Patent Publication Number: US-2009238134-A1

Title: Wireless communication apparatus, wireless transmission method and wireless reception method

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-70167, filed Mar. 18, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present invention relates to a wireless communication apparatus that transmits a wireless signal and a wireless communication apparatus that receives a wireless signal. 
     2. Description of the Related Art 
     In wireless communication, a transmission frame format consisted of a plurality of blocks is generally used. For example, one frame of the transmission frame format includes an RS (Reference Signal), control information, a CRC (Cyclic Redundancy Check) of the control information, data, and a CRC of the data. 
     The improvement of the channel estimation accuracy remains a problem in wireless communication. The RSs are discretely arranged in the current 3GPP (3rd Generation Partnership Project). Therefore, the accuracy of the channel estimation of control information and data between RSs is improved by averaging the RSs or performing linear interpolation or other processes. However, even if such a method is used, the following capability is reduced when the channel fluctuation is fast, and the degradation of the channel estimation accuracy is inevitable. 
     Consequently, an estimation method of propagation characteristics of received signals is known, in which part of properly decoded control information or data is regarded equivalent to an RS to decode sequentially transmitted data (see, for example, Japanese Laid-Open Patent Publication No. 2003-115783). 
     For example, assuming that the control information is properly decoded in a certain frame, the control information can be regarded equivalent to the RS because the control information is known information. Therefore, the RS of the frame to be transmitted next and the known control information are used to artificially widen the width of the RS, thereby preventing the degradation of the channel estimation of data to be transmitted next. 
     However, in the conventional channel estimation method, if there is an error in decoding of the previous control information or the like, the control information or the like may not be artificially used as the RS. Therefore, the method may not function in a poor channel environment, and the throughput may be reduced. 
     SUMMARY 
     According to an aspect of the embodiments, a wireless communication apparatus transmits a wireless signal, the wireless communication apparatus including a dividing unit that divides data transmitted in a data area of a frame format of the wireless signal into a plurality of segments. The wireless communication apparatus includes an encoding unit that encodes the data segmented by the dividing unit segment by segment. 
     The object and advantages of the embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram for explaining an overview of a wireless communication apparatus; 
         FIG. 2  is a diagram illustrating a configuration example of the wireless communication system according to a first embodiment; 
         FIG. 3  is a diagram illustrating an example of a frame format; 
         FIG. 4  is a diagram illustrating an example of a frame format in which the transmission rate is variable between segments; 
         FIG. 5  is a block diagram of a configuration of a wireless base station; 
         FIG. 6  is a diagram illustrating a data configuration example of rate instruction information; 
         FIG. 7  is a block diagram of a configuration of a mobile terminal; 
         FIG. 8  is a diagram illustrating an example of a frame format according to a second embodiment; 
         FIG. 9  is a block diagram of a configuration of the wireless base station; 
         FIG. 10  is a diagram illustrating a data configuration example of power instruction information; 
         FIG. 11  is a diagram for explaining a pseudo RS; 
         FIG. 12  is a diagram illustrating an example of a frame format according to a third embodiment; 
         FIG. 13  is a diagram illustrating  FIG. 12  with time-frequency axes; 
         FIG. 14  is a diagram illustrating a data configuration example of rate instruction information; 
         FIG. 15  is a block diagram of a configuration of the mobile terminal; 
         FIG. 16  is a flow chart of a pseudo RS process of the mobile terminal; 
         FIG. 17  is a diagram illustrating an example of a frame format according to a fourth embodiment; 
         FIG. 18  is a diagram illustrating  FIG. 17  with time-frequency axes; 
         FIG. 19  is a diagram illustrating a data configuration example of power instruction information; 
         FIG. 20  is a block diagram of a configuration of the wireless base station according to a fifth embodiment; 
         FIG. 21  is a diagram illustrating a data configuration example of division instruction information; and 
         FIG. 22  is a diagram illustrating the relationship between segments and transmission rate. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a diagram for explaining an overview of a wireless communication apparatus. A wireless communication apparatus  1  illustrated in  FIG. 1  is a wireless communication apparatus on the data transmitting side. A wireless communication apparatus  2  is a wireless communication apparatus on the data receiving side.  FIG. 1  depicts a frame format of a wireless signal transmitted from the wireless communication apparatus  1  to the wireless communication apparatus  2 . 
     The wireless communication apparatus  1  includes dividing unit  1   a  and encoding unit  1   b . The wireless communication apparatus  2  includes receiving unit  2   a  and decoding unit  2   b.    
     The dividing unit  1   a  of the wireless communication apparatus  1  divides data transmitted in a data area  3  of the frame format of the wireless signal into a plurality of segments. 
     The encoding unit  1   b  encodes data  3   a ,  3   b , and  3   n  segmented by the dividing unit  1   a , segment by segment. 
     The receiving unit  2   a  of the wireless communication apparatus  2  receives the wireless signal in the frame format, in which data of the data area  3  is divided into a plurality of segments. 
