Abstract:
Radio communication system includes radio transmitter containing unit dividing transmission data into first-code blocks each having N-bit data, unit adding error detection codes to first-code blocks, unit assigning first-code blocks to second-code blocks each including M carriers each having L symbols, and unit transmitting second-code blocks, and radio receiver containing unit receiving second-code blocks, unit converting second-code blocks into first-code blocks, based on values of M and L, unit subjecting first-coded blocks to error correction decoding, unit detecting error of code block of first-code blocks subjected to error correction decoding, unit generating retransmission-request signal for requesting retransmission of code block including error, if error is detected, and unit transmitting retransmission-request signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a Continuation Application of PCT Application No. PCT/JP2006/300899, filed Jan. 16, 2006, which was published under PCT Article 21(2) in English. 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-010702, filed Jan. 18, 2005, the entire contents of which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a multi-carrier radio communication system and, more particularly, to a radio communication system, radio transmission apparatus and radio reception apparatus for error correction in retransmission. 
   2. Description of the Related Art 
   In a conventional retransmission control scheme in multi-carrier communication, a mobile station and a base station generally perform the following processes (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2004-104574). The mobile station measures a reception channel quality for each carrier or carrier group, and transmits information about the measured reception channel quality to the base station. When an error is found in received data from the base station, the mobile station issues a retransmission request to the base station. Upon reception of the retransmission request, the base station transmits retransmission data to the mobile station. In this case, the base station transmits this retransmission data using a carrier other than the carrier or carrier group determined to be unusable based on the reception channel quality. The mobile station then demodulates this retransmission data. 
   However, in the above-described prior art, a channel response estimation means is required to accurately determine channel responses. A large overhead is also required to feed back, to the transmission side, the information of the channel responses and carrier to be used. Additionally, it is a challenge to increase a system throughput in communication, and decrease a processing amount for retransmission control and channel response estimation. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the invention, there is provided a radio communication system comprising:
         a radio transmitter comprising: a division unit configured to divide transmission data into a plurality of first code blocks each having N-bit data (N is an integer of not less than 1); an addition unit configured to add a plurality of error detection codes to the first code blocks, respectively; an assignment unit configured to assign the first code blocks to a plurality of second code blocks each including M (M is an integer of not less than 1 and not more than a carrier count) carriers each having L (L is an integer of not less than 1) symbols; and a transmission unit configured to transmit the second code blocks to which the first code blocks are assigned; and   a radio receiver comprising: a reception unit configured to receive the second code blocks transmitted by the transmission unit; a conversion unit configured to convert the received second code blocks into the first code blocks to which the error detection codes are added, based on values of M and L; a correction decoding unit configured to subject the first coded blocks obtained by the conversion unit to error correction decoding; a detection unit configured to detect an error of at least one code block of the first code blocks subjected to the error correction decoding; a generation unit configured to generate a retransmission request signal for requesting a retransmission of the code block including the error, if the error is detected by the detection unit; and a transmission unit configured to transmit the retransmission request signal, and   the radio transmitter further comprising: a reception unit configured to receive the retransmission request signal from the radio receiver; a count unit configured to count number of times of reception of the retransmission request signal; and a change unit configured to change values of M and L in accordance with the counted number.       

   In accordance with a second aspect of the invention, there is provided a radio communication system comprising:
         a radio transmitter comprising: a division unit configured to divide transmission data into a plurality of first code blocks each having N-bit data (N is an integer of not less than 1); an addition unit configured to add a plurality of error detection codes to the first code blocks, respectively; an assignment unit configured to assign the first code blocks to a plurality of second code blocks each including M (M is an integer of not less than 1 and not more than a carrier count) carriers each having L (L is an integer of not less than 1) symbols; and a transmission unit configured to transmit the second code blocks to which the first code blocks are assigned; and   a radio receiver comprising: a reception unit configured to receive the second code blocks transmitted by the transmission unit; a conversion unit configured to convert the received second code blocks into the first code blocks to which the error detection codes are added, based on first values of M and L; a correction decoding unit configured to subject the first coded blocks obtained by the conversion unit to error correction decoding; a detection unit configured to detect an errors of at least one code block of the first code blocks subjected to the error correction decoding; a generation unit configured to generate a retransmission request signal for requesting a retransmission of the code block including the error, if the error is detected by the detection unit; and a transmission unit configured to transmit the retransmission request signal; and   the radio transmitter further comprising: a reception unit configured to receive the retransmission request signal from the radio receiver; a calculation unit configured to calculate an error rate indicating an error detection degree in the code block in correspondence with the first values of M and L based on the retransmission request signal; an error rate storage unit configured to store the error rate in correspondence with the first values of M and L; and a change unit configured to change the first values of M and L to second values of M and L corresponding to the code block with an error rate lower than the error rate corresponding to the first values of M and L, with reference to the stored error rate.       

   In accordance with a third aspect of the invention, there is provided a radio transmission apparatus comprising: a transmission unit configured to multiplex carriers in a frequency direction and transmits data to a partner apparatus; and a change unit configured to change, for each retransmission of the data, a combination of a carrier count and a symbol count for determining a code block which is a minimum unit for error detection of the data, based on a channel response between the radio transmission apparatus and the partner apparatus. 
