Abstract:
Methods and systems for supporting scalable bandwidth in radio telecommunications networks are provided. When signals are transmitted to user equipments using a transmitter of a radio telecommunication network, the signals are frequency multiplexed, each signal lying within a frequency band having an equal or narrower bandwidth than a reception bandwidth of each user equipment that is to receive a signal. Then the multiplexed signal is converted to a time domain signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to methods and systems for supporting scalable bandwidth in radio telecommunications networks. In a preferred embodiment the present invention provides methods for use in a transmitter of a base station (BTS) and in a receiver of a user equipment (UE) of a radio telecommunications network employing orthogonal frequency division multiple access (OFDMA). 
       BACKGROUND OF THE INVENTION 
       [0002]    To meet an anticipated increase in user demand for high data rate and improved service quality in the future, the 3GGP has identified that it will be desirable to develop new networks for deployment in the medium to long term that provide data rates of up to 100 MBPS in the downlink direction and 50 MBPS in the uplink direction. In order to achieve this increased data rate with acceptable quality such networks will implement OFDMA and have a maximum downlink transmission bandwidth of 20 MHz. 
         [0003]    Notwithstanding the desired 20 MHz peak bandwidth criterion set out above, it is likely that for one reason or another cells with lower bandwidth such as 5 MHz, 10 MHz, 15 MHz, or even 1.25 MHz or 2.5 MHz will also exist. These lower bandwidths may arise, for example, because during the deployment phase of the network not all cells will be upgraded to the full 20 MHz capacity at the same time, or due to spectrum availability restrictions only a narrow bandwidth radio spectrum is available for transmission in a particular area. 
         [0004]    It is also desirable that UEs (user equipment) having different reception capabilities, i.e. maximum reception bandwidths that UE can support, can communicate with such networks. As will be appreciated, higher capability handsets are likely to be more complex and therefore more expensive, and thus some users will be willing to trade off performance to obtain a cheaper handset. 
         [0005]    Accordingly, there is a need for systems and methods, to allow UEs of differing reception bandwidths to operate within the network having differing transmission bandwidth, and preferably which facilitate efficient sharing of transmitter bandwidth among the UEs in such circumstances. 
       SUMMARY OF THE INVENTION 
       [0006]    In a first aspect the present invention provides a method of processing a plurality of signals, for transmission to two or more UEs using a transmitter of a radio telecommunication network having a first transmission bandwidth, wherein at least one of the UEs has a maximum reception bandwidth less than the transmission bandwidth of the transmitter, the method including; 
         [0000]    frequency multiplexing the plurality of signals for transmission to the UEs such that in the multiplexed signal, each of the plurality of signals lies within a frequency band having an equal or narrower bandwidth than the reception bandwidth of each UE which is to receive the signal; and
 
converting the multiplexed signal to a time domain signal.
 
         [0007]    Each of the plurality of signals preferably occupies one or more sub-carrier frequencies within the first transmission bandwidth. 
         [0008]    The step of converting the multiplexed signal to a time domain signal is preferably performed so as to maintain the mutual orthogonality of all sub-carriers forming the multiplexed signal. 
         [0009]    Preferably the step of converting the multiplexed signal to a time domain signal includes, performing an inverse fast Fourier transform (IFFT) on the multiplexed signal having size dependent on the transmission bandwidth of the transmitter. 
         [0010]    In the preferred embodiments the method includes positioning a frequency band containing a signal for a given UE within the multiplexed signal such that the centre frequency of the frequency band is aligned with one of a group of predefined frequencies. 
         [0011]    Preferably the group of predefined frequencies are equally spaced within the transmission bandwidth. 
         [0012]    In a particularly preferred embodiment when the transmission bandwidth has 1201 or 901 or 601 sub-carriers, the predefined frequencies are spaced apart by 150 sub-carriers. 
         [0013]    Preferably frequency band in which a UE&#39;s signal lies is defined to be encompassed by a camping frequency band of the UE intended to receive the signal. 
         [0014]    In a second aspect the present invention provides a method of transmitting a plurality of signals to two or more UEs using a transmitter of a radio telecommunication network, including processing the signals in accordance an embodiment of the first aspect of the present invention; 
         [0000]    further processing the time domain signal; and
 
transmitting said time domain signal.
 