     The decoding unit  2   b  decodes data  3   a ,  3   b , and  3   n  of the wireless signal received by the receiving unit  2   a , segment by segment. 
     After segmenting and encoding the transmission data on the transmission side as described, the transmission rate of the data  3   a ,  3   b , . . . , and  3   n  can be varied segment by segment, for example. Specifically, the transmission rate of the data  3   a  of the segment near the RS can be set high, and the transmission rate of the data  3   n  of the segment far from the RS can be set low. 
     As a result, the data  3   n  of the segment at a location away from the RS can also be appropriately decoded on the receiving side even in a poor channel environment because the transmission rate is low. 
     In this way, segmenting and encoding of data enables maintaining throughput even in a poor channel environment. 
     A first embodiment will be described in detail with reference to the drawings. 
       FIG. 2  is a diagram illustrating a configuration example of a wireless communication system according to the first embodiment.  FIG. 2  illustrates a wireless base station  11  and a mobile terminal  12 . The mobile terminal  12  is, for example, a cellular phone. The wireless base station  11  and the mobile terminal  12  can apply various communication systems, such as TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access), and CDMA (Code Division Multiple Access). 
       FIG. 3  is a diagram illustrating an example of a frame format. The wireless base station  11  and the mobile terminal  12  transmit and receive data based on the frame format illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , an RS  21 , control information  22 , and a CRC  23  of the control information  22  are allocated to one frame. In a data area where data is allocated, one frame is divided into a plurality of segments  24   a ,  24   b , . . . ,  24   n , and the data encoded in the unit of segments  24   a ,  24   b , . . . , and  24   n  and the CRC of the data are allocated. The data allocated to the segments  24   a ,  24   b , . . . , and  24   n  is decoded in the unit of segments  24   a ,  24   b , . . . , and  24   n.    
     The wireless base station  11  determines the transmission rate (modulation scheme and coding rate) of data transmitted in the unit of segments  24   a ,  24   b , and  24   n  according to the distance from the RS  21 . 
       FIG. 4  is a diagram illustrating an example of a frame format in which the transmission rate is variable between segments. As illustrated in  FIG. 4 , the transmission rate of data is set high in the segment  24   a  near the RS  21 . On the other hand, the transmission rate of data is set low in the segment  24   n  far from the RS  21 . 
     In the segment  24   a  at a location near the RS  21 , the difference between a channel estimation value obtained using the RS  21  and the actual channel estimation value in the segment  24   a  is small. Therefore, the decoding accuracy of data of the segment  24   a  is high, and data in high transmission rate (low redundancy) can be accurately decoded. 
     Meanwhile, in the segment  24   n  at a location far from the RS  21 , the difference between a channel estimation value obtained using the RS  21  and the actual channel estimation value in the segment  24   n  is large. Therefore, the decoding accuracy of data of the segment  24   n  is low, and the data is transmitted and received in low transmission rate (high redundancy) to allow accurate decoding. 
     In the example of  FIG. 4 , the modulation scheme of the segment  24   a  at a location closest to the RS  21  is 16QAM (Quadrature Amplitude Modulation), and the coding rate is 0.6. The modulation scheme of the segment  24   n  at a location farthest from the RS  21  is QPSK (Quadrature Phase Shift Keying), and the coding rate is 0.5. 
     Making the transmission rate of the segments  24   a ,  24   b , . . . ,  24   n  variable according to the distance from the RS  21  enables maintaining throughput even in a poor channel environment. 
     Although both of the modulation multi-level number and the coding rate are variable in  FIG. 4 , one of them may be fixed while only the other is variable. In  FIG. 4 , the CRC is not illustrated. 
       FIG. 5  is a block diagram of a configuration of the wireless base station  11 . As illustrated in  FIG. 5 , the wireless base station  11  includes a data generating unit  31 , a control information generating unit  32 , an RS generating unit  33 , a receiving unit  34 , an uplink stream transmission frame demodulating/decoding unit  35 , a scheduler  36 , a data framing unit  37 , modulating units  38  and  40 , a control information framing unit  39 , a multiplexing unit  41 , and a transmitting unit  42 . 
     The data generating unit  31  generates data to be transmitted to the mobile terminal  12 . The control information generating unit  32  generates control information to be transmitted to the mobile terminal  12 . The RS generating unit  33  generates an RS to be transmitted to the mobile terminal  12 . 
     The receiving unit  34  receives a wireless signal wirelessly transmitted from the mobile terminal  12  through an antenna Rx. 
     An MCS (Modulation and Coding Scheme) is inputted to the uplink stream transmission frame demodulating/decoding unit  35  from the scheduler  36 . The MCS is information including a modulation scheme and a coding rate of an uplink stream wireless signal transmitted by the mobile terminal  12 . The uplink stream transmission frame demodulating/decoding unit  35  demodulates and decodes an uplink stream wireless signal received by the receiving unit  34  based on the MCS informed from the scheduler  36 . 
