WO2009110628A1

WO2009110628A1 - Relay communication system

Info

Publication number: WO2009110628A1
Application number: PCT/JP2009/054372
Authority: WO
Inventors: Tetsu Ikeda; Yuefeng Zhou
Original assignee: Nec Corporation
Priority date: 2008-03-06
Filing date: 2009-03-03
Publication date: 2009-09-11
Also published as: TW201001953A; GB0804207D0

Abstract

A relay communication system is provided in which downlink data is communicated from a base station to one or more remote communications devices via one or more relay stations. The first relay station is arranged to receive the downlink data from the base station within a first frequency band and to forward the received data within a second different frequency band. For uplink data, the relay station is arranged to receive the uplink data and to transmit the uplink data towards the base station within the second frequency band.

Description

DESCRIPTION

RELAY COMMUNICATION SYSTEM

TECHNICAL FIELD

The present invention relates to a communication system and to components thereof for providing relay services to mobile or fixed communication devices. The invention has particular but not exclusive relevance to relay services used in WiMAX, as currently being defined in IEEE 802.16j.

BACKGROUND ART

For multihop relay communication, two types of relaying methods can be considered. They are called in-band relaying and out-of-band relaying. In- band relaying uses the same frequency band for communication with higher and lower level communication nodes. Out-of-band relaying uses different frequency bands for communication with higher and lower level communication nodes. Generally, in-band relaying is feasible for operators with limited spectrum and out-of-band relaying is good for operators who have multiple carrier frequencies because of smaller interference.

In a conventional out-of-band relay system, if carrier frequency F1 is used for communication between a base station and a relay station, then a carrier frequency F2 is used for communication between the relay station and mobile stations served by the relay station. In this case, frequency F1 is transmitted by the base station for downlink (DL) traffic and by the relay station for uplink (UL) traffic, and frequency F2 is transmitted by the relay station for DL traffic and by the mobile station for UL traffic. Although the purpose of using out-of-band frequency is to reduce interference, since the relay station is usually located near the cell edge, this conventional relay method may not reduce inter- cell interference adequately because both frequency F1 and frequency F2 are transmitted near the cell edge. Frequency F1 is transmitted by the relay station near the cell edge and frequency F2 is transmitted by the mobile station near the cell edge in the UL. Interference will result with such an arrangement when the boundary between a relay zone and an access zone is adaptively controlled, for example, in the manner defined by IEEE802.16J. In particular, IEEE802.16J defines that the boundary between the relay zone and the access zone is determined by load conditions and coordination among neighboring cells is difficult.

DISCLOSURE OF INVENTION

The present invention aims to provide an alternative relay method and system to the one discussed above. Preferred embodiments provide a relay method and system which uses plural frequencies, but which use only one frequency (or one group of frequencies) near the cell edge to reduce inter-cell interference.

According to one aspect, the present invention provides a relay station for use in a relay communications system, the relay station comprising: means for receiving downlink data within a first frequency band; means for transmitting the received downlink data within a second different frequency band; means for receiving uplink data within said second frequency band; and means for transmitting the received uplink data within the second frequency band.

The downlink data may be received from a base station or another relay station. Similarly, the received uplink data may be received from another relay station or from a communications device which generated the uplink data.

In one embodiment the first frequency band and said second frequency band are each defined by a respective different carrier frequency. In an alternative embodiment, the first frequency band and said second frequency band are each defined by a respective different group of sub-carriers selected from an available set of sub-carriers. In this case, each group of carriers may define one or more non-contiguous frequency sub-bands. Time division duplexing may be used to reduce interference between the transmitted uplink and downlink data. In this case, the means for receiving the downlink data may be arranged to receive the downlink data during a first time interval and the means for receiving the uplink data may be arranged to receive the uplink data during a second different time interval. Additionally, the means for transmitting the downlink data may be arranged to transmit the downlink data during a third time interval which is different from the first and second time intervals; and the means for transmitting the uplink data may be arranged to transmit the uplink data during a fourth time interval which is different from the first, second and third time intervals. One or more transceiver circuits may be used within the relay station to provide the claimed transmitting and receiving means.

