Patent Publication Number: US-2013235951-A1

Title: Transmit Diversity Scheme

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 13/334,788, filed Dec. 22, 2011, which is a continuation of application Ser. No. 11/993,555, filed Apr. 23, 2008, which is a §371 of International application No. PCT/JP2006/317389, filed Aug. 28, 2006, which claims priority to Australian Patent Application No. 2005904682, filed Aug. 26, 2005, and Australian Patent Application No. 2006203698, filed Aug. 25, 2006, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to methods for implementing transmit diversity in a telecommunication network. 
     BACKGROUND ART 
     As their name implies, “Super 3G” mobile telecommunications networks are intended to provide improvements over today&#39;s 3G mobile telecommunications networks. One such improvement being targeted is a tenfold improvement of the existing 3G data rate meaning Super 3G networks should provide a target data rate in the downlink direction of 100 Mbps and for in the uplink direction of 50 Mbps. It is expected that services available in future Super 3G mobile telecommunications networks shall be similar to the existing 3G HSDPA (High Speed Downlink Packet Access), MBMS (Multimedia broadcast-multicast services) and HSUPA (High Speed Uplink Packet Access) service but with significantly higher data rates. 
     In order to achieve such a high data rate in Super 3G networks a new radio access technology—orthogonal frequency division multiplexing (OFDM) has been introduced together with higher modulation (64-QAM) and using turbo or LDPC (low density parity check) coding schemes as well as other features such as multiple input multiple output (MIMO). OFDM is a modulation technique that can be used for high speed data communication, whose main idea is to send data in parallel over a number of spectrally overlapping orthogonal sub-channels. 
     OFDM is considered to have the certain advantages over other radio access technologies, including the following:
         High spectral efficiency can be obtained by a careful selection of the frequencies for the so-called sub-carriers, by defining the frequency spacing between sub-carriers equal to the reciprocal of the OFDM symbol duration.   OFDM has superior power efficiency over other technologies as there is no crowding in signal space.   OFDM can be made robust to multi-path interference by introducing guard interval in between consecutive OFDM symbols in the time domain.   OFDM is robust to narrow band interference.       