     The data received from the mobile terminal  12  includes control information. The control information includes information such as ACK/NACK (Acknowledgement/Negative Acknowledgement) information indicating a retransmission request of data and CQI (Channel Quality Indicator) information. The uplink stream transmission frame demodulating/decoding unit  35  outputs the demodulated control information to the scheduler  36 . 
     The scheduler  36  schedules downlink stream and uplink stream data. The scheduler  36  also determines the modulation scheme and the coding rate (MCS: Modulation and coding scheme) of the mobile terminal  12  when scheduling the uplink stream data and informs the modulation scheme and the coding rate to the uplink stream transmission frame demodulating/decoding unit  35 . The scheduler  36  further outputs the uplink stream modulation scheme and the coding rate as control information to the control information framing unit  39  to inform the uplink stream modulation scheme and the coding rate to the mobile terminal  12 . 
     The scheduler  36  determines rate instruction information of downlink stream data to be transmitted to the mobile terminal  12 . The rate instruction information is information indicating the transmission rate of the segments  24   a ,  24   b , . . . , and  24   n , and is information—such as the transmission rate of the segment  24   a  being 16QAM with a coding rate of 0.6, and the transmission rate of the segment  24   b  being 16QAM with a coding rate of 0.5. 
       FIG. 6  is a diagram illustrating a data configuration example of the rate instruction information. As illustrated in  FIG. 6 , the rate instruction information includes a field of segment number and a field of MCS. 
     The segment number corresponds to, for example, the segments  24   a ,  24   b , . . . , and  24   n  illustrated in  FIG. 4 . The smaller the segment number, the closer is the corresponding segment to the RS  21 , and the larger the number, the farther is the corresponding segment to the RS  21 . Therefore, the smaller the segment number, the higher is the transmission rate, and the larger the segment number, the lower is the transmission rate. 
     The rate instruction information illustrated in  FIG. 6  is stored in a storage device (storage unit) (not illustrated), and the scheduler  36  acquires the rate instruction information from the storage device. There are a plurality of patterns in the rate instruction information, and a plurality of pieces of information are stored in the storage device. 
       FIG. 5  will be further described. The scheduler  36  refers to the storage device based on CQI information of the control information outputted from the uplink stream transmission frame demodulating/decoding unit  35  to acquire predetermined rate instruction information from among the plurality of pieces of the rate instruction information. Specifically, the scheduler  36  determines the rate instruction information according to the wireless quality, such as fading variation. The scheduler  36  outputs the determined rate instruction information to the data framing unit  37  and the modulating unit  38 . The scheduler  36  also informs the determined rate instruction information as control information to the control information framing unit  39  to inform the rate instruction information to the mobile terminal  12 . 
     The scheduler  36  outputs the ACK/NACK information of the control information outputted from the uplink stream transmission frame demodulating/decoding unit  35  to the data generating unit  31 , the control information generating unit  32 , and the RS generating unit  33 . The data generating unit  31 , the control information generating unit  32 , and the RS generating unit  33  generate retransmission data according to the ACK/NACK information. 
     When the uplink stream data is not appropriately received, the scheduler  36  outputs the control information of that fact to the control information framing unit  39  to request the mobile terminal  12  for retransmission. 
     The rate instruction information is inputted to the data framing unit  37  from the scheduler  36 . The data framing unit  37  separates the data outputted from the data generating unit  31  into segments and encodes the data based on the segment numbers and the coding rates included in the rate instruction information. Examples of the encoding include Reed-Solomon encoding and turbo encoding. 
     The rate instruction information is inputted to the modulating unit  38  from the scheduler  36 . The modulating unit  38  modulates the data outputted from the data framing unit  37  segment by segment based on the segment numbers and the coding rates included in the rate instruction information. 
     The control information framing unit  39  encodes the control information outputted from the control information generating unit  32  and the control information outputted from the scheduler  36 . The modulating unit  40  modulates the control information outputted from the control information framing unit  39 . Although the coding rate and the modulation scheme of the control information are generally fixed, the coding rate and the modulation scheme may be changed by an instruction from a higher-level apparatus, such as an RNC (Radio Network Control), of the wireless base station  11 . 
     The multiplexing unit  41  multiplexes the data outputted from the modulating unit  38 , the control information outputted from the modulating unit  40 , and the RS outputted from the RS generating unit  33 , and outputs them to the transmitting unit  42 . The multiplexing unit  41  outputs a frame format, as illustrated in  FIG. 4 . 
     The transmitting unit  42  converts the data outputted from the multiplexing unit  41  to a wireless signal and wirelessly transmits the signal to the mobile terminal  12  through the antenna Tx. 
       FIG. 7  is a block diagram of a configuration of the terminal  12 . As illustrated in  FIG. 7 , the mobile terminal  12  includes a receiving unit  51 , a separating unit  52 , a channel estimating unit  53 , demodulating units  54  and  56 , a control information decoding unit  55 , a data decoding unit  57 , an error detecting unit  58 , an uplink stream control information generating unit  59 , an uplink stream transmission frame framing unit  60 , and a transmitting unit  61 . 