         [0015]    In a third aspect the present invention provides a method, in a UE, of receiving a signal having a first transmission bandwidth, said signal being formed by frequency multiplexing a plurality of signals such that each of the signals lies within a frequency band in the multiplexed signal having an equal or narrower bandwidth than the reception bandwidth of each UE which is to use the signal, the method including: 
         [0000]    camping on a camping frequency band within the first transmission bandwidth;
 
receiving the portion of the signal falling within substantially the whole reception bandwidth of the UE,
 
converting the received time domain signal to a frequency domain signal having a bandwidth substantially equal to the reception bandwidth of the UE.
 
         [0016]    The method can further include receiving signalling data to indicate the frequency position of the camping frequency band. 
         [0017]    The method can include, performing a fast Fourier transform (FFT) to convert the received time domain signal to a frequency domain signal. The FFT size is preferably determined by the reception bandwidth of the UE. Most preferably the frequency domain signal generated by the FFT substantially covers the entire reception bandwidth of the UE. 
         [0018]    In the event that the reception bandwidth of the UE is less than the transmission bandwidth of the transmitter, the method can include, tuning the receiver to receive a predetermined portion of the bandwidth of the transmitted signal. 
         [0019]    In a further aspect the present invention provides a method of operating a transmitter of a radio communications network having a first transmission bandwidth, to enable communication with a plurality of UEs, at least one of which has a maximum reception bandwidth less than the transmission bandwidth of the transmitter, the method including: 
         [0000]    transmitting, to one or more UEs, at least one of the following types of channels on common frequency band, having a bandwidth no more than the smallest maximum reception bandwidth amongst said plurality of UEs:
 
a broadcast channel, a paging channel, a synchronisation channel, a shared channel.
 
         [0020]    Most preferably the common frequency band is located in aligned with the central frequency of the transmitter bandwidth. 
         [0021]    The method can include signalling to a UE in an idle mode to camp on a frequency band encompassing said common frequency band. 
         [0022]    In the event that a UE, having a reception bandwidth less than the transmission capability of the transmitter, is to move from an idle mode in which it is camped on a frequency band encompassing said common frequency band, into an active mode, the method can include signalling to the UE to receive and/or transmit in a frequency band not encompassing said common frequency band. 
         [0023]    In another aspect the present invention provides a method of operating a UE in communication with a transmitter of a radio communications network, which has transmission bandwidth larger than the reception bandwidth of the UE, the method including; 
         [0000]    receiving and/or transmitting data in first frequency band corresponding to predetermined portion of the transmission bandwidth, when in idle mode, and
 
receiving and/or transmitting data in a second frequency band not encompassing the first frequency band, when in an active mode.
 
         [0024]    The method can include receiving signal from the transmitter to change reception and transmission bands. 
         [0025]    Preferably the first frequency band is centred within the transmission bandwidth of the transmitter. More preferably the first frequency band has a bandwidth equal to or less than the smallest maximum reception bandwidth of the UE. 
         [0026]    In a further aspect there is provided method of operating a base station in a radio telecommunications network, said base station being configured to transmit a signal having a first transmission bandwidth, the method including: 
         [0000]    defining a plurality of camping bands within the transmission bandwidth to be used by user equipment, wherein at least one of said camping bands has a bandwidth smaller than the transmission bandwidth; and
 
assigning each user equipment a camping band on the basis of the maximum reception bandwidth of the UE.
 
