Transmitting device and transmitting method

A transmitting device and method enables improved reception quality on the receiving side when LDPC-CC (Low-Density Parity-Check Convolutional Codes) encoding is used. The transmitting device includes an LDPC-CC encoding section, a sorting section for sorting the encoded data acquired by the LDPC-CC encoding section into a first encoded data set corresponding to the column number of the column containing “1” in a part of an LDPC-CC check matrix H from which a protograph is excluded and a second encoded data set corresponding to the column numbers of the columns other than that, and a frame constructing section (control section) for constructing a transmission frame where the first and second encoded data sets are arranged in positions different in time or frequency in the transmission frame.

TECHNICAL FIELD

The present invention relates to a transmitting apparatus and transmitting method for performing error correction coding of a signal sequence using an LDPC-CC (Low-Density Parity-Check Convolutional Code).

BACKGROUND ART

Recently, as an error correcting code to realize high error correction performance in a feasible circuit cost, an LDPC (Low-Density Parity-Check) code attracts attentions. An LDPC code provides high error correction performance and can be mounted in a simple manner, and is therefore adapted to error correction coding schemes such as the fast wireless LAN system in IEEE802.11n and a digital broadcast system.

An LDPC code is an error correcting code defined in a form of a low-density parity-check matrix H. That is, an LDPC code is a block code having the same length as the column length N of check matrix H.

However, like Ethernet (trademark), most of present communication systems have a feature of communicating transmission information on a per variable-length packet basis or on a per frame basis. If an LDPC code, which is a block code, is applied to such systems, for example, a problem arises in the method of applying a fixed-length LDPC code block to a variable-length Ethernet (trademark) frame. In IEEE802.11n, although padding and puncturing are applied to a transmission information sequence to adjust the transmission information sequence length and the LDPC code block length, if padding and puncturing are performed, it is difficult to prevent a change in the coding rate and redundant sequence transmission.

As such an LDPC code of a block code (hereinafter referred to as “LDPC-BC” (Low-Density Parity-Check Block Code)), an LDPC-CC (Low-Density Parity-Check Convolutional Code) is studied which can encode and decode an information sequence of an arbitrary length (e.g. see Non-Patent Document 1 and Non-Patent Document 2).

An LDPC-CC is a convolutional code defined by a low-density parity-check matrix, and, for example,FIG. 1shows a parity-check matrix HT[0, n] of an LDPC-CC of coding rate R=½ (=b/c).

Here, the elements h1(m)(t) and h2(m)(t) in HT[0, n] have “0” or “1.” Also, all the other elements than h1(m)(t) and h2(m)(t) included in HT[0, n] have “0.” Also, M is the memory length in the LDPC-CC, and n is the codeword length of the LDPC-CC. As shown inFIG. 1, the LDPC-CC check matrix has features that the check matrix has a parallelogram shape, in which “1's” are assigned only to the diagonal elements and their surrounding elements in the matrix and “0's” are assigned to the lower left elements and upper right elements in the matrix.

Here, referring to the coding rate R=½ (=b/c) as an example, in the case of h1(0)(t)=1 and h2(0)(t)=1, the LDPC-CC is encoded by implementing the following equation based on check matrix HT[0, n].

Here, unrepresents the transmission information sequence, and v1,nand v2,nrepresent the transmission codeword sequences.

FIG. 2shows an example of an LDPC-CC encoder that implements equation 1.

Shift registers11-1to11-M and shift registers14-1to14-M hold v1,n−1and v2,n−1(i=0, . . . , M), respectively, transmit the values to the right neighboring shift registers at the timing the next input is received, and hold the values transmitted from the left neighboring shift registers.

Weight multipliers12-0to12-M and13-0to13-M switch the values of h1(m)and h2(m)between 0 and 1, based on control signals transmitted from weight control section17.

Weight control section17transmits the values of h1(m)and h2(m)at a timing to weight multipliers12-0to12-M and13-0to13-M, based on the number of counts transmitted from bit number counter16and a check matrix held in weight control section17. By performing exclusive-OR of the outputs of weight multipliers12-0to12-M and13-0to13-M, mod2adder15calculates v2,n−1. Bit number counter16counts the number of bits of a transmission information sequence unreceived as input.

By employing the above configuration, LDPC-CC encoder10can encode an LDPC-CC based on a check matrix.

An LDPC-CC encoder has a feature that this encoder can be realized with a very simple circuit, compared to a circuit that performs multiplication with a generation matrix and an LDPC-BC encoder that performs calculations based on the backward (forward) substitution method. Also, an LDPC-CC is an encoder for convolutional codes, so that it is not necessary to encode a transmission information sequence divided per fixed-length block, and it is possible to encode an information sequence of an arbitrary length.

By the way, it is possible to apply the sum-product algorithm to LDPC-CC decoding. Therefore, decoding algorithms that involve maximum likelihood sequence estimation such as the BCJR (Bahl, Cocke, Jeinek, Raviv) algorithm and the Viterbi algorithm, need not be used, so that it is possible to complete decoding processing with small processing delay. Further, a pipeline-type decoding algorithm is proposed utilizing the parallelogram shape of a check matrix in which “1's” are allocated (e.g. see Non-Patent Document 1).

If the decoding performances of an LDPC-CC and LDPC-BC are compared using parameters by which the circuit cost of the decoders are equal, it is shown that the decoding performance of an LDPC-CC is superior.

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, although the above LDPC-CC encoder has been argued under, mainly, the AWGN (Additive White Gaussian Noise) environment, this encoder has not been studied sufficiently in the fading environment in wireless communication.

Generally, although interleaving processing and retransmission processing are effective to improve received quality (i.e. error rate performance) in the fading environment, effective interleaving processing and retransmission processing for LDPC-CC's have not been studied sufficiently.

In view of the above, it is therefore an object of the present invention to provide a transmitting apparatus and transmitting method that can improve received quality on the receiving side when LDPC-CC coding processing is adopted.

Means for Solving the Problem

An aspect of the transmitting apparatus of the present invention employs a configuration having: an encoding section configured to encode a low-density parity-check convolutional code to form an encoded data; a sorting section configured to sort the encoded data acquired in the encoding section, into a first encoded data group corresponding to column numbers where there are “1's” in places outside protographs in a low-density parity-check convolutional code check matrix, and a second encoded data group corresponding to column numbers where there are non “1's” in places outside protographs in a low-density parity-check convolutional code check matrix; and a frame configuring section configured to generate a frame in which the first encoded data group and the second encoded data group are allocated to different positions in time or frequency in a frame.

An aspect of the transmitting apparatus of the present invention employs a configuration further having: a first interleaver that interleaves the first encoded data group; and a second interleaver that interleaves the second encoded data group, and in which the frame configuring section configures a transmission frame in which the first encoded data group interleaved in the first interleaver and the second encoded data group interleaved in the second interleaver are allocated to different positions in time or frequency in a frame.

An aspect of the transmitting apparatus of the present invention employs a configuration, in which, based on feedback information from a communicating party, the frame configuring section determines a position in frequency to which the first encoded data group is allocated.

An aspect of the transmitting apparatus of the present invention employs a configuration, in which, when a retransmission request is received, the frame configuring section retransmits the first encoded data group more preferentially than the second encoded data group.

An aspect of the transmitting apparatus of the present invention employs a configuration further having an M-ary modulation section that allocates the first encoded data group to fixed bits among a plurality of bits forming a symbol, and performs M-ary modulation.