     The receiving unit  51  receives the wireless signal wirelessly transmitted from the wireless base station  11  through the antenna Rx. 
     The separating unit  52  separates the wireless signal received by the receiving unit  51  into an RS, control information, and data. 
     The channel estimating unit  53  calculates a channel estimation value based on the RS separated by the separating unit  52 . 
     The demodulating unit  54  demodulates the control information based on the channel estimation value calculated by the channel estimating unit  53 . The control information decoding unit  55  decodes the demodulated control information. 
     The demodulating unit  56  demodulates the data separated by the separating unit  52  based on the channel estimation value calculated by the channel estimating unit  53  and the control information decoded by the control information decoding unit  55 . The control information includes rate instruction information, and the demodulating unit  56  demodulates the segmented data according to the rate instruction information. Thus, the demodulating unit  56  demodulates the data segment by segment based on the rate instruction information. 
     The data decoding unit  57  decodes the segmented data based on the rate instruction information included in the control information. Thus, the data decoding unit  57  decodes the data segment by segment based on the rate instruction information. 
     The error detecting unit  58  detects an error of data based on the CRC of the decoded data. 
     The uplink stream control information generating unit  59  generates uplink stream control information based on the control information decoded by the control information decoding unit  55 . 
     The uplink stream transmission frame framing unit  60  generates a frame to be transmitted to the wireless base station  11 . An RS, control information, and data are inputted to the uplink stream transmission frame framing unit  60 , and an uplink stream transmission frame is generated. 
     The transmitting unit  61  converts the data outputted from the uplink stream transmission frame framing unit  60  to a wireless signal and wirelessly transmits the signal to the base station  11  through the antenna Tx. 
     Although only the wireless base station  11  segments and transmits the data in the description of  FIGS. 5  and  7 , the mobile terminal  12  can also segment and transmit the data. In that case, the scheduler  36  of the wireless base station  11  also determines the rate instruction information of the mobile terminal  12 . As in the description of  FIG. 6 , the rate instruction information of the mobile terminal  12  is stored in the storage device, and the scheduler  36  determines the rate instruction information of the mobile terminal  12  with reference to the storage device. The wireless base station  11  inputs the determined rate instruction information of the mobile terminal  12  into the control information and transmits the information to the mobile terminal  12 . The mobile terminal  12  segments the data based on the received rate instruction information, generates data in the frame format illustrated in  FIG. 4 , and wirelessly transmits the data to the wireless base station  11 . Specifically, the uplink stream transmission frame framing unit  60  of  FIG. 7  includes a data framing unit and a modulating unit similar to the data framing unit  37  and the modulating unit  38  of  FIG. 5 . The data framing unit and the modulating unit segment, encode, and modulate the data based on the rate instruction information included in the control information decoded by the control information decoding unit  55 . 
     In this way, the wireless base station  11  and the mobile terminal  12  segment the data and make the transmission rate variable in each segmented data. This enables maintaining throughput even in a poor channel environment. 
     A second embodiment will now be described. In the first embodiment, the data is segmented, and the transmission rate of the segmented data is variable. In the second embodiment, the transmission power of the segmented data is variable. 
       FIG. 8  is a diagram illustrating an example of a frame format according to the second embodiment. As illustrated in  FIG. 8 , an RS  71 , control information  72 , and a CRC  73  of the control information  72  are allocated to one frame. In a data area where data is allocated, one frame is divided into a plurality of segments  74   a ,  74   b , . . . , and  74   n , and the data encoded in the unit of segments  74   a ,  74   b , . . . , and  74   n  and the CRC of the data (not illustrated) are allocated. The data allocated to the segments  74   a ,  74   b , . . . , and  74   n  is decoded in the unit of segments  74   a ,  74   b , . . . , and  74   n.    
     In the segment  74   a  at a location near the RS  71 , the difference between a channel estimation value obtained using the RS  71  and the actual channel estimation value in the segment  74   a  is small. Therefore, the decoding accuracy of data of the segment  74   a  is high, and data in low transmission power can be accurately decoded. 
     Meanwhile, in the segment  74   n  at a location far from the RS  71 , the difference between a channel estimation value obtained using the RS  71  and the actual channel estimation value in the segment  74   n  is large. Therefore, the decoding accuracy of data of the segment  74   a  is low, and the data is transmitted in high transmission power to allow accurate decoding. 
     Making the transmission power of the segments  74   a ,  74   b , . . . ,  74   n  variable according to the distance from the RS  71  enables maintaining throughput even in a poor channel environment. 
       FIG. 9  is a block diagram of a configuration of the wireless base station. In  FIG. 9 , the same components as in  FIG. 5  are designated with the same reference numerals, and the description will not be repeated. 
     The scheduler  81  determines power instruction information of data to be transmitted to the mobile terminal  12 . The power instruction information is information indicating the transmission power of the segments  74   a ,  74   b , . . . , and  74   n  and is information of the transmission power, such as the segment  74   a  at 9 dB and the segment  74   b  at 10 dB. 