         [0027]    Preferably the method includes transmitting one or more channels shared by a plurality of UE on a common frequency band within the transmission bandwidth. 
         [0028]    The method can further include signalling a user equipment to camp on the common frequency band when said UE is to be moved into an idle state. The method can further include signalling a user equipment to camp on a camping band not encompassing the common frequency band when said UE is to be moved into an active state. 
         [0029]    In another aspect the present invention provides a device for transmitting a signal in a radio telecommunications network within a first transmission bandwidth, to a plurality of receivers, the device including: multiplexing means for multiplexing a plurality of frequency domain signals for transmission to the receivers such that in the multiplexed signal, each of the plurality of signals lies within a frequency band having an equal or narrower bandwidth than a reception bandwidth of each receivers which is to receive the signal; and means for converting the multiplexed signal to a time domain signal for transmission to the receivers. 
         [0030]    The device can further include transmission band allocation means configured to allocate a frequency band to each signal to be transmitted such that for each signal the centre frequency of the frequency band is aligned with one of a group of predefined frequencies. 
         [0031]    In a further aspect the present invention provides a receiver adapted to receive a signal having a first transmission bandwidth, said signal being formed by frequency multiplexing a plurality of signals such that each of the signals lies within a frequency band in the multiplexed signal having an equal or narrower bandwidth than the reception bandwidth of each receiver which is to use the signal, the receiver including: means to determine a first frequency band within the first transmission bandwidth on which to receive a signal; a receiver configured to receive a portion of the transmitted signal falling within first frequency band; means to convert a received signal to a frequency domain signal having a bandwidth substantially equal to the reception bandwidth of the receiver. 
         [0032]    In another aspect the present invention provides a base station including one or more components to implement a method according to any one of the preceding aspects of the invention. 
         [0033]    In yet another aspect the present invention provides a user equipment including one or more components to implement a method according to any one of the preceding aspects of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Preferred embodiments of the present invention will now be described by way of non-limiting example only with reference to the accompanying drawings, in which: 
           [0035]      FIG. 1  depicts a schematic diagram of a base station transmitter and two UEs operating in a network according to the present invention; 
           [0036]      FIG. 2  is a diagram showing transition of the UE between an idle state and an active state in a network operating in accordance with the present invention; 
           [0037]      FIG. 3  shows various options for mapping bandwidth allocations for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception capabilities in a 20 MHz bandwidth cell according to an embodiment of the present invention; 
           [0038]      FIG. 4  shows various options for mapping bandwidth allocations for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception capabilities in a 15 MHz bandwidth cell according to an embodiment of the present invention; 
           [0039]      FIG. 5  shows various options for mapping bandwidth allocations for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception capabilities in a 10 MHz bandwidth cell according to an embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0040]    It will be convenient to describe the preferred embodiments using terminology adopted by the 3GPP, however the present invention should not be considered as being limited to application in networks operating according to a 3GPP standard. 
         [0041]    Preferred embodiments of the present invention will now be described in the context of a OFDMA telecommunications network having UEs with 5 MHz, 10 MHz, 15 MHz and 20 MHz reception bandwidth. It is assumed that the maximum reception bandwidth supported by the lowest capability UE in the network is 5 MHz. This is a reasonable assumption as current WCDMA UEs have a 5 MHz reception bandwidth, and it is expected that in the future UEs will at least support this standard. Given this assumption, it should also be realised that the discussion herein is limited to the case where cell bandwidth is 10 MHz or more, since for lower cell bandwidths such as 5 MHz (or below) all UEs will be seen by the network as having the a reception capability equal to the transmission bandwidth of the cell. In the preferred embodiments the parameters for downlink transmission processing are as indicated in Table 1. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Parameters for downlink transmission scheme in a preferred embodiment 
               
             
          
           
               
                   
                 Transmission BW 
               
             
          
           
               
                   
                 1.25 
                 2.5 
                 5 
                 10 
                 15 
                 20 
               
               
                   
                 MHz 
                 MHz 
                 MHz 
                 MHz 
                 MHz 
                 MHz 
               
               
                   
                   
               
             
          
           
               
                 Sub-frame duration 
                 0.5 ms     
               
               
                 Sub-carrier spacing 
                 15 kHz 
               
             
          
           
               
