing a wide-band carrier wave includes at least two
diversity antennas 704A, 704B for sampling an electromagnetic field
associated with the wide-band carrier wave 712 transmitted from the
mobile station 102.
[0089] The diversity antennas 704A, 704B are coupled to a wide-band
carrier receiver (WCR) 702 which receives and demodulates the
wide-band carrier wave 712 at the second symbol rate. The WCR 702
may include receive antenna branches 706A, 706B, each coupled to an
individual diversity antenna 704A, 704B. Each receive antenna
branch 706A, 706B demodulates the wide-band carrier wave 712
separately, and outputs a receive antenna branch-specific digital
signal 708A, 708B.
[0090] The receive antenna branch-specific digital signals 708A,
708B are inputted into a base band domain (BBD) 710 of the network
element 700 for further processing. The BBD 710 outputs processed
signals 714 to the higher layers of the GSM/EDGE telecommunications
system.
[0091] In an exemplary embodiment, the base station 700 utilizes an
interference rejection combining (IRC) algorithm in the uplink
reception. The IRC algorithm may be directed at the receive antenna
branch-specific digital signals 708A, 708B and implemented with a
digital signal processor and software in the base band domain 710
of the base station 700.
[0092] In an IRC algorithm, multiple copies of versions of a signal
containing the same data are received. The signals are combined so
that the impact of interference is minimized.
[0093] IRC algorithms provide a well-known solution for reducing
interference caused by overlapping carrier waves. It is assumed
that a person skilled in the art is capable of implementing IRC
algorithms in GSM/EDGE telecommunications systems without further
description.
[0094] To enhance the operation of IRC, the number and properties
of potential interferers of each radio channel may be taken into
account in channel allocation, as described above. Efficient
channel allocation in association with the usage of wide-band
carriers may comprise following requirements. To make sure that
interference caused by overlapping carriers does not increase too
much in the system some interference control should be performed.
To keep the interference level of the wide-band carriers users in
acceptable level the channel allocation should control the usage of
radio channel frequencies in such a manner that only a certain
number of interfering signals hit inside allocated wide-band
carrier. Thus, the radio channels should be allocated in such a
manner that interference is optimised for a wide-band carriers.
This maximises the spectral efficiency of the wide-band
carriers.
[0095] IRC receivers may also be utilized in mobile terminals.
Thus, the embodiment described above may be utilized in the
downlink transmission direction as well.
[0096] With reference to FIG. 8, an exemplary embodiment is
illustrated with a flow chart.
[0097] In step 800, a channel allocation request is received by a
network element responsible for channel allocation. Let us assume
in this example that the network element is a base station
controller. The cause for the channel allocation request may be a
mobile originating or a mobile terminating call, for example. The
requested channel to be allocated is a wide-band carrier.
[0098] In step 802, the base station controller determines
available idle time slots in the cell where the terminal is
located.
[0099] In step 804, the base station controller determines the
number and properties of potential interferers regarding the
available idle radio channels. This is based on the measurement
results reported by the terminals of the system.
[0100] In step 806, the base station controller determines the
cells the channel to be allocated would potentially interfere. This
is also based on the measurement results reported by the terminals
of the system.
[0101] In step 808, the base station controller prioritizes the
available idle radio channels by comparing the number and
properties of potential interferers of a plurality of radio
channels with each other and taking also the number of interfered
cells into account.
[0102] In step 810, the base station controller checks whether
calculated interference date indicates that a wide-band carrier
channel may be allocated on an idle channel.
[0103] If a channel with low enough number of interferers with
suitable properties is found, the channel is allocated in step
812.
[0104] There may be situations that a suitable channel for a
wide-band carrier was not found. In an embodiment, the time slot
usage of the serving cell and/or surrounding interfered and
interfering cells may be rearranged 814 with intercell handovers so
that a good enough time slots for a wide-band carrier may become
available. For example, a interference free time slot may be
arranged for a wide-band carrier by directing terminals to perform
intercell handovers for time slot to another. For example, a
terminal using the same time slot on an adjacent carrier may be
requested to perform a handover to a different time slot.
[0105] If it is not possible to get an interference free time slot,
a low interference time slot may be arranged. A low interference
time slot may be such that it is interfered by interferers of
suitable number and properties in such a way that interference
rejection combining can be efficiently utilized. For example, it is
not desirable that two wide-band carrier users are in adjacent
frequencies in the same time slots.
[0106] If a channel with low enough number of interferers with
suitable properties can be arranged the channel is allocated in
step 812.
[0107] If the base stations are utilizing frequency hopping the
above described solution may be used with only minor modifications.
As the terminals are hopping from frequency carrier to another
according to a predetermined hopping sequence only time slots are
taken into account in evaluating interference. The actual number of
interferers cannot be counted, as the terminals are hopping using
different hopping sequences and the situation is changing form
frame to frame, but an average value may be obtained.
[0108] Various embodiments may be utilized in systems where the
time slot timing between base stations is knows. This is the case
in synchronized systems. In non-synchronized systems time slot
timing between base stations may be may be estimated using methods
known in the art. For example, OTD (Observed Time Difference) of
terminal may be utilized.
[0109] In non-synchronized systems, the time slots transmitted by
the different base stations are not synchronized. Thus, a time slot
for a base station may interfere two time slots used by an adjacent
base station, for example. This may be taken into account when
determining potential interferers and caused interference.
[0110] In an exemplary embodiment, the proposed solution is applied
in link adaptation. Link adaptation is the selection of modulation
and coding method for a connection. In some cases modulation and
coding methods used on a connection may not offer best possible
throughput or quality because of the varying conditions on the
radio path. In an embodiment, the number and properties of
potential interferers in a plurality of available radio channels
are determined. This information is used to aid link adaptation
procedures.
[0111] In an exemplary embodiment, the proposed solution is applied
to a terminal of a cellular telecommunication system. The terminal
may be configured to allocate radio channels to connections between
the terminal and base stations of the telecommunication system.
FIG. 9 illustrates an example of the structure of a terminal. The
terminal comprises a controller 900, a transceiver 902 connected to
the controller 900, an antenna 904 connected to the transceiver 902
and user interface 906 connected to the controller. The user
interface may comprise a microphone, a speaker and a display, for
example.
[0112] In an exemplary embodiment, the controller 900 is configured
to determine the number and properties of potential interferers in
a plurality of available radio channels, and perform channel
allocation on a connection on the basis of the determination. The
controller may transmit the channel allocation information to a
base station in the system using the transceiver 902 and the
antenna 904.
[0113] Various embodiments may be realized in a network element
comprising a control unit or a controller. The controller may be
configured to perform at least some of the steps described in
connection with the flowcharts of FIGS. 3 and 8. The embodiments
may be implemented as a computer program comprising instructions
for executing a computer process for allocating a radio channel to
a connection between a terminal and a base station in a cellular
telecommunication system by determining the number and properties
of potential interferers in a plurality of available radio
channels, and performing channel allocation on the basis of the
determination.
[0114] The computer program may be stored on a computer program
distribution medium readable by a computer or a processor. The
computer program medium may be, for example but not limited to, an
electric, magnetic, optical, infrared or semiconductor system or
device. The computer program medium may include at least one of the
following: a computer readable medium, a program storage medium, a
record medium, a computer readable memory, a random access memory,
and an erasable programmable read-only memory.
[0115] Even though various embodiments have been described above
with reference to an example according to the accompanying
drawings, it is clear that the embodiments are not restricted
thereto but it can be modified in several ways within the scope of
the appended claims.
* * * * *