Abstract:
A method of providing transmit diversity for a secondary synchronization channel (S-SCH) includes generating a S-SCH signal, performing a frequency switched transmit diversity (FSTD) process on the S-SCH signal to create a first processed signal, performing a precoding vector switching (PVS) process on the first processed signal to create a processed S-SCH signal, and transmitting the processed S-SCH signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 60/895,623 filed Mar. 19, 2007 which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    This application is related to wireless communications. 
       BACKGROUND 
       [0003]    The third generation partnership project (3GPP) and its progeny 3GPP2, are directed towards the advancement of technology for radio interfaces and network architectures for wireless communication systems. Part of 3GPP involves the use of orthogonal frequency division multiple access (OFDMA) as a technology for downlink (DL) communications in an evolved UMTS terrestrial radio access (e-UTRA) network. At initial access, a wireless transmit/receive unit (WTRU) may receive and process a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH) in order to acquire timing, frequency offset, and a cell identification (ID). 
         [0004]    At initial cell search, the S-SCH may be received by the WTRU. However, the WTRU has no knowledge of the number of transmit antennas at the cell. Therefore, it is preferable that a transmit diversity scheme not requiring knowledge of the number of transmit antennas be used in the network. Several transmit diversity schemes, such as time switched transmit diversity (TSTD), frequency switched transmit diversity (FSTD) and precoding vector switching (PVS) have been considered. 
         [0005]    It would be desirable to have a transmit diversity scheme for the S-SCH for an e-UTRA network that achieves high performance. 
       SUMMARY 
       [0006]    A method and apparatus is disclosed for providing transmit diversity for a secondary synchronization channel (S-SCH). This may include applying a FSTD process and a PVS process to a S-SCH prior to transmitting the S-SCH. 
         [0007]    More specifically, the S-SCH may be processed with an FSTD to a first orthogonal frequency domain multiplexed (OFDM) symbol with a first sequence in a lower bandwidth and a second sequence in an upper bandwidth and a second OFDM symbol with the first sequence in the upper bandwidth and the second sequence in the lower bandwidth. A precoding matrix may be applied to the first and second symbols. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
           [0009]      FIG. 1  shows an example of a wireless communication system in accordance with an embodiment; 
           [0010]      FIG. 2  shows a functional block diagram of a WTRU and an eNB of  FIG. 1 ; 
           [0011]      FIG. 3  is a block diagram of a transmit diversity scheme in accordance with an embodiment; 
           [0012]      FIG. 4  shows a S-SCH symbol structure in accordance with the embodiment shown in  FIG. 3 ; 
           [0013]      FIG. 5  shows a S-SCH with preceding in accordance with the embodiment shown in  FIG. 3 ; 
           [0014]      FIG. 6  shows a S-SCH symbol structure using 2 interleaved sequences in accordance with the embodiment shown in  FIG. 4 ; and 
           [0015]      FIG. 7  shows a S-SCH symbol structure using 2 interleaved sequences and PVS in accordance with the embodiment shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to a Node-B, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. 
         [0017]      FIG. 1  shows a wireless communication system  100  including a plurality of WTRUs  110  and an e Node-B (eNB)  120 . As shown in  FIG. 1 , the WTRUs  110  are in communication with the eNB  120 . Although three WTRUs  110  and one eNB  120  are shown in  FIG. 1 , it should be noted that any combination of wireless and wired devices may be included in the wireless communication system  100 . 
         [0018]      FIG. 2  is a functional block diagram  200  of the WTRU  110  and the eNB  120  of the wireless communication system  100  of  FIG. 1 . As shown in  FIG. 2 , the WTRU  110  is in communication with the eNB  120 . The WTRU  110  is configured to receive the primary synchronization channel (P-SCH) and secondary synchronization channel (S-SCH) from the eNB  120 . Both the eNB and the WTRU are configured to process signals that are modulated and coded. 