When the relay station is turned on or enters a service area of the base station or another relay station, it will perform a network entry procedure to make connection to the base station or its super-ordinate relay station. Within this procedure, the relay station may perform registration and capability negotiation, at least to inform essential out-of-band relay parameters, such as supported carrier frequencies, guard band, supported bandwidth etc.

The relay station may also support the transmission of pre-defined sequences, such as middle-amble, for power control, synchronization, and radio resource management within different bands.

The relay station may also insert a time period or gap in receiving or transmitting data when it switches operation between different carrier frequencies. According to another aspect, the present invention also provides a base station for use in a relay communication system, the base station comprising: means for transmitting, within a first frequency band, downlink data to one or more remote communication devices via one or more relay stations; means for receiving uplink data within said first frequency band from one or more local communication devices; and means for receiving, from the one or more remote communication devices via said one or more relay stations, uplink data within a second different frequency band.

The present invention also provides a method of communicating data between a base station and one or more remote communication devices, the method comprising: transmitting downlink data for the one or more remote communication devices within a first frequency band; receiving the transmitted downlink data at a relay station and transmitting the received downlink data within a second frequency band to the one or more communication devices directly or via one or more further relay stations; receiving at the relay station, uplink data from the one or more communication devices directly or via said one or more further relay stations; and transmitting the received uplink data within a second different frequency band.

BRIEF DESCRIPTION OF THE DRAWINGS

These and various other aspects of the invention will become apparent, from the following detailed description of embodiments which are given by way of example only and which are described with reference to the accompanying drawings in which: Figure 1a schematically illustrates a downlink (DL) configuration of an out-of-band relay system in which frequency F1 is used for DL communications between a base station and a relay station and frequency F2 is used for DL communications between the relay station and a mobile station served by the relay station;

Figure 1 b schematically illustrates an uplink (UL) configuration of an out-of-band relay system in which frequency F2 is used for UL communications between a base station and a relay station and frequency F2 is used for UL communications between the relay station and a mobile station served by the relay station;

Figure 2 schematically illustrates a structure of an IEEE802.16J frame, which includes a downlink (DL) subframe and an uplink (UL) subframe, both of which are divided into an access zone and a relay zone; Figure 3 illustrates a frame configuration used by the base station in the two hop relay system illustrated in Figure 1 and a frame configuration used by the relay station in the two hop relay system illustrated in Figure 1 ;

Figure 4 is a block diagram illustrating circuitry of the base station shown in Figure 1 ; Figure 5a schematically illustrates a downlink (DL) configuration of a three hop out-of-band relay system;

Figure 5b schematically illustrates an uplink (UL) configuration of a three hop out-of-band relay system;

Figure 6 illustrates a frame configuration used by the base station in the three hop relay system illustrated in Figure 5, a frame configuration used by a first tier relay station in the three hop relay system illustrated in Figure 5 and a frame configuration used by a second tier relay station in the three hop relay system illustrated in Figure 5;

Figure 7 illustrates a frame configuration used by the base station in another three hop relay system, a frame configuration used by a first tier relay station in the other three hop relay system and a frame configuration used by a second tier relay station in the other three hop relay system;

Figure 8 is a block diagram illustrating alternative circuitry of the first tier relay station in the system shown in Figure 5;

Figure 9 illustrates an alternative relay system where OFDMA modulation is used for the communications between the base station, the relay stations and the mobile stations; Figure 10 is a block diagram illustrating the main components of the base station and each of the relay stations illustrated in Figure 9

Figure 11a illustrates possible interference caused by multiple frequencies near an edge of a cell boundary; and

Figure 11b illustrates the way in which the interference problems illustrated in Figure 11a may be reduced.