An aspect of the transmitting method of the present invention includes: encoding a low-density parity-check convolutional code to form an encoded data; sorting the encoded data into a first encoded data group corresponding to column numbers where there are “1's” in places outside protographs in a low-density parity-check convolutional code check matrix, and a second encoded data group corresponding to column numbers where there are non “1's” in places outside protographs in a low-density parity-check convolutional code check matrix; allocating the first encoded data group and the second encoded data group to different positions in time or frequency in a frame; and transmitting the frame.

An aspect of the transmitting method of the present invention includes: a low-density parity-check convolutional code encoding step; a step of sorting encoded data acquired in the low-density parity-check convolutional code encoding step, into a first encoded data group corresponding to column numbers where there are “1's” in places outside protographs in a low-density parity-check convolutional code check matrix, and a second encoded data group corresponding to a rest of the column numbers; and a step of retransmitting the first encoded data group more preferentially than the second encoded data group.

ADVANTAGEOUS EFFECT OF THE INVENTION

The present invention sorts encoded data acquired in an LDPC-CC encoding section into a first encoded data group corresponding to column numbers where there are “1 's” in places outside the protographs in an LDPC-CC check matrix, and a second encoded data group corresponding to the rest of the column numbers, and performs transmission, retransmission or mapping for protecting the first encoded data group particularly, so that it is possible to improve the error rate performance upon sum-product decoding and acquire received data of good error rate performance on the receiving side.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings.

First, before explaining the specific configuration and operations according to embodiments, the fundamentals of the present invention will be explained.

In LDPC code, coding data (i.e. codeword) is acquired by multiplying information vector n by generation matrix G. That is, coding data (codeword) c can be represented by c=n×G. Here, the generation matrix G is calculated based on check matrix Ha designed in advance. To be more specific, the generation matrix G satisfies G×HT=0.

FIG. 3shows an example of check matrix H of an LDPC-CC according to an embodiment. InFIG. 3, the matrixes Hnpsurrounded by the dotted lines in check matrix H are referred to as “protographs.” Cheek matrix H includes a plurality of protographs like Hnp,1, Hnp,2, Hnp,3, Hnp,4, and so on. Further, additionally, in check matrix H, “1's” are allocated to the positions surrounded by a circle in the figure. The “1's” allocated to positions apart from the protographs in check matrix H, are used to integrate likelihoods on the decoding side (i.e. receiving side).

The sum-product decoding algorithm on the receiving side is as follows.

In the following explanation, assume that a binary (M×N) matrix H={Hmn} is the check matrix of an LDPC code that is the decoding target. Subsets A(m) and B(n) in set [1, N]={1, 2, . . . , N} are defined as shown in the following equations.
A(m)≡{n:Hmn=1}  (Equation 2)
B(n)≡{m:Hmn=1}  (Equation 3)

Here, A(m) indicates a set of column indices with “1” in the m-th row of check matrix H, and B(n) indicates a set of row indices with “1” in the n-th row of the check matrix.

Step A•1 (initialization): priori value logarithm ratio βmn=0 is set for all combinations (m, n) fulfilling Hmn=1. Also, loop variable number (i.e. the number of iterations) 1sum=1 is set, and the maximum number of loops 1sum,maxis set.

Step A•2 (row processing): an extrinsic value logarithm ratio αmnis updated for all combinations (m, n) fulfilling Hmn=1 in the order from m=1, 2, . . . , M, using the following updating equations.

Here, f represents the Gallager function, and λnrepresents the log-likelihood per bit.

Step A•3 (column processing): an extrinsic value logarithm ratio βmnis updated for all combinations (m, n) fulfilling Hmn=1 in the order from n=2, . . . , N, using the following updating equation.

Step A•5 (the count of the number of iterations): if 1sum<1sum,max, 1sumis incremented, and the step returns to step A•2. In the case of 1sum=1sum,max, sum-product decoding is finished, and an estimated sequence of a transmission sequence is acquired based on the log-likelihood Ln.

By the way, as shown inFIG. 3, the bits forming a transmission bit sequence (i.e. information bit sequence) acquired by coding processing of an LDPC-CC, such as n1,1, n1,2, n1,3, n1,4, n2,1, n2,2, n2,3, n2,4, n3,1, n3,2, n3,3, n3,4, n4,1, n4,2, n4,3, n4,4, and so on, correspond to the columns of check matrix H. This is because a check equation HwTis equal to 0. Here, a vector w is represented by n1,1, n1,2, n1,3, n1,4, n2,1, n2,2, n2,3, n2,4, n3,1, n3,2, n3,3, n3,4, n4,1, n4,2, n4,3, n4,4, and so on.

FIG. 4shows the Tanner graph prepared based on the check matrix inFIG. 3. InFIG. 4, the Tanner graph surrounded by dotted lines represented by reference numeral1001relates to protograph Hnp,1(where the region inside the dotted lines corresponds to the Tanner graph for the protograph). Similarly, the Tanner graph surrounded by dotted lines represented by reference numeral1002relates to protograph Hnp,2, the Tanner graph surrounded by dotted lines represented by reference numeral1003relates to protograph Hnp,3, and the Tanner graph surrounded by dotted lines represented by reference numeral1004relates to protograph Hnp,4.

Also, inFIG. 4, dotted lines connecting variable nodes and cheek nodes correspond to the edges of “1's” surrounded by circles in check matrix H ofFIG. 3.

In sum-product decoding, the probability is propagated based on the Tanner graphs ofFIG. 4. In this case, the positions of edges connecting variable nodes and check nodes play an important role in probability propagation. InFIG. 4, to propagate the possibility acquired by the Tanner graphs corresponding to protographs, especially, dotted-line edges play a very important role. That is, “1” surrounded by a circle in the check matrix ofFIG. 3plays an important role in possibility propagation.

For example, the edge that plays a role of propagating the possibility acquired by protograph Hnp,4to the protograph Hnp,3, is represented by dotted line1006. Similarly, the edge that plays a role of propagating the possibility acquired by protograph Hnp,4to protograph Hnp,2, is represented by dotted line1005.

Also, referring to protograph Hnp,3, the edge that plays a role of propagating the possibility acquired by protograph Hnp,3to protograph Hnp,1, is represented by dotted line1007. Similarly, the edge that plays a role of propagating the possibility acquired by protograph Hnp,3to protograph Hnp,2, is represented by dotted line1008.

As described above, among the transmission bit sequences corresponding to the column numbers of check matrix H acquired from LDPC-CC coding processing, transmission bit sequences nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ) corresponding to column numbers where there are “1's” in places not related to protographs, play an important role in probability propagation.

The present invention is made with reference to the presence of such transmission bit sequences nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ) that play an important role in possibility propagation to improve received quality.

Especially, the present invention improves received quality by devising a transmitting method and retransmitting method of a transmission bit sequence, from a viewpoint that, among transmission bit sequences corresponding to column numbers of check matrix H, transmission sequences corresponding to column numbers where there are “1's” in places not related to protographs, are important to improve received quality.

FIG. 5shows a configuration example of a transmitting apparatus according to Embodiment 1 of the present invention.

Sorting section121receives as input positional information122about the positions represented by circles inFIG. 3(i.e. information about the positions of “1's” among positions outside protographs in the check matrix) from LDPC-CC encoding section102, in addition to encoded data120. Sorting section121then sorts encoded data120into transmission bit sequences associated with the column numbers indicated by positional information122(i.e. encoded data #A (103_A)) and transmission bit sequences corresponding to the other column numbers (i.e. encoded data #B (103_B)). Further, sorting section121outputs encoded data #A (103_A) to interleaving section #A (104_A) and encoded data #B (103_B) to interleaving section #B (104_B).