   In accordance with a fourth aspect of the invention, there is provided a radio reception apparatus comprising: a reception unit configured to receive a plurality of first code blocks each including M (M is an integer of not less than 1 and not more than a carrier count) carriers each having L (L is an integer of not less than 1) symbols; a conversion unit configured to convert the received first code blocks into a plurality of second code blocks each having N bit data (N is an integer of not less than 1) to which the error detection codes are added, based on values of M and L; a correction decoding unit configured to subject the second coded blocks obtained by the conversion unit to error correction decoding; a detection unit configured to detect an error of at least one code block of the first code blocks subjected to the error correction decoding; and a generation unit configured to generate a retransmission request signal for requesting a retransmission of the code block including the error, if the error is detected by the detection unit. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a view showing transmission and reception of a signal between radio communication systems according to an embodiment of the present invention; 
       FIG. 2  is a graph showing an example of the frequency characteristics of a transmission signal used in the radio communication system according to the embodiment of the present invention; 
       FIG. 3  is a graph showing another example of the frequency characteristics of the transmission signal used in the radio communication system according to the embodiment of the present invention; 
       FIG. 4  is a flowchart showing an example of processes in a transmitter and a receiver according to the first embodiment of the present invention; 
       FIG. 5  is a block diagram showing the transmitter according to the first embodiment of the present invention; 
       FIG. 6  is a block diagram showing the receiver according to the first embodiment of the present invention; 
       FIG. 7  is a graph showing an example of a code block mapping pattern according to the embodiment of the present invention; 
       FIG. 8  is a graph showing another example of the code block mapping pattern according to the embodiment of the present invention; 
       FIG. 9  is a graph showing a state wherein a multi-path has a low temporal spread, and errors in carriers tend to simultaneously occur in the code block mapping pattern shown in  FIG. 8 ; 
       FIG. 10  is a graph showing a state wherein the multi-path has the low temporal spread, and the errors in carriers tend to simultaneously occur in the code block mapping pattern shown in  FIG. 7 ; 
       FIG. 11  is a graph showing a state wherein a multi-path has a small temporal variation, and errors in a specific carrier occur over some symbols in the code block mapping pattern shown in  FIG. 7 ; 
       FIG. 12  is a graph showing a state wherein a multi-path has a small temporal variation, and errors in the specific carrier occur over some symbols in the code block mapping pattern shown in  FIG. 8 ; 
       FIG. 13  is a flowchart showing an example of processes in a transmitter and a receiver according to the second embodiment of the present invention; 
       FIG. 14  is a block diagram showing the transmitter according to the second embodiment of the present invention; 
       FIG. 15  is a block diagram showing the receiver according to the second embodiment of the present invention; 
       FIG. 16  is a flowchart showing an example of processes in a transmitter and a receiver according to the third embodiment of the present invention; 
       FIG. 17  is a block diagram showing the transmitter according to the third embodiment of the present invention; 
       FIG. 18  is a block diagram showing the receiver according to the third embodiment of the present invention; 
       FIG. 19  is a flowchart showing an example of processes in a transmitter and a receiver according to the fourth embodiment of the present invention; 
       FIG. 20  is a block diagram showing the transmitter according to the fourth embodiment of the present invention; 
       FIG. 21  is a block diagram showing the receiver according to the fourth embodiment of the present invention; 
       FIG. 22  is a flowchart showing an example of processes in a transmitter and a receiver according to the fifth embodiment of the present invention; 
       FIG. 23  is a block diagram showing a receiver configuration according to the fifth embodiment of the present invention; 
       FIG. 24  is a flowchart showing an example of processes in a transmitter and a receiver according to the sixth embodiment of the present invention; 
       FIG. 25  is a block diagram showing a transmitter configuration according to the sixth embodiment of the present invention; and 
       FIG. 26  is a block diagram showing a receiver configuration according to the sixth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A radio communication system, a radio transmission apparatus and radio reception apparatus will be described in detail below with reference to accompanying drawing according to an embodiment of the present invention. 
   As shown in  FIG. 1 , the radio communication system in the embodiment includes a transmitter  101  and a receiver  102 . The transmitter  101  and the receiver  102  perform radio communication with each other using a multi-carrier signal multiplexed on the frequency axis. The transmitter  101  transmits a transmission signal  103  to the receiver  102 . When the receiver  102  cannot correctly receive the transmission signal  103 , the receiver  102  issues a retransmission request signal  104  to the transmitter  101 . Upon reception of the retransmission request signal  104 , the transmitter  101  retransmits, to the receiver  102 , the data requested to be retransmitted. 
   The frequency characteristics of the transmission signal  103  used in the multi-carrier radio communication system of the embodiment will be described in detail below with reference to  FIGS. 2 and 3 . 
   The transmission signal  103  is the multi-carrier signal multiplexed on the frequency axis. A carrier multiplexing scheme of the transmission signal  103  is not particularly limited. For example, the carrier of the transmission signal  103  may be multiplexed using an orthogonal frequency as shown in  FIG. 2 , or a guard band as shown in  FIG. 3 . 
   The embodiment of the present invention has been made to solve the above problems, and has as its object to provide a radio communication system, radio transmission apparatus and radio reception apparatus for decreasing a retransmission count and increasing a throughput. 
   In the radio communication system, radio transmission apparatus and radio reception apparatus according to the embodiment of the present invention, the retransmission count can decrease, and the system throughput can increase. 
   First Embodiment 
   The processes in a transmitter  101  and a receiver  102  according to the first embodiment will be exemplified below with reference to  FIG. 4 . In the first embodiment, a code block mapping pattern used in the transmitter  101  and the receiver  102  is set in advance, or determined by using the same algorithm and data in the transmitter  101  and the receiver  102 . Note that the code block mapping pattern is a combination of a carrier count M and a symbol count L (M and L are natural numbers) to which a code block is assigned. The code block is a minimum unit for performing error detection. 
   First, before data transmission, each of the transmitter  101  and the receiver  102  performs a code block mapping pattern determination process (steps S 401  and S 402 ) for transmitting and receiving data. In this code block mapping pattern determination process, a given code block mapping pattern is selected from a plurality of code block mapping pattern candidates. These code block mapping pattern candidates are determined from the code block mapping patterns transmitted and received between the transmitter  101  and the receiver  102  at the timing when synchronization between the transmitter  101  and the receiver  102  is established. In this case, assume that the code block mapping pattern is notified from an upper layer. Alternatively, the code block mapping pattern may be uniquely determined based on information notified from the transmitter  101 , or the unique index of the receiver  102 . 
   The transmitter  101  then performs a transmission process for transmission data by using the code block mapping pattern selected in step S 401  (step S 403 ). This transmission process includes processes such as code block division, error detection code addition, error correction encoding, interleaving, code block mapping, modulation, and the like. In this example, the data is divided into code blocks D 1  to D 4 , and then transmitted. 
