Abstract:
Disclosed is an encoding processing apparatus in which reception precision characteristics are improved by specially adapting puncture processing in respect of the code words for each encoding system. A puncture section ( 130 ) switches between a puncture pattern for a first code word partial sequence obtained on the basis of the head and tail in a fixed information block, and a puncture pattern for a second code word partial sequence obtained on the basis of the middle portion, excluding the head and tail. Also, the puncture section ( 130 ) receives the number of retransmissions of information from a retransmission control section ( 180 ) and switches the puncture pattern for the second code word partial sequence in accordance with the number of retransmissions. In addition, the puncture section ( 130 ) prioritising systematic bits over parity bits when puncturing the first code word partial sequence.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a radio communication apparatus. 
       BACKGROUND ART 
       [0002]    In mobile communication which has become widespread toady, communication with high accuracy is required in various channel environments. Further, as a means to realize communication with high accuracy even in severe channel environments, error correction encoding processing is performed on transmission data. 
         [0003]    In 3GPP (see Non-Patent Literature 1), a plurality of fixed information blocks formed with a predetermined number of bits K are formed from a series of transmission sequences, and error correction encoding processing is performed per this fixed information block. There is no problem when that series of transmission data sequences can be divided by K. In contrast to this, when that series of transmission data sequences cannot be divided by K, bit padding is performed on that series of transmission data sequences to arrange padding bits in the head part of that series of transmission data sequences, so that the total number of bits is made a number that can be divided by K. Then, encoding processing is performed on the data sequences in which padding bits are arranged, per fixed information block. By this means, it is possible to perform encoding processing of constraint length K uniformly. 
         [0004]    Further, error correction encoding schemes include convolutional encoding scheme (for example, see Patent Literature 1) and turbo encoding scheme (for example, see Non-Patent Literature 2). 
         [0005]    Then, afterwards, modulation processing is performed in modulation section on codewords obtained by error correction encoding processing, and before the modulation processing, puncturing (i.e. decimation) is performed to perform rate matching. In 3GPP, there are stipulations about a turbo encoder and a rate matching apparatus for performing puncturing. Further, there is a stipulation that when performing rate matching after performing puncturing processing, information bits (i.e. systematic bits) are not deleted, but only parity bits are deleted out of turbo-encoded data sequences. 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. 2001-203588 
       
     
       Non-Patent Literature 
     NPL 1 
     NPL 2 
       [0000]    
       
         Claude Berrou, “Near Optimum Error Correcting Coding And Decoding: Turbo-Codes,” IEEE Trans. On Communications, Vol. 44, No. 10, October 1996. 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    By the way, generally, it is known that reception accuracy characteristics at a receiving side varies depending on encoding processing at a transmitting side. 
         [0009]    However, in the above-described encoding processing, no consideration has been made for the reception accuracy characteristics at a receiving side. Further, in the above-described conventional puncturing processing that is performed on codewords, no consideration has been made for characteristics of convolutional encoding and turbo encoding and reception accuracy characteristics. 
         [0010]    It is therefore an object of the present invention to provide a communication apparatus for improving reception accuracy characteristics by devising puncturing processing on codewords for each encoding scheme. 
       Solution to Problem 
       [0011]    A radio communication apparatus according to the present invention employs a configuration to transmit an encoded codeword sequence, comprising: an encoding section that contain a convolutional encoder that performs convolutional encoding on a fixed information block formed with K bits; and a puncturing section that punctures the codeword sequence obtained by encoding processing in the encoding section based on a puncturing pattern, switching puncturing patterns for a first codeword subsequence that is obtained based on a head part and a tail part of the fixed information block and a second codeword subsequence that is obtained based on a center part, not including the head part and the tail part. 