       FIG. 10  is a diagram illustrating a data configuration example of the power instruction information. As illustrated in  FIG. 10 , the power instruction information includes a field of segment number and a field of transmission power. 
     The segment number corresponds to, for example, the segments  74   a ,  74   b , . . . , and  74   n  illustrated in  FIG. 8 . The smaller the segment number, the closer is the corresponding segment to the RS  21 , and the larger the number, the farther is the corresponding segment to the RS  21 . Therefore, the smaller the segment number, the lower is the transmission power, and the larger the segment number, the higher is the transmission power. 
     The power instruction information illustrated in  FIG. 10  is stored in a storage device, and the scheduler  81  acquires the power instruction information from the storage device. There are a plurality of patterns in the power instruction information, and a plurality of pieces of information are stored in the storage device (storage unit). 
       FIG. 9  will be further described. The scheduler  81  refers to the storage device based on CQI information of the control information outputted from the uplink stream transmission frame demodulating/decoding unit  35  to acquire the power instruction information. Specifically, the scheduler  81  determines predetermined power instruction information according to the wireless quality, such as fading variation. The scheduler  81  outputs the determined power instruction information to the transmitting unit  82 . 
     The power instruction information is inputted to the data framing unit  37  from the scheduler  81 . The data framing unit  37  segments and encodes the data based on the segment numbers included in the power instruction information. 
     The power instruction information is inputted to the transmitting unit  82  from the scheduler  81 . The transmitting unit  82  makes the power of data of the segments outputted from the multiplexing unit  41  variable based on the segment numbers and the transmission power included in the power instruction information. 
     Other processes of  FIG. 9  are similar to those in  FIG. 5 . The power instruction information is not included in the downlink stream control information to be transmitted to the mobile terminal  12 . This is because the mobile terminal  12  can perform decoding and demodulation without the power instruction information. The block configuration of the mobile terminal  12  is the same as in  FIG. 7 . 
     Although only the wireless base station  11  segments and transmits the data in the above description, the mobile terminal  12  can also segment and transmit the data. In that case, the scheduler  81  of the wireless base station  11  also determines the power instruction information of the mobile terminal  12 . As in the description of  FIG. 10 , the power instruction information of the mobile terminal  12  is stored in the storage device, and the scheduler  81  determines the power instruction information of the mobile terminal  12  with reference to the storage device. The wireless base station  11  inputs the determined power instruction information of the mobile terminal  12  into the control information and transmits the information to the mobile terminal  12 . The mobile terminal  12  segments the data based on the received power instruction information, generates data in the frame format illustrated in  FIG. 8 , and wirelessly transmits the data to the wireless base station  11 . 
     Specifically, the uplink stream transmission frame framing unit  60  of  FIG. 7  includes the same functions as the data framing unit  37  of  FIG. 9  and segments and encodes the data based on the power instruction information included in the control information decoded by the control information decoding unit  55 . 
     The transmitting unit  61  includes the same functions as the transmitting unit  82  of  FIG. 9  and makes the transmission power of the segmented data variable based on the power instruction information included in the control information decoded by the control information decoding unit  55 . 
     In this way, the wireless base station  11  and the mobile terminal  12  segment the data and make the transmission power variable in each segmented data. This enables maintaining throughput even in a poor channel environment. 
     A third embodiment will now be described. In the first embodiment, the transmission rate of the segmented data can be varied so that the transmission rate becomes low. In the third embodiment, the transmission rate of the segmented data can be varied so that the transmission rate becomes high. A pseudo RS will be described first. 
       FIG. 11  is a diagram for explaining the pseudo RS.  FIG. 11  illustrates frames  91  and  92 . The frame  92  follows the frame  91 . 
     The data of the frame  91  is already known when the wireless base station  11  or the mobile terminal  12  receives the frame  92  from a partner apparatus. Therefore, the wireless base station  11  or the mobile terminal  12  can artificially use part or all of the control information and data of the frame  91  as an RS of the frame  92 . 
     For example, the wireless base station  11  or the mobile terminal  12  uses not only the RS of the frame  92 , but also the known control information and the data of the frame  91 , as a pseudo RS to perform the channel estimation of the frame  92 . 
     In this way, the known data or the like of the previously received frame is used as a pseudo RS to artificially extend the width of the RS, thereby preventing the degradation of the channel estimation. 
     Meanwhile, in the pseudo RS, if there is an error in the control information or in decoding of data, the control information and the data may not be used as a pseudo RS. In this case, the width of the pseudo RS is shortened, and the channel estimation is degraded. 
     Thus, the closer to the RS, the lower is the transmission rate set, thereby reducing the errors caused by decoding of data, and extending the width of the pseudo RS. 
       FIG. 12  is a diagram illustrating an example of a frame format according to a third embodiment. As illustrated in  FIG. 12 , an RS  101 , control information  102 , and a CRC  103  of the control information  102  are allocated to one frame. In a data area where data is allocated, one frame is divided into a plurality of segments  104   a ,  104   b , . . . , and  104   n , and the data encoded in the unit of segments  104   a ,  104   b , . . . , and  104   n  and the CRC of the data (not illustrated) are allocated. The data allocated to the segments  104   a ,  104   b , . . . , and  104   n  is decoded in the unit of segments  104   a ,  104   b , . . . , and  104   n.    