BEST MODE FOR CARRYING OUT THE INVENTION First Exemplary Embodiment

Figure 1a illustrates the downlink operation and Figure 1b illustrates the uplink operation of a relay communication system according to a first embodiment. As shown, the system includes a base station 1 which is operable to communicate with mobile stations 3 within its cell 5 and with relay station 7. The base station 1 can communicate directly with local mobile stations 3-1 and indirectly with mobile stations 3-2 and 3-3 via the relay station 7. As illustrated in Figure 1a, in the downlink, the base station 1 transmits in a first frequency band (F1) to the local mobile stations 3-1 and to the relay station 7 and the relay station 7 transmits in a second frequency band (F2) to mobile stations 3-2 and 3-3. As illustrated in Figure 1b, in the uplink, the mobile stations 3-2 and 3-3 transmit in the second frequency band (F2) to the relay station 7 and the relay station 7 transmits in the second frequency band (F2) to the base station 1.

A time division duplexing scheme is used in this embodiment to separate the downlink and uplink transmissions between the base station 1 , the mobile stations 3 and the relay station 7. The frame structure used in this embodiment is illustrated in Figure 2. As shown, each frame 9 is divided into a DL subframe 11 and an UL subframe 13. The subframes are in turn divided into an access zone 15 and a relay zone 17. The access zones 15 are used to communicate data between the base station 1 and the local mobile stations 3-1 (associated with the base station) and to communicate data between the relay station 7 and the mobile stations 3-2 and 3-3 (associated with the relay station 7). The relay zones 17 are used to communicate data between the base station 1 and the relay station 7. As illustrated in Figure 2, the boundaries between the access and relay zones are adaptively controlled, depending on the traffic conditions.

Figure 3 illustrates the frequencies used by the base station 1 , the mobile stations 3 and the relay station 7, in this embodiment. As shown, the base station 1 transmits and receives data in the first frequency band (F1) in all zones except for the relay zone 17-2 in which it receives uplink data from the relay station 7 in the second frequency band (F2). Similarly, the relay station 7 transmits and receives data in the second frequency band (F2) in all zones except for the relay zone 17-1 in which it receives downlink data from the base station 1 in the first frequency band (F1). In this embodiment, the relay station 7 inserts a short gap (time period) between the zones in which the relay station 7 transmits or receives on different carrier frequencies, in order to allow the relay station 7 time to switch between the carrier frequencies.

As the base station 1 is located near the centre of the cell 5, the major inter-cell interference sources are the relay station 7 and the mobile stations 3-2 and 3-3 that are located near the cell edge. None of these devices transmits in the first frequency band (F1) and so the first frequency band (F1) will not be a major interfering frequency. The relay station 7 and the mobile stations 3-2 and 3-3 all transmit in the second frequency band (F2), so the frequencies used in neighbouring cells should be chosen to reduce interference with this second frequency band.

Figure 4 is a block diagram illustrating the main components of the base station 1 used in this embodiment. As shown, the base station 1 includes one or more antennas 21 for transmitting and receiving electromagnetic carrier signals in the radio frequency range. The antenna 21 is connected to transmitter circuitry 23 and receiver circuitry 25 via a switch 27. As shown, the transmitter circuitry 23 includes a frame generator 31 for generating the frame 9 discussed above; a mapper 32 for mapping the downlink data to symbols in the frame; a modulator 33 for modulating the transmission symbols in accordance with a chosen modulation scheme; a digital to analogue converter 35 for converting the modulated digital signal into an analogue signal; and an up- converter 37 for up-converting the modulated analogue signal to the selected transmission frequency for transmission via the antenna 21. Similarly, the receiver circuitry 25 includes a down-converter 39 for down converting the received radio frequency signal; an analogue to digital converter 41 for converting down converted analogue signals into corresponding digital signals; a demodulator 43 for demodulating the received signals in accordance with the modulation scheme used by the device that transmitted the data; a demapper 44 for demapping the demodulated symbols to recover the data and a frame extractor 45 for reconstituting the uplink data (Rx).