   Assume that during data transmission from the transmitter  101  to the receiver  102 , errors occur due to any reason in the code blocks D 1 , D 2 , and D 3 . The receiver  102  performs a data reception process (step S 404 ). If the error cannot be corrected even when the receiver  102  performs the reception process for the data in which the error has occurred, the receiver  102  issues, to the transmitter  101 , a retransmission request of the code blocks D 1 , D 2 , and D 3  in which the errors have not been corrected. In this case, the reception process includes processes such a channel response estimation, channel response correction, demodulation, code block demapping, deinterleaving, error correction decoding, error detection, and the like. 
   In accordance with the transmission count of the retransmission request, the receiver  102  changes the code block mapping pattern in the code block mapping pattern determination process (step S 405 ). In accordance with the reception count of the retransmission request, the transmitter  101  changes the code block mapping pattern in the code block mapping pattern determination process (step S 406 ). As described above, after changing the code block mapping pattern, the transmitter  101  performs the transmission process for the retransmission data D 1 , D 2 , and D 3 , and, e.g., new data D 5 , and then transmits these data to the receiver  102  (step S 407 ). In accordance with the code block mapping pattern determined in step S 405 , the receiver  102  performs the reception process for the transmitted data (step S 408 ). 
   The transmitter  101  according to the first embodiment will be described below with reference to  FIG. 5 . 
   The transmitter  101  includes a code block division unit  501 , error detection code addition unit  502 , error correction encoding unit  503 , interleaving unit  504 , code block mapping unit  505 , QPSK (quadrature phase-shift keying) modulation unit  506 , IFFT (inverse fast Fourier transformer)  507 , P/S (parallel-to-serial conversion) unit  508 , GI (guard interval) insertion unit  509 , DAC (digital-to-analog converter)  510 , IF/RF (intermediate-frequency/radio frequency) units  511  and  512 , ADC (analog-to-digital converter)  513 , reception processing unit  514 , division processing unit  515 , retransmission control unit  516 , and code block mapping control unit  517 . 
   The code block division unit  501  divides the data transmitted from the transmitter  101  into C code blocks each having N-bit data. 
   The error detection code addition unit  502  adds an error detection parity bit to the N-bit data divided in the code blocks. For example, the error detection parity bit which is added by the error detection code addition unit  502  is a CRC (cyclic redundancy check code) parity bit. 
   The error correction encoding unit  503  performs an error correction encoding process for the data to which the parity bit is added by the error detection code addition unit  502 . For example, the error correction encoding unit  503  performs the error correction encoding process such as a convolution encoding, turbo encoding, and LDPC (low-density parity check) encoding. The interleaving unit  504  performs an interleaving process for the data which has undergone the error correction encoding process by the error correction encoding unit  503 . 
   The code block mapping unit  505  assigns data having L symbols to each of M carriers. In this case, N_enc=M×L holds when a bit count after encoding the code block is set to N_enc. Also, n=M×C holds when the total carrier count is set to n. Hence, the code block mapping unit  505  assigns C code block data to each of the n carriers. The carrier count M and the symbol count L are determined by the code block mapping control unit  517  described later. 
   The QPSK modulation unit  506  maps the data assigned to the n carriers into a plane with an I signal and a Q signal. In the first embodiment, QPSK is exemplified as a modulation scheme. However, another modulation scheme such as QAM (quadrature amplitude modulation) and π/4 shift QPSK can also be used. 
   The IFFT  507  inversely Fourier-transforms the QPSK-modulated signal, and converts the transformed signal into a signal on an orthogonal frequency. In this embodiment, OFDM (orthogonal frequency division multiplexing) for assigning the carrier to the orthogonal frequency as in  FIG. 2  is used. However, FDM (frequency division multiplexing) for inserting the guard band is also possible as in  FIG. 3 . After that, by parallel-to-serial conversion, the P/S unit  508  converts, into a serial signal, a parallel signal inversely Fourier-transformed by the IFFT  507 . 
   The GI insertion unit  509  inserts the GI to the serial signal output from the P/S unit  508 . The DAC  510  performs digital-to-analog conversion (to be referred to as DAC hereinafter) to convert the signal to which the GI is inserted, into the analog signal. The IF/RF unit  511  performs intermediate frequency conversion and radio frequency conversion to convert the signal output from the DAC  510  into the radio frequency signal. The converted signal is transmitted from an antenna to the receiver  102 . 
   The IF/RF unit  512  converts the signal which has been transmitted from the receiver  102  and received by the antenna into a baseband frequency signal. The ADC  513  performs analog-to-digital conversion (to be referred to ADC hereinafter) to digitize the received signal which is converted into the baseband frequency signal. The reception processing unit  514  demodulates the received signal converted into the digital signal, performs error correction decoding, and the like. The reception processing unit  514  corresponds to a transmission processing unit  617  (described later) in the receiver  102 . The reception processing unit  514  and the transmission processing unit  617  can employ any communication scheme as far as the reception processing unit  514  and the transmission processing unit  617  have the same scheme. 
   The division processing unit  515  divides the received signal obtained from the reception processing unit  514  into the reception data and a retransmission request signal if present. The retransmission control unit  516  uses the retransmission request signal to determine a specific packet to be retransmitted. 
   The retransmission control unit  516  instructs the upper layer to perform a retransmission procedure for the packet requested to be retransmitted. The retransmission control unit  516  also issues a request to change the code block mapping pattern in retransmission. 
   Upon reception of a request to change the code block mapping pattern, the code block mapping control unit  517  changes the code block mapping pattern. For example, the code block mapping control unit  517  counts the number of times of reception of the retransmission request signal from the receiver  102 . When the retransmission request signal is received a predetermined number of times, the code block mapping control unit  517  changes the code block mapping pattern. The type of code block mapping pattern to be changed will be described in more detail below with reference to  FIGS. 7 and 8 . 
   The receiver  102  according to the first embodiment will be described with reference to  FIG. 6 . 