                 Sampling frequency 
                 1.92 
                 3.84 
                 7.68 
                 15.36 
                 23.04 
                 30.72 
               
               
                   
                 MHz 
                 MHz 
                 MHz 
                 MHz 
                 MHz 
                 MHz 
               
               
                   
                 (3.84/2 
                   
                 (2 × 3.84 
                 (4 × 3.84 
                 (6 × 3.84 
                 (8 × 3.84 
               
               
                   
                 MHz) 
                   
                 MHz) 
                 MHz) 
                 MHz) 
                 MHz) 
               
               
                 FFT size 
                 128 
                 256 
                 512 
                 1024 
                 1536 
                 2048 
               
               
                 Number of occupied 
                  76 
                 151 
                 301 
                  601 
                  901 
                 1201 
               
               
                 sub-carriers 
               
               
                   
               
             
          
         
       
     
         [0042]    It should be understood however that the present invention is not limited to the particular exemplary bandwidths and UE capabilities described above but may be applicable generally to networks having scalable transmission bandwidths and UEs of differing reception bandwidth. 
         [0043]      FIG. 1  depicts a schematic representation of a base station transmitter  100  operating in accordance with an embodiment of the present invention. In the present embodiment the base station  100  is transmitting to two UEs  102  and  104 . UE  102  has 5 MHz reception bandwidth and UE  104  has 20 MHz reception bandwidth. 
         [0044]    In order to transmit to two UEs at the same transmission time interval (TTI) the base station  100  needs to multiplex the signals to be transmitted. In the preferred embodiment multiplexing is implemented in the frequency domain prior to conversion of the entire frequency multiplexed signal into time domain signal, using a single IFFT block  110 . 
         [0045]    The multiplexing scheme used in this embodiment is relatively simple, with the transmission bandwidth being split into two blocks of sub-carriers  106  and  108 , wherein the data for the UE 1   102  is multiplexed on a block of 301 consecutive sub-carriers centred at DC 1  and the data for the UE 2   104  is multiplexed on the remaining block 900 sub-carriers. It should be noted that the signal for UE 2  is 1201 sub-carriers wide and is centred at DC 2 . 
         [0046]    It should also be noted that different multiplexing schemes can be used, for example, schemes that assignments sub-carriers between the UEs such that they are interleaved, so long as the sub-carriers carrying data for a particular UE are contained within a pass-band less than or equal to the maximum reception bandwidth of the UE. 
         [0047]    In the event that additional UEs were being transmitted to by the base station  100  the available transmission bandwidth could be further divided amongst UEs so long as the sub-carriers assigned to a particular UE are contained within a pass-band no greater than the maximum reception bandwidth of the UE. 
         [0048]    Once the frequency domain multiplexing is of the UE data is performed, an inverse fast Fourier transform (IFFT)  110  is applied to the entire frequency band of the transmitter to generate a time domain signal. In the illustrative embodiment the IFFT applied is a 2048 point IFFT, however other IFFT sizes can be used depending upon the available bandwidth of the transmitter (see table 1 above). As discussed above only one IFFT is conducted across the entire set of sub carriers, rather than conducting separate IFFTs on each camping band. This simplifies base transceiver station design as only one IFFT block whose size is only dependent on transmitter bandwidth is needed for each transmitter antenna. 
         [0049]    As is typical to OFDMA systems, next a cyclic prefix is added to the time domain signal in a manner that will be known to those skilled in the art at  112 . This signal then undergoes further processing at  114  prior to transmission by a base station antenna  116 . The transmitted signal is then received by each of the UEs  102  and  104 . 
