Abstract:
Disclosed are an encoding ratio setting method and a radio communication device which can avoid encoding of control information at an encoding ratio lower than necessary and suppress lowering of the transmission efficiency of the control information. In the device, an encoding ratio setting unit ( 122 ) sets the encoding ratio R′ control  of the control information which is time-multiplexed with user data, according to the encoding ratio R data  of the user data, ΔPUSCHoffset as the PUSCH offset of each control information, and ΔRANKoffset as the rank offset based on the rank value of the data channel using Expression (1). 
     
       
         
           
             
               
                 
                   
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     Where ┌x┐ is an integer not greater than x, and max(x,y) is the greater one among X and Y.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a coding rate setting method and a radio communication apparatus used for a radio communication system using adaptive modulation and the multiple input multiple output (MIMO) technology. 
       BACKGROUND ART 
       [0002]    For an uplink channel of 3rd generation partnership project radio access network long term evolution (3GPP RAN LTE, hereinafter referred to as “LTE”), single-carrier transmission is adapted to achieve a low peak to average power ratio (PAPR). 
         [0003]    Further, for an LTE uplink channel, to achieve high throughput, adaptive modulation (AMC: adaptive modulation and coding) is used so as to select the modulation and coding scheme (MCS) pattern for each user depending on the channel quality indicator (CQI) of each user. 
         [0004]    Further, introduction of the MIMO system is being considered to achieve higher transmission rate and to further improve the efficiency of use of frequency. Introduction of a rank transmission technique is also considered such as rank adaptation with which the rank indication (the number of rank) is adaptively switched depending on the status of a spatial propagation path to further improve transmission rate. 
         [0005]    Under these circumstances, an agreement is made to time-multiplex control information and user data using the physical uplink shared channel (PUSCH) of the same subframe so as to maintain low PAPR even when both control information and user data are transmitted at the same time in an LTE uplink channel (see Non-Patent Literature 1). 
         [0006]    The number of coded symbols, Q′, of control information to be multiplexed with user data is set based on equation 1. 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
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         [0000]    where ┌x┐ is an integer not greater than x, and min(x,y) is the value of the smaller one of x and y. 
         [0007]    In equation 1, M sc  is the number of subcarriers per PUSCH subframe, and ΔPUSCIHoffset is a PUSCH offset which varies per control information such as ACK/NACK, rank indicator (RI), or CQI. ΔPUSCHoffset is reported from a higher layer (see Non-Patent Literature 1). 
         [0008]    O is the number of control information bits, and R data  is represented by equation 2. 
         [0000]    
       
         
           
             
               
                 
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         [0000]    In equation 2, K is the number of bits on r-th block, C is the number of blocks per PUSCH subframe, and N symb  is the number of symbols per PUSCH subcarrier. The actual coding rate of user data is obtained by dividing R data  in equation 2 by the number of bits per symbol, and is in proportion to R data  equation 2. Accordingly, R data  in equation 2 will be hereinafter referred to as “user data coding rate.” 
         [0009]    In equation 1, Q1 is the number of coded symbols of control information that is set based on the number of control information bits O, user data coding rate R data , and PUSCH offset ΔPUSCHoffset, per control information. Q2 is the upper limit value of the number of coded symbols of control information. As shown in equation 1, the number of coded symbols of control information, Q′, is set by the smaller one of the number of symbols Q1 and upper limit value Q2. 
         [0010]    Here, equation I is modified to provide equation 3. As is the case with R data  in equation 2, the actual coding rate of control information is obtained by dividing R control  in equation 3 by the number of bits per symbol, and is in proportion to R control  in equation 3. Accordingly, R control  in equation 3 will be hereinafter referred to as “control information coding rate (coding rate of control information).” 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
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         [0000]    where ┌x┐ is an integer not greater than x, and max(x,y) is the value of the greater one of x and y. In equation 3, R1 is the coding rate that is set based on user data coding rate R data  and PUSCH offset, ΔPUSCHoffset, per control information. R2 is the lower limit value of control information coding rate R control . As is shown in equation 3, control information coding rate R control  is set to the value of the greater value of coding rate R1 and lower limit value R2. A case will be described below where coding rate R1 is greater than lower limit value R2, and control information coding rate R control  is set as coding rate R1. 
         [0011]    In this case, in equation 3, when PUSCH offset ΔPUSCHoffset is greater than 0, control information coding rate R control  is set lower than user data coding rate R data . Generally, unlike user data, control information is not retransmitted. Therefore, by setting PUSCH offset ΔPUSCHoffset, to be greater than 0 and using equation 3, it is possible to lower control information coding rate R control  than user data coding rate R data  to enhance the capability of error correction of control information. 
       CITATION LIST 
     Non-Patent Literature 
       [0000]    
       
