Abstract:
A method and an apparatus for reducing overhead in signaling for downlink dual codewords in a wireless transmit receive unit (WTRU) with spatial multiplexing are disclosed. The method includes signaling a number of codewords to be used, signaling modulation scheme coding, reducing overhead for signaling of transport block size (TBS), and/or reducing overhead for signaling associated with error correction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/952,091 filed on Jul. 26, 2007, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention is related to wireless communications. 
       BACKGROUND 
       [0003]    To keep the technology competitive, both third generation partnership project (3GPP) and 3GPP2 are considering long term evolution (LTE) for radio interface and network architecture. 
         [0004]    To take advantage of multiple-input multiple-output (MIMO) technology, also called spatial multiplexing, two codewords are used for hybrid automatic repeat request (HARQ) in the downlink (DL) communication of evolved universal terrestrial radio access (E-UTRA). However, the dual codeword operation increases signaling overhead. 
         [0005]    If the assignment information for a codeword is signaled independently of the other codeword&#39;s assignment information, then the signaling requirements are substantially increased. For example, if the transport block size (TBS) for each codeword is indicated by six bits in an assignment, then the dual codeword operation requires twelve bits for TBS signaling. 
         [0006]    In general, if each codeword uses N HARQ processes, resulting in ┌log 2  N┐ bits overhead, then dual codeword operation uses 2N HARQ processes. Approximately |log 2 (2N) 2 | bits are needed for signaling HARQ process identifiers (IDs) when full flexibility is allowed. 
         [0007]    To reduce the signaling, more efficient signaling schemes would be beneficial for dual codeword operation. 
       SUMMARY 
       [0008]    A method and apparatus for reducing overhead for signaling of dual codeword information in a wireless communication system with spatial multiplexing includes signaling a number of codewords to be used, the modulation and coding for each codeword, the transport block size for each codeword, and/or the HARQ process IDs for each codeword. 
         [0009]    A method for reducing signaling overhead for a MIMO-capable wireless transmit/receive unit (WTRU) receiving and using the modulation of a primary codeword and a secondary codeword, the transport block size of the primary codeword and the secondary codeword, and a HARQ process ID for the primary codeword and the secondary codeword is also described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A more detailed understanding may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0011]      FIG. 1  shows a wireless communication system including a Node-B and a WTRU; 
           [0012]      FIG. 2  illustrates a downlink assignment message format; 
           [0013]      FIG. 3  shows a downlink signaling procedure; and 
           [0014]      FIGS. 4A ,  4 B, and  4 C collectively illustrate signaling of TBS in accordance with a disclosed method. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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. 
         [0016]    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 including a Node-B  110  and a WTRU  120 . As shown in  FIG. 1 , in addition to components included in a typical WTRU, the WTRU  120  includes a processor  125 , a receiver  126  which is in communication with the processor  125 , a transmitter  127  which is in communication with the processor  125 , and an antenna  128  which is in communication with the receiver  126  and the transmitter  127  to facilitate the transmission and reception of wireless data. The WTRU  120  wirelessly communicates with a base station (Node-B)  110 . 
         [0018]      FIG. 2  shows a downlink assignment message  200 . The downlink assignment message  200  comprises assignment parameter fields including a modulation and coding scheme (MCS) and TBS field  210 , an HARQ process ID field  220  and an “other information” field  230 . These assignment parameter fields  210 ,  220  and  230  included in the downlink assignment message  200  are signaled from the Node-B  110  to the WTRU  120  via a physical downlink control channel (PDCCH). Although not described in detail herein, one of skill in the art would understand that the assignment message  200  may also be applicable for transmission via an uplink channel. 
         [0019]    In a first embodiment, overhead is reduced for signaling the modulation and the number of codewords in a downlink signaling assignment. In this embodiment, a plurality of bits, (such as three bits), are used to jointly indicate the number of codewords (i.e., streams) used in the downlink communication of E-UTRA and the modulation type used for those one or two codewords. 
         [0020]      FIG. 3  shows a downlink signaling procedure  300  according to the first embodiment. In step  310 , the Node-B  110  determines the modulation scheme to use (step  310 ). In step  320 , the Node-B  110  determines the number of bits for the TBS. In step  330 , the Node-B  110  determines which HARQ process is to be used. Although shown in  FIG. 3  as three separate decisions or determinations,  310 ,  320 ,  330  in a specific order, those of skill in the art would understand that this is for ease of explanation. One decision, or multiple decisions in a different order, may be made. 
         [0021]    Still referring to  FIG. 3 , in step  340 , the Node-B  110  signals the modulation types, the TBSs and the HARQ process ID parameters via a downlink channel, (such as the PDCCH), to the WTRU  120 . In step  350 , the WTRU  120  uses the parameters received from the Node-B  110  in detecting and decoding received downlink data. The codeword modulation signaling described in this embodiment is summarized in Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Modulation of 
                 Modulation of the 
               