     However, OFDM is quite sensitive to impairments such as phase noise, carrier frequency offset, I/Q imbalance, phase distortion and linearity issues, which can introduce inter-carrier interference, reduce SINR (Signal to Interference and Noise Ratio) and create intermodulation problems. These identified impairments always exist in implementations of OFDM and affect the ability to apply higher level modulation schemes and coding schemes, therefore making it more difficult to achieve the target data rates discussed above. Moreover they are also expensive to mitigate or reduce. 
     DISCLOSURE OF INVENTION 
     In broad concept the present inventor has identified that by introducing transmission diversity (TX diversity) provided by Space-Time encoding, into a network using OFDM at least partial compensation for the above identified impairments may be achieved. 
     In particular there is provided an algorithm for performing transmit diversity encoding in a transmitter and transmit diversity decoding in a receiver respectively. Embodiments of the present invention can conveniently be described in the context of a so-called “Super 3G” radio communications network. However the present invention should not be considered as being limited to this type of network. 
     In a first aspect the present invention provides a method of processing at least one sequence of data symbols to be transmitted over a wireless channel including N sub-carriers having different frequencies; the method including the steps of: 
     defining, in the at least one sequence of data symbols, a plurality of blocks of data symbols, each of the blocks of data symbols including one data symbol corresponding to each of the N sub-carriers, 
     processing each of the blocks of data symbols such that the correspondence between at least two of the data symbols in the block and their respective sub-carriers are changed, to create a processed block in which each data symbol corresponds to one of the sub-carriers; 
     for each processed block of data symbols, generating a corresponding conjugated block of data symbols which includes N data symbols that are the complex conjugate of a corresponding data symbol in the processed block of data symbols; 
     processing pairs of the processed blocks of data symbols for transmission on a first antenna on the N sub-carriers in a temporal first order; and 
     processing pairs of the conjugated blocks of data symbols for transmission on a second antenna on the N sub-carriers in the reverse temporal order. 
     The method can further include defining blocks of data symbols in one sequence of data symbols and where the pairs of processed blocks correspond to blocks of N data symbols received sequentially. Alternatively the method can include processing a plurality of sequences of data. In this case, to generate a corresponding plurality of blocks of data symbols, each of the blocks of data symbols including one data symbol corresponding to each of the N sub-carriers. 
     Processing each of the blocks of data symbols such that the correspondence between at least two of the data symbols in the block and their respective sub-carriers are changed can include changing the correspondence between the majority of the data symbols in the block and their respective sub-carriers. Processing each of the blocks of data symbols such that the correspondence between at least two of the data symbols in the block and their respective sub-carriers are changed can include changing the correspondence between the all of the data symbols in the block and their respective sub-carriers. 
     Processing each of the blocks of data symbols such that the correspondence between at least two of the data symbols in the block and their respective sub-carriers are changed preferably includes interleaving the data symbols in each block to change the respective correspondence with the N sub-carriers. 
     In a second aspect the present invention provides a method of processing at least one sequence of data symbols to be transmitted over a wireless channel; including 
     (a) defining, in the at least one sequence of data symbols, a plurality of blocks of data symbols; 
     (b) processing the least one sequence of data symbols on a block-by-block basis to provide frequency diversity in the subsequently transmitted signal; 
     (c) processing the blocks of data symbols in group s of two or more blocks to provide time diversity in the subsequently transmitted signal; and 
     (d) processing the blocks of data for transmission over at least two antennas to provide for spatial diversity in the subsequently transmitted signal. 
     Step (b) preferably includes, processing each of the blocks of data symbols such that the correspondence between at least two of the data symbols in the block and their respective sub-carriers are changed, to create a processed block in which each data symbol corresponds to one of the sub-carriers. 
     Step (c) can include, for each processed block of data symbols, generating a corresponding conjugated block of data symbols which includes N data symbols that are the complex conjugate of a corresponding data symbol in the processed block of data symbols. 
     Step (d) can include, processing groups of the processed blocks of data symbols for transmission on a first antenna on the N sub-carriers in a temporal first order; and processing equivalent groups of the conjugated blocks of data symbols for transmission on a second antenna on the N sub-carriers in a different temporal order. 
     In a third aspect the present invention provides a transmit diversity encoder configured to process at least one sequence of data symbols to be transmitted over a wireless channel including N sub-carriers having different frequencies, the encoder including: 
     a block defining stage configured to define, in the at least one sequence of data symbols, a plurality of blocks of data symbols; 
     a frequency encoder configured to process the blocks of data symbols to provide frequency diversity within the blocks of data symbols; 
     a space-time encoder configured to process the blocks of data in groups of two or more blocks to provide time diversity between blocks for transmission over different antennas. 
     Preferably the frequency encoder is configured to interleave the data symbols of a block in the frequency domain, to provide frequency diversity in the block. 
     The space-time encoder can be configured to generate a conjugated block of data symbols corresponding to each frequency encoded block of data symbols, including N data symbols that are the complex conjugate of a corresponding data symbol in the frequency encoded block of data symbols; and process pairs of the frequency encoded blocks for transmission on a first antenna in a temporal first order; and pairs of the conjugated blocks for transmission on a second antenna in the reverse temporal order. 
     In a further aspect there is provided a transmitter for a wireless communications network including at least two transmission antennas and a transmit diversity encoder as described herein. In another aspect the present invention provides a base station for a wireless communications network including such a transmitter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Illustrative embodiments of the present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a transmitter including TX diversity encoder according to first embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a transmitter including TX diversity encoder according to second embodiment of the present invention; 
         FIG. 3A  illustrates a TX diversity coding pilot and data symbol arrangement applicable to a single user&#39;s data to be transmitted with a high data-rate, according to one embodiment of the present invention; 
         FIG. 3B  illustrates a TX diversity coding pilot and data symbol arrangement applicable to a single user&#39;s data to be transmitted with a high data-rate, according to one embodiment of the present invention; 
         FIG. 4A  illustrates a TX diversity coding pilot and data symbol arrangement applicable to multiple users&#39; data to be transmitted with a low data-rate or for signaling, according to an embodiment of the present invention; 
         FIG. 4B  illustrates a TX diversity coding pilot and data symbol arrangement applicable to multiple users&#39; data to be transmitted with a low data-rate or for signaling, according to an embodiment of the present invention; 
         FIG. 5A  illustrates a TX diversity coding pilot and data symbol arrangement applicable to multiple users&#39; data to be transmitted with a low data-rate or for signaling, according to an embodiment of the present invention; 
         FIG. 5B  illustrates a TX diversity coding pilot and data symbol arrangement applicable to multiple users&#39; data to be transmitted with a low data-rate or for signaling, according to an embodiment of the present invention; 
         FIG. 6  illustrates schematically a prior art space-time encoder; 
         FIG. 7  depicts a symbol sequence for input into the frequency encoder depicted in  FIG. 1 ; 
         FIG. 8  depicts a symbol sequence of  FIG. 7  after block shifting has been applied according to an embodiment of the present invention; 
         FIG. 9  depicts a symbol sequence of  FIG. 8  after interleaving according to an embodiment of the present invention; 
         FIG. 10  illustrates schematically a space-time encoder according to an embodiment of the present invention; 
         FIG. 11A  depicts an output symbol sequence from a STC encoder operating in accordance with an embodiment of the present invention; 
         FIG. 11B  depicts an output symbol sequence from a STC encoder operating in accordance with an embodiment of the present invention; 
         FIG. 12  depicts a symbol sequence for input into the frequency encoder depicted in  FIG. 2 ; 
         FIG. 13  illustrates schematically a space-time encoder according to a further embodiment of the present invention; 
         FIG. 14  depicts an output symbol sequence from a STC encoder of  FIG. 13 ; 
         FIG. 15  depicts an output symbol sequence from a STC encoder operating in accordance with another embodiment of the present invention; and 
         FIG. 16  is a block diagram illustrating a receiver configured to receive a signal encoded according to an embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     As discussed above, the present inventor has determined that prior art space-time encoding methods can be adapted for use in a telecommunications network that employs OFDM to at least partially ameliorate one or more of the drawbacks mentioned above.  FIG. 6  depicts a typical space-time encoding (STC) arrangement operating according to the prior art. This base station  700  includes two antennas  702  and  704  to transmit a pair of symbols S n  and S n+1  over channels α 0  and α 1 , respectively to user equipment (UE)  706 . Using the prior art STC technique, the pair of symbols S n  and S n+1  is transmitted on the antenna  702  and the pair −S* n+1  and S* n  is transmitted on the antenna  704 . 
     In order to perform the decoding at the UE  706 , the symbols received at the UE  706  can be represented 
         R   n   =Ŝ   n ×{circumflex over (α)} 0 +(− Ŝ*   n+1 )×{circumflex over (α)} 1  
 