Here, although a case has been described with the present embodiment where LDPC-CC encoding section102holds information associated with a check matrix and outputs positional information122from LDPC-CC encoding section102to sorting section121, for example, if sorting section121holds positional information122about a check matrix, LDPC-CC encoding section102needs not output positional information122to sorting section121.

Interleaving section #A (104_A) receives as input encoded data #A (103_A) and frame configuration signal114from frame configuration signal generating section113, interleaves encoded data #A (103_A) based on the frame configuration of frame configuration signal114, and outputs resulting interleaved data #A (105_A) to control section106.

Interleaving section #B (104_B) receives as input encoded data #B (103_B) and frame configuration signal114, interleaves encoded data #B (103_B) based on the frame configuration of frame configuration signal114, and outputs resulting interleaved data #B (105_B) to control section106.

Control section106rearranges interleaved data #A (105_A) and interleaved data #B (105_B) in the order according to frame configuration signal114, and outputs rearranged data107to modulating section108.

Modulating section108receives as input rearranged data107, control information116from control information generating section115and frame configuration signal114from frame configuration signal generating section113, produces modulated signal109by modulating rearranged data107and control information116according to frame configuration signal114, and outputs modulated signal109to radio section110.

Radio section110produces transmission signal111by performing predetermined radio processing such as frequency conversion and amplification on the modulated signal, and outputs transmission signal111from antenna112as a radio wave.

Here, frame configuration signal generating section113generates a signal including information about the frame configuration, as frame configuration signal114. Also, control information generating section115receives as input frame configuration signal114, and generates control information116including information for allowing the communicating party to find frequency synchronization or time synchronization and information for reporting the modulation scheme of a modulation signal to the communicating party.

FIG. 6shows a configuration example of a receiving apparatus that receives a signal transmitted from transmitting apparatus100ofFIG. 5. In receiving apparatus200, radio section203receives as input received signal202received by receiving antenna201. Radio section203produces modulated signal204by performing predetermined radio processing such as frequency conversion and amplification on received signal202, and outputs modulated signal204to quadrature demodulation section205.

Quadrature demodulation section205produces baseband signal206by performing quadrature demodulation of modulated signal204. Channel variation estimating section207receives as input baseband signal206, produces channel variation estimation signal208by, for example, detecting the preamble included in baseband signal206and estimating channel variations based on the preamble, and outputs channel variation estimation signal208to log-likelihood ratio calculating section211.

Control information detecting section209receives as input baseband signal206, detects the preamble included in baseband signal206and finds time synchronization or frequency synchronization based on the preamble. Also, control information detecting section209detects control information included in baseband signal206and outputs the control information as control signal210.

Log-likelihood ratio calculating section211receives as input baseband signal206, channel variation estimation signal208and control signal210. As shown in, for example, Non-Patent Documents 3, 4 and 5, log-likelihood ratio calculating section211calculates log-likelihood ratios on a per bit basis, based on channel variation estimation signal208and baseband signal206, divides these log-likelihood ratios into, for example, two types as in sorting section121of transmitting apparatus100ofFIG. 5, and outputs log-likelihood ratio signal #A (212_A) and log-likelihood ratio signal #B (212_B).

Deinterleaving section #A (213_A) receives as input log-likelihood ratio signal #A (212_A) and produces deinterleaved log-likelihood ratio #A (214_A) by performing deinterleaving opposite to the interleaving in interleaving section #A (104_A). Similarly, deinterleaving section #B (213_B) receives as input log-likelihood ratio signal #B (212-B) and produces deinterleaved log-likelihood ratio #B (214_B) by performing deinterleaving opposite to the interleaving in interleaving section #B (104_B).

Next, the operations of transmitting apparatus100according to the present embodiment will be explained.

Control section106has a function as a frame configuration means for configuring a transmission frame in which interleaved data #A (105_A) and interleaved data #B (105_B) are allocated to different positions in time or frequency in the frame.

Control section106combines data interleaved in interleaving section #A and data interleaved in interleaving section #B such that the frame configuration of modulated signal109outputted from modulating section108is as shown in, for example,FIG. 7AorFIG. 7B.

InFIG. 7AandFIG. 7B, the horizontal axis represents time.FIG. 7AandFIG. 7Bshow examples where interleaved data #A (105_A) and interleaved data #B (105_B) are allocated to different positions in time in a frame. InFIG. 7, reference code301is a preamble and is a symbol for transmitting, for example, information for allowing the communicating party to find frequency synchronization or time synchronization, information for reporting the modulation scheme of a modulated signal to the communicating part, and a known signal for estimating channel variation. Reference code302is a symbol for transmitting data interleaved in interleaving section #A (104_A), and reference code303is a symbol for transmitting data interleaved in interleaving section #B (104_B).

Here, as shown inFIG. 7AandFIG. 7B, symbol302for transmitting data interleaved in interleaving section #A (104_A) and symbol303for transmitting data interleaved in interleaving section #B (104_B) are allocated apart on the time axis, so that it is possible to realize probability propagation with alleviated influence of fading variations.

For example, the effects will be explained in the case of performing allocation as shown inFIG. 7A. Except when the speed of fading variation is extremely slow, there is a low possibility that symbol302for transmitting data interleaved in interleaving section #A and symbol303for transmitting data interleaved in interleaving section303, both have lower received field intensity, and one of the symbols has increased received field intensity.

That is, one of symbol302and symbol303can ensure high received quality. By this means, as understood from the Tanner graph inFIG. 4, according to the relationships of probability propagation between protographs, it is possible to alleviate the influence of degradation of received field intensity due to the influence of fading. This is because the log-likelihood ratio of high received field intensity always is present in protographs.

Next, an example of an interleaving method will be explained in detail usingFIG. 8andFIG. 9.FIG. 8andFIG. 9illustrate cases where block interleaving is performed, as an example of an interleaving method.

FIG. 8shows an example of interleaving processing in interleaving section #B (104_B) ofFIG. 5. As shown inFIG. 8A, input data n1,1, n1,4, n2,1, n2,4, n3,1, n3,4, n4,1, n4,4, and so on, received as input in order, are written in a memory horizontally and then written downward in order. Next, data is read out vertically, and, after that, data is read out rightward in order. By this processing, data received as input in the order shown inFIG. 8Bis interleaved, so that data is outputted in the order shown inFIG. 8C.

FIG. 9shows an example of interleaving processing in interleaving section #A (104_A) ofFIG. 5. The same block interleaving as inFIG. 8is performed for input data n1,2, n1,3, n2,2, n2,3, n3,2, n3,3, n4,2, n4,3, and so on, received as input in order. That is, by performing writing and reading processing on the memory as shown inFIG. 9A, data received as input in the order shown inFIG. 9Bis interleaved, so that data is outputted in the order shown inFIG. 9C.

Also, the method of interleaving is not limited to the methods shown inFIG. 8andFIG. 9, and, ideally, random interleaving is preferable. Here, what interleaving method is adopted is not an essential to the present invention, and, even when the block interleaving method shown inFIG. 8andFIG. 9is adopted, it is possible to provide a significant effect of improving received quality.

As described above, the present embodiment provides: LDPC-CC encoding section102; sorting section121that sorts encoded data acquired in LDPC-CC encoding section102into first encoded data group103_A corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC check matrix H, and second encoded data group103_B corresponding to the rest of the column numbers; and a frame configuration section (control section106) that configures a transmission frame in which first encoded data group103_A and second encoded data group103_B are allocated to different positions in time or frequency in the frame. By this means, in the Tanner graph prepared in sum-product decoding section217of receiving apparatus200, even in the fading environment, it is possible to always provide log-likelihood ratios of high received field intensity in protographs, and, as a result, acquire received data218of good error rate performance.