   The receiver  102  includes an IF/RF unit  601 , ADC  602 , GI removing unit  603 , S/P unit  604 , FFT  605 , channel response estimation unit  606 , channel response correction unit  607 , QPSK demodulation unit  608 , code block demapping unit  609 , deinterleaving unit  610 , error correction decoding unit  611 , error detection unit  612 , code block concatenation unit  613 , retransmission request processing unit  614 , code block demapping control unit  615 , multiplex processing unit  616 , transmission processing unit  617 , DAC  618 , and IF/RF unit  619 . 
   The IF/RF unit  601  converts the received signal which has been transmitted from the transmitter  101  and received by the antenna, into the baseband frequency signal. The ADC  602  digitizes the baseband frequency signal. The GI removing unit  603  removes the GI from the received signal which has been digitized. The S/P unit  604  converts the signal from which the GI is removed, into n parallel signals. The FFT  605  converts these parallel signals into time axis signals. 
   The channel response estimation unit  606  estimates a channel response by using a known signal such as a pilot signal included in the received signal. The channel response correction unit  607  corrects distortion of the channel response by using the channel response estimated by the channel response correction unit  607 . 
   The QPSK demodulation unit  608  QPSK-demodulates the signal whose channel response is corrected. This demodulation process corresponds to a modulation process performed by the QPSK modulation unit  506  in the transmitter  101 . Hence, when the transmitter  101  employs another modulation scheme in the modulation process, the receiver  102  also employs a demodulation scheme corresponding to the modulation scheme of the transmitter  101  in the demodulation process. 
   The code block demapping unit  609  converts the n parallel signals output from the QPSK demodulation unit  608  into the C code blocks each having M carriers and L symbols. In this case, the carrier count M and the symbol count L are designated by the code block demapping control unit  615 . 
   Each of the deinterleaving unit  610  inputs the code block output from the code block demapping unit  609 , and performs the deinterleaving process. Each of the error correction decoding units  611  performs the error correction decoding process for the deinterleaved signal. The error correction decoding unit  611  also performs an error correction decoding process, e.g., Viterbi decoding, turbo decoding, and LDPC decoding corresponding to the error correction encoding unit  503  of the transmitter  101 . 
   Each of the error detection units  612  inputs an output signal from the error correction decoding unit  611 , and detects whether an error occurs in the received signal having undergone the error correction decoding process. The error detection unit  612  detects the error by using the parity bit added by the error detection code addition unit  502  in the transmitter  101 . When no error is detected in the received signal, the error detection unit  612  outputs the signal to the code block concatenation unit  613 . The code block concatenation unit  613  concatenates the code blocks to each other, and outputs the concatenated code blocks as the reception data. 
   Alternatively, when the errors are detected in one or more code blocks, the error detection unit  612  specifies the code block in which the error is detected, and then outputs the signal indicating the specified code block to the retransmission request processing unit  614 . The retransmission request processing unit  614  outputs the retransmission request signal to request the retransmission process. 
   Upon reception of the retransmission request information from the retransmission request processing unit  614 , the code block demapping control unit  615  changes the code block mapping pattern based on this information. The change algorithm of the code block demapping control unit  615  is the same as that of the code block mapping control unit  517  of the transmitter  101 . 
   The retransmission request signal generated by the retransmission request processing unit  614  may include information serving as the code block mapping pattern which is determined between the transmitter  101  and the receiver  102  in advance. The code block mapping pattern may be determined on the system in advance. Alternatively, some code block mapping patterns may be stored in the retransmission request processing unit  614 , and the transmitter  101  and the receiver  102  may be controlled in advance to have the same code block mapping pattern. 
   The multiplex processing unit  616  multiplexes the retransmission request information with the transmission data. For example, the multiplex processing unit  616  multiplexes the plurality of data using time multiplexing, frequency multiplexing, or code multiplexing. The transmission processing unit  617  modulates the transmission signal output from the multiplex processing unit  616 , and performs the error correction encoding and the like. The transmission processing unit  617  corresponds to the reception processing unit  514  in the transmitter  101 . The DAC  618  converts the output signal from the transmission processing unit  617  into an analog signal. The IF/RF unit  619  performs intermediate frequency conversion and radio frequency conversion to convert this analog signal into the radio frequency signal. The converted signal is transmitted from the antenna to the transmitter  101 . 
   An example of the code block mapping pattern will be described below with reference to  FIGS. 7 and 8 . 
     FIGS. 7 and 8  show an example of the code block mapping pattern. In this example, the carrier count n is 16. Two sets of pilot symbols each including two symbols in front and rear positions, and a data symbol including  16  symbols are time-multiplexed to form one data slot. In the example shown in  FIGS. 7 and 8 , four code blocks # 1  to # 4  are provided. One data slot includes these code blocks and the pilot symbols in the front and rear of each of these code blocks. For example, two data slots are shown in  FIGS. 7 and 8 . The data symbol and pilot symbol are multiplexed in a frequency multiplexing scheme, a code multiplexing scheme, or the like. 
     FIG. 7  shows the example of the code block mapping pattern for assigning the four carriers to one code block.  FIG. 8  shows the example of the code block mapping pattern for assigning the  16  carriers to one code block. For example, when the transmitter  101  receives the retransmission request signal K (K is an integer equal to or larger than 1) times during transmission using the code block mapping pattern as shown in  FIG. 7 , the code block mapping control unit  517  changes the code block mapping pattern to that shown in  FIG. 8 . Alternatively, when the transmitter  101  receives the retransmission request signal K times during transmission using the code block mapping pattern as shown in  FIG. 8 , the code block mapping control unit  517  changes the code block mapping pattern to that shown in  FIG. 7 . 
   A state wherein a data error occurs in the carrier in accordance with the channel response will be described below with reference to  FIGS. 9 ,  10 ,  11 , and  12 .  FIGS. 9 and 10  show a state wherein a multi-path has a low temporal spread, and errors in carriers tend to occur at the same time. 