         R   n+1   =Ŝ   n+1 ×{circumflex over (α)} 0 +( Ŝ*   n )×{circumflex over (α)} 1  
 
     as: Where 
     
         
         
           
             Ŝ n  and Ŝ n+1  are estimated symbols which requires to be found 
             {circumflex over (α)} 0  and {circumflex over (α)} 1  are channel estimates from the antennas  1  and  2  respectively 
           
         
       
    
     Equation 1 
     In this example, the estimated received symbol Ŝ n  and Ŝ n+1  can be found using the following expressions 
     
       
         
           
             
               
                 
                   
                     
                       
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     However, in a telecommunications network using OFDM, consecutive data symbols on a sub-channel are not transmitted consecutively on the air interface, rather consecutive data symbols are transmitted at the same time on different sub-carriers (frequencies). 
     Three methods for implementing TX diversity using TX diversity encoder according to an embodiment of the present invention will be described in relation to the following transmission circumstances:
         1. An implementation of TX diversity for use with high data rate user traffic, such as would typically arise when making high speed down link data packet transmissions to a UE e.g. application traffic.   2. Two implementations of TX diversity adapted for use with low data rate user traffic, such as signaling and/or control information. For this type of traffic two schemes will be described as follows:
           a. A TX diversity implementation adapted for use when data symbols from a single user are time multiplexed with other users&#39; traffic; and   b. ATX diversity implementation adapted for use when data symbols from a single user are frequency multiplexed with other users&#39; traffic   
               

