Abstract:
An apparatus and method for processing fast feedback payload data to generate symbols for transmission through a fast feedback channel in a wireless network are presented. The technique first encodes payload data using a tail biting convolutional code. The encoded bits are then de-multiplexed to five different data subblocks in a sequential fashion. Subblock interleaving is then used to interleave the data of the subblocks according to a predetermine scheme. A bit selector then selects interleaved subblock bit for output. The selected bits may then be modulated by a modulator using quadrature phase shift keying (QPSK). The resulting symbols may then be mapped to a predetermined fast feedback subcarriers within a feedback channel.

Description:
The present application claims the benefit of previously filed provisional patent application Ser. No. 61/173,204, filed on Apr. 28, 2009 which is co-owned with the present application. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to channel coding and, more particularly, to channel coding techniques for use in a wireless channel. 
     BACKGROUND OF THE INVENTION 
     When performing channel adaptation within a multicarrier wireless channel, a feedback channel is often used to provide a feedback of channel information. Techniques for providing channel coding within such a feedback channel are needed that perform well and are of low complexity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a wireless network arrangement that may utilize aspects of the present invention; 
         FIG. 2  is a block diagram illustrating a system for processing fast feedback payload data to generate symbols for transmission through a fast feedback channel in accordance with an embodiment of the present invention; 
         FIG. 3  is a diagram illustrating a generator for use in generating a tail biting convolutional code of rate 1/5 and a constraint length of K=7 in accordance with an embodiment of the present invention; 
         FIG. 4  is a block diagram illustrating a channel encoder that uses a tail biting convolutional code of rate 1/5 and constraint length of K=7 in accordance with an embodiment of the present invention; and 
         FIG. 5  is a diagram illustrating three distributed FMTs that may carry a mapped symbol sequence d 0  d 1  d 2  . . . d 35  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views. 
       FIG. 1  is a block diagram illustrating a wireless network arrangement  10  that may utilize aspects of the present invention. As shown in the figure, the wireless network arrangement  10  includes a wireless base station  12  that is communicating wirelessly with multiple wireless mobile stations  14 ,  16 . As is the convention, communication from the base station  12  to the mobile stations  14 ,  16  will be referred to herein as downlink communication and communication from the mobile stations  14 ,  16  to the base station  12  will be referred to as uplink communication. Although illustrated with two mobile stations, it should be understood that more or less mobile stations may be communicating with a base station at a particular point in time. In the illustrated embodiment, the base station  12  and the mobile stations  14 ,  16  each have multiple antennas. Multiple input, multiple output (MIMO) communication techniques may therefore be used within the wireless network arrangement  10 . In addition, multicarrier communications techniques (e.g., orthogonal frequency division multiplexing (OFDM), orthogonal frequency division multiple access (OFDMA), etc.) may also be implemented within the wireless network arrangement  10 . 
     In some wireless systems, the downlink channel between a base station and mobile station may support multiple transmission modes. In addition, the transmission mode of the downlink channel may adapt over time based on channel and traffic conditions. When an adaptive downlink channel is used, a fast feedback channel may be provided from the mobile station to the base station to allow feedback of channel quality data (e.g., channel quality indicator, etc.) for use in adapting the channel. The fast feedback channel may also be used to feedback MIMO related information to the base station to support downlink adaptation. Desirably, channel coding should be used to enhance the accuracy of the communication within the fast feedback channel. The channel coding should provide good performance while also being relatively low complexity. In at least one aspect of the present invention, a tail-biting convolutional coding technique is provided that is well suited for use within a wireless fast feedback channel. With reference to  FIG. 1 , the tail-biting convolutional coding technique may be used to code feedback information being uplinked from, for example, the mobile station  16  to the base station  12 . Other applications also exist. 
       FIG. 2  is a block diagram illustrating a system  20  for processing fast feedback payload data to generate symbols for transmission through a fast feedback channel in a wireless network in accordance with an embodiment of the present invention. First, the fast feedback payload data is encoded in a channel encoder  22  that uses a tail biting convolutional code. The coded output sequence is then modulated in the modulator  24  using quadrature phase shift keying (QPSK). The modulated symbols are then combined with a pilot sequence and the resulting symbol sequence is mapped to data subcarriers, in a mapper  26 , for transmission through the fast feedback channel. 
     In at least one embodiment, the payload data consists of l information bits a 0  a 1  a 2  . . . a l-1 . These bits are encoded to M bits b 0  b 1  b 2  . . . b M-1  using the channel encoder  22 , which is described in greater detail below. When l≦12, the information bits a 0  a 1  a 2  . . . a l-1  are encoded using a linear block code (N,l). When 12&lt;l≦24, the information bits a 0  a 1  a 2  . . . a l-1  are split into two parts; namely, Part A consisting of 
               a   0     ⁢     a   1     ⁢     a     2   ⁢               ⁢   …   ⁢           ⁢     a       ⌊     l   2     ⌋     -   1             
and Part B consisting of
 