       Advantageous Effects of Invention 
       [0012]    According to the present invention, it is possible to provide an encoding processing apparatus for improving reception accuracy characteristics by devising puncturing processing on codewords for each encoding scheme. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a block diagram showing a configuration of a radio communication system according to Embodiment 1 of the present invention; 
           [0014]      FIG. 2  is a block diagram showing a configuration of an encoding processing section in  FIG. 1 ; 
           [0015]      FIG. 3  shows a table indicating interleaver parameters used in the interleaver shown in  FIG. 2 ; 
           [0016]      FIG. 4  shows error characteristics per bit position in a fixed information block with code constraint length K (convolutional encoding scheme); 
           [0017]      FIG. 5  shows error characteristics per bit position in a fixed information block with code constraint length K (turbo encoding scheme); 
           [0018]      FIG. 6  shows switching of puncturing patterns; 
           [0019]      FIG. 7  shows puncturing patterns corresponding to encoding rates; and 
           [0020]      FIG. 8  is a block diagram showing a configuration of a radio communication apparatus according to Embodiment 2 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In embodiments, the same parts will be assigned the same reference numerals and overlapping explanations will be omitted. 
       Embodiment 1 
       [0022]    As shown in  FIG. 1 , radio communication system  10  is provided with radio communication apparatus  100  and radio communication apparatus  200 . 
         [0023]    In  FIG. 1 , radio communication apparatus  100  is provided with buffer  110 , encoding processing section  120 , puncturing section  130 , modulation section  140 , radio transmission section  150 , radio reception section  160 , demodulation section  170 , and retransmission control section  180 . 
         [0024]    Buffer  110  maintains transmission data of the initial transmission and outputs the transmission data to encoding processing section  120 . Further, buffer  110  outputs the maintained data corresponding to a retransmission control signal to encoding processing section  120 , based on the retransmission control signal from retransmission control section  180 . 
         [0025]    Encoding processing section  120  contains a convolutional encoder. This convolutional encoder receives as input a fixed information block formed with K bits, and performs convolutional encoding processing per fixed information block. The convolutional encoder performs convolutional encoding processing at code constraint length V. Code constraint length V is the number adding one to the number of shift registers that are provided in the convolutional encoder. 
         [0026]    Specifically, encoding processing section  120  is provided with interleaver  122  and constituent encoders  124 - 1 ,  2 , as shown in  FIG. 2 . Then, the above-described convolutional encoder is provided in each of constituent encoders  124 - 1 ,  2 . 
         [0027]    Interleaver  122  receives as input a fixed information block and performs interleaving processing on this fixed information block using a predetermined interleaving pattern. 
         [0028]    This interleaving processing is represented by the following equation: 
         [0000]      c′ i =C Π(i)  
 
         [0029]    where a bit sequence of the fixed information block is expressed by c 0 , c 1 , . . . c K-1  and an interleaved bit sequence is expressed by c′ 0 , c′ 1 , . . . , c′ K-1 . Further, i=0, 1, . . . and (K−1) and Π(i)=(f 1 ·i+f 2 ·i 2 ) mod K are satisfied, and f 1  and f 2  are natural numbers depending on K. 
         [0030]    For example, it is possible to use the table of  FIG. 3  for interleaver parameters for i, Ki, f1, and f2. 
         [0031]    Constituent encoders  124 - 1 ,  2  perform convolutional encoding processing on input data sequences. Constituent encoder  124 - 1  performs convolutional encoding processing on the fixed information block itself. Constituent encoder  124 - 2  performs convolutional encoding processing on the fixed information block interleaved in interleaver  122 . 
         [0032]    The codeword sequence thus obtained by error correction encoding processing in encoding processing section  120  is output to puncturing section  130 . 
         [0033]    Puncturing section  130  punctures a codeword sequence received from encoding processing section  120 . Puncturing section  130  switches the puncturing patterns for the first codeword subsequence that is obtained based on the head part and the tail part of the fixed information block, and the second codeword subsequence that is obtained based on the center part, not including the head part and the tail part. Further, puncturing section  130  receives information about the number of retransmissions from retransmission control section  180 , and switches the puncturing pattern for the second codeword subsequence based on the number of retransmissions. Further, puncturing section  130  punctures a systematic bit with priority over a parity bit in the first codeword subsequence. 
         [0034]    Modulation section  140  performs modulation processing on the transmission data punctured in puncturing section  130 , and outputs the obtained modulated signal to radio transmission section  150 . 