     It should be noted that exemplary embodiments are described by way of example only and that the present invention is not limited to these implementations. 
     The illustrative TX diversity methods can be implemented in transmitters of the type depicted in  FIGS. 1 and 2 . In this regard,  FIG. 1  depicts a first transmitter configuration capable of implementing an embodiment of the present invention. 
     The transmitter  100  receives a sequence of data symbols  102  at a TX diversity encoder  104  which includes frequency encoder block  106  and space-time encoder  108 , details of the operation of which will be described in detail below in relation to preferred embodiments. 
     The space-time encoder  108  outputs two encoded data streams  110 . 1  and  110 . 2  corresponding to the two antennas  112 . 1  and  112 . 2 . Each of the data streams  110 . 1  and  110 . 2  are passed to a respective OFDM modulation stage  114 . 1  and  114 . 2  to undergo OFDM modulation. 
     The output of the OFDM modulation stage  114 . 1  and  114 . 2  is then filtered in respective filtering stages  116 . 1  and  116 . 2  before conversion to an analogue signal by the digital to analogue conversion stages  118 . 1  and  118 . 2 . The analogue signal is then used to modulate the radio frequency carrier signal by blocks  120 . 1  and  120 . 2  for transmission via respective antennas  112 . 1  and  112 . 2 . 
     Further details of the operation of the TX diversity encoder  104  and the OFDM modulation stages  114 . 1  and  114 . 2  become apparent on reading the description of the preferred embodiment. 
       FIG. 2  is similar to  FIG. 1  in that it depicts an exemplary transmitter configuration capable of implementing an embodiment of the present invention. Components of the transmitter  200  of  FIG. 2  that are equivalent to components depicted in  FIG. 1  have been labeled with corresponding reference numerals, and their operation will not be discussed in detail. 
     In  FIG. 2 , the transmitter  200  receives an input data sequence  102  which is input into the TX diversity encoder  202 . In the embodiment of  FIG. 2  the TX diversity encoder  202  includes an initial stage  204  where serial to parallel conversion of the data symbol sequence  102  is performed and frequency encoding and interleaving is also conducted. The frequency encoded interleaved data for each of the end sub-carriers is then applied to a space-time encoder  206 . The output of the space-time encoder is then passed to the OFDM modulation stages  208 . 1  and  208 . 2  corresponding to respective antennas  112 . 1  and  112 . 2  of the transmitter  200 . Further detail of the operation of the TX diversity encoder  202  and the OFDM modulation stages  208 . 1  and  208 . 2  will be described below. 
       FIGS. 3A ,  3 B,  4 A,  4 B,  5 A and  5 B depict the user and pilot data symbols to be transmitted over a given time period on two antennas ( 112 . 1  and  112 . 2 ). In this example, on each of the antennas  112 . 1  and  112 . 2  the respective chunks of data symbols  302  and  304  are transmitted across N sub-carrier frequencies which are depicted as columns  306 . 1  to  306 .N. Transmissions on a given time slot are represented across rows of the diagram, meaning all data symbols on row  308 . 0  are transmitted simultaneously on their respective sub-carriers  1  to N followed by data symbols of row  308 . 1  and so on until the end of the time period depicted when data symbols on row  308 .K are transmitted. 
     In a first embodiment of the TX diversity scheme illustrated in  FIGS. 3A and 3B , which can be advantageously applied to high data rate user traffic, e.g. high speed down link data packet transmissions to a UE the data symbols of a single user occupy the whole OFDM physical channel unit (i.e. all sub-carrier frequencies over the selected time period) and are not multiplexed with other user&#39;s data symbols. This is illustrated in  FIGS. 3A and 3B , which depict the pilot and data symbol arrangement  300  for transmission on a first antenna ( 112 . 1 ) and a second antenna ( 112 . 2 ) after the TX diversity encoding applicable for OFDM technology. 
     In this example, the pilot pattern  310 . 1  and  310 . 2  for both antennas  112 . 1  and  112 . 2  are comprised of pilot symbols  312 . 1  for antenna  112 . 1  interleaved in the frequency domain with the pilot symbols  312 . 2  for antenna  112 . 2 . The pilot pattern vector transmitted on antenna  112 . 1  is orthogonal with that transmitted on antenna  112 . 2 . This allows the UE to distinguish a received signal from antenna  112 . 1  from the signal received from antenna  112 . 2 . As can be seen the pilot patterns  310 . 1  and  310 . 2  are time multiplexed with user traffic (data rows  308 . 0  to  308 .K) on each sub-carrier  306 . 1  to  306 .N. 
     In this embodiment, time diversity between the two data symbols transmitted on the antennas  112 . 1  and  112 . 2  is provided by reversing the order of transmission of corresponding pairs of symbol blocks on the two antennas. For example, take the pair of symbols blocks  314 . 1 A and  314 . 1 B which, on antenna  112 . 1 , are transmitted in a first order i.e. symbol block  314 . 1 A followed by symbol block  314 . 1 B. On the second antenna  112 . 2  the corresponding symbol blocks  314 . 2 A and  314 . 2 B are transmitted in the opposite order, i.e. symbol block  314 . 2 B followed by symbol block  314 . 1 B. 
     When implementing the present embodiment, the frequency encoder block  106  of the transmitter  100  of  FIG. 1  takes the number of sub-carriers allocated to the user for data packet transmission, which is N in this case, as an input and performs a block shifting process as illustrated in  FIG. 7 . 
       FIG. 7  depicts a sequence of received data symbols (e.g. input sequence  102  of  FIG. 1 ). The first N data symbols S( 0 ) to S(N−1) are grouped to form a first symbol block S 0 . The next N data symbols S(N) to S( 2 N−1) are grouped to form symbol block S 1 , which is time shifted so as to be paired with vector S 0 . Similarly following symbol blocks S 2  and S 3  etc are paired together on a block-by-block basis as shown in  FIG. 8 . 
     The symbols in each block of N symbols (e.g. S 1 ) are then interleaved to generate a corresponding interleaved block of symbols (e.g. X 1 ) of length N as being illustrated in  FIG. 9 . This interleaving of consecutive symbols in a block, e.g. S 1 , maximizes the frequency diversity of consecutive symbols by preventing consecutive symbols from being transmitted on adjacent sub-carrier frequencies. This interleaving step could also be integrated with other data traffic from other users to maximize the frequency diversity of the whole transmitter bandwidth. 
     The interleaved blocks of symbols (e.g. X 1 ) are then passed to the space-time encoder ( 108  of  FIG. 1 ), in parallel for space-time encoding. The space-time encoder  108  then takes pair of symbols e.g. [X( 0 ), X(N)], [X( 1 ), X(N+1)], [X( 2 ), X(N+2)] . . . as inputs and performs space-time encoding on a pair-by-pair basis for each sub carrier depicted in  FIG. 10 . In  FIG. 10  a symbol pair X( 0 ) and X(N) for a first sub-carrier are received, and further processed for transmission on a first antenna  112 . 1 . As described above the complex conjugate of the symbol pair X*( 0 )-X*(N) are transmitted on the second antenna  112 . 2  on the same sub-carrier. This is illustrated more clearly in  FIGS. 11A and 11B  which depict the output of the space time encoder  108 . 
       FIGS. 11A and 11B  depict the symbol sequences  1200 . 1  and  1200 . 2  for transmission on antennas  112 . 1  and  112 . 2  respectively. On the first antenna  112 . 1  symbols X( 0 ) to X(N−1) are transmitted across the N sub-carrier frequencies, followed by symbols X(N) to X( 2 N−1), whereas on the second antenna  112 . 2  symbols −X*(N) to −X( 2 N−1) are first transmitted across the sub-carriers, followed by symbols X*( 0 ) to X*(N−1). 
     Alternative methods of achieving of TX diversity using a TX diversity encoder according to an embodiment of the present invention for use with low data rate user traffic, such as signaling and/or control information for establishing peer to peer communication between UE and BS will now be described in connection with  FIGS. 4A ,  4 B,  5 A and  5 B.  FIGS. 4A and 4B  depict the situation where the data symbols from a single user are time multiplexed with other user traffic, whereas  FIGS. 5A and 5B  depict the situation where a user&#39;s data is frequency multiplexed with other user traffic. 
     Turning firstly to  FIGS. 4A and 4B , which depict a TX diversity implementation adapted for use when data symbols from a single user is time multiplexed with other users traffic.  FIGS. 4A and 4B , depict the pilot and data symbol arrangement  400  for transmission on a first antenna ( 112 . 1 ) and a second antenna ( 112 . 2 ) after the TX diversity encoding applicable for OFDM technology according to a second embodiment of the present invention. In this example, the pilot pattern  310 . 1  and  310 . 2  for both antennas  112 . 1  and  112 . 2  are the same as in the previous embodiment. As in the previous embodiment, the pilot patterns  310 . 1  and  310 . 2  are time multiplexed with multiple users&#39; traffic. 