               
                   
                   
                 Number of 
                 the primary 
                 secondary 
               
               
                   
                 Signaling 
                 codewords 
                 codeword 
                 codeword 
               
               
                   
                   
               
             
             
               
                   
                 000 
                 1 
                 QPSK 
                 N/A 
               
               
                   
                 001 
                 1 
                 16QAM 
                 N/A 
               
               
                   
                 010 
                 1 
                 64QAM 
                 N/A 
               
               
                   
                 011 
                 2 
                 QPSK 
                 QPSK 
               
               
                   
                 100 
                 2 
                 16QAM 
                 QPSK 
               
               
                   
                 101 
                 2 
                 16QAM 
                 16QAM 
               
               
                   
                 110 
                 2 
                 64QAM 
                 16QAM 
               
               
                   
                 111 
                 2 
                 64QAM 
                 64QAM 
               
               
                   
                   
               
             
          
         
       
     
         [0022]    To reduce signaling overhead further, the number of bits used for the TBS and the HARQ process IDs may also be reduced as discussed in the second and third embodiments, respectively. 
         [0023]      FIGS. 4A-4C  illustrate a second embodiment, whereby overhead is reduced for signaling the TBS when dual codewords are used. 
         [0024]    In a first example shown by  FIG. 4A , the TBS of the primary codeword  410  is indicated using six bits, and a lesser number of bits (five, in this example) are used to indicate the TBS of the secondary codeword  420 . Using a lesser number of bits for the TBS of the secondary codeword may be made possible, for example, by reducing the resolution of the TBS for the secondary codeword  420 . 
         [0025]    In a second example shown by  FIG. 4B , the same primary codeword  410  is used, and a secondary codeword  430  having three bits is used to indicate the difference between the TBS of the primary codeword  410  and the secondary codeword  430 . In this manner, the difference between the TBS of the primary codeword  410  and the TBS of the second codeword  430  (i.e., three bits) is signaled, instead of only signaling the TBS of the second codeword. 
         [0026]    In a third example shown by  FIG. 4C , the same primary codeword  410  is used, and a secondary codeword  440  having four bits is used to indicate the difference between the TBS of the primary codeword  410  and the secondary codeword  440 . 
         [0027]    In a third embodiment, overhead for signaling HARQ process IDs is reduced as will be described hereinafter. It should be understood that each single codeword uses N HARQ processes, that results in an overhead of ┌log 2  N┐ bits. Dual codeword operation therefore uses 2N HARQ processes. The number of codewords may be indicated by other signaling such as for the MCS, TBS, precoder information, and the like. 
         [0028]    A first alternative implements a fixed division of the HARQ processes that are used for the primary and the secondary codewords. For example, the primary codeword may use only HARQ processes  1 ,  2 , . . . , N, and the secondary codeword may use only HARQ processes N+1, N+2, . . . , 2N. In this case, the signaling overhead is 2┌log 2  N┐ bits. Alternatively, because the primary codeword and the secondary codeword experience different channel qualities, non-equal numbers of HARQ processes may be assigned to each codeword. 
         [0029]    A second alternative for reducing downlink signaling overhead for HARQ process IDs allows limited pairs of HARQ processes ({ 1   a,    1   b }, { 2   a,    2   b }, . . . , {Na, Nb}) for a primary and secondary codeword pair. For a single codeword transmission or retransmission, any single HARQ process (i.e.,  1   a,    2   b,  etc.) is allowed. This limits the usage of the HARQ processes. The signaling overhead is ┌log 2  N┐+1 bits determined by the single codeword case. Table 2 is an example of the proposed signaling method with N=6. The proposed method is also applicable to other N values. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Number 
                   
                   
                   
               
               
                 of codewords 
                 HARQ 
                 HARQ process ID 
                 HARQ process 
               
               
                 (indicated by other 
                 process ID 
                 of primary 
                 ID of secondary 
               
               
                 signals) 
                 Signaling 
                 codeword 
                 codeword 
               