         [0050]    Prior to discussing the processing of the signals received by the UEs  102  and  104  it is useful to briefly discuss the operation of the UEs, and in particular how they may transition between an idle state and an active state. 
         [0051]    As will be known to those skilled in the art for much of the time a UE will exist in an idle state in which it performs very little or no transmission and/or reception. In such a state the UE will typically remain tuned to a particular frequency band, which will be referred to herein as a camping band. The idle state is indicated in  FIG. 2  as state  200 . From time to time a UE will need to move into an active state  206 , e.g. to make a call or send or receive other data. The active states are split into the MAC-Dormant or MAC-Active states and are indicated on  FIG. 2  by reference numerals states  202  and  204  in  FIG. 2 . The MAC-Active state  204  is used when data transmission and or reception is rather active, whereas the MAC-Dormant state  202  is used when UE transmission and or reception activity is temporarily terminated. 
         [0052]    When a UE is in an idle state, it is necessary for it to regularly read the Broadcast Channel (BCH) for location area updates and other information as well as the Paging Channel (PCH). Additionally, when UEs are first attached to the network it will be necessary for the UE to receive synchronization channel and broadcast channel to obtain an initial time and frequency synchronization and cell search information from the network. In order to facilitate these processes, networks operating according to an embodiment of the present invention provide each of these channels in a single frequency band, referred as herein to the “common band”. In the preferred embodiment the common band is aligned with the centre of the transmission band of the transmitter. 
         [0053]    In order for each UE connected to the network to be able to receive all signals transmitted on the common band, the common band has a bandwidth of less than or equal to the maximum reception bandwidth of the lowest capacity UE operating in the network. In an embodiment using the assumptions stated above, this means that the synch channel, BCH, PCH and SCH are confined to a single 5 MHz frequency band. 
         [0054]    To avoid UEs to having to unnecessarily change reception (or camping) bands and retune their receivers to receive the synch channel, BCH, PCH and SCH when necessary, preferred embodiments of the present invention require all UEs in an idle state to camp on the frequency band that encompasses the common band. In order not to have too many UEs operating in the common band (other than those in idle state, which consume little or no system resources), when a UE is requested to, or requests to, move into an active state, the network may request the UE to move to a different frequency band until it returns to an idle state. 
         [0055]    In order to better illustrate allocation of camping bands in networks with scalable transmitter and receiver bandwidth  FIGS. 3 ,  4  and  5  illustrate exemplary band allocation possibilities for a 20 MHz bandwidth cell, 15 MHz bandwidth cell and 10 MHz bandwidth cell, respectively, for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception bandwidth capability. 
         [0056]      FIG. 3  illustrates an exemplary band allocation scheme for a 20 MHz bandwidth cell for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception bandwidths. The cell bandwidth is indicated by a frequency axis  300 , which is gradated in sub-carriers (rather than in Hz) illustrating a 1201 sub-carrier frequency range from f −600  to f +600 . Using the system parameters set out in Table 1 this can be seen to equate to a 20 MHz transmission bandwidth. Block  302 , which is centred on f 0 , is the common band in which the synch channel, BCH, PCH and SCH of the cell is transmitted. 
         [0057]    Bands  304  to  330  represent an exemplary set of bandwidth assignments for UEs operating in this 20 MHz cell. Because the current cell has a transmission bandwidth of 20 MHz there is only one possible reception band of 20 MHz, namely band  304 . Because the bandwidth of the cell and Band  304  match, it is centred on f 0 . 
         [0058]    In this embodiment 3 possible  15 MHz  reception bands are defined, namely bands  306 ,  308  and  310 , which are centred on frequencies f 0 , f −150  and f +150  respectively. Because all of these bands  306 ,  308  and  310  encompass the common band  302 , a 15 MHz UE in either the idle state or active state can camp on one of these bands. 