     Again the respective chunks of data symbols  302  and  304  are transmitted across N sub-carrier frequencies which are depicted as columns  306 . 1  to  306 .N. Transmissions on a given time slot are represented across rows of the diagram, meaning all data symbols on row  308 . 0  are transmitted simultaneously on their respective sub-carriers  1  to N followed by data symbols of row  308 . 1  and so on until the end of the time period depicted when data symbols on row  308 .K are transmitted. In this embodiment the data of multiple users are transmitted across all sub-carriers in a time multiplexed manner, meaning that each row e.g.  308 . 0  of data in the chunks  302  contains data symbols relating to only a single UE, e.g. UE 0  to UE K . 
     In this embodiment, partial TX diversity and full frequency diversity can be achieved by using the following method. 
     Data corresponding to each UE are rate matched so that the number of symbols transmitted on the predefined number of sub-carriers is equal for each user. In this way the block shifting step described in connection with the first embodiment can be avoided. The frequency encoder  106  of the TX diversity encoder  104  therefore, begins by performing block frequency interleaving on data symbol blocks e.g. S 0  corresponding to each UE, to achieve frequency diversity. 
     Next the space-time encoder  108  operates on the input symbol sequences corresponding to two UEs in order to form a pair of symbol blocks for space-time encoding as shown in  FIGS. 13 and 14 . This process is similar to that described in connection with the first embodiment. However, as depicted in  FIG. 12  the paired, interleaved symbol blocks X UE1  and X UE2  relating to different UE data are passed to the space-time encoder ( 108  of  FIG. 1 ), in parallel for space-time encoding. The space-time encoder  108  then takes pair of symbols e.g. [X UE1 ( 0 ), X UE2 ( 0 )], [X UE1 ( 1 ), X UE2 ( 1 )], . . . [X UE1 (N), X UE2 (N)] as inputs and performs space-time encoding on a pair-by-pair basis for each sub carrier depicted in  FIG. 13 . In  FIG. 13  a symbol pair X UE1 ( 0 ), X UE2 ( 0 ) for a first sub-carrier are received, and further processed for transmission on a first antenna  112 . 1 . As described above the complex conjugate of the symbol pair X* UE1 ( 0 ) and −X* UE2 ( 0 ) are transmitted on the second antenna  112 . 2  on the same sub-carrier. 
     In accordance with this method,  FIG. 14  depicts the symbol sequences  1500 . 1  and  1500 . 2  for transmission on antennas  112 . 1  and  112 . 2  respectively. On the first antenna  112 . 1  symbols X UE1 ( 0 ) to X UE1 (N−1) are transmitted across the N sub-carrier frequencies, followed by symbols X UE2 ( 0 ) to X UE2 (N−1), whereas on the second antenna  112 . 2  symbols −X* UE2 ( 0 ) to −X* UE2 (N−1) are first transmitted across the sub-carriers, followed by symbols −X* UE1 ( 0 ) to X* UE1 (N−1). 
       FIGS. 5A and 5B  depict a second method of implementing TX diversity that can be advantageously implemented in the situation where a user&#39;s data is frequency multiplexed with other user traffic.  FIGS. 5A and 5B , depict the pilot and data symbol arrangement  500  for transmission on a first antenna ( 112 . 1 ) and a second antenna ( 112 . 2 ) after the TX diversity encoding applicable for OFDM technology according to a third embodiment of the present invention. Again, the pilot pattern  310 . 1  and  310 . 2  for both antennas  112 . 1  and  112 . 2  are the same as in the previous embodiments. As in the previous embodiment, the pilot patterns  310 . 1  and  310 . 2  are time multiplexed with multiple users&#39; traffic. 
     Respective chunks of data symbols  302  and  304  are transmitted across N sub-carrier frequencies which are depicted as columns  306 . 1  to  306 .N. Transmissions on a given time slot are represented across rows of the diagram, meaning all data symbols on row  308 . 0  are transmitted simultaneously on their respective sub-carriers  1  to N followed by data symbols of row  308 . 1  and so on until the end of the time period depicted when data symbols on row  308 .K are transmitted. In this embodiment the data of multiple users are transmitted in all timeslots but are transmitted only on a single sub-carrier, i.e. the users&#39; traffic are frequency multiplexed. Thus in  FIGS. 5A and 5B  meaning that each column e.g.  306 . 1  of data symbols in the chunk  302  contains data symbols relating to only a single UE, e.g. UE 1 . 
     Alternative methods of achieving of TX diversity that are adapted for use with low data rate user traffic, such as signaling and/or control information for establishing peer to peer communication between UE and BS will now be described in connection with  FIGS. 4A ,  4 B,  5 A and  5 B.  FIGS. 4A and 4B  depict the situation where the data symbols from a single user are time multiplexed with other user traffic, whereas  FIGS. 5A  and  5 B depict the situation where a user&#39;s data is frequency multiplexed with other user traffic, whereas each row e.g.  308 . 0  of data contains data symbols relating to all UEs to be transmitted on different frequency sub-carriers. To implement TX diversity on this type of data traffic the frequency encoder  106  of the TX diversity encoder  104  is transparent and the space-time encoder  108  functions as shown in  FIG. 6 . 
     Returning to  FIG. 1  in each of the cases described above, the outputs of the space-time encoder  108  (irrespective of the nature of the data and TX diversity method applied) are then input to the respective OFDM modulators  114 . 1  and  114 . 2  for serial to parallel conversion, modulation using Inverse Fast Fourier Transform and insertion of the cyclic prefix for the purpose of combating multipath delay symbols prior to further processing by blocks  116  to  120  and transmission. 
     As mentioned above,  FIG. 2  depicts a second TX hardware configuration configured for use with an embodiment of the present invention. In  FIG. 2  the TX diversity encoder  202  is configured to operate in the following fashion. 
     For high data rate user traffic and low data rate user traffic that is time multiplexed, as in  FIGS. 4A and 4B , the initial stage  204  receives a block of N symbols to be transmitted on the N sub-carriers and performs an interleaving procedure as described in connection with  FIG. 9 . However, in the case of low rate traffic that is frequency multiplexed as depicted in  FIGS. 5A and 5B  this stage is transparent, and the traffic from the plurality of users is input in parallel into the space-time encoder  206 . 
     In this embodiment, the space-time encoder  206  of  FIG. 2  performs space-time encoding on each sub-carrier by taking a pair of symbols on one sub-carrier and performing space-time encoding on each pair of symbols according to  FIG. 15 . The space time encoding of  FIG. 15  operates in a similar fashion to  FIG. 6  except that rather than operating on the input data symbols S n  and S n+1  directly, it operates on the interleaved symbols generated by the initial stage  204 , i.e. X n  and X n+1 . In this regard, the symbol pair X n  and X n+1  is transmitted on the antenna  112 . 1  and the symbol pair −X* n=1  and X* n  is transmitted on the antenna  112 . 2 . 
       FIG. 16  depicts a block diagram of a receiver operating according to an embodiment of the present invention. In  FIG. 16  the receiver  1700  receives a radio frequency signal at antenna  1702 . The received signal is demodulated at the RF demodulation stage  1704  and converted to a digital signal by the analogue to digital converter  1706 . The digital signal is then passed to the cyclic prefix removal stage  1708  and the common pilot symbols are removed. 
     The traffic signals undergo serial to parallel conversion in block  1710  and signals corresponding to the N sub-carriers are passed to the FFT stage  1712  for Discrete Fourier Transform using FFT processing algorithm. The N frequency domain signals are then converted back into a serial data stream by the parallel to serial converter  1714  and passed to the descrambling and despreading stage  1716 . The output of the descrambling and despreading stage  1716  is passed to the pilot data separation stage  1718  where pilot symbols are removed for use by the channel estimation stage  1720  to generate a channel estimate for transmission antennas  1  and  2 . 
     The channel estimates corresponding to two transmission antennas are passed to the equalization and transmission diversity decoding stage  1722  which operates as discussed below. The frequency decoding block  1724  processes the output of the equalization transmission diversity decoding stage  1722  and passes a first output signal to the signaling decoder  1726  and a second output signal to the data channel decoder  1728 . 
     Control information decoded by the fast signaling decoder  1726  is then passed through the controller  1730  which is responsible for configuring the following blocks:
         Serial to parallel block  1710 ;   FFT block  1712 ;   Parallel to serial block  1714 ;   Descrambling &amp; de-spreading block  1716 ; and   Pilot &amp; data separation block  1718 ;
 