The base station 1 also includes a controller 47 for controlling the position of the switch 27 in accordance with the boundary between the DL and UL subframes. In particular, the controller 47 switches the switch 27 so that during the DL subframes, the transmitter circuitry 23 is connected to the antenna 21 and so that during the UL subframes the receiver circuitry 25 is connected to the antenna 21. The controller 47 also controls the frequency used by the up-converter 37 so that the transmission frequency is centred at the first frequency (F1). The controller 47 also controls the frequency used by the down-converter 39, so that during the access zone 15-2 the signals received at the first frequency (F1) from the local mobile stations 3-1, will be down- converted by the down-converter 39 to recover the uplink data transmitted by the local mobile stations 3-1 ; and so that during the relay zone 17-2, the signals received at the second frequency (F2) from the relay station 7, will be down- converted by the down-converter 39 to recover any uplink data from the remote mobile stations 3-2 and 3-3.

In this embodiment, the relay station 7 has a similar structure to that of the base station 1. The main difference will be in the timing and frequencies used by its controller to control the transmission and reception functions of the relay station 7, in accordance with the operation discussed above. There will of course be other differences between the base station 1 and the relay station 7, but these are not important to the understanding of the present invention and have not been illustrated in the figures. For example, the base station 1 will also have a connection (typically a fibre or other wired connection) to the core network, which the relay station 7 will not have. Setup

When the relay station 7 is turned on or enters the service area of the base station 1 , it will perform a network entry procedure to establish a connection with the base station 1. Within this procedure, the relay station 7 in the present embodiment will perform registration and capability negotiation with the base station 1 , so that the base station 1 is informed of, among other things, essential out-of-band relay parameters such as the supported carrier frequencies, guard band, supported bandwidth etc. As those skilled in the art will appreciate, the above relay station 7 should also support the transmission of pre-defined sequences, such as a middle-amble, within its frames for power control, QoS control, synchronization, radio resource management within different bands etc. The relay station 7 will also be responsible for controlling handover of the mobile station 3, if it moves to another cell 5 or if the mobile station 3 moves closer to the base station 1 such that it can communicate directly with the base station 1. Second Exemplary Embodiment

The first embodiment illustrated a multihop (two hop) relay method of communicating data between a base station 1 and a number of remote mobile stations 3-2 and 3-3 via a single relay station 7. Figure 5 illustrates a similar multihop relay system in which remote mobile stations 3-4 and 3-5 can communicate with the base station 1 via a first tier relay station 7-1 and a second tier relay station 7-2. Figure 5a illustrates the signals transmitted and the frequencies used for downlink data transmission and Figure 5b illustrates the signals transmitted and the frequencies used for uplink data transmission. As shown, in the downlink, the base station 1 transmits downlink data to the first tier relay station 7-1 and to the local mobile stations 3-1 in the first frequency band (F1); the first tier relay station 7-1 transmits downlink data to mobile stations 3-2 and 3-3 and to second tier relay station 7-2 in the second frequency band (F2); and the second tier relay station 7-2 transmits downlink data to mobile stations 3-4 and 3-5 in the first frequency band (F1). In the uplink, the mobile stations 3-4 and 3-5 transmit uplink data to the second tier relay station 7-2 in the first frequency band (F1); second tier relay station 7-2 transmits uplink data to the first tier relay station 7-1 in the first frequency band (F1); the mobile stations 3-2 and 3-3 transmit uplink data to the first tier relay station 7-1 in the second frequency band (F2); the local mobile stations 3-1 transmit uplink data to the base station 1 in the first frequency band (F1); and the first tier relay station 7-1 transmits uplink data to the base station 1 in the second frequency band (F2).

Figure 6 illustrates the frame structure and frequencies used by the base station 1 , the mobile stations 3 and the relay stations 7, in this second embodiment. As shown, the frame structure of the base station 1 (BS frame) is the same as in the first embodiment. The frame structure used by the first tier relay station 7-1 (RS1 frame) is, however, different to the frame structure used in the first embodiment. In particular, the downlink subframe 11 is divided into three parts or zones - an access zone 15-1 for transmitting downlink data (on F2) to mobile stations 3-2 and 3-3; a first relay zone 17-1 for transmitting downlink data (also on F2) to the second tier relay station 7-2 and a second relay zone 17-2 for receiving downlink data (on F1) transmitted from the base station 1. Similarly, the uplink subframe 13 is also divided into three parts or zones - an access zone 15-2 for receiving uplink data (on F2) transmitted by the mobile stations 3-2 and 3-3; a third relay zone 17-3 for receiving uplink data (on F1) from the second tier relay station 7-2; and a fourth relay zone 17-4 for transmitting uplink data (on F2) to the base station 1. As shown in Figure 6, the frame of the second tier relay station 7-2 (RS2 frame) is divided in a similar manner to the RS1 frame, except they do not include relay zones which correspond to relay zones 17-2 and 17-4 illustrated in the RS1 frame.