               
                   
               
             
             
               
                 2 
                 0000 
                 1a 
                 1b 
               
               
                 2 
                 0001 
                 2a 
                 2b 
               
               
                 2 
                 0010 
                 3a 
                 3b 
               
               
                 2 
                 0011 
                 4a 
                 4b 
               
               
                 2 
                 0100 
                 5a 
                 5b 
               
               
                 2 
                 0101 
                 6a 
                 6b 
               
               
                 1 
                 0000 
                 1a 
                 N/A 
               
               
                 1 
                 0001 
                 2a 
                 N/A 
               
               
                 1 
                 0010 
                 3a 
                 N/A 
               
               
                 1 
                 0011 
                 4a 
                 N/A 
               
               
                 1 
                 0100 
                 5a 
                 N/A 
               
               
                 1 
                 0101 
                 6a 
                 N/A 
               
               
                 1 
                 0110 
                 N/A 
                 1b 
               
               
                 1 
                 0111 
                 N/A 
                 2b 
               
               
                 1 
                 1000 
                 N/A 
                 3b 
               
               
                 1 
                 1001 
                 N/A 
                 4b 
               
               
                 1 
                 1010 
                 N/A 
                 5b 
               
               
                 1 
                 1011 
                 N/A 
                 6b 
               
               
                   
               
             
          
         
       
     
         [0030]    The signaling overhead in the second alternative is dominated by the single codeword case. In the case of dual codewords, the dual codeword uses less signaling overhead. By signaling predetermined pairs of codewords, the amount of signaling is greatly reduced. If the number of codewords is two, then extra pairs in addition to the pairs of the HARQ processes used in the second method are added for the dual codeword to increase flexibility in usage of the HARQ processes. Extra pairs allow the transmission of misaligned HARQ processes on the two codewords. This third alternative, shown in Table 3, has the same overhead as the second alternative, but has less restraint in usage of the HARQ processes. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 HARQ 
                 HARQ 
               
               
                 Comparison 
                   
                 HARQ 
                 process ID 
                 process ID 
               
               
                 of primary to 
                 Number of 
                 process ID 
                 of primary 
                 of secondary 
               
               
                 secondary codeword 
                 codewords 
                 signaling 
                 codeword 
                 codeword 
               
               
                   
               
             
             
               
                 The same 
                 2 
                 0000 
                 1a 
                 1b 
               
               
                 The same 
                 2 
                 0001 
                 2a 
                 2b 
               
               
                 The same 
                 2 
                 0010 
                 3a 
                 3b 
               
               
                 The same 
                 2 
                 0011 
                 4a 
                 4b 
               
               
                 The same 
                 2 
                 0100 
                 5a 
                 5b 
               
               
                 The same 
                 2 
                 0101 
                 6a 
                 6b 
               
               
                 HARQ process ID of 
                 2 
                 0110 
                 1a 
                 2b 
               
               
                 secondary codeword 
               
               
                 differs by 1 
               
               
                 HARQ process ID of 
                 2 
                 0111 
                 2a 
                 3b 
               
               
                 secondary codeword 
               
               
                 differs by 1 
               
               
                 HARQ process ID of 
                 2 
                 1000 
                 3a 
                 4b 
               
               
                 secondary codeword 
               
               
                 differs by 1 
               
               
                 HARQ process ID of 
                 2 
                 1001 
                 4a 
                 5b 
               
               
                 secondary codeword 
               
               
                 differs by 1 
               
               
                 HARQ process ID of 
                 2 
                 1010 
                 5a 
                 6b 
               
               
                 secondary codeword 
               
               
                 differs by 1 
               
               
                 HARQ process ID of 
                 2 
                 1011 
                 6a 
                 1b 
               
               
                 secondary codeword 
               
               
                 differs by 1 
               
               
                 HARQ process ID of 
                 2 
                 1100 
                 1a 
                 3b 
               
               
                 secondary codeword 
               
               
                 differs by 2 
               
               
                 HARQ process ID of 
                 2 
                 1101 
                 2a 
                 4b 
               
               
                 secondary codeword 
               
               
                 differs by 2 
               
               
                 HARQ process ID of 
                 2 
                 1110 
                 4a 
                 6b 
               
               
                 secondary codeword 
               
               
                 differs by 2 
               
               
                 HARQ process ID of 
                 2 
                 1111 
                 5a 
                 1b 
               