Also, although the frame configuration shown inFIG. 7has been described with the present embodiment as an example of a transmission frame configuration, the present invention is not limited to this, and an essential requirement is to configure a transmission frame in which first encoded data group103_A and second encoded data group103_B are allocated to different positions in time or frequency in the frame. For example, even if another symbol (such as a data symbol and control symbol) is inserted between first encoded data group103_A and second encoded data group103_B, it is possible to provide the same effect as above.

Although an example case has been described above with the present embodiment where the present invention is applied to single carrier communication, it is equally possible to apply the present invention to multicarrier communication. Next, an embodiment will be explained where the present invention is applied to multicarrier communication. Specifically, an example case will be explained where the present invention is applied to OFDM (Orthogonal Frequency Division Multiplexing) communication.

InFIG. 10in which the same components as inFIG. 5are assigned the same reference numerals, serial-to-parallel (“S/P”) conversion section401of transmitting apparatus400receives as input modulated signal109acquired from modulating section108.

FIG. 11, in which the same components as inFIG. 6are assigned the same reference numerals, shows a configuration example of a receiving apparatus that receives a signal transmitted from transmitting apparatus400inFIG. 10.

In receiving apparatus500, FFT•P/S conversion section501receives as input modulated signal204outputted from radio section203. FFT•P/S conversion section501performs FFT processing of modulated signal204and then performs parallel-to-serial conversion processing of the result, and outputs resulting baseband signal502.

FIG. 12andFIG. 13show examples of the frame configuration of a signal that is transmitted from transmitting apparatus400inFIG. 10. InFIG. 12andFIG. 13, the horizontal axis represents time and the vertical axis represents frequency. There are a plurality of subcarriers in the frequency axis direction. Here, assume that there are subcarriers #1to #n.

Similar toFIG. 7, inFIG. 12, a data group comprised of data interleaved in interleaving section #A and a data group comprised of data interleaved in interleaving section #B, are allocated in group units on the time axis (i.e. these data groups are allocated in different times). InFIG. 12, although data interleaved in interleaving section #A and data interleaved in interleaving section #B are arranged in order, it is naturally possible to arrange these data in the reverse order.

InFIG. 13, a data group comprised of data interleaved in interleaving section #A and a data group comprised of data interleaved in interleaving section #B, are allocated in group units on the frequency axis (i.e. these data groups are allocated in different frequencies). By this means, for example, even in the fading environment where frequency selective fading is caused, there is a low possibility that the data group comprised of data interleaved in interleaving section #A and the data group comprised of data interleaved in interleaving section #B, both have lower received field intensity, and, consequently, one of these data groups has larger received field intensity. As a result, it is possible to always provide log-likelihood ratios of high received field intensity in protographs, and, as a result, acquire received data of good error rate performance on the receiving side.

Here, although the frame configurations inFIG. 12andFIG. 13have been described as an example of a transmission frame configuration, the present invention is not limited to this, and an essential requirement is to allocate a data group comprised of data interleaved in interleaving section #A ofFIG. 10and a data group comprised of data interleaved in interleaving section #B ofFIG. 10, to different positions in time or frequency in the frame. For example, even if another symbol (such as a data symbol and control symbol) is inserted between a data group comprised of data interleaved in interleaving section #A and a data group comprised of data interleaved in interleaving section #B, it is possible to provide the same effect as above.

Also, although an example case has been described above with the present embodiment where the present invention is applied to single carrier communication and OFDM communication, the present invention is not limited to this, and, even if the present invention is applied to other multicarrier schemes other than the OFDM scheme, it is equally possible to implement the present invention. Also, for example, the present invention is applicable to the spread spectrum communication scheme, the SC-FDMA (Single Carrier Frequency Division Multiple Access) communication scheme, and so on.

Also, as a different frame configuration from those inFIG. 7,FIG. 12andFIG. 13, the frame configurations inFIG. 14andFIG. 15are possible. Here, an essential requirement is to allocate a data group comprised of data interleaved in interleaving section #A and a data group comprised of data interleaved in interleaving section #B such that the influence of fading is alleviated in at least one of these data groups.

In the case of configuring the frames shown inFIG. 14andFIG. 15, first, a data group comprised of data interleaved in interleaving section #A is split into two, and a data group comprised of data interleaved in interleaving section #B is split into two.

The frame configuration shown inFIG. 14is made by allocating split data groups in interleaving section #A and split data groups in interleaving section #B alternately in the time domain.

The frame configuration shown inFIG. 15is made by allocating split data groups in interleaving section #A and split data groups in interleaving section #B alternately in the frequency domain.

Here, it is equally possible to perform different interleaving between interleaving section #A and interleaving section #B.

Based on feedback information from the communicating party, the present embodiment controls the allocation of significant bits for probability propagation in an LDPC-CC (i.e. an encoded data group corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC check matrix) in the frequency domain. An example case will be explained with the present embodiment, using the LDPC-CC shown inFIG. 3andFIG. 4.

FIG. 16illustrates an example of the flow of information on the time axis, where a base station transmits data to a terminal.FIG. 16Ashows a modulated signal that is transmitted from the base station, in the time axis direction, andFIG. 16Bshows a modulated signal that is transmitted from the terminal, in the time axis direction.

The base station transmits control information symbol601, and the terminal receives this control information symbol601and thereby finds, for example, frequency/time synchronization. Next, the base station transmits pilot symbol602, and the terminal receives this pilot symbol602and thereby estimates a propagation environment of radio waves.

Next, the terminal transmits symbol603for transmitting feedback information. Specifically, the terminal receives pilot symbol602transmitted from the base station, prepares feedback information based on the estimated propagation environment of radio waves, and transmits this information by symbol603.

Next, the base station transmits transmitting method report symbol604. Here, based on feedback information symbol603transmitted from the terminal, the base station changes the transmitting method of a modulated signal that is transmitted from the base station (i.e. in the present embodiment, the allocation of an encoded data group corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC cheek matrix, in the frequency domain or in the time domain). In this case, transmitting method report symbol604is the symbol for reporting the changed content to the terminal.

Next, the base station transmits channel estimation symbol605. The terminal receives this channel estimation symbol, thereby estimating channel variation. Next, the base station transmits data symbol606.

FIG. 17, in which the same components as inFIG. 10are assigned the same reference numerals, shows a configuration example of the base station according to the present embodiment.

In base station700, receiving section703receives as input received data702received by receiving antenna701. Receiving section703produces received data704by performing predetermined reception processing such as frequency conversion, detection and decoding on received signal702.

Feedback information extracting section705receives as input received data704, extracts feedback information706, which is transmitted from the terminal, from received data704, and outputs this feedback information706to frame configuration signal generating section113.

Frame configuration signal generating section113determines a frame configuration based on feedback information706, and outputs frame configuration signal114including information about the determined frame configuration. The method of determining a frame configuration will be described later usingFIG. 19andFIG. 20.

FIG. 18, in which the same components as inFIG. 11are assigned the same reference numerals, shows a configuration example of the terminal according to the present embodiment.

In terminal800, feedback information generating section801receives as input channel variation estimation signal208. Feedback information generating section801prepares and outputs feedback information802based on channel variation estimation signal208to transmitting section804. Transmitting section804receives as input feedback information802and transmission digital data803, and produces transmission signal805by generating a modulated signal based on the frame configuration and performing predetermined radio processing such as frequency conversion and amplification on this modulated signal. Transmission signal805is outputted from antenna806as a radio wave.