The structure of the base station 1 and of the relay stations 7 is the same as that shown in Figure 4 and will not therefore be described again. The only difference will be the operation of the controller 47 to control the timings and transmission/reception frequencies used in accordance with the above description.

In this embodiment, the base station 1 and the first tier relay station 7-1 are both located sufficiently far from the edge of the cell 5 that the signals transmitted by them do not cause significant interference in neighbouring cells. The main source of interference will come from the signals transmitted by the second tier relay station 7-2 and the mobile stations 3-4 and 3-5, which are located near the cell boundary. As can be seen from the above discussion, therefore, only the first frequency band (F 1) is likely to cause any inter-cell interference and this can be minimized by careful selection of frequency bands used in neighbouring cells. Modifications and Alternatives In the above embodiments, the relay station(s) 7 and the base station 1 included various digital circuits for modulating and processing uplink and downlink data. As those skilled in the art will appreciate, these digital circuits may be defined by hardware circuits using, for example, dedicated DSPs or ASIC circuits or by general purpose programmable circuits configured in accordance with software modules or code. Such software can be provided on a computer readable medium such as a CD-ROM or can be provided on a carrier signal and obtained by, for example, downloading the software over a computer network. The software may also form part of the operating system of the relay station or the base station. In the second embodiment described above, the second tier relay station 7-2 and the mobile stations 3-4 and 3-5 directly communicating with it were arranged to transmit their data in the first frequency band (F1). This offers the advantage of re-using the first frequency, thereby minimizing the bandwidth requirements of the cell 5. However, if the second tier relay station 7-2 is quite close to the base station 1 or to a mobile station 3-1 served directly by the base station 1 , then this re-use of the first frequency can create interference. In an alternative embodiment, the second tier relay station 7-2 and the mobile stations 3-4 and 3-5 communicating directly with it, may be arranged to transmit their data on a third frequency (F3). Figure 7 illustrates the frames used in such an embodiment. The relay stations 7 and base station 1 used in such an embodiment may have the same structure as that illustrated in Figure 4. However, in some embodiments the base station 1 and the relay stations 7 may include multiple transmit and receive circuits. In this case, these different circuits may be configured to transmit/receive on a dedicated frequency. Figure 8 is a block diagram illustrating how multiple receive circuits 25-1 , 25-2 and 25-3 may be employed in parallel by the first tier relay station 7- 1. As shown, in this embodiment, the first tier relay station 7-1 includes first receiver circuitry 25-1 that operates to receive signals on the second frequency (F2); second receiver circuitry 25-2 for receiving signals on the first frequency (transmitted by the base station 1); and third receiver circuitry 25-3 for receiving signals on the third frequency (transmitted by the second tier relay station 7-2). As those skilled in the art will appreciate, the general operation of the controller 47 will be different in this embodiment, as during normal use it will only be required to control the switching of the different transmit and receive circuitry to the antenna at the relevant times as defined by the desired frame format described above. Although, the controller 47 may also control the operating frequencies of the up/down-converters from time to time, if the frequencies assigned to the relay stations 7 and/or the base station 1 change.

In the embodiments described above, the data transmitted by the base station 1 and the relay stations 7 was modulated onto a suitable carrier in the radio frequency range. For example, in OFDM-based systems, this may be done in a two stage process, with a first modulation scheme being used to modulate the data onto a plurality of sub-carriers, which are then modulated onto a carrier frequency at the relevant frequency (F1 , F2 etc). As those skilled in the art will appreciate, some parts of these modulation techniques may be performed in the digital domain, whilst other parts may be performed in the analogue domain. For example, the data may be modulated on to the plurality of sub-carriers in the digital domain, converted into an analogue signal and then up-converted to the desired transmission frequency using analogue mixers or the like.