   In this channel response, as in  FIG. 9 , when the code block mapping unit  505  maps to assign the code block to the  16  carriers, the errors occur in most data such as the code blocks  901 ,  904 ,  906 , and  908  at a high probability. As a result, many errors cannot be corrected because the error correction limit of the error correction decoding unit  611  is exceeded. Unlike in the case shown in  FIG. 9 , when the code block mapping unit  505  maps to assign the code block to the four carriers as shown in  FIG. 10 , a code block error occurrence rate (to be simply referred to as an error rate) is divided into the code blocks. Hence, the error can be corrected by deinterleaving of the deinterleaving unit  610 , and the error correction decoding process of the error correction decoding unit  611  at a high probability. Note that the code block error rate is expressed by the (number of error code blocks of transmitted code blocks)/(number of transmitted code blocks). 
   Alternatively,  FIGS. 11 and 12  show a state wherein a multi-path has a small temporal variation, and errors in a specific carrier occur over some symbols. In this channel response state, as shown in  FIG. 11 , when the code block mapping unit  505  maps to assign the code block to the four carriers, the errors occur in most data such as the code blocks  1101 ,  1103 ,  1106 , and  1108  at a high probability. As a result, many errors cannot be corrected because the error correction limit of the error correction decoding unit  611  is exceeded. Unlike in the case shown in  FIG. 11 , when the code block mapping unit  505  maps to assign the code block to the  16  carriers as shown in  FIG. 12 , a code block error rate is divided into the code blocks. Hence, the error can be corrected by deinterleaving of the deinterleaving unit  610 , and the error correction decoding process of the error correction decoding unit  611  at a high probability. 
   As described above, since the code block mapping unit  505  changes the code block mapping pattern, the error rate changes in accordance with the channel response after error correction decoding is performed by the error correction decoding unit  611 . 
   As described above, in the radio communication system according to the first embodiment, when the error occurs in the data symbol, the code block mapping pattern shape is changed. Accordingly, the error rate in accordance with the channel response can decrease. Hence, in the radio communication system according to the first embodiment, the retransmission count of the overall system can decrease, and the system throughput can increase without a large overhead for the processes such as estimation and feedback of the channel response, and the throughput. 
   Second Embodiment 
   The processes of a transmitter  101  and a receiver  102  according to the second embodiment will be exemplified below with reference to  FIG. 13 . In the second embodiment, the transmitter  101  includes a database which stores an error rate for each code block mapping pattern, and updates this database every time a retransmission request is received. The receiver  102  estimates the code block mapping pattern of the data from the transmitter  101 . Note that the same reference numerals as in  FIG. 4  in the first embodiment denote the same steps in  FIG. 13 , and a description thereof will be omitted. 
   The transmitter  101  performs processes in steps S 401  and S 403 . In step S 401 , a code block mapping pattern with the low error rate is selected from code block mapping pattern candidates obtained by negotiation between the transmitter  101  and the receiver  102  when synchronization is established. The code block mapping pattern candidates may be determined as a system in advance, or uniquely determined based on information notified from the transmitter  101  or a unique index of the receiver  102 . 
   In this case, unlike the first embodiment, the receiver  102  does not perform a code block mapping pattern determination process. 
   Since the receiver  102  does not know the code block mapping pattern transmitted from the transmitter  101 , the receiver  102  performs a mapping pattern blind estimation process for estimating the code block mapping pattern transmitted from the transmitter  101  (step S 1301 ). In this estimation process, the receiver  102  estimates the code block mapping pattern used to transmit data D 1  to D 4  from the transmitter  101 . 
   In this estimation process, for example, a reception process is performed using all the patterns of the code block mapping pattern candidates, and the code block mapping pattern in which no error is detected is estimated to be the code block mapping pattern used by the transmitter  101 . 
   Assume that during data transmission from the transmitter  101  to the receiver  102 , errors occur due to any reason in the code blocks D 1 , D 2 , and D 3 . That is, when the data reception process is performed by using the code block mapping pattern estimated in step S 1301 , errors are detected in the code blocks D 1 , D 2 , and D 3  (step S 404 ). The receiver  102  issues, to the transmitter  101 , the retransmission request of the code blocks D 1 , D 2 , and D 3  in which the errors cannot be corrected. 
   Upon reception of the retransmission request from the receiver  102 , the transmitter  101  updates the database which stores the block error rate of the code block mapping pattern (step S 1302 ). In accordance with the number of times of reception of the retransmission request, the transmitter  101  changes the code block mapping pattern in the code block mapping pattern determination process (step S 1303 ). In step S 1303 , with reference to the preceding transmitted code block mapping pattern and the error rate for each code block mapping pattern, the code block mapping pattern used for retransmission is determined. In step S 1303 , for example, when the relationship between a carrier count M and a symbol count L of the preceding transmitted code block mapping pattern is expressed by M&gt;L, a code block mapping pattern with the lowest error rate is selected from the code block mapping patterns in which the relationship between the carrier count M and the symbol count L of the code block mapping pattern to be used for retransmission is expressed by M&lt;L. Alternatively, in step S 1303 , when the relationship of the preceding transmitted code block mapping pattern is expressed by M&lt;L, a code block mapping pattern with the lowest error rate is selected from the code block mapping patterns in which the relationship between M and L of the code block mapping pattern for retransmission is expressed by M&gt;L. 
   After changing the code block mapping pattern, the transmitter  101  performs a transmission process in step S 407 . As in processes in steps S 1301  and S 404 , the receiver  102  performs a mapping pattern blind estimation process, and a data reception process by using a data reception process. 
   The transmitter  101  according to the second embodiment will be described below with reference to  FIG. 14 . Note that the same reference numerals as in  FIG. 5  in the first embodiment denote the same components in  FIG. 14 , and a description thereof will be omitted. 
   A code block mapping error rate measurement unit  1401  records pieces of information of the carrier count M and symbol count L in the code block used for code block mapping of a code block mapping control unit  1402 , and pieces of information of the carrier count M and symbol count L and its error rate which are transmitted based on the number of the code block requested to be retransmitted by the receiver  102 , while updating the pieces of information every time the retransmission request is issued. 
   The code block mapping control unit  1402  determines the carrier count M and symbol count L of the code block, and outputs the information of the carrier count M and symbol count L to a code block mapping unit  505 . With reference to the error rate for each code block mapping pattern stored in the code block mapping error rate measurement unit  1401 , the code block mapping control unit  1402  determines the carrier count M and symbol count L. 