         [0019]    In addition to the components that may be found in a typical WTRU, the WTRU  110  includes a processor  215 , a receiver  216 , a transmitter  217 , and an antenna  218 . The receiver  216  and the transmitter  217  are in communication with the processor  215 . The antenna  218  is in communication with both the receiver  216  and the transmitter  217  to facilitate the transmission and reception of wireless data. 
         [0020]    In addition to the components that may be found in a typical eNB, the eNB  120  includes a processor  225 , a receiver  226 , a transmitter  227 , and an antenna  228 . The receiver  226  and the transmitter  227  are in communication with the processor  225 . The antenna  228  is in communication with both the receiver  226  and the transmitter  227  to facilitate the transmission and reception of wireless data. 
         [0021]    In one embodiment, a combined FSTD and PVS transmit diversity scheme is used for S-SCH symbol transmission in E-UTRA. This transmit diversity scheme allows S-SCH detection at the WTRU without prior knowledge of the number of transmit antennas of the cell. The number of transmit antennas using the transmit diversity technique is transparent to the WTRU, resulting in simple and efficient detection of the S-SCH. The transmit diversity technique also carries more information about the cell such as, but not limited to, reference signal hopping indicators and a number of transmit antennas for the broadcast channel 
         [0022]      FIG. 3  is a block diagram of an S-SCH transmit diversity scheme  300  in accordance with one embodiment. An S-SCH sequence  302  is input into a FSTD processor  304 , as explained herein. The FSTD processor may be includes in processor  225  in the eNB of  FIG. 2 . The signal is then input into a PVS processor  306 , as explained herein. The PVS processor  306  may also be included in processor  225  of the eNB of  FIG. 2 . The output of the PVS processor  306  are the S-SCH symbols  308  which are then transmitted. The S-SCH symbols  308  may be transmitted by the transmitter  227  as shown in  FIG. 2 . A robust S-SCH design may provide full transmit diversity gain for S-SCH. A robust S-SCH transmission design may also provide a sufficient number of cell (group) IDs, cell-specific parameters, and other cell related information. The information carried by a plurality of S-SCH symbols may be used to convey the number of cell (group) IDs and cell specific information, such as a reference signal hopping indicator and the number of transmit antennas for the broadcast channel (BCH), for example. 
         [0023]      FIG. 4  is a diagram showing an S-SCH symbol structure  400  in accordance with the embodiment shown in  FIG. 3 . After the S-SCH sequence  302  of  FIG. 3 , is processed through the FSTD processor  304  of  FIG. 3 , the result is two separate S-SCH transmission symbols, S 1  ( 402 ) and S 2  ( 404 ). S 1  ( 402 ) is the first S-SCH symbol and has a Constant Amplitude Zero Auto-correlation Code (CAZAC) sequence, shown as G 1  ( 406 ), transmitted in the lower band  408  of the central bandwidth, and a second CAZAC sequence, shown as G 2  ( 410 ), transmitted in the upper band  412  of the central bandwidth. The central bandwidth may be, for example, 1.25 MHz or 2.5 Mhz. One skilled in the art may recognize that the methods and apparatus disclosed herein are not frequency specific. The CAZAC sequence may be, for example, a Generalized Chirp-like (GCL) sequence, a Zadoff-Chu sequence, or the like. 
         [0024]    The second S-SCH symbol, S 2  ( 404 ) is a mirror version of the first S-SCH symbol S 1  ( 402 ). The sequence G 2  ( 414 ) is transmitted in the lower band  408 , and the sequence G 1  ( 416 ) is transmitted in the upper band  412 . 
         [0025]      FIG. 5  shows an S-SCH with a precoding matrix  500  in accordance with the embodiment shown in  FIG. 3 . The precoding matrix is applied to S 1  ( 402 ) and S 2  ( 404 ) of  FIG. 4 . The upper band  412  of S 1  ( 402 ) is multiplied by V 1,2  ( 502 ) and the upper band  412  of S 2  ( 404 ) is multiplied by V 2,2  ( 504 ). The lower band  408  of S 1  ( 402 ) is multiplied by V 1,1  ( 506 ) and the lower band  408  of S 2  ( 404 ) is multiplied by V 2,1  ( 508 ). V 1,1 , V 2,2 , V 2,1  and V 2,2  are the elements of a precoding matrix when PVS is used. The precoding matrix V is represented by: 
         [0000]    
       