In the above embodiments, the relay station(s) 7 and the base station 1 were configured to transmit on one carrier frequency and to receive on multiple carrier frequencies. In an embodiment, where OFDMA (Orthogonal Frequency Division Multiple Access) modulation is used, the sub-carriers transmitted may be divided into different groups, with the base station 1 being configured to use one group of sub-carriers for its communications and with the relay station(s) being configured to use another group of sub-carriers for its communications. The effect will be the same - namely that near the cell boundary, only one group of sub-carriers will be used which are likely to interfere with devices in neighbouring cells. Therefore, inter-cell interference can be minimized by appropriate selection of the sub-carrier frequencies assigned to each group in neighbouring cells. Figure 9 illustrates such an embodiment, where the group of sub-carriers allocated to the base station 1 is shown at 59-1 ; the group of sub-carriers allocated to the first relay station 7-1 is shown at 59-2; and the group of sub-carriers allocated to the second relay station 7-2 is shown at 59-3. Figure 9 also shows that in this embodiment, the same carrier frequency (F1) is used for the transmissions of all stations - it is only the sub-carriers which are different. As those skilled in the art will appreciate, the allocated sub-carriers do not have to be contiguous within the available bandwidth. They are shown in Figure 9 as being contiguous for ease of understanding only. Figure 10 illustrates the main components of the base station 1 used in such an OFDMA embodiment. As shown, the structure is similar to that shown in Figure 4. In operation, the mapper 32 maps the downlink data to be transmitted onto a group of sub-carriers allocated to the base station for downlink communications. The modulator 33 then modulates each allocated sub-carrier with the data mapped to that sub-carrier. The modulated sub- carriers are then combined and converted into the time domain by an Inverse Fast Fourier Transform (IFFT) block 63. The time domain data is then converted into analogue data by the DAC 35 and then up-converted onto the carrier signal at the transmission frequency (F1). On the reception side, the received signal is also received on the same carrier frequency (F1) and down converted by the down-converter 39. The down converted signal is then digitized by the ADC 41. The digitized signal is then converted into the frequency domain by the FFT block 65. The signals in the different frequency bins of the FFT which correspond to the group of sub-carriers allocated for the uplink data are then extracted and processed by the demodulator 43 to recover the uplink data from each sub-carrier. The uplink data from all the allocated sub-carriers is then extracted by the demapper 44 and then passed to the frame extractor 45 to recover the uplink data (Rx). In this embodiment, the controller 47 will control the operation of the mapper/demapper and of the modulator/demodulator circuits so that the correct sub-carriers are modulated/demodulated during the relevant access and relay zones discussed above. The above embodiments have described a base station that communicates with a number of mobile stations either directly or indirectly via one or more relay stations. The mobile station may be a portable computer device, such as a laptop, portable telephone, PDA or the like. As those skilled in the art will appreciate, it is not essential that the above described relay system be used for mobile communications devices. The system can be used to extend the coverage of base stations in a network having one or more fixed computing devices as well as or instead of the mobile communicating devices.

As discussed above, the relay station(s) receives downlink data within a first frequency band and forward that data within a second frequency band. In the uplink, the relay station receives uplink data in the second frequency band and also transmits the uplink data in the second frequency band. The relay station may itself be a mobile communications device (to which some of the downlink data is directed) or it may be a simple relay device that forwards all downlink data towards other communications devices. For example, the relay station may be laptop computer that is configured to transmit and receive internet data for the user associated with the laptop and also configured to act as a relay for other laptops which are not in range of the base station. In the above embodiments, the base stations, relay stations and mobile/fixed communications devices transmitted radio frequency signals. As those skilled in the art will appreciate, the relay system described above can operate at any suitable frequency, but will typically operate with carrier frequencies in the range of a few MHz to tens of GHz. In the second embodiment described above, two relay stations were provided, with one being subordinate to the other one. As those skilled in the art will appreciate, there may be any number of such subordinate relay stations and there may be a number of relay stations communicating directly with the base station, each having one or more subordinate relay stations. In embodiments where there are multiple relays stations near the cell boundary 5, the transmission frequency of those relay stations is preferably the same, in order to avoid multiple frequency overlap with the neighbouring cell. This is illustrated in Figure 11. In particular, Figure 11a illustrates the additional interference that can result if two or more relay stations operating at different carrier frequencies are located near the cell boundary; and Figure 11b illustrates that this problem can be overcome by configuring the relay stations 7 that are close to the cell boundary 5 to transmit on the same frequency band (in this example frequency F2).