   The receiver  102  according to the second embodiment will be described below with reference to  FIG. 15 . Note that the same reference numerals as in  FIG. 4  in the first embodiment denote the same components in  FIG. 15 , and a description thereof will be omitted. 
   A buffer  1501  temporarily stores a signal which has undergone a QPSK demodulation process by the QPSK demodulation unit  608 . After that, processes are performed by the respective units from a code block demapping unit  609  to an error detection unit  612 . The receiver  102  repeats these processes for each code block mapping pattern candidate. That is, the receiver  102  performs the processes of the respective units from the code block demapping unit  609  to the error detection unit  612  for the possible values of M and L. 
   A block mapping pattern estimation unit  1502  includes a storage unit which stores all the patterns of the code block mapping pattern candidates. That is, the block mapping pattern estimation unit  1502  stores the values of M and L corresponding to each of all the code block mapping patterns. 
   The block mapping pattern estimation unit  1502  estimates that the code block mapping pattern with the lowest error rate of the code block mapping patterns processed in the units from the code block demapping unit  609  to the error detection unit  612  is the code block mapping pattern which has been used in transmission. When performing decoding process using this code block mapping pattern, a retransmission request processing unit  614  generates a retransmission request signal of the code block in which the error has been detected. 
   As described above, in the radio communication system according to the second embodiment, the transmitter selects and transmits the code block mapping pattern with the low error rate to reliably decrease the error rate. Hence, in the radio communication system according to the second embodiment, the retransmission count of the overall system can decrease, and the system throughput can increase without a large overhead for the processes such as estimation and feedback of the channel response, and the throughput. 
   Third Embodiment 
   The processes of a transmitter  101  and a receiver  102  according to the third embodiment will be exemplified below with reference to  FIG. 16 . In the third embodiment, the transmitter  101  includes a database which stores an error rate for each code block mapping pattern, and updates this database every time a retransmission request is received. The receiver  102  estimates the code block mapping pattern of the data from the transmitter  101 . Note that the same reference numerals as in  FIG. 4  in the first embodiment denote the same steps in  FIG. 16 , and a description thereof will be omitted. 
   The transmitter  101  performs processes in steps S 401  and S 403 , and the receiver  102  performs step S 402 . Assume that an error occurs between the transmitter  101  and the receiver  102  due to any reason in the code blocks D 1 , D 2 , and D 3 , and the receiver  102  cannot correct the errors in the data in the reception process in step S 404 . 
   The error rate of the code block mapping pattern used in transmission is updated (step S 1601 ). When the error is detected in the reception process in step S 404 , the receiver  102  issues a retransmission request to the transmitter  101 , and determines the code block mapping pattern by using information of the error rate for each code block mapping pattern (step S 1602 ). The receiver  102  multiplexes the retransmission request and the code block mapping pattern, and transmits the multiplexed retransmission request and the code block mapping pattern to the transmitter  101 . 
   In the third embodiment, the retransmission request of the code blocks D 1 , D 2 , and D 3  and the code block mapping pattern are multiplexed and transmitted. In step S 1602 , when the relationship between the carrier count M and the symbol count L of the preceding transmitted code block mapping pattern is expressed by M&gt;L, the code block mapping pattern with the low error rate for retransmission is selected from the code block mapping patterns in which the relationship is expressed by M&lt;L. Alternatively, when the relationship between the carrier count M and the symbol count L is expressed by M&lt;L, the code block mapping pattern with the low error rate for retransmission is selected from the code block mapping patterns in which the relationship between the carrier count M and the symbol count L is expressed by M&gt;L. The code block mapping pattern information fed back to the transmitter  101  may be the carrier count M and the symbol count L, or the index for uniquely determining M and L. For example, this index makes the values of M and L correspond to one numerical value. In accordance with this index, a transmission data amount can be reduced. 
   Upon reception of the retransmission request from the receiver  102 , the transmitter  101  reads the code block mapping pattern information multiplexed with the retransmission request, and determines the code block mapping pattern (step S 1603 ). After that, a transmission process is performed by using the code block mapping pattern obtained in step S 1603  to transmit data (step S 407 ). In this case, upon reception of the retransmission request of the code blocks D 1 , D 2 , and D 3 , the code blocks D 1 , D 2 , and D 3 , and a new data D 5  are transmitted. 
   The receiver  102  performs a reception process for the signal from the transmitter  101  by using the code block mapping pattern obtained in step S 1602  (step S 408 ), updates an error rate update process for each code block mapping pattern in accordance with an error detection result in the reception process (step S 1604 ), and shifts to a standby state for the next code block mapping pattern determination process. 
   The transmitter  101  according to the third embodiment will be described below with reference to  FIG. 17 . Note that the same reference numerals as in  FIG. 5  in the first embodiment denote the same components in  FIG. 17 , and a description thereof will be omitted. 
   A division processing unit  1701  divides the code block mapping pattern information multiplexed with the retransmission request, and the reception data which are transmitted from the receiver  102 . A code block mapping control unit  517  inputs the code block mapping pattern information, and sets the input information to the code block mapping pattern corresponding to the input information. The initial value of the code block mapping pattern is uniquely determined commonly to the receiver  102 . 
   A retransmission control unit  1702  instructs, to an upper layer, a procedure of retransmitting the packet required to be retransmitted. Unlike a retransmission control unit  516 , the retransmission control unit  1702  does not request to the code block mapping control unit  517  to change the code block mapping pattern in retransmission. 
   The receiver  102  according to the third embodiment will be described with reference to  FIG. 18 . Note that the same reference numerals as in  FIG. 6  in the first embodiment denote the same components in  FIG. 18 , and a description thereof will be omitted. 
   A code block mapping error rate measurement unit  1801  records pieces of information of the carrier count M and symbol count L in the code block used for code block mapping of a code block demapping control unit  1802 , and pieces of information of the carrier count M and symbol count L and its error rate which are transmitted based on the number of the code block requested to be retransmitted, while updating the pieces of information every time the retransmission request is issued. 