         3GPP TS 36.212 v 8.4.0, “Uplink transport channels and control information” 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0013]    However, when control information coding rate R control  is set simply by using only user data coding rate R data  and PUSCH offset ΔPUSCH offset , per control information, there is a possibility that adaptive modulation is applied depending on a channel quality indicator of user, and efficiency of control information transmission is decreased when rank indication of a data channel (hereinafter referred to as “data CH”) in which user data is transmitted, is transmitted. 
         [0014]    For example, when rank 2 is applied to a data CH and reception quality is deteriorated due to interference between streams (inter-stream interference), in adaptive modulation, user data MCS is lowered and user data coding rate R data  is set lower to prevent the decrease in the efficiency of transmission due to deteriorated reception quality. 
         [0015]    In such a case where user data MCS is lowered by adaptive modulation, if control information coding rate R control  is set based on equation 3, control information coding rate R control  may be set excessively low. As a result of this, for example, even when the rank indication of a control channel (hereinafter referred to as “control CH”), in which control information is transmitted, is not transmitted, and the control CH is not subject to the influence of interference between streams, control information is encoded at a lower coding rate to have excessively high quality, therefore lowering the efficiency of control information transmission. 
         [0016]    In view of the above, it is therefore an object of the present invention to provide a coding rate setting method and a radio communication apparatus that can prevent control information from being encoded at an excessively low coding rate and can suppress the decrease in the efficiency of control information transmission. 
       Solution to Problem 
       [0017]    A coding rate setting method according to the present invention sets a user data coding rate to be adaptively set according to a channel quality indicator of a user as a reference value, corrects the reference value based on a type of control information to be time-multiplexed with the user data and a rank indication of a data channel in which the user data is transmitted, and 
         [0000]    sets the corrected reference value as a control information coding rate. 
         [0018]    A radio communication apparatus according to the present invention comprises a coding rate obtaining section that sets a user data coding rate to be adaptively set according to a channel quality indicator of a user as a reference value, obtains the reference value corrected based on a type of control information to be time-multiplexed with the user data and a rank indication of a data channel in which the user data is transmitted, as a the control information coding rate, and an encoding section that encodes the control information based on the control information coding rate. 
       Advantageous Effects of Invention 
       [0019]    According to the present invention, it is possible to prevent control information from being encoded at an excessively low coding rate, and suppress the decrease in the efficiency of control information transmission. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a block diagram showing a main configuration of a terminal according to Embodiment 1 of the present invention; 
           [0021]      FIG. 2  is a block diagram showing a main configuration of a coding rate setting section according to Embodiment 1 of the present invention; 
           [0022]      FIG. 3  shows an example of a rank information offset table according to Embodiment 1 of the present invention; 
           [0023]      FIG. 4  shows another example of a rank information offset table according to Embodiment 1 of the present invention; 
           [0024]      FIG. 5  is a block diagram showing a main configuration of a terminal according to Embodiment 2 of the present invention; 
           [0025]      FIG. 6  is a block diagram showing a main configuration of a coding rate setting section according to Embodiment 2 of the present invention; 
           [0026]      FIG. 7  shows an example of a rank information offset table according to Embodiment 2 of the present invention; 
           [0027]      FIG. 8  shows another example of a rank information offset table according to Embodiment 2 of the present invention; and 
           [0028]      FIG. 9  shows yet another example of a rank information offset table according to Embodiment 2 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0030]    A case will be described here with the present embodiment where a control information coding rate is set by a offset corresponding to a rank indication of a data CH in which user data is transmitted, when adaptive modulation is applied according to a channel quality indicator of a user. Control information may include ACK/NACK, R1, and CQI, for example, and is time-multiplexed with user data to be transmitted from a terminal apparatus (hereinafter referred to as “terminal”) to a base station apparatus (hereinafter referred to as “base station”). 
         [0031]    The control information coding rate can be set either at a base station or at a terminal. A case will be described below where the control information coding rate is set at a terminal. 