               
                 secondary codeword 
               
               
                 differs by 2 
               
               
                 The same 
                 1 
                 0000 
                 1a 
                 N/A 
               
               
                 The same 
                 1 
                 0001 
                 2a 
                 N/A 
               
               
                 The same 
                 1 
                 0010 
                 3a 
                 N/A 
               
               
                 The same 
                 1 
                 0011 
                 4a 
                 N/A 
               
               
                 The same 
                 1 
                 0100 
                 5a 
                 N/A 
               
               
                 The same 
                 1 
                 0101 
                 6a 
                 N/A 
               
               
                 The same 
                 1 
                 0110 
                 N/A 
                 1b 
               
               
                 The same 
                 1 
                 0111 
                 N/A 
                 2b 
               
               
                 The same 
                 1 
                 1000 
                 N/A 
                 3b 
               
               
                 The same 
                 1 
                 1001 
                 N/A 
                 4b 
               
               
                 The same 
                 1 
                 1010 
                 N/A 
                 5b 
               
               
                 The same 
                 1 
                 1011 
                 N/A 
                 6b 
               
               
                   
               
             
          
         
       
     
         [0031]    Table 4 shows an example of the proposed signaling of a fourth alternative with N=6 and allowing the HARQ process ID of either codeword to differ by one index number. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                 HARQ 
               
               
                   
                   
                   
                 HARQ 
                 process 
               
               
                   
                 Number 
                 HARQ 
                 process ID 
                 ID of 
               
               
                 Compared to 
                 of code- 
                 process ID 
                 of primary 
                 secondary 
               
               
                 Second method 
                 words 
                 Signaling 
                 codeword 
                 codeword 
               
               
                   
               
             
             
               
                 The same 
                 2 
                 0000 
                 1a 
                 1b 
               
               
                 The same 
                 2 
                 0001 
                 2a 
                 2b 
               
               
                 The same 
                 2 
                 0010 
                 3a 
                 3b 
               
               
                 The same 
                 2 
                 0011 
                 4a 
                 4b 
               
               
                 The same 
                 2 
                 0100 
                 5a 
                 5b 
               
               
                 The same 
                 2 
                 0101 
                 6a 
                 6b 
               
               
                 HARQ process ID of 
                 2 
                 0110 
                 1a 
                 2b 
               
               
                 secondary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 0111 
                 2a 
                 3b 
               
               
                 secondary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1000 
                 3a 
                 4b 
               
               
                 secondary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1001 
                 4a 
                 5b 
               
               
                 secondary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1010 
                 5a 
                 6b 
               
               
                 secondary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1011 
                 6a 
                 1b 
               
               
                 secondary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1100 
                 2a 
                 1b 
               
               
                 primary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1101 
                 3a 
                 2b 
               
               
                 primary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1110 
                 5a 
                 4b 
               
               
                 primary codeword differs 
               
               
                 by 1 
               
               
                 HARQ process ID of 
                 2 
                 1111 
                 6a 
                 5b 
               
               
                 primary codeword differs 
               
               
                 by 1 
               
               
                 The same 
                 1 
                 0000 
                 1a 
                 N/A 
               
               
                 The same 
                 1 
                 0001 
                 2a 
                 N/A 
               
               
                 The same 
                 1 
                 0010 
                 3a 
                 N/A 
               
               
                 The same 
                 1 
                 0011 
                 4a 
                 N/A 
               
               
                 The same 
                 1 
                 0100 
                 5a 
                 N/A 
               
               
                 The same 
                 1 
                 0101 
                 6a 
                 N/A 
               
               
                 The same 
                 1 
                 0110 
                 N/A 
                 1b 
               
               
                 The same 
                 1 
                 0111 
                 N/A 
                 2b 
               
               
                 The same 
                 1 
                 1000 
                 N/A 
                 3b 
               
               
                 The same 
                 1 
                 1001 
                 N/A 
                 4b 
               
               
                 The same 
                 1 
                 1010 
                 N/A 
                 5b 
               
               
                 The same 
                 1 
                 1011 
                 N/A 
                 6b 
               
               
                   
               
             
          
         
       
     
         [0032]    An evolved Node-B (eNode-B) may realign the HARQ process IDs of the two codewords whenever the misalignment between HARQ process IDs of the two codewords is larger than a predetermined threshold. Therefore, the impact of the HARQ process ID signaling described above has the least limitation and impact on usage of the HARQ processes. 
         [0033]    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). 
         [0034]    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. 
         [0035]    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.