         [0035]    Radio transmission section  150  performs a predetermined radio transmission processing, such as D/A conversion and up-conversion, on the modulated signal, and transmits the obtained radio signal to radio communication apparatus  200  via an antenna. 
         [0036]    Radio reception section  160  receives the signal transmitted from radio communication apparatus  200  via an antenna. Radio reception section  160  performs a predetermined reception radio processing, such as down conversion and A/D conversion, on a radio received signal, and outputs the obtained signal to demodulation section  170 . 
         [0037]    Demodulation section  170  demodulates the signal received from radio reception section  160 . 
         [0038]    Retransmission control section  180  extracts information about whether or not reception succeeded (i.e. ACK/NACK information) from the signal demodulated in demodulation section  170 . This information about whether or not reception succeeded is information that is fed back based on a result of determination that is made by radio communication apparatus  200  by determining whether or not reception of the received signal transmitted from radio communication apparatus  100  succeeded. 
         [0039]    Upon receiving NACK information, retransmission control section  180  outputs retransmission control information to buffer  110  and outputs information about the number of transmissions to puncturing section  130  to order retransmission of transmission data corresponding to this NACK information. 
         [0040]    An operation of radio communication apparatus  100  having the above configuration will be described below. 
         [0041]    Transmission data output from buffer  110  is encoded in encoding processing section  120 . The codeword sequence obtained by this encoding processing is punctured in puncturing section  130 . Here, puncturing section  130  switches puncturing patterns according to “the part in a codeword sequence.” 
         [0042]    Here, error characteristics per bit position in a fixed information block formed with K bits when convolutional encoding is employed is shown in  FIG. 4 . In  FIG. 4 , the horizontal axis indicates a bit position and the vertical axis indicates a bit error rate (BER). 
         [0043]    As shown in  FIG. 4 , the BER of the bit position group in the center part of the fixed information block, not including the head part and the tail part, is poor. On the other hand, the BER in the head part and the tail part, each formed with M bits, is better than the BER in the center part. Here, M bits are proportional to code constraint length V. 
         [0044]    Further,  FIG. 5  shows error characteristics per bit position in a fixed information block formed with K bits when turbo encoding scheme is employed. In  FIG. 5 , the horizontal axis indicates a bit position and the vertical axis indicates a bit error rate (BER). 
         [0045]    As shown in  FIG. 5 , the BER of the bit position group formed with M bits in the head part of the fixed information block is good. Here, M bits are proportional to code constraint length V. 
         [0046]    On the other hand, although the BER in parts other than the above head part is poorer than the BER in the head part, the BER in certain bit positions is high. Here, the certain bit positions showing higher BER correspond to the bit positions that are positioned within M bits in the head part of the fixed information block that is interleaved in interleaver  122 . 
         [0047]    That is, in the fixed information block immediately before being input into the convolutional encoder, the head part and the tail part, each formed with M bits, tend to show better BER than the BER in the center part. That is, the difference of BER characteristics arises between the first codeword subsequence that is obtained based on the head part and the tail part and the second codeword subsequence that is obtained based on the center part, not including the head part and the tail part of the fixed information block. This is caused because tail bits are added to the tail of a fixed information block, so that all shift register values provided in the convolutional encoder are returned to 0. 
         [0048]    Therefore, puncturing section  130  switches the puncturing patterns for the first codeword subsequence that is obtained based on the head part and the tail part of the fixed information block and the second codeword subsequence that is obtained based on the center part, not including the head part and the tail part. By this means, it is possible to perform puncturing taking into account the difference of reception accuracy characteristics corresponding to the part of the codeword sequence. 
         [0049]      FIG. 6  shows switching of puncturing patterns.  FIG. 6  shows, in particular, a case where the coding rate is ⅓. Further, Xa in  FIG. 6  indicates a systematic bit, Xb and Xc indicate a parity bit, and Xa, Xb, and Xc correspond to the reference numerals in  FIG. 2 . 
         [0050]    In  FIG. 6 , puncturing pattern P 1  is applied to the first codeword subsequence (the first 3×M bits and 3×M bits before tail bits in  FIG. 6 ) that is obtained based on the head part and the tail part of the fixed information block. Puncturing pattern P 1  is a pattern in which systematic bit Xa is punctured. In this regard, in the matrix showing puncturing patterns, element 0 indicates that puncturing is performed and element 1 indicates that puncturing is not performed. Further, the first row corresponds to systematic bit Xa and the second row and the third row correspond to parity bits Xb and Xc, respectively. 