Here, although the method of generating feedback information (such as CSI (Channel State Information)) in feedback information generating section801does not affect the present invention, examples include the following methods: a method of quantizing channel variation estimation signal208and feeding back the quantized channel estimation signal and a method of preparing compressed channel estimation signal information from channel variation estimation signal208and feeding back this information, where the transmitting method is determined in the base station; and a method of preparing information about the control method (transmitting method) that is requested to the communicating party, from channel variation estimation signal208, and feeding back this information, where the transmitting method is determined in the terminal.

Next, a specific example will be explained where significant bits for probability propagation in an LDPC-CC (i.e. an encoded data group corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC) are allocated based on feedback information from a terminal.

FIG. 19shows an example of the method of allocating significant bits to subcarriers.FIG. 19Ashows a characteristic curve for estimated channel variation, where the horizontal axis represents frequency and the vertical axis represents received field intensity. Further, the characteristic curve shown inFIG. 19is prepared based on channel variation estimation signal208from terminal800inFIG. 18. Here,FIG. 19illustrates an example where the terminal receives an OFDM symbol comprised of six subcarriers.

As shown inFIG. 19B, assume that, in the case of arranging the field intensity of subcarriers in ascending order, field intensity increases in the order from subcarrier #3, subcarrier #2, subcarrier #5, subcarrier #4, subcarrier #1and subcarrier #6.

In this case, in order to protect significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in the LDPC-CC shown inFIG. 3, as shown inFIG. 19C, these significant bits are allocated to subcarriers #1, #4and #6of high received field intensity upon reception in the terminal. As described above, the base station, which is the transmitting side of significant bits, or the terminal, which is the receiving side of significant bits, may determine to which subcarriers the significant bits are allocated.

Thus, by transmitting significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), using subcarriers of high received field intensity (i.e. good received quality), it is possible to provide an effect of improving error rate performance of received data acquired by decoding in a terminal.

Although a case has been described above with the example shown inFIG. 19C, where significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), are allocated to three subcarriers #1, #4and #6, the present invention is not limited to this, and an important point is to transmit significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), using subcarriers of good received quality preferentially.

Such data allocation control is performed in control section106of the base station inFIG. 17.

FIG. 20shows the method of allocating significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), to subcarriers, as a different example from the method shown inFIG. 19. A feature ofFIG. 20lies in that the allocation method is simplified compared to that ofFIG. 19. The allocation method ofFIG. 20is effective especially when there is a large number of subcarriers for use.

According to the method shown inFIG. 20, first, a plurality of subcarriers are grouped to form a subcarrier block. For example, as shown inFIG. 20A, the subcarrier block comprised of subcarriers #1to #8is referred to as “subcarrier block #1.” Similarly, the subcarrier block comprised of subcarriers #9to #16is referred to as “subcarrier block #2,” the subcarrier block comprised of subcarriers #17to #24is referred to as “subcarrier block #3,” and the subcarrier block comprised of subcarriers #25to #32is referred to as “subcarrier block #4.”

FIG. 20Ashows a characteristic curve for estimated channel variation, where the horizontal axis represents frequency and the vertical axis represents received field intensity. Also, as shown inFIG. 20B, the magnitudes of received quality in subcarrier block units are compared. Here, for example, in the case of arranging subcarrier blocks in ascending order of received quality, assume that subcarrier block #2, subcarrier block #3, subcarrier block #1and subcarrier block #4are provided in order.

In this case, to protect significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in the LDPC-CC shown inFIG. 3, as shown inFIG. 20C, these significant bits are allocated to subcarrier blocks #1and #4of high received field intensity upon reception in the terminal.

Although a case has been described above with the example shown inFIG. 20C, where significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), are allocated to two subcarrier blocks #1and #4, the present invention is not limited to this, and an important point is to transmit significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), using subcarrier blocks of good received quality preferentially.

Here, in the case of allocating significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in subcarrier block units as shown inFIG. 20, compared to the case where bits are allocated in subcarrier units as shown inFIG. 19, it is possible to provide an advantage of reducing the amount of calculations required to perform rearrangement in ascending order of received quality.

As described above, based on feedback information from the communicating party, the present embodiment controls the allocation of significant bits for probability propagation in an LDPC-CC (i.e. an encoded data group corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC check matrix) in the frequency domain, so that the receiving side can produce received data of good error rate performance.

Also, although an example ease has been described above with the present embodiment where interleaving is performed, according to the present embodiment, it is possible to improve the error rate performance of received data without performing interleaving.

Also, although an example case has been described with the present embodiment where the present invention is applied to OFDM communication, the present invention is not limited to this, and, even when the present invention is applied to other multicarrier communication than OFDM communication, it is equally possible to implement the present invention

Also, like OFDMA (Orthogonal Frequency Division Multiple Access) shown in Non-Patent Document 6, even if the present invention is applied to a communication scheme where the communicating party (i.e. terminal) varies per subcarrier (or subcarrier block), by allocating data to the same subcarriers (or subcarrier blocks) as above on a per communicating party basis, it is possible to provide the same effect as in the above embodiments.

Further, even if the present invention is applied to the MIMO (Multiple-Input Multiple-Output) communication scheme shown in Non-Patent Document 7, it is effective to adopt the method of, based on feedback information from the communicating party, determining allocation of symbols for propagating important data for probability propagation in an LDPC-CC, so that it is possible to implement the present invention in the same way as in the above-described examples. In this case, the number of streams to be transmitted increases in MIMO transmission, and, consequently, it is preferable that the base station determines to which streams and subcarriers the symbols for propagating important data for probability propagation in an LDPC-CC are allocated.

The retransmission method will be explained with the present embodiment, where it is possible to improve the error rate performance of received data efficiently in the case of using an LDPC-CC. In the present embodiment, an example case will be explained using the LDPC-CC ofFIG. 3andFIG. 4explained in Embodiment 1.

FIG. 21shows an example of data flow between the base station and terminal according to the present embodiment. This flow is as follows.

<1>: The base station transmits frame #1including data to the terminal. In this case, the data represents data encoded by the LDPC-CC explained in Embodiment 1.

<2>: The terminal receives frame #1and reports to the base station that retransmission is not necessary, because the decoding result includes no error.

<3>: The base station has not received a “retransmission request” from the terminal, and therefore transmits frame #2including data to the terminal. In this case, the data represents data encoded by the LDPC-CC explained in Embodiment 1.

<4>: The terminal receives frame #2and requests retransmission to the base station, because the decoding result includes error.

<5>: The base station has received a “retransmission request” from the terminal, and therefore transmits frame #P2, which is partial data of frame #2, to the terminal.

<6>: The terminal receives frame #P2and requests retransmission to the base station, because the decoding result includes error.

<7>: The base station has received a “retransmission request” from the terminal, and therefore transmits frame #P2′, which is partial data P2′ of frame #2(different from frame #P2), to the terminal.

<8>: The terminal receives frame #P2′ and requests retransmission to the base station because the decoding result includes error.

<9>: The base station has received a “retransmission request” from the terminal, and therefore transmits frame #P2, which is partial data of frame #2, to the terminal.

<10>: The terminal receives frame #P2and requests retransmission, because the decoding result includes error.

<11>: The base station has received a “retransmission request” from the terminal, and therefore transmits frame #2′, which is partial data of frame #2, to the terminal.