               a     ⌊     l   2     ⌋       ⁢     a     ⌊       l   2     +   1     ⌋       ⁢     a       ⌊     l   2     ⌋     +   2       ⁢           ⁢   …   ⁢           ⁢       a     l   -   1       .           
Part A is encoded to
 
               N   2     ⁢           ⁢     bits   (       b   0     ⁢     b   1     ⁢     b   2     ⁢           ⁢   …   ⁢           ⁢     b       N   2     -   1         )           
using linear block code
 
             (       N   2     ,     ⌊     l   2     ⌋       )         
and Part B is encoded to
 
               N   2     ⁢           ⁢     bits   (       b     N   2       ⁢     b       N   2     +   1       ⁢     b       N   2     +   2       ⁢           ⁢   …   ⁢           ⁢     b     N   -   1         )           
using a linear block code
 
               (       N   2     ,     l   -     ⌊     l   2     ⌋         )     .         
The values of parameters L and M are set to l and 60, respectively. The value of K bufsize  may be set as follows:
 
               K   bufsize     =     {         30           l   =   7     ,   8   ,   9               5   ⁢   l             l   =   10     ,   11             60         12   ≤   l   ≤   24                   
The coded sequence b 0  b 1  b 2  . . . b M  is then modulated to
 
               M   2     ⁢           ⁢     symbols   (       c   0     ⁢     c   1     ⁢     c   2     ⁢           ⁢   …   ⁢           ⁢     c       M   2     -   1         )           
in the modulator  24  using QPSK. The modulated symbols
 
               c   0     ⁢     c   1     ⁢     c   2     ⁢           ⁢   …   ⁢           ⁢     c       M   2     -   1             
and the pilot sequence are then combined to form symbol sequence d 0  d 1  d 2  . . . d 35  which is then mapped by the mapper  26  to the data subcarriers of the fast feedback channel.
 
     As described above, the channel encoder  22  of  FIG. 2  encodes the fast feedback payload data using a tail biting convolutional code. Various coding rates may be used. In at least one embodiment, a tail biting convolutional code of rate 1/5 and a constraint length of K=7 is used. This tail biting convolutional code uses the following generator polynomials to generate its five coded bits:
         G 1 =171 OCT      G 2 =133 OCT      G 3 =165 OCT      G 4 =117 OCT      G 5 =127 OCT  
 
 FIG. 3  is a diagram illustrating a generator  30  for use in generating this code. As illustrated, the generator  30  includes six 1-bit delay units (shift registers)  32 ,  34 ,  36 ,  38 ,  40 ,  42  and twenty modulo-2 adders  44 .
       