to correctly receive and demodulate the desired signal according to different topologies of traffic multiplexing at the transmitted base station.
       

     For the high data-rate user traffic as shown in  FIGS. 3A and 3B  these blocks are configured to receive and demodulate entire block (time and frequency) when performing TX diversity decoding and frequency decoding. For the low data rate user traffic as depicted in  FIGS. 4A ,  4 B,  5 A and  5 B, the data received shall be processed depending on the type of multiplexing used. In the event that the multiple users&#39; data is time-division multiplexed (TDM) (see  FIGS. 4A and 4B ), two consecutive symbols in time domain are received and demodulated on all allocated sub-carriers. In this case the UE is configured to either receive and demodulate one symbol earlier and one symbol on time on all allocated sub-carriers; or one symbol on time and one symbol later on all allocated sub-carriers. This will depend on the way in which user data is multiplexed. The user equipment will receive suitable signaling data to inform it of this. When the multiple users&#39; data is frequency-division multiplexed (FDM) (as per  FIGS. 5A and 5B ), all symbols on all allocated sub-carrier are received and demodulated. 
     The equalization and TX diversity decoding block  1722 , performs the TX diversity decoding as follows. For the high data-rate user traffic as shown in  FIGS. 3A and 3B  an estimated symbol can be found using the following mathematical expression: 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           S 
                           ^ 
                         