         [0051]    On the other hand, puncturing pattern P 2  is applied to the second codeword subsequence obtained based on the center part, not including the head part and the tail part. Puncturing pattern P 2  punctures parity bits without puncturing systematic bits. 
         [0052]    That is, puncturing section  130  punctures a systematic bit with priority over a parity bit in the first codeword subsequence, which shows better reception characteristics. 
         [0053]    Further, upon retransmission, puncturing section  130  switches puncturing patterns from the puncturing pattern of the second codeword subsequence, which shows relatively poorer reception characteristics, to a pattern that is different from the pattern in previous transmission. That is, puncturing section  130  switches the puncturing pattern for the second codeword subsequence based on the number of retransmissions.  FIG. 7  shows puncturing patterns corresponding to redundancy versions (RVs)  1  and  2  at a coding rate of ⅓, ⅜, and 5/12, respectively. Puncturing section  130  switches, for example, the puncturing pattern of RV  1  and the puncturing pattern of RV 2  that match the set coding rate, according to the number of retransmissions. 
         [0054]    As described above, according to the present invention, it is possible to perform puncturing taking into account the difference of reception accuracy characteristics corresponding to the part of a codeword sequence, so that reception accuracy characteristics can be improved at a receiving side. 
       Embodiment 2 
       [0055]    A case will be described with Embodiment 2 where a convolutional code is used instead of a turbo code. 
         [0056]      FIG. 8  is a block diagram showing a configuration of radio communication apparatus  300  according to Embodiment 2 of the present invention. In  FIG. 8 , radio communication apparatus  300  is provided with encoding processing section  310  and puncturing section  320 . Encoding processing section  310  contains a convolutional encoder. This convolutional encoder receives as input a fixed information block formed with K bits, and performs convolutional encoding processing per fixed information block. The convolutional encoder performs convolutional encoding processing at code constraint length V. Code constraint length V is expressed as the number in which one is added to the number of shift registers that are provided in the convolutional encoder. Here, encoding processing section  310  is not provided with an interleaver, unlike encoding processing section  120  that performs turbo encoding. 
         [0057]    Therefore, error characteristics per bit position in the fixed information block formed with K bits, which is obtained in encoding processing section  310 , is the same shown in  FIG. 4 . 
         [0058]    Thus, puncturing section  320  switches puncturing patterns for the first codeword subsequence that is obtained based on the head part and the tail part of the fixed information block and the second codeword subsequence that is obtained based on the center part, not including the head part and the tail part. Here, puncturing section  320  increases the number of bits to puncture in the first codeword subsequence than the second codeword subsequence. 
         [0059]    Further, puncturing section  320  receives information about the number of retransmissions from retransmission control section  180 , and switches the puncturing pattern for the second codeword subsequence based on the number of retransmissions. 
         [0060]    As described above, according to the present embodiment, it is possible to perform puncturing taking into account the difference of reception accuracy characteristics corresponding to the part of a codeword sequence, so that reception accuracy characteristics can be improved at a receiving side. 
       Other Embodiments 
       [0061]    Cases have been described with Embodiment 1 and Embodiment 2 where puncturing patterns for puncturing a second codeword subsequence based on the number of retransmissions. If taking into account characteristics of convolutional encoding or turbo encoding and reception accuracy characteristics, it is possible to perform the following retransmission control. That is, in retransmission, before encoding, it is possible to perform transmission after encoding only the bits other than the head part and the tail part (i.e. the center part, not including the head part and the tail part) in a fixed information block. In this regard, in the first transmission, it is possible to perform the same processing as in Embodiment 1 and Embodiment 2. 
         [0062]    The disclosure of Japanese Patent Application No. 2009-025120, filed on Feb. 5, 2009, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0063]    The radio communication apparatus according to the present invention is useful for improving reception accuracy characteristics by devising puncturing processing on codewords for each encoding scheme.