     In the segment  104   a  at a location near the RS  101 , the transmission rate is set low so that reliable encoding is performed without error. The transmission rate is set high with increasing distance from the RS  101 . 
     In the example of  FIG. 12 , the modulation scheme of the segment  104   a  closest to the RS  101  is QPSK, and the coding rate is 0.5. The modulation scheme of the segment  104   n  farthest from the RS  101  is 16QAM, and the coding rate is 0.6. 
     In this way, the data of the segment near the RS  101  is reliably decoded by reducing the transmission rate of the segment near the RS  101 . This enables reliably extending the width of the pseudo RS even in a poor channel environment, thereby preventing the degradation of the channel estimation and maintaining throughput. 
       FIG. 13  is a diagram illustrating  FIG. 12  with time-frequency axes. The horizontal axis of  FIG. 13  denotes time, and the vertical axis denotes frequency. As illustrated in  FIG. 13 , the transmission rate of the data of the segment near the RS is low. The transmission rate of the data of the segment at the location far from the RS (central part of data in high transmission rate in  FIG. 13 ) is high. If there is no error in decoding of nearby data, the range of the areas of the RS illustrated in  FIG. 13  spreads to the central part of the data in high transmission rate based on the pseudo RS. This enables preventing the degradation of the channel estimation of the part of the data in high transmission rate illustrated in  FIG. 13 . 
     The block configuration of the wireless base station  11  is similar to that in  FIG. 5 . However, the content of the rate instruction information is different. 
       FIG. 14  is a diagram illustrating a data configuration example of the rate instruction information. As illustrated in  FIG. 14 , the rate instruction information includes a field of segment number and a field of MCS. 
     The segment number corresponds to, for example, the segments  104   a ,  104   b , . . . , and  104   n  illustrated in  FIG. 12 . The smaller the segment number, the closer is the corresponding segment to the RS  101 , and the larger the number, the farther is the corresponding segment to the RS  101 . Therefore, the smaller the segment number, the lower is the transmission rate, and the larger the segment number, the higher is the transmission rate. 
     The rate instruction information illustrated in  FIG. 14  is stored in a storage device, and the scheduler  36  acquires the rate instruction information from the storage device. There are a plurality of patterns in the rate instruction information, and a plurality of pieces of information are stored in the storage device. 
       FIG. 15  is a block diagram of a configuration of the mobile terminal. In  FIG. 15 , the same components as in  FIG. 7  are designated with the same reference numerals, and the description will not be repeated. 
     As illustrated in  FIG. 15 , the mobile terminal  12  includes a pseudo-channel estimating unit  111  and a channel estimation value combining unit  112 . The pseudo-channel estimating unit  111  sets the decoded control information and the data as a pseudo RS to calculate a pseudo-channel estimation value. 
     The channel estimation value combining unit  112  combines the channel estimation value calculated by the channel estimating unit  53  and the pseudo-channel estimation value calculated by the pseudo-channel estimating unit  111  to calculate a channel estimation value. 
     The channel estimating unit  53  calculates the channel estimation value based on the RS of the currently receiving frame. The pseudo-channel estimating unit  111  calculates the pseudo-channel estimation value based on the already known control information and data of the previous frame. For example, the channel estimating unit  53  uses the RS of the frame  92  illustrated in  FIG. 11  to calculate the channel estimation value. The pseudo-channel estimating unit  111  uses the control information and the data of the frame  91  to calculate the pseudo-channel estimation value. 
       FIG. 16  is a flow chart of a pseudo RS process of the mobile terminal. The mobile terminal  12  calculates the channel estimation value according to the following steps. 
     In step S 1 , the mobile terminal  12  decodes the control information. 
     In step S 2 , the mobile terminal  12  determines whether decoding of the control information has been performed without error. If the decoding has been performed without error, the process proceeds to step S 3 . If there is an error in decoding, the process proceeds to step S 11 . 
     In step S 3 , the mobile terminal  12  regards the control information of the frame as an RS and updates the pseudo-channel estimation value. 
     In step S 4 , the mobile terminal  12  decodes the n-th data of frame (n: positive integer between 1 to N, N: the number of segments). 
     In step S 5 , the mobile terminal  12  determines whether the n-th data block has been decoded without error. If the decoding has been performed without error, the process proceeds to step S 6 . If there is an error in decoding, the process proceeds to step S 10 . 
     In step S 6 , the mobile terminal  12  compares the values of n and N. If the value of n is smaller than N, the process proceeds to step S 7 . If the value of n is equal to or greater than N, the process proceeds to step S 9 . 
     In step S 7 , the mobile terminal  12  also regards the information of the n-th data block as the RS and updates the pseudo-channel estimation value. The channel estimation value combining unit  112  combines the pseudo-channel estimation value with the channel estimation value calculated by the channel estimating unit  53 . 