FIG. 22, in which the same components as inFIG. 17are assigned the same reference numerals, shows a configuration example of the base station according to the present embodiment.

In base station900, frame configuration signal generating section113receives as input feedback information706. Frame configuration signal generating section113acquires information as to whether or not transmitted data includes error, where the information is included in feedback information706and transmitted from the terminal, identifies whether or not to retransmit data based on this information, and outputs frame configuration signal114including this identification result.

Interleaving section903receives as input retransmission encoded data #A (902_A), retransmission encoded data #B (902_B) and frame configuration signal114, and, when frame configuration signal114indicates a retransmission, interleaves one of retransmission encoded data #A (902_A) and retransmission encoded data #B (902_B), and outputs interleaved data904.

Next, the operations of storage section901_A and storage section901_B will be explained in detail with reference toFIG. 21.

InFIG. 21, with frame #P2, which is the first retransmission data, data corresponding to significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in the LDPC-CC described inFIG. 3andFIG. 4(i.e. retransmission encoded data #A (902_A)), is transmitted among data subjected to LDPC-CC coding and transmitted in frame #2ofFIG. 21.

Thus, by preferentially retransmitting significant bits for probability propagation, nk,1and nk,3(k=1, 2, 3, 4, 5, . . . ), it is possible to reduce the number of retransmissions and suppress the amount of data to be retransmitted, so that it is possible to improve data transmission efficiency in a system.

InFIG. 21, with frame #2P′, which is second retransmission data, data corresponding to bits other than significant bits for probability propagation in the LDPC-CC described inFIG. 3andFIG. 4, that is, data corresponding to bits, nk,1and nk,4(k=1, 2, 3, 4, 5, . . . ) (i.e. retransmission encoded data #B (902_B)), is transmitted among data subjected to LDPC-CC coding and transmitted in frame #2ofFIG. 21.

By this means, upon the second retransmission, it is possible to reduce the possibility that error is caused.

In the example shown inFIG. 21, the same data as in the first retransmission (i.e. nk,2and nk,3(k=1, 2, 3, 4, 5, . . . )) is retransmitted upon the third retransmission, and the same data as in the second retransmission (i.e. nk,1and nk,4(k=1, 2, 3, 4, 5, . . . )) is retransmitted upon the fourth retransmission.

Therefore, interleaving section903inFIG. 22interleaves retransmission encoded data #A (902_A) upon the first and third retransmissions, interleaves retransmission encoded data #B (902_B) upon the second and fourth retransmissions, and outputs the result as interleaved data904.

Control section106receives as input interleaved data #A (105_A), interleaved data #B (105_B), interleaved data904and frame configuration signal114, and, if frame configuration signal114indicates a retransmission, outputs interleaved data904as transmission data107. By contrast, if frame configuration signal114does not indicate a retransmission, the operations of control section106are the same as in Embodiment 1.

FIG. 23, in which the same components as inFIG. 18are assigned the same reference numerals, shows a configuration example of the terminal according to the present embodiment.

In terminal1100, control information detecting section209receives as input baseband signal206. Control information detecting section209detects, from baseband signal206, the symbol indicating the type of frame data transmitted from the base station, identifies, based on that symbol, whether or not data transmitted from the base station is retransmission data and the number of retransmissions, and outputs control signal210including this identification result.

Log-likelihood ratio calculating section211receives as input baseband signal206, channel variation estimation signal208and control signal210, and, if control signal210does not indicate retransmission data, outputs log-likelihood ratio signal #A (212_A) and log-likelihood ratio calculating section #B (212_B) in the same way as in Embodiment 1. By contrast, if control signal210indicates retransmission data, log-likelihood ratio calculating section211outputs log-likelihood ratio signal1101for retransmission to deinterleaving section1102.

Deinterleaving section1102is used for retransmission, and performs deinterleaving processing opposite to the interleaving processing in interleaving section903of base station900, on log-likelihood ratio signal1101for retransmission, and inputs deinterleaved log-likelihood ratio signal1103for retransmission.

Sum-product decoding section217receives as input rearranged log-likelihood ratio216, deinterleaved log-likelihood signal1103for retransmission and control signal210. Further, if control signal210does not indicate retransmission data, sum-product decoding section217produces received data218by performing sum-product decoding using rearranged log-likelihood ratio216, and produces decision signal1104by deciding whether or not decoded data includes error. By contrast, if control signal210does not indicate that the data is retransmission data, sum-product decoding section217produces received data218by performing sum-product decoding using rearranged log-likelihood ratio216and deinterleaved log-likelihood ratio signal1103that are received as input in advance, and produces decision signal1104by deciding whether or not the decoded data includes error.

Retransmission request information generating section1105receives as input decision signal1104, generates retransmission request information1106indicating to request a retransmission when received data includes error or indicating not to request a retransmission if received data does not include error, and outputs retransmission request information1106to transmitting section804.

Transmitting section804receives as input retransmission request information1106and transmission digital data803, and produces transmission signal805by generating a modulated signal based on the frame configuration and performing predetermined radio processing such as frequency conversion and amplification on this modulated signal.

FIG. 24shows the frame configuration of a transmission signal from the base station on the time axis (FIG. 24A) and the frame configuration of a transmission signal from the terminal (FIG. 24B). Preambles1201and1204are the symbols for allowing the communicating party to estimate channel variation. Data type report symbol1202is the symbol for reporting whether or not transmission data1203is retransmission data and the number of retransmissions, to the communicating party (i.e. terminal).

Retransmission request symbol1205is the symbol for requesting a retransmission to the communicating party (i.e. base station). Data symbol1206is the symbol for transmitting data.

As described above, according to the present embodiment, by preferentially retransmitting significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in an LDPC-CC, it is possible to transmit error-free data to the communicating party with a fewer number of retransmissions, so that it is possible to improve data transmission efficiency in a system.

Next, the configurations of the base station and the terminal shown inFIG. 22andFIG. 23, are shown inFIG. 25andFIG. 26, respectively. The configurations ofFIG. 25andFIG. 26differ from those ofFIG. 22andFIG. 23in that, in the case of not retransmission data, interleaving of significant bits for probability propagation nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), is not distinguished from interleaving of the rest of the bits, nk,1and nk,4(k=1, 2, 3, 4, 5, . . . ).

In base station1300ofFIG. 25in which the same components as inFIG. 17are assigned the same reference numerals, LDPC-CC encoding section102outputs encoded data1301, which is acquired by coding using an LDPC-CC, to interleaving section1302, storage section1304and interleaving section (for retransmission)1306.

Interleaving section1302receives as input encoded data1301and frame configuration signal114, and, if frame configuration signal114does not indicate a retransmission, interleaves encoded data1301and outputs interleaved data1303to control section1308.

Storage section1304receives as input encoded data1301and frame configuration signal114, and, if frame configuration signal114does not indicate a retransmission, stores encoded data1301received as input. By contrast, if frame configuration signal114indicates a retransmission and an odd number of retransmissions such as one and three, storage section1304outputs significant bits for probability propagation nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ). Also, if frame configuration signal114indicates an even number of retransmissions such as two and four, storage section outputs bits, nk,1and nk,4(k=1, 2, 3, 4, 5, . . . ).

Interleaving section1306is the interleaver for retransmission data, and receives as input retransmission encoded data1307and frame configuration signal114, interleaves retransmission encoded data1305and outputs interleaved retransmission encoded data1307to control section1308.