         
           
             
               
                 
                   V 
                   = 
                   
                     [ 
                     
                       
                         
                           
                             V 
                             
                               1 
                               , 
                               1 
                             
                           
                         
                         
                           
                             V 
                             
                               1 
                               , 
                               2 
                             
                           
                         
                       
                       
                         
                           
                             V 
                             
                               2 
                               , 
                               1 
                             
                           
                         
                         
                           
                             V 
                             
                               2 
                               , 
                               2 
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where V ij  is the (1,j) th  element of the precoding matrix. 
         [0026]    In general, let N V  denote the number of different precoding matrices used for S-SCH symbols. For each S-SCH symbol, its equivalent is multiplied by a precoding vector. Consider a precoding matrix: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     = 
                     
                       
                         [ 
                         
                           
                             
                               1 
                             
                             
                               j 
                             
                           
                           
                             
                               
                                 - 
                                 j 
                               
                             
                             
                               1 
                             
                           
                         
                         ] 
                       
                       · 
                       
                          
                         
                           j 
                            
                           
                               
                           
                            
                           k 
                            
                           
                               
                           
                            
                           θ 
                         
                       
                     
                   
                   , 
                   
                     
                       where 
                        
                       
                           
                       
                        
                       θ 
                     
                     = 
                     0 
                   
                   , 
                   
                     π 
                     2 
                   
                   , 
                   π 
                   , 
                   
                     
                       
                         3 
                          
                         π 
                       
                       2 
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    Then, N V =4. Furthermore, the value k can be fixed during one OFDM symbol duration or it can be in a range of 1≦k≦K, where K≦N G , where N G  is the sequence length of CAZAC sequence G 1  or G 2 . N G     1    and N G     2    can be defined as the sequence lengths of G 1  ( 406 ) and G 2  ( 408 ), respectively. The maximum number of hypotheses that can be supported is equal to: 
         [0000]      N G     1   −1×N G     2   −1×N V .  (Equation 3) 
         [0000]    For example, if N G     1   =N G     2   =31 and N V =4, then the maximum number of hypotheses that can be supported equals 3600 (30×30×4). The pair of S-SCH symbols can be transmitted Q times. For example, if Q=1, the symbols are transmitted every radio frame, where a radio frame is 10 ms in length. The time distance between two S-SCH symbols may be fixed. 
         [0027]      FIG. 6  shows a S-SCH symbol structure using 2 interleaved sequences in accordance with the embodiment shown in  FIG. 4 . Integer M CAZAC sequences of length K may be mapped to subcarriers in an interleaved pattern to generate one S-SCH symbol. If M equals 2, for example, a first subcarrier  610  carries d 1  ( 602 ) multiplied by G 1,1  ( 604 ), where d 1  ( 602 ) is the first data symbol carried on the S-SCH and G 1,1  ( 604 ) is the first chip/symbol of the first CAZAC sequence with a length K. A third subcarrier  614  carries d 1  ( 602 ) multiplied by G 1,2  ( 606 ). The fifth subcarrier  620  carries d 1  ( 602 ) multiplied by G 1,3  ( 608 ). The second subcarrier  612  carries d 2  ( 616 ), which is the second data symbol carried on the S-SCH, multiplied by G 2,1  ( 618 ), which is the first chip/symbol of the second CAZAC sequence with length K. Each CAZAC sequence may carry an information symbol (such as BPSK modulation or QPSK modulation). That is, each information symbol may be spread by a CAZAC sequence of length K. The K spread symbols may be mapped to equal-distant subcarriers in an interleaved pattern. Information symbols may be mapped to non-overlapping subcarriers after spreading. 
         [0028]      FIG. 7  shows an S-SCH symbol structure using 2 interleaved sequences and PVS  700  in accordance with the embodiment shown in  FIG. 5 . Let M=2, for example. The two interleaved CAZAC sequences in the first S-SCH symbol S 1  ( 702 ) are precoded by └V 1,1 V 1,2 ┘. Similarly, the two interleaved CAZAC sequences in the second S-SCH symbol ( 704 ) are precoded by └v 2,1 v 2,2 ┘. The precoding matrix for the pair of S-SCH symbols is equivalent to 
         [0000]    
       
         
           
             
               [ 
               
                 
                   
                     
                       V 
                       
                         1 
                         , 
                         1 
                       
                     
                   
                   
                     
                       V 
                       
                         1 
                         , 
                         2 
                       
                     
                   
                 
                 
                   
                     
                       V 
                       
                         2 
                         , 
                         1 
                       
                     
                   
                   
                     
                       V 
                       
                         2 
                         , 
                         2 
                       
                     
                   
                 
               
               ] 
             
             . 
           
         
       
     
         [0029]    Turning to  FIG. 7 , and by way of example, G 1,1  ( 706 ) is precoded by V 1,1  ( 708 ) in the first S-SCH symbol S 1  ( 702 ). G 1,1  ( 706 ) is precoded by V 2,1  ( 722 ) in the second S-SCH symbol S 2  ( 704 ). G 2,1  ( 716 ) is precoded by V 1,2  ( 718 ) in the first S-SCH symbol S 1  ( 702 ) and G 2,1  ( 716 ) is precoded by V 2,2  ( 722 ) in the second SCH symbol S 2  ( 704 ). More generally, in the first symbol S 1  ( 702 ), G 1,k  ( 710 ) is precoded by V 1,1  ( 708 ) and G 2,K  ( 712 ) is precoded by V 1,2  ( 718 ) and in the second SCH symbol S 2  ( 704 ) G 1,k  ( 710 ) is precoded by V 2,1  ( 720 ) and G 2,k  is precoded by V 2,2  ( 722 ). The maximum number of hypotheses supported is equal to N V ×(K−1) 2 . For example, if K=31 and N V =4, then the maximum number of hypotheses supported equals 3600. A pair of S-SCH symbols may be transmitted Q times every radio frame (10 ms). The time distance between any two S-SCH symbols is fixed. 
         [0030]    Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0031]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0032]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB) module.