   The code block demapping control unit  1802  determines the carrier count M and symbol count L of the code block, and outputs the information of the carrier count M and symbol count L to a code block demapping unit  609 . With reference to the error rate for each code block mapping stored in the code block demapping error rate measurement unit  1801 , the code block demapping control unit  1802  determines the carrier count M and symbol count L. 
   A multiplex processing unit  1803  multiplexes the code block mapping pattern information and the retransmission request information together with the transmission data. 
   As described above, in the radio communication system according to the third embodiment, since the receiver selects the code block mapping pattern with the low error rate and feeds back the selected code block mapping pattern to the transmitter, the error rate can be reliably decreased. Hence, in the radio communication system according to the third embodiment, the retransmission count of the overall system can decrease, and the system throughput can increase without a large overhead for the process such as estimation of the channel response, and the throughput. 
   Fourth Embodiment 
   An example of the process of a transmitter  101  and a receiver  102  according to the fourth embodiment will be described below with reference to  FIG. 19 . In the fourth embodiment, the transmitter  101  includes a database which stores an error rate for each code block mapping pattern, and updates this database every time a retransmission request is received. The transmitter  101  transmits not only data but also its code block mapping pattern information. Note that the same reference numerals as in  FIGS. 4 and 13  in the first embodiment and second embodiment denote the same steps in  FIG. 19 , and a description thereof will be omitted. 
   The transmitter  101  performs code block mapping pattern determination process (step S 1901 ). The determined code block mapping pattern information is multiplexed to the transmission data. The multiplexed code block mapping pattern information may be a carrier count M and symbol count L, or an index for uniquely determining M and L. 
   The transmitter  101  then processes the transmission data in step S 403  (step S 1902 ). The transmitter  101  transmits the transmission data and the code block mapping pattern information to the receiver  102  (step S 1902 ). 
   Assume that an error occurs due to any reason between the transmitter  101  and the receiver  102 , and errors occur in code blocks D 1 , D 2 , and D 3 . The receiver  102  determines the code block mapping pattern from the multiplexed code block mapping pattern information (step S 1903 ). Assume that errors are detected in the code blocks D 1 , D 2 , and D 3  as a result of the data reception process in step S 404  by using the determined code block mapping pattern. The receiver  102  issues, to the transmitter  101 , the retransmission request of the code blocks D 1 , D 2 , and D 3  in which the errors cannot be corrected. 
   Upon reception of the retransmission request from the receiver  102 , the transmitter  101  performs an error rate update process for each mapping pattern in step S 1302 . The transmitter  101  performs a mapping pattern determination process in step S 1303 . After changing the code block mapping pattern, the transmitter  101  performs the transmission process for the retransmission data D 1 , D 2 , and D 3 , and a new data D 5  to transmit the code block mapping pattern information and data to the receiver  102  (step S 1904 ). 
   The receiver  102  then performs the mapping pattern determination process as in step S 1903  (step S 1905 ), and the reception process as in step S 404  (step S 408 ). 
   The transmitter  101  according to the fourth embodiment will be described with reference to  FIG. 20 . Note that the same reference numerals as in  FIGS. 5 and 14  in the first embodiment and second embodiment denote the same components in  FIG. 20 , and a description thereof will be omitted. 
   A code block mapping control unit  2001  determines the carrier count M and the symbol count L of the code block, and outputs the information of the carrier count M and the symbol count L to a code block mapping unit  505 . With reference to an error rate for each code block mapping stored in a code block mapping error rate measurement unit  1401 , the code block mapping control unit  2001  determines the carrier count M and the symbol count L. The code block mapping pattern information containing the information of the carrier count M and the symbol count L is output to a transmission processing unit  2002 . 
   The transmission processing unit  2002  performs the transmission process for the code block mapping pattern information output from the code block mapping control unit  2001 . This transmission process includes processes such as error detection code addition, error correction encoding, interleaving, modulation, and the like. 
   A multiplex processing unit  2003  multiplexes the transmission data output from a GI insertion unit  509 , and the code block mapping pattern information output from the transmission processing unit  2002 . The multiplex processing unit  2003  multiplexes data by time division multiplexing, frequency multiplexing, or diffusion code multiplexing, or specified carrier mapping. 
   The receiver  102  according to the fourth embodiment will be described below with reference to  FIG. 21 . Note that the same reference numerals as in  FIG. 6  in the first embodiment denote the same components in  FIG. 21 , and a description thereof will be omitted. 
   A division processing unit  2101  divides the data received from the transmitter  101  into a data portion and a data portion containing the code block mapping pattern information. The division processing unit  2101  can employ any division scheme as far as the division scheme corresponds to that of the multiplex processing unit  2003  of the transmitter  101 . The division processing unit  2101  outputs the data portion to a GI removing unit  603 , and outputs the data portion containing the code block mapping pattern information to a reception processing unit  2102 . 
   The reception processing unit  2102  obtains the code block mapping pattern information from the data portion containing the code block mapping pattern information. The reception processing unit  2102  can employ any processing scheme as far as the processing scheme corresponds to that of the transmission processing unit  2002  of the transmitter  101 . The reception processing unit  2102  performs processes such as channel response estimation, channel response correction, demodulation, deinterleaving, error correction decoding, error detection, and the like. 
   A code block demapping control unit  2103  determines the code block mapping pattern based on the code block mapping pattern information obtained by the reception processing unit  2102 . The determined code block mapping pattern is output to a code block demapping unit  609 . 
   As described above, in a radio communication system according to the fourth embodiment, the transmitter selects the code block mapping pattern with the low error rate, and multiplexes the selected code block mapping pattern with the code block mapping pattern information to transmit data. Accordingly, the error rate can be decreased reliably. Hence, in the radio communication system according to the fourth embodiment, the retransmission count of the overall system can decrease, and the system throughput can increase without a large overhead for the processes such as estimation and feedback of the channel response, and the throughput. 