This application is based upon and claims the benefit of priority from United Kingdom patent application No. 0804207.9, filed on March 6, 2008, the disclosure of which is incorporated herein in its entirety by reference.

Claims

1. A relay station for use in a relay communications system, the relay station comprising: means for receiving downlink data from a base station or another relay station, within a first frequency band; means for transmitting the received downlink data within a second different frequency band, to a communications device; means for receiving, from the communications device, uplink data within said second frequency band; and means for transmitting the received uplink data within the second frequency band to the base station or to the other relay station.

2. A relay station according to claim 1 , wherein said communications device is one of: a mobile communications device, a fixed communications device and another relay station.

3. A relay station according to claim 1 , wherein said first frequency band and said second frequency band are each defined by a respective different carrier frequency on which the respective data is carried.

4. A relay station according to claim 1 or 2, wherein said first frequency band and said second frequency band are each defined by a respective different group of sub-carriers selected from an available set of sub-carriers.

5. A relay station according to any of claims 1 to 4, operable to use time division duplexing to reduce interference between the transmitted uplink and downlink data.

6. A relay station according to any of claims 1 to 5, operable to use time division duplexing to reduce interference between the transmitted downlink data and received uplink data.

7. A relay station according to any of claims 1 to 6, wherein said means for receiving said downlink data is operable to receive said downlink data during a first time interval and wherein said means for receiving said uplink data is operable to receive said uplink data during a second different time interval.

8. A relay station according to claim 7, wherein said means for transmitting said downlink data is operable to transmit said downlink data during a third time interval which is different from said first and second time intervals.

9. A relay station according to claim 8, wherein said means for transmitting said uplink data is operable to transmit said uplink data during a fourth time interval which is different from said first, second and third time intervals.

10. A relay station according to any of claims 1 to 9, operable to transmit and receive data in frames comprising a downlink sub-frame and an up-link sub-frame.

11. A relay station according to claim 10, wherein the downlink sub-frame comprises a first portion during which the means for transmitting downlink data is operable to transmit said downlink data towards said communications device and a second portion during which the means for receiving downlink data is operable to receive said downlink data.

12. A relay station according to claim 11 , operable to communicate with another relay station in addition to said communication device and wherein the downlink sub-frame further comprises a third portion during which the means for transmitting downlink data is operable to transmit said downlink data towards said other relay station.

13. A relay station according to claim 12, wherein said third portion is between said first portion and said second portion within the frame.

14. A relay station according to any of claims 10 to 13, wherein the uplink sub-frame comprises a first portion during which the means for transmitting uplink data is operable to transmit said uplink data and a second portion during which the means for receiving uplink data is operable to receive said uplink data.

15. A relay station according to claim 14, operable to communicate with another relay station in addition to said communication device and wherein the uplink sub-frame further comprises a third portion during which the means for receiving uplink data is operable to receive said uplink data from said other relay station.

16. A relay station according to claim 15, wherein said third portion of the uplink sub-frame is between said first portion and said second portion within the frame.

17. A relay station according to any of claims 1 to 16, operable to insert a gap between transmitting or receiving data on different carrier frequencies.

18. A relay station according to any of claims 1 to 17, operable to perform a network entry procedure upon establishment within the operating range of the base station or another relay station.

19. A relay station according to claim 18, wherein the network entry procedure is for performing a registration and capability negotiation with the base station or other relay station, so that the base station or other relay station is informed of out-of-band relay parameters including the supported carrier frequencies, guard band and supported bandwidth.