Control section1308receives as input interleaved encoded data1303, interleaved retransmission encoded data1307and frame configuration signal114, and, if frame configuration signal does not indicate a retransmission, selects and outputs interleaved encoded data1303. By contrast, if frame configuration signal114indicates a retransmission, control section1308selects and outputs interleaved retransmission encoded data1307.

FIG. 26, in which the same components as inFIG. 23are assigned the same reference numerals, shows a configuration example of a terminal that communicates with base station1300ofFIG. 25. In terminal1400, log-likelihood ratio calculating section211receives as input baseband signal206and control signal210, and, if control signal210does not indicate a retransmission, outputs calculated log-likelihood ratio1401to deinterleaving section1402. By contrast, if control signal210indicates a retransmission, log-likelihood ratio calculating section211outputs calculated log-likelihood ratio1101to deinterleaving section (for retransmission)1102.

Sum-produce decoding section217receives as input deinterleaved log-likelihood ratio1403, deinterleaved log-likelihood ratio for retransmission1103and control signal210. Further, if control signal210does not indicate retransmission data, sum-product decoding section217produces received data218by performing sum-product decoding using deinterleaved log-likelihood ratio1403, and produces decision signal1104by deciding whether or not the decoded data includes error. By contrast, if control signal210indicates retransmission data, sum-product decoding section217produces received data218by performing sum-product decoding using deinterleaved log-likelihood ratio1403and deinterleaved log-likelihood ratio signal for retransmission1103that are received as input in advance, and produces decision signal1104by deciding whether or not the decoded data includes error.

In the present embodiment, an important point is to preferentially retransmit significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in an LDPC-CC. Therefore, data transmitting methods except upon retransmission do not affect the effects of the retransmission method of the present embodiment. Also, the method upon a second or subsequent retransmission is not limited to the above embodiment.

Also although an example case has been described above with the present embodiment where the present invention is applied to single-carrier communication, the present invention is not limited to this, and, even if the present invention is applied to multicarrier communication such as OFDM communication, it is equally possible to implement the present invention. Further, it is equally possible to apply the present invention to, for example, the spread spectrum communication scheme and the SC-FDMA communication scheme. Further, it is equally possible to apply the present invention to the MIMO communication scheme described in Non-Patent Document 7.

The method of mapping data on a modulated symbol will be explained with the present embodiment, using an LDPC-CC and M-ary modulation which has 16 signal points or more such as 16 QAM and 64 QAM.

FIG. 27, in which the same components as inFIG. 5are assigned the same reference numerals, shows a configuration example of the transmitting apparatus according to the present embodiment. Transmitting apparatus1500ofFIG. 27differs from transmitting apparatus100ofFIG. 5in directly inputting interleaved encoded data105_A and105_B acquired from interleaving section #A (104_A) and interleaving section #B (104_B), in modulating section108.

FIG. 28shows a configuration example of a transmitting apparatus which is different from inFIG. 27. In transmitting apparatus1600ofFIG. 28in which the same components as inFIG. 27are assigned the same reference numerals, encoded data1601acquired from LDPC-CC encoding section102is outputted to interleaving section1602, and interleaved encoded data1603is outputted to modulating section108.

Here,FIG. 29illustrates a state of a signal point allocation (i.e. mapping) of four inputted bits, b1, b2, b3and b4, in the in-phase I and quadrature Q plane, when the modulation scheme is 16 QAM.

By the way, as shown in Non-Patent Document 8, when the modulation scheme in modulating section108is 16 QAM, the possibility of error (represented by the numeric value of a log-likelihood ratio) is not uniform between b1, b2, b3and b4inFIG. 29. When signal point allocation is provided as shown inFIG. 29, the possibility of error is equal between b1and b2, and the possibility of error is equal between b3and b4.

Therefore, the present embodiment proposes the method of allocating significant bits for probability propagation (in the present embodiment, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . )) to one of the set of b1and b2and the set of b3and b4. InFIG. 29, assume that significant bits for probability propagation are allocated to the set of b2and b3. Therefore, other bits than significant bits for probability propagation (i.e. nk,1and nk,4(k=1, 2, 3, 4, 5, . . . )) are allocated to the set of b1and b4.

This processing will be explained using the configurations shown inFIG. 27andFIG. 29.

In transmitting apparatus1500ofFIG. 27, modulating section108receives as input interleaved encoded data #A (105_A), interleaved encoded data #B (105_B) and frame configuration signal114.

In transmitting apparatus1600ofFIG. 28, interleaving section1602performs interleaving processing of significant bits and the rest of the bits included in encoded data1601, separately. Modulating section108performs the same mapping processing as inFIG. 29, on the interleaved significant bits and the rest of the interleaved bits.

By performing such allocation (mapping), the receiving apparatus can find the log-likelihood ratio and improve the error rate performance upon performing decoding based on the log-likelihood ratio.

An important point of the present embodiment is to allocate significant bits for probability propagation in an LDPC-CC (i.e. nk,2and nk,3(k=1, 2, 3, 4, 5, . . . )) in a fixed manner upon allocating bits to signal points in 16 QAM. By this means, it is possible to improve error rate performance of significant bits for probability propagation, so that it is possible to efficiently improve the error rate performance of received data which is finally acquired.

Also, although an example of allocating bits to signal points in 16 QAM has been described usingFIG. 29with the present embodiment, the present invention is not limited to this. Also, although 16 QAM has been described as an example of a modulation scheme, the present invention is not limited to this, and it is equally possible to apply the present invention to 64 QAM as shown in Non-Patent Document 8. Further, the present invention is naturally applicable to 128 QAM, 256 QAM, and so on.

Also although an example case has been described above with the present embodiment where the present invention is applied to single-carrier communication, the present invention is not limited to this, and, even if the present invention is applied to multicarrier communication such as OFDM communication, it is equally possible to implement the present invention. Further, it is equally possible to apply the present invention to, for example, the spread spectrum communication scheme and the SC-FDMA communication scheme. Further, it is equally possible to apply the present invention to the MIMO communication scheme described in Non-Patent Document 7.

An embodiment will be explained below where the feedback control described in Embodiment 2 is applied to the OFDMA communication scheme.

FIG. 30shows the relationship between a base station and terminals, where there are terminal #X, terminal #Y and terminal #Z in the range in which the base station can perform communication. The terminals receive symbols for channel variation estimation transmitted from the base station, and transmit these symbols to the base station as feedback information. In the case ofFIG. 30, the base station receives feedback information from terminal #X, terminal #Y and terminal #Z.

FIG. 31shows an example of the frame configuration of a modulated signal that is transmitted from the base station on the time axis and the frequency axis. Based on feedback information from the terminals, the base station allocates symbols to transmit to terminal #X, terminal #Y and terminal #Z, on the time axis and the frequency axis.

In the example shown inFIG. 31, subcarriers #1to #n are divided into three in the frequency axis direction. InFIG. 31, symbols for terminal #X (or #Y or #Z) represent the symbols that are transmitted from the base station to terminal #X (or #Y or #Z).

In the case of OFDMA, as shown inFIG. 31, terminals to allocate to subcarriers vary according to time. In addition, as in Embodiment 2, among a plurality of symbols to transmit to, for example, terminal #X, the present embodiment determines symbols for transmitting significant bits for probability propagation, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ), in an LDPC-CC, based on feedback information from terminal #X.

Thus, even in the case of OFDMA, if the same processing as in Embodiment 2 is applied to terminals, it is possible to provide the same effect as in Embodiment 2.

Also, although the following has not been described above with the present embodiment, in the case of performing coding with puncturing, by puncturing other bits than significant bits (i.e. a first encoded data group corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC cheek matrix), it is possible to set a larger coding rate without degrading quality.