                         i 
                       
                       = 
                       
                         
                           
                             
                               R 
                               i 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               R 
                               
                                 N 
                                 + 
                                 i 
                               
                               * 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                           
                         
                         
                           
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                               * 
                             
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     and 
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     
                       
                         
                           S 
                           
                             N 
                             + 
                             i 
                           
                         
                         ^ 
                       
                       = 
                       
                         
                           
                             
                               R 
                               
                                 N 
                                 + 
                                 i 
                               
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           - 
                           
                             
                               R 
                               i 
                               * 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                           
                         
                         
                           
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                               * 
                             
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     where 
                      
                     
                       
 
                     
                      
                     
                       N 
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       number 
                        
                       
                           
                       
                        
                       of 
                        
                       
                           
                       
                        
                       sub 
                        
                       
                         - 
                       
                        
                       carriers 
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       which 
                        
                       
                           
                       
                        
                       data 
                        
                       
                           
                       
                        
                       symbols 
                        
                       
                           
                       
                        
                       are 
                        
                       
                           
                       
                        
                       transmitted 
                        
                       
                           
                       
                        
                       in 
                        
                       
                           
                       
                        
                       parallel 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         0 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           N 
                           + 
                           i 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       first 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.1 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         1 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           N 
                           + 
                           i 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       second 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.2 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
     For the low data rate user traffic as depicted in  FIGS. 4A and 4B  when the UE is configured to receive and demodulate one OFDM symbol earlier and one OFDM symbol on time, the following mathematical expression (Equation 4) is used to perform TX diversity demodulation to find an estimated Ŝ i    
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           S 
                           ^ 
                         
                         i 
                       
                       = 
                       
                         
                           
                             
                               R 
                               i 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           - 
                           
                             
                               R 
                               
                                 i 
                                 - 
                                 N 
                               
                               * 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                           
                         
                         
                           
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                               * 
                             