       FIG. 4  is a block diagram illustrating a channel encoder  50  that uses the tail biting convolutional code of rate 1/5 and constraint length of K=7 in accordance with an embodiment of the present invention. The channel encoder  50  of  FIG. 4  may be used, for example, as the channel encoder  22  of  FIG. 2 . As shown in  FIG. 4 , the channel encoder  50  includes a rate 1/5 tail biting convolutional code encoder  52 , a channel interleaver  54 , and a bit selector  56 . The rate 1/5 tail biting convolutional code encoder  52  receives an input data block and encodes the block using the 1/5 tail biting convolutional code. The resulting encoded bits are then demultiplexed into five subblocks, denoted A subblock  60 , B subblock  62 , C subblock  64 , D subblock  66 , and E subblock  68  in  FIG. 4 . The five subblocks  60 ,  62 ,  64 ,  66 ,  68  may be implemented using, for example, one or more memory or digital storage devices. If the input data block has L information bits, for example, the encoder output bits will be sequentially distributed into the five subblocks  60 ,  62 ,  64 ,  66 ,  68  with the first L encoder output bits going to the A subblock  60 , the second L encoder output bits going to the B subblock  62 , the third L encoder output bits going to the C subblock  64 , and so on. The subblock data bits are then delivered to corresponding subblock interleavers  70 ,  72 ,  74 ,  76 , and  78  for subblock interleaving. A table for interleaving index with length of 128 entries may be generated as follows:
 
 x= 1:128
 
index=(15 x+ 32×2)mod 128+1.
 
When the number of information bits is less than 128, the corresponding index table can be generated by removing the entries whose values are larger than the number of information bits. The channel interleaver output sequence shall consist of the interleaved A and B subblock sequences, followed by interleaved C, D, and E subblock sequences.
 
     If L information bits are input to the encoder  52  of  FIG. 4 , the output sequence of the channel interleaver  54  will consist of 5 L bits denoted as d i , i=0, 1, . . . , 5 L. Parameter K bufsize  is used to indicate the size of the buffer used for repetition. The buffer size is not larger than 5 L. If the output bits are M, the output sequence can be expressed as c j =d j mod K     bufsize   , j=0, 1, . . . , M. 
     In at least one embodiment, the fast feedback channel consists of 3 distributed FMTs with 2 pilots allocated in each FMT. As described previously in connection with  FIG. 2 , the modulated symbols output by the modulator 
             24   ⁢           ⁢     c   0     ⁢     c   1     ⁢     c   2     ⁢           ⁢   …   ⁢           ⁢     c       M   2     -   1             
are combined with a pilot sequence and the resulting symbol sequence d 0  d 1  d 2  . . . d 35  is mapped to data subcarriers of the fast feedback channel in the mapper  26 . These data subcarriers are part of the 3 distributed FMTs.  FIG. 5  is a diagram illustrating three distributed FMTs  80 ,  82 ,  84  that may carry the mapped symbol sequence d 0  d 1  d 2  . . . d 35  in accordance with an embodiment of the present invention. As shown, the first FMT  80  has symbols d 0  through d 11  mapped across two subcarriers. Similarly, the second FMT  82  has symbols d 12  through d 23  and the third FMT  84  has symbols d 24  through d 35  mapped across two subcarriers each.
 
     The techniques and structures of the present invention may be implemented in any of a variety of different forms. For example, features of the invention may be embodied within laptop, palmtop, desktop, and tablet computers having wireless capability; personal digital assistants (PDAs) having wireless capability; cellular telephones and other handheld wireless communicators; pagers; satellite communicators; cameras having wireless capability; audio/video devices having wireless capability; network interface cards (NICs) and other network interface structures; base stations; wireless access points; integrated circuits; as instructions and/or data structures stored on machine readable media; and/or in other formats. Examples of different types of machine readable media that may be used include floppy diskettes, hard disks, optical disks, compact disc read only memories (CD-ROMs), digital video disks (DVDs), Blu-ray disks, magneto-optical disks, read only memories (ROMs), random access memories (RAMs), erasable programmable ROMs (EPROMs), electrically erasable programmable ROMs (EEPROMs), magnetic or optical cards, flash memory, and/or other types of media suitable for storing electronic instructions or data. 
     In at least one embodiment, the techniques of the present invention are partially or fully performed within one or more digital processing devices. The digital processing device may include, for example, a general purpose microprocessor, a digital signal processor (DSP), a reduced instruction set computer (RISC), a complex instruction set computer (CISC), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and/or others, including combinations of the above. Hardware, software, firmware, and hybrid implementations may be used. 
     In the foregoing detailed description, various features of the invention are grouped together in one or more individual embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of each disclosed embodiment. 
     Although the present invention has been described in conjunction with certain embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.