20. A relay station according to any of claims 1 to 19, operable to transmit and receive data in frames and wherein the transmitted frames includes predefined sequences of data for power control, synchronization and radio resource management within different sub-bands.

21. A relay station according to any of claims 1 to 20, operable to control handover of mobile communication devices to a base station or another relay station.

22. A relay station according to any of claims 1 to 21 , comprising a single transceiver circuit operable to transmit and receive said downlink and said uplink data in said first and second frequency bands.

23. A relay station according to claim 22, wherein said single transceiver circuit is operable to transmit and receive within three or more frequency bands.

24. A base station for use in a relay communication system, the base station comprising: means for transmitting, within a first frequency band, downlink data to one or more local communication devices; means for transmitting, within said first frequency band, downlink data to one or more remote communication devices via a relay station; means for receiving uplink data within said first frequency band from said one or more local communication devices; and means for receiving, from the one or more remote communication devices via said relay station, uplink data within a second different frequency band.

25. A base station according to claim 24, wherein said first frequency band and said second frequency band are each defined by a respective different carrier frequency on which the respective data is carried.

26. A base station according to claim 24, wherein said first frequency band and said second frequency band are each defined by a respective different group of sub-carriers selected from an available set of sub-carriers.

27. A base station according to any of claims 24 to 26, operable to use time division duplexing to reduce interference between the transmitted downlink data and the received uplink data.

28. A base station according to any of claims 24 to 27, wherein said means for transmitting said downlink data to the one or more local communication devices is operable to transmit said downlink data during a first time interval and wherein said means for receiving said uplink data from said one or more local communication devices is operable to receive said uplink data during a second different time interval.

29. A base station according to claim 28, wherein said means for transmitting said downlink data to said one or more remote communication devices is operable to transmit said downlink data during a third time interval which is different from said first and second time intervals.

30. A base station according to claim 29, wherein said means for receiving said uplink data from said one or more remote communication devices is operable to receive said uplink data during a fourth time interval which is different from said first, second and third time intervals.

31. A base station according to any of claims 24 to 30, comprising a single transceiver circuit operable to transmit and receive said downlink and said uplink data in said first and second frequency bands.

32. A method of communicating data between a base station and one or more remote communication devices, the method comprising: transmitting downlink data for the one or more remote communication devices within a first frequency band towards a relay station; receiving the transmitted downlink data at the relay station and transmitting the received downlink data within a second frequency band to the one or more communication devices directly or via one or more further relay stations; receiving at the relay station, uplink data from the one or more communication devices directly or via said one or more further relay stations; and transmitting the received uplink data within a second different frequency band.

33. A method according to claim 32, comprising the steps of: transmitting the received downlink data to a subordinate relay station and at the subordinate relay station, transmitting the downlink data within the first frequency band to one or more communication devices, receiving at the subordinate relay station uplink data from the one or more communication devices within said first frequency band; and transmitting the received uplink data from the subordinate relay station within the first frequency band.

34. A frame structure for use in a relay communication system, the frame structure comprising a downlink sub-frame and an uplink sub-frame, the downlink sub-frame having a first portion during which downlink data is transmitted towards a communications device and a second portion during which downlink data is received; the uplink sub-frame having a first portion during which uplink data is transmitted and a second portion during which uplink data is received; and wherein said the transmission of said uplink data is performed within a frequency band that is different from a frequency band in which the downlink data is received.

35. A communications device operable to communicate with other communications devices using the frame structure of claim 34.

36. A frame structure for use in a base station, the frame structure comprising a downlink sub-frame and an uplink sub-frame, the downlink sub- frame having a first portion during which downlink data is transmitted towards a communications device and a second portion during which downlink data is transmitted towards a relay station; the uplink sub-frame having a first portion during which uplink data is received from said communications device and a second portion during which uplink data is received from said relay station; and wherein said the reception of said uplink data from said relay station is performed within a frequency band that is different from a frequency band in which the downlink data is transmitted.

37. A computer implementable instructions product comprising computer implementable instructions for configuring a programmable computer device as the relay station of any of claims 1 to 23 or as the base station of any of claims 24 to 31 or as the communications device of claim 35.