     In step S 8 , the mobile terminal  12  adds 1 to the value of n, and the process proceeds to step S 4 . 
     In step S 9 , the mobile terminal  12  returns the ACK to the transmission side (wireless base station  11 ). 
     In step S 10 , the mobile terminal  12  returns the NACK to the transmission side and requests retransmission of data. 
     In step S 11 , the mobile terminal  12  returns the NACK to the transmission side and requests retransmission of data. 
     In this way, reducing the transmission rate of the segment near the RS and reliably decoding the data of the segment near the RS enable reliably extending the width of the pseudo RS, thereby preventing the degradation of the channel estimation and maintaining throughput. 
     The wireless base station  11  may also include the pseudo RS. In that case, the uplink stream transmission frame demodulating/decoding unit  35  illustrated in  FIG. 5  includes the channel estimating unit  53 , the pseudo-channel estimating unit  111 , and the channel estimation value combining unit  112  of  FIG. 15 . The uplink stream transmission frame demodulating/decoding unit  35  calculates the pseudo-channel estimation value from the received control information and data and demodulates and decodes the data. 
     A fourth embodiment will now be described. In the third embodiment, the transmission rate of the segmented data can be varied so that the transmission rate becomes high. In the fourth embodiment, the transmission power of the segmented data can be varied so that the transmission power becomes low. 
       FIG. 17  is a diagram illustrating an example of a frame format according to the fourth embodiment. As illustrated in  FIG. 17 , an RS  121 , control information  122 , and a CRC  123  of the control information  122  are allocated to one frame. In a data area where data is allocated, one frame is divided into a plurality of segments  124   a ,  124   b , . . . , and  124   n , and the data encoded in the unit of segments  124   a ,  124   b , . . . , and  124   n  and the CRC of the data are allocated. The data allocated to the segments  124   a ,  124   b , . . . , and  124   n  is decoded in the unit of segments  124   a ,  124   b , . . . , and  124   n.    
     In the segment  124   a  at a location near the RS  121 , the transmission power is set high so that reliable encoding is performed without error. The transmission power is set low with increasing distance from the RS  121 . 
     In this way, the data of the segment near the RS  121  is reliably decoded by increasing the transmission power of the segment near the RS  121 . This enables reliably extending the width of the pseudo RS even in the worst channel environment, thereby preventing the degradation of the channel estimation. 
       FIG. 18  is a diagram illustrating  FIG. 17  with time-frequency axes. The horizontal axis of  FIG. 18  denotes time, and the vertical axis denotes frequency. As illustrated in  FIG. 18 , the transmission power of the data of the segment near the RS is high. The transmission power of the data of the segment at a location far from the RS (central part of data in low transmission power in  FIG. 18 ) is low. If there is no error in decoding of nearby data, the range of the areas of the RS illustrated in  FIG. 18  spreads to the central part of the data in low transmission power based on the pseudo RS. This enables preventing the degradation of the channel estimation of the part of the data in low transmission power illustrated in  FIG. 18 . 
     The block configuration of the wireless base station  11  is similar to that in  FIG. 9 . However, the content of the power instruction information is different. 
       FIG. 19  is a diagram illustrating a data configuration example of the power instruction information. As illustrated in  FIG. 19 , the power instruction information includes a field of segment number and a field of transmission power. 
     The segment number corresponds to, for example, the segments  124   a ,  124   b , . . . , and  124   n  illustrated in  FIG. 17 . The smaller the segment number, the closer is the corresponding segment to the RS  121 , and the larger the number, the farther is the corresponding segment to the RS  121 . Therefore, the smaller the segment number, the higher is the transmission power, and the larger the segment number, the lower is the transmission rate. 
     The power instruction information illustrated in  FIG. 19  is stored in a storage device, and the scheduler  81  acquires the power instruction information from the storage device. There are a plurality of patterns in the power instruction information, and a plurality of pieces of information are stored in the storage device. The configuration of the mobile terminal  12  is the same as in  FIG. 15 . 
     In this way, increasing the transmission power of the segment near the RS and reliably decoding the data of the segment near the RS enable reliably extending the width of the pseudo RS, thereby preventing the degradation of the channel estimation. 
     The wireless base station  11  may also include the pseudo RS. In that case, the uplink stream transmission frame demodulating/decoding unit  35  illustrated in  FIG. 5  includes the channel estimating unit  53 , the pseudo-channel estimating unit  111 , and the channel estimation value combining unit  112  of  FIG. 15 . The uplink stream transmission frame demodulating/decoding unit  35  calculates the pseudo-channel estimation value from the received control information and data and demodulates and decodes the data. 
     A fifth embodiment will now be described. In the fifth embodiment, the number of segments can be varied according to the wireless quality. For example, the number of the segments  24   a ,  24   b , . . . , and  24   n  illustrated in  FIG. 3  can be varied. 
       FIG. 20  is a block diagram of a configuration of the wireless base station according to the fifth embodiment. In  FIG. 20 , the same components as in  FIG. 5  are designated with the same reference numerals, and the description will not be repeated. 