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     where 
                      
                     
                       
 
                     
                      
                     
                       N 
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       number 
                        
                       
                           
                       
                        
                       of 
                        
                       
                           
                       
                        
                       sub 
                        
                       
                         - 
                       
                        
                       carriers 
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       which 
                        
                       
                           
                       
                        
                       data 
                        
                       
                           
                       
                        
                       symbols 
                        
                       
                           
                       
                        
                       are 
                        
                       
                           
                       
                        
                       transmitted 
                        
                       
                           
                       
                        
                       in 
                        
                       
                           
                       
                        
                       parallel 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         0 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           i 
                           - 
                           N 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       first 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.1 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         1 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           i 
                           - 
                           N 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       second 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.2 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
     In the case where the UE is configured to receive and demodulate one OFDM symbol on time and one OFDM symbol later, the following mathematical expressing (Equation 5) is used to perform TX diversity demodulation to find an estimated Ŝ i    
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           S 
                           ^ 
                         
                         i 
                       
                       = 
                       
                         
                           
                             
                               R 
                               i 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               R 
                               
                                 N 
                                 + 
                                 i 
                               
                               * 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                           
                         
                         
                           
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                               * 
                             
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     where 
                      
                     
                       
 
                     
                      
                     
                       N 
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       number 
                        
                       
                           
                       
                        
                       of 
                        
                       
                           
                       
                        
                       sub 
                        
                       
                         - 
                       
                        
                       carriers 
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       which 
                        
                       
                           
                       
                        
                       data 
                        
                       
                           
                       
                        
                       symbols 
                        
                       
                           
                       
                        
                       are 
                        
                       
                           
                       
                        
                       transmitted 
                        
                       
                           
                       
                        
                       in 
                        
                       
                           
                       
                        
                       parallel 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         0 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           N 
                           + 
                           i 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       first 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.1 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         1 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           N 
                           + 
                           i 
                         
                       
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       second 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.2 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   5 
                 
               
             
           
         
       
     
     For the low data rate user traffic as depicted in  FIGS. 5A and 5B  which uses FDM the two consecutively received symbols Ŝ i  and Ŝ i+1  can be TX diversity demodulated as follow using the following expressions: 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           S 
                           ^ 
                         
                         i 
                       
                       = 
                       
                         
                           
                             
                               
                                 R 
                                 i 
                               
                               × 
                               
                                 
                                   α 
                                   ^ 
                                 
                                 0 
                                 * 
                               
                             
                             + 
                             
                               
                                 R 
                                 
                                   i 
                                   + 
                                   1 
                                 
                                 * 
                               
                               × 
                               
                                 
                                   α 
                                   ^ 
                                 
                                 1 
                               
                             
                           
                           
                             
                               
                                 
                                   α 
                                   ^ 
                                 
                                 0 
                               
                               × 
                               
                                 
                                   α 
                                   ^ 
                                 
                                 0 
                                 * 
                               
                             
                             + 
                             
                               
                                 
                                   α 
                                   ^ 
                                 
                                 1 
                               
                               × 
                               
                                 
                                   α 
                                   ^ 
                                 
                                 1 
                                 * 
                               
                             
                           
                         
                          
                         
                             
                         
                          
                         and 
                       
                     
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     
                       
                         
                           S 
                           
                             i 
                             + 
                             1 
                           
                         
                         ^ 
                       
                       = 
                       
                         
                           
                             
                               R 
                               
                                 i 
                                 + 
                                 1 
                               
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           - 
                           
                             
                               R 
                               i 
                               * 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                           
                         
                         
                           
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               0 
                               * 
                             
                           
                           + 
                           
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                             
                             × 
                             
                               
                                 α 
                                 ^ 
                               
                               1 
                               * 
                             
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     
                         
                     
                      
                     where 
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         0 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           i 
                           + 
                           1 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       first 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.1 
                     
                      
                     
                       
 
                     
                      
                     
                       
                         
                           α 
                           ^ 
                         
                         1 
                       
                        
                       
                           
                       
                        
                       is 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       average 
                        
                       
                           
                       
                        
                       channel 
                        
                       
                           
                       
                        
                       estimate 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       position 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       
                         R 
                         
                           i 
                           + 
                           1 
                         
                       
                        
                       
                           
                       
                        
                       on 
                        
                       
                           
                       
                        
                       the 
                        
                       
                           
                       
                        
                       second 
                        
                       
                           
                       
                        
                       antenna 
                        
                       
                           
                       
                        
                       112.2 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   6 
                 
               
             
           
         
       
     
     The frequency decoding block  1724  performs block (K×N) de-interleaving on the TX diversity decoded symbols from block  1722 . Where N is the number of sub-carriers which is allocated to a UE and K is the number of symbols in the block. 
     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.