         [0059]    There are also three 10 MHz bands defined, being bands  312 ,  314  and  316 , centred on frequencies f 0 , f −300  and f +300  respectively. Band  312  is the only 10 MHz band that encompass the common band  302 , and hence is the only 10 MHz band that may have 10 MHz UEs in either an idle state or an active state camp on it. Only 10 MHz UEs in an active state may camp one of the non-central 10 MHz bands  314  or  316 . 
         [0060]    There are seven 5 MHz bands defined, being bands  318 ,  320 ,  322 ,  324 ,  326 ,  328  and  330 , centred on frequencies f 0 , f −300 , f +300 , f −450 , f −150  f +150 , and f +450  respectively. Band  318 , centred on frequency f 0 , is the only 5 MHz band that encompasses the common band  302 , and hence is the only 5 MHz band that may have 5 MHz UE in either an idle state or an active state camped on it. Only 5 MHz UEs in an active state may camp on one of the non-central 5 MHz bands  320  to  330 . If any of the non-central 5 MHz bands  320  to  330  were to be used as camping band for a UE in an idle state, the UE would need to re-tune its receiver to the common band from time to time to receive the Broadcast Channel (BCH) for location area updates and other information, which is not desirable. The network would also have to be reconfigured to perform paging (and other signalling) outside the common band, which is also not desirable. 
         [0061]      FIG. 4  illustrates an exemplary band allocation scheme for a 15 MHz bandwidth cell for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception bandwidths. The cell bandwidth is indicated by a frequency axis  400 , which is gradated in sub-carriers (rather than in Hz) illustrating a 901 sub-carrier frequency range from f −450  to f +450 . Using the system parameters set out in Table 1 this can be seen to equate to a 15 MHz transmission bandwidth. As in  FIG. 3  block  302 , which is centred on f 0 , is the common band in which the synch channel, BCH, PCH and SCH of the cell is transmitted. 
         [0062]    Bands  402  to  416  represent an exemplary set of bandwidth assignments for UEs operating in this 15 MHz cell. Because the current cell has a transmission bandwidth of 15 MHz, UEs with reception bandwidths of both 20 MHz and 15 MHz have a reception band covering the entire transmission bandwidth of the cell, and are represented by bands  402  and  404 , which are centred on f 0 . 
         [0063]    There are three 10 MHz reception bands are defined, namely bands  406 ,  408  and  410 , which are centred on frequencies f 0 , f −150  and f +150  respectively. Because all of these bands  406 ,  408  and  410  encompass the common band  302 , a 10 MHz UE in either an idle state or an active state can camp on one of these bands. 
         [0064]    There are also three 5 MHz bands defined, being bands  412 ,  414  and  416 , centred on frequencies f 0 , f −300  and f +300  respectively. Band  412  is the only 5 MHz band that encompasses the common band  302 , and hence is the only 5 MHz band that may have 5 MHz UEs in either an idle state or an active state camped on it. Only 5 MHz UE in active state may camp on one of the non-central 5 MHz bands  414  or  416 . 
         [0065]      FIG. 5  illustrates an exemplary band allocation scheme for a 10 MHz bandwidth cell for UEs having 5 MHz, 10 MHz, 15 MHz and 20 MHz reception bandwidths. The cell bandwidth is indicated by a frequency axis  500 , which is gradated in sub-carriers (rather than in Hz) illustrating a 601 sub-carrier frequency range from f −300  to f +300 . Using the system parameters set out in Table 1 this can be seen to equate to a 10 MHz transmission bandwidth. As in  FIGS. 3 and 4  block  302 , which is centred on f 0 , is the common band in which the synch channel, BCH, PCH and SCH of the cell is transmitted. 
         [0066]    Bands  502  to  512  represent an exemplary set of bandwidth assignments for UEs operating in this cell. Because the current cell has a transmission bandwidth of 10 MHz, UEs with reception bandwidths of 20 MHz, 15 MHz and 10 MHz have a reception band covering the entire transmission bandwidth of the cell, and are represented by bands  502 , to  506 , which are centred on f 0 . 
         [0067]    There are three 5 MHz reception bands defined, namely bands  508 ,  510  and  512 , which are centred on frequencies f 0 , f −150  and f +150  respectively. Band  508  is the only 5 MHz band that encompasses the common band  302 , and hence is the only 5 MHz band that a 5 MHz UE in either an idle state or an active state may camp on. Only 5 MHz UEs in active state may camp on one of the non-central 5 MHz bands  510  or  512 . 