As an applied example of this, in the case of performing, for example, hybrid ARQ, there is a method of, first, puncturing other bits than significant bits (i.e. a first encoded data group corresponding to column numbers where there are “1's” in places outside protographs in an LDPC-CC check matrix) and retransmitting the punctured bits upon retransmission.

The puncturing method will be explained with the present embodiment for adjusting the coding rate of an LDPC-CC having a cheek matrix where there are “1's” in elements outside protographs, as shown inFIG. 3.

Non-Patent Document 9 discloses a puncturing method whereby the transmitting apparatus periodically decide bits as puncture bits (i.e. non-transmitted bits) every predetermined interval, and transmits other bits than the puncture bits. The receiving apparatus decodes all bits including the puncture bits, using the log-likelihood ratio of the bits transmitted from the transmitting apparatus. According to the puncturing method disclosed in Non-Patent Document 2, puncture bits are periodically decided. Consequently, significant bits for probability propagation may be punctured, and, the error correcting performance after puncturing varies depending on which bits are determined as puncture bits.

The present embodiment proposes a puncturing method based on significant bits for probability propagation and other bits than the significant bits for probability propagation. The puncturing method will be explained below in detail, using an LDPC-CC having the check matrix shown inFIG. 3as an example. Also,FIG. 32shows the check matrix ofFIG. 3again, and the puncturing method of the present embodiment will be explained usingFIG. 32. InFIG. 32, the sequence shown inFIG. 32Ais the transmission sequence of a coding rate of ½ before puncturing, and the sequence shown inFIG. 32Bis the transmission sequence of a coding rate of ⅘ after puncturing.

As described in Embodiment 1, in the check matrix inFIG. 32, nk,2and nk,3(k=1, 2, 3, 4, 5, . . . ) where there are “1's” in places outside protographs, are significant bits for probability propagation.

According to the puncturing method proposed in the present embodiment, the number of puncture bits (non-transmitted bits) per unit (e.g. puncture period) selected from significant bits for probability propagation, nk,2and nk,3, is set smaller than the number of puncture bits (non-transmitted bits) per unit selected from bits, nk,1and nk,4, other than significant bits for probability propagation, nk,2and nk,3.

For example, as shown inFIG. 32, the number of puncture bits per unit (16 bits) selected from significant bits for probability propagation, nk,2and nk,3, is 0, and the number of puncture bits per unit (16 bits) selected from bits, nk,1and nk,4, other than the significant bits for probability propagation, nk,2and nk,3, is six.

Also, a case has been described above with the example shown inFIG. 32, where significant bits for probability propagation, nk,2and nk,3, are not selected as puncture bits (non-transmitted bits) and are always transmitted. However, it is not that significant bits for probability propagation, nk,2and nk,3, should not be selected as puncture bits (non-transmitted bits) (in the case where the coding rate to be provided by puncturing is high, a case may occur where significant bits for probability propagation, nk,2and nk,3, have to be selected as puncture bits (non-transmitted bits)).

As described above, the number of puncture bits (non-transmitted bits) per unit (e.g. puncture period) selected from significant bits for probability propagation, nk,2and nk,3, is set smaller than the number of puncture bits (non-transmitted bits) per unit selected from bits, nk,2and nk,4, other than the significant bits for probability propagation, nk,2and nk,3, so that it is possible to provide the same effect as above.

Also, in the case of preferentially selecting other bits than significant bits for probability propagation as puncture bits and not puncturing the significant bits for probability propagation as much as possible, it is possible to suppress the degradation of received quality (i.e. degradation of error correcting performance) more reliably upon adopting puncturing. This is because, when more significant bits for probability propagation are punctured, degradation of received quality is more likely to be caused, and, when fewer significant bits for probability propagation are punctured, degradation of received quality is less likely to be caused.

Thus, according to the present embodiment, the number of puncture bits (non-transmitted bits) per unit (e.g. puncture period) selected from significant bits for probability propagation, nk,2and nk,3, is set smaller than the number of puncture bits (non-transmitted bits) per unit selected from bits, nk,1and nk,4, other than the significant bits for probability propagation, nk,2and nk,3.

FIG. 33shows an example of the configuration of the transmitting section according to the present embodiment. Transmitting section3100shown inFIG. 33is provided with LDPC-CC encoding section3101, puncturing section3102, interleaving section3104and modulating section3106.

LDPC-CC encoding section3101receives as input information X and a control signal, and generates information X and parity P based on this control signal. LDPC-CC encoding section3101outputs generated information X and parity P to puncturing section3102.

Puncturing section3102receives as input information X and a control signal, and performs puncturing according to the above rule. That is, puncturing section3102determines puncture bits such that the number of puncture bits (non-transmitted bits) per unit (e.g. puncture period) selected from significant bits for probability propagation, nk,2and nk,3, is set smaller than the number of puncture bits (non-transmitted bits) per unit selected from bits, nk,1and nk,4, other than the significant bits for probability propagation, nk,2and nk,3, and puncturing section3102performs puncturing. Here, the coding rate is set, that is, the puncturing method is determined based on, for example, the channel state and the packet loss occurrence condition which are acquired from the communicating party, so that a control signal may be generated, or the transmitting apparatus may set the coding rate, that is, determine the puncturing method to generate a control signal. Puncturing section3102outputs punctured data3103to interleaving section3104.

Modulating section3106receives as input interleaved data3105and a control signal, generates a transmission signal by performing processing such as mapping, quadrature modulation and frequency conversion on interleaved data3105base on this control signal, and outputs this transmission signal.

The receiving apparatus performs, for example, BP (Belief Propagation) decoding, sum-product decoding, shuffled BP decoding, normalized BP decoding and offset BP decoding. By this means, even when the transmitting side performs puncturing, it is possible to decode data. Here, the receiving apparatus needs to assign zero to puncture bits as the log-likelihood ratio.

As described above, according to the present embodiment, the number of puncture bits (non-transmitted bits) per unit (e.g. puncture period) selected from significant bits for probability propagation, is set smaller than the number of puncture bits (non-transmitted bits) per unit selected from other bits than the significant bits for probability propagation. By this means, it is possible to suppress the degradation of received quality (i.e. degradation of error correcting performance) upon puncturing.

The present invention is not limited to all the above embodiments, and can be implemented with various changes. For example, although cases have been described above with embodiments where the present invention is realized using, mainly, an encoder and transmitting apparatus, the present invention is not limited to this, and it is equally possible to apply the present invention even when the present invention is realized using a power line communication apparatus.

Also, it is equally possible to use this coding method and transmitting method as software. For example, it is possible to store program that performs the above coding method and transmitting method in a ROM (Read Only Memory) and operate this program by a CPU (Central Processor Unit).

Also, it is equally possible to store program that operates the above coding method and transmitting method in a computer-readable storage medium, record the program stored in the storage medium in a RAM (Random Access Memory), and operate the computer according to the program.

Also, it is not needless to say that the present invention is useful in not only wireless communication but also visible light communication and light communication.

The disclosures of Japanese Patent Application No. 2007-184540, filed on Jul. 13, 2007, and Japanese Patent Application No. 2008-181616, filed on Jul. 11, 2008, including the specifications, drawings and abstracts, are incorporated herein by reference in their entireties.

The present invention is widely applicable to wireless systems using an LDPC-CC, and it is suitable when the present invention is applied to, for example, the OFDM-MIMO communication system. Also, the present invention is widely applicable to not only wireless communication systems but also communication systems using an LDPC-CC (e.g. power line communication system).