     A scheduler  131  outputs division instruction information to the data framing unit  37 , the information including the number of segments to which data will be allocated. The data framing unit  37  divides the data into a predetermined number of pieces based on the number of segments of the division instruction information and encodes the data. 
       FIG. 21  is a diagram illustrating a data configuration example of the division instruction information. As illustrated in  FIG. 21 , the division instruction information includes a field of SIR (Signal to Interference Ratio) and a field of the number of segments. The number of segments increases as the value of the SIR decreases. The division instruction information is stored in a storage device. 
       FIG. 20  will be further described. The scheduler  131  acquires the division instruction information from the storage device based on the wireless quality such as the SIR. The SIR is included in the CQI information from the uplink stream transmission frame demodulating/decoding unit  35 . The scheduler  131  outputs the division instruction information acquired based on the SIR to the data framing unit  37 . The scheduler  131  also outputs the acquired division instruction information to the control information framing unit  39  as control information. 
     The mobile terminal  12  is the same as in  FIG. 7 . However, the demodulating unit  56  and the data decoding unit  57  demodulate and decode the segmented data segment by segment based on the division instruction information included in the control information. 
     The mobile terminal  12  can also make the number of segments of the data variable. In that case, the scheduler  131  of the wireless base station  11  also determines the division instruction information of the mobile terminal  12 . The division instruction information of the mobile terminal  12  is stored in the storage device, and the scheduler refers to the storage device to determine the division instruction information of the mobile terminal  12 . The wireless base station  11  inputs the determined division instruction information of the mobile terminal  12  into the control information and transmits the information to the mobile terminal  12 . The mobile terminal  12  segments the data based on the division instruction information included in the received control information and wirelessly transmits the data to the wireless base station  11 . 
     In this way, making the number of segments variable enables improving the channel estimation accuracy by increasing the number of segments in a poor propagation channel environment. In a favorable propagation channel environment, the number of segments is decreased to reduce the CRC bits, thereby ensuring throughput. 
     The fifth embodiment can also be applied to the first to fourth embodiments. Thus, the transmission rate and the transmission power can be varied, and the number of segments can also be varied. 
     A sixth embodiment will now be described. In the sixth embodiment, the coding rate is calculated by formulas. In the sixth embodiment, the wireless base station  11  and the mobile terminal  12  include a block configuration similar to that in the first and third embodiments. However, the wireless base station  11  includes an AMC (Auto Modulation Control) and a transmission rate calculating unit. 
       FIG. 22  is a diagram illustrating a relationship between the segments and the transmission rate. The horizontal axis of  FIG. 22  denotes numbers indicating locations of the segments. For example, the segments  24   a  and  24   b  of  FIG. 3  correspond to 1 and 2 on the horizontal axis of  FIG. 22 . The vertical axis denotes the transmission rate. 
     A straight line A 1  of  FIG. 22  illustrates an example in which the transmission rate becomes higher with increasing distance from the RS to the location of the segment. A straight line A 2  illustrates an example in which the transmission rate becomes lower with increasing distance from the RS to the location of the segment. In  FIG. 22 , rate( 1 ) denotes the transmission rate of the leading segment determined by the AMC. 
     The calculation of the slopes of the straight lines A 1  and A 2  of the transmission rate calculating unit will be described. The number of bits of the data to be transmitted is the same as when the coding rate is not changed (normal data transmission). The coding rate in the n-th segment is defined as rate (n). The slope to be calculated is defined as r, the number of bits per segment is defined as T, the coding rate is defined as rO, and the number of segments is defined as N. 
     The following formula (1) is established to conform the transmission bits to the transmission bits during the normal data transmission. 
     
       
         
           
             
               
                 
                   
                     
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     The following formula (2) is established to change the coding rate according to the slopes of the straight lines A 1  and A 2 . 
       rate( n )=rate(1)+ r ·( n−i )  (2) 
     The slope r is obtained by assigning formula (2) to formula (1). 
     
       
         
           
             
               
                 
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     The scheduler  36  informs the transmission rate calculated by the transmission rate calculating unit to the data framing unit  37  and the modulating unit  38 . As a result, the coding rate can be determined segment by segment. 
     Although the coding rate is changed only in the time direction in the description above, the same can also be obtained in the frequency direction. Two dimensional expansion of time and frequency is also possible. 
     In this way, the transmission rate of segment can be determined by calculating the transmission rate by computation. 
     Although the transmission rate and the transmission power are variable in each segment in the first to sixth embodiments, the number of times of code multiplexing may also be variable in each segment in the CDMA system. Code sequences orthogonal to each other are prepared for each user in the CDMA system. After normal demodulation, the spreading codes are multiplied, and the pieces of the user data are combined. On the receiving side, multiplying (dispreading) the spreading codes that are independent for each user enables extracting data user by user. The number of times of multiplexing of users is called a number of times of code multiplexing. 
     In the disclosed apparatus, throughput can be maintained even in a poor channel environment. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to an illustration of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.