         [0068]    Using  FIG. 3  as an example, when a UE initiates a request to be moved to the Active state (for example: to update its location, to initiate call or to respond to a page), it uses the Random Access Channel (RACH) in the uplink and will receive a response on the Shared Channel (SCH) in the downlink within the common band. In the event that a UE needs to change from the Idle to the Active state the system will order the UE to tune to a non-centre band, e.g. bands  320 ,  322 ,  324 ,  326 ,  328  or  330  if the UE is a 5 MHz UE, or bands  314  or  316  if it is has a 10 MHz reception bandwidth. This is done to reduce load on the common band  302 . In this state the UE will monitor the shared control channel (SCCH) to receive the shared data channel (SDCH) in that non-centre band. In preferred embodiments UEs will move (or shall be moved) back to the Idle state, in which they will camp on a central band encompassing the common band, when there is no connectivity. 
         [0069]    Returning now to  FIG. 1 , the process of reception of the signal transmitted by BTS  100 , by the two UEs  102  and  104 , will be described. In order to receive the transmitted signal, each of the UEs  102  and  104  tunes its carrier frequency to appropriate central frequency, i.e.  DC 1    for  UE 1     102  and  DC 2    for  UE 2     104 . Because of the reception bandwidth restrictions of  UE 1     102 , only a 5 MHz portion of the entire 20 MHz transmitted bandwidth is received by  UE 1     102  using RF block  118 . 1 . Conversely, because  UE 2     104  has a 20 MHz reception bandwidth all of the transmitted bandwidth is received (using RF block  118 . 2 ), including the portion of the transmitted signal that is intended to be transmitted only to UE 1  (i.e. the signal multiplexed on sub-carrier block  106 ). 
         [0070]    Next the received signals undergo further RF processing and analogue to digital conversion in blocks  120 . 1  and  120 . 2 , in UEs  102  and  104  respectively. As can be seen from table 1, in the preferred embodiments the sampling frequency of digital samples at the output of block  120 . 1  and  120 . 2  is 7.68 MHz and 30.72 MHz. The cyclic prefix is then removed in blocks  122 . 1  and  122 . 2 , in UEs  102  and  104 . 
         [0071]    Both UEs then perform an FFT ( 124 . 1  and  124 . 2  in UEs  102  and  104  respectively) to convert the time domain signal into a frequency domain signal. Because of the radio tuning step performed initially, the size of the FFT performed is dictated by the reception bandwidth of the UE, and not by the position of the desired sub-carriers within cell transmission band. As can be seed from Table 1,  UE 1    will use always 512 point FFT, because it has a 5 MHz reception bandwidth and is seeking to extract  301  desired sub-carriers, In order to simplify the UE the size of the FFT performed is not dependent on whether or not other UEs have data multiplexed on the RF signal. Accordingly,  UE 2    will use always 2048 point FFT, because it has a 20 MHz reception bandwidth. Signalling data or other means can then be used to tell  UE 2    to discard (or not decode) data on the sub-carriers transmitted in frequency block  106 . 
         [0072]    The present invention should not be construed as being limited to the reception, common and camping bands described herein, as the definition of such bands described above is somewhat arbitrary. More (or less) bands could be defined. For example in the 20 MHz bandwidth cell, 15 MHz bands could be defined with any central frequency between f −150  and f +150 . Similarly 10 MHz bands could be defined with centre frequencies anywhere between f −300  and f +300 . Also the common band could be defined at any point along the bandwidth of the cell. Notwithstanding this the illustrative bands described herein are considered to be an advantageous in so far as they minimise overlap of bands and thus minimise signalling and design complexity. They also provide enough flexibility for system to efficiently manage resource allocation to a large number of UEs of different capability to use the same cell transmission bandwidth simultaneously. Moreover, the definition of transmission and reception bands, and the mapping of physical channel (such as SCCH, SDCH and pilot) are advantageous in that any UE shall see only one mapping regardless of which band it is camping on. This is desirable since this will significantly reduces UE implementation complexity. 
         [0073]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.