   The above-described radio communication system according to the fourth embodiment is effective for a radio communication scheme using a frequency-divided multi-carrier. The above-described radio communication system according to the fourth embodiment is also effective for a radio communication scheme using OFDM in a forward link. 
   Fifth Embodiment 
     FIG. 22  shows the processes of a transmitter and a receiver according to the fifth embodiment. Note that the same reference numerals as in  FIGS. 4 and 16  in the first embodiment and third embodiment denote the same steps in  FIG. 22 , and a description thereof will be omitted. 
   The process of a transmitter  101  is the same as that in the third embodiment shown in  FIG. 16 . The process of the receiver in the fifth embodiment is different from that in the third embodiment in that a channel response estimation process (step S 2201 ) is performed for performing a mapping pattern determination process (step S 1602 ). In third embodiment, the channel response estimation process for performing the data reception process is also performed, but the result of the channel response estimation process is not used for the mapping pattern determination process. 
     FIG. 23  shows an arrangement of the receiver in the fifth embodiment. Note that the same reference numerals as in  FIGS. 6 and 18  in the first embodiment and third embodiment denote the same components in  FIG. 23 , and a description thereof will be omitted. The receiver arrangement of the fifth embodiment is different from that ( FIG. 18 ) of the third embodiment in that a channel response estimation result obtained by a channel response estimation unit  606  is used not only for the channel response correction unit  607  but also for a code block demapping control unit  2301 . In consideration of the code block error rate obtained by a code block mapping pattern error rate measuring unit  1801 , the code block demapping control unit  2301  determines code block mapping pattern candidates to be used in retransmission. Additionally, a proper code block mapping pattern is selected from the code block mapping pattern candidates by using information from the channel response estimation unit  606 . For example, as a result of channel response estimation, if it is determined that the channel response is a channel response shown in  FIGS. 7 and 8 , the code block mapping pattern with a low temporal spread is selected with high priority to decrease the error rate. If it is determined that the channel response is a channel response shown in  FIGS. 9 and 10 , the code block mapping pattern with a high spread in a frequency direction is selected with high priority to decrease the error rate. 
   Note that the arrangement of the transmitter  101  according to the fifth embodiment is the same as that of the transmitter  101  according to the third embodiment shown in  FIG. 17 . 
   As described above, the radio communication system in the fifth embodiment is constructed, and the receiver uses the channel response estimation result to determine the code block mapping pattern. Hence, the code block mapping pattern suitable for the current channel response can be selected. Therefore, the error rate in retransmission can be decreased, the retransmission count of the overall system can be decreased, and the system throughput can increase in the radio communication system. 
   Sixth Embodiment 
     FIG. 24  shows an example of the processes of a transmitter  101  and a receiver  102  according to the sixth embodiment. Note that the same reference numerals as in  FIGS. 4 and 13  in the first embodiment and second embodiment denote the same steps in  FIG. 24 , and a description thereof will be omitted. 
   The sixth embodiment is different from the fourth embodiment in that the product of M×L (M is the carrier count, and L is the symbol count) in the code block mapping pattern for each data slot, a modulation scheme, an error correction method, and an encoding rate are not constant, and a data transmission speed is variable. In this case, as shown in  FIG. 24 , an MCS (modulation scheme, encoding method, and encoding rate) is determined (step S 2401 ) in addition to the code block mapping pattern. The mapping pattern and MCS information which are multiplexed with data must be notified from the transmitter  101  to the receiver  102  in a transmission process (step S 2402 ) using the determined MCS. In the receiver, since the mapping pattern and the MCS are demultiplexed to perform the reception process, the mapping pattern and the MCS information to be used for the data portion reception process are determined (step S 2403 ). 
     FIG. 25  shows an arrangement of the transmitter  101  according to the sixth embodiment. Note that the same reference numerals as in  FIGS. 5 ,  14 , and  20  in the first embodiment, second embodiment, and fourth embodiment denote the same components in  FIG. 25 , and a description thereof will be omitted. 
   The arrangement in  FIG. 25  is different from that shown in  FIG. 20  in that a code block mapping MCS control unit  2505  determines the code block mapping pattern in correspondence with the result obtained by a code block error rate measurement unit  1401 . A divided code block count and bit count, the encoding scheme and encoding rate, an interleave length, the modulation scheme are determined and respectively notified to a code block division unit  2501 , error correction encoding processing unit  2502 , interleaving unit  2503 , and adaptive modulation unit  2504 . These pieces of information are multiplexed with the data, and notified to the receiver. These units perform the data transmission process based on the information obtained by the code block mapping MCS control unit  2505 . 
     FIG. 26  shows an arrangement of the receiver  102  according to the sixth embodiment. Note that the same reference numerals as in  FIGS. 6 and 21  in the first embodiment and fourth embodiment denote the same components in  FIG. 26 , and a description thereof will be omitted. 
   The arrangement in  FIG. 26  is different from that in  FIG. 21  in that the MCS information for the data reception process is obtained by separating the MCS information in addition to the code block mapping pattern multiplexed by the transmitter, and performing the reception process. A code block demapping MCS control unit  2605  notifies the code block demapping unit  609  of the information of the carrier count M and symbol count L of the code block mapping pattern, and respectively notifies an adaptive demodulation unit  2601 , deinterleaving unit  2602 , error correction decoding unit  2603 , and code block concatenation unit  2604  of the modulation scheme, interleaving length, encoding scheme and encoding rate, and division code block count and bit count. These units perform data reception process based on the information obtained by the code block demapping MCS control unit  2605 . 
   As described above, in the sixth embodiment, a system is constructed, in which the product of M×L (M is the carrier count, and L is the symbol count) in the code block, the modulation scheme, the error correction method, and the encoding rate are not predetermined, and the data transmission speed is variable. As a result, channel responses can be flexibly processed. Accordingly, a radio communication system can be implemented in which the error rate in retransmission can decrease, a retransmission count in an overall system can be reduced, and a system throughput increases. 
   The above-described embodiments of the present invention can be applied to a cellular or radio LAN as far as the radio communication system employs the multi-carrier. Furthermore, the embodiments of the present invention can also be applied to a part of IEEE 802.16 and UWB. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.