         [0032]      FIG. 1  is a block diagram showing a main configuration of a terminal according to the present embodiment. In  FIG. 1 , receiving section  110  of terminal  100  comprises radio receiving section  111 , cyclic prefix (CP) removing section  112 , fast Fourier transform (FFT) section  113 , propagation path estimation section  114 , demodulation section  115 , and decoding section  116 . Further, in  FIG. 1 , transmission section  120  of terminal  100  comprises coding rate setting section  121 , coding rate setting section  122 , coding modulation section  123 , coding modulation section  124 , channel multiplexing section  125 , discrete Fourier transform-spread-OFDM (DFT-s-OFDM) section  126 , CP adding section  127 , and radio transmission section  128 . 
         [0033]    Radio receiving section  111  converts a received signal received via an antenna to a baseband signal, and outputs the baseband signal to CP removing section  112 . 
         [0034]    CP removing section  112  removes a cyclic prefix (CP) from the baseband signal output from radio receiving section  111  and outputs, as a time domain signal, the baseband signal without a CP to FFT section  113 . 
         [0035]    FFT section  113  obtains a frequency domain signal by performing a fast Fourier transform on the time domain signal output from CP removing section  112 , and outputs the obtained frequency domain signal to propagation path estimation section  114  and demodulation section  115 . 
         [0036]    Propagation path estimation section  114  estimates the propagation path environment of the received signal by using a pilot signal contained in the frequency domain signal output from FFT section  113 , and outputs the estimation result, which is the estimated propagation path environment of the received signal, to demodulation section  115 . 
         [0037]    Demodulation section  115  applies a propagation path compensation with respect to the frequency domain signal which is output from FFT section  113 , and from which the pilot signal is removed, based on the estimation result output from propagation path estimation section  114 . Further, demodulation section  115  demodulates the frequency domain signal after propagation path compensation based on the same MCS as used at the base station, i.e. the same modulation scheme and coding rate, etc. to obtain a demodulated signal, and outputs the obtained demodulated signal to decoding section  116 . 
         [0038]    Decoding section  116  corrects errors with respect to the demodulated signal output from demodulation section  115 , to obtain a decoded signal. Then, decoding section  116  extracts, from the obtained decoded signal, information such as an information data sequence, the number of bits per block K r , the number of subcarriers per subframe M sc , the number of symbols per subcarrier N symb , a PUSCH offset, and a data CH rank indication (the number of a rank for a data CH). Information about M sc  and N symb  are set at favorable values at a base station by being adaptively modulated according to the CQI transmitted from terminal  100 . Decoding section  116  outputs the extracted information on K r , M sc  and N symb  to coding rate setting section  121 , and outputs the extracted information on the PUSCH offset and the data CH rank indication to coding rate setting section  122 . 
         [0039]    Coding rate setting section  121  sets user data coding rate R data  based on information on K r , M sc , and N symb  input from decoding section  116 , based on equation 2. Coding rate setting section  121  outputs the set user data coding rate R data  to coding rate setting section  122  and coding modulation section  123 . 
         [0040]    Coding rate setting section  122  sets control information coding rate R′ control  based on information on user data coding rate R data , the PUSCH offset, and the data CH rank indication. The internal configuration of coding rate setting section  122  and the method of setting control information coding rate R′ control  will be described later. Coding rate setting section  122  outputs the set control information coding rate R′ control  to coding modulation section  124 . 
         [0041]    Coding modulation section  123  generates encoded data by encoding the input user data based on information on user data coding rate R data  output from coding rate setting section  121 , and generates data CH transmission data by modulating the generated encoded data. Coding modulation section  123  outputs the generated data CH transmission data to channel multiplexing section  125 . 
         [0042]    Coding modulation section  124  generates encoded data by encoding control information based on coding rate R′ control  output from coding rate setting section  122 , and generates control CH transmission data by modulating the generated encoded data. Coding modulation section  124  outputs the generated control CH transmission data to channel multiplexing section  125 . 
         [0043]    Channel multiplexing section  125  time-multiplexes the data CH transmission data output from coding modulation section  123  and the control CH transmission data output from coding modulation section  124 , to generate multiplexed transmission data. Channel multiplexing section  125  outputs the multiplexed transmission data to DFT-s-OFDM section  126 . 
         [0044]    DFT-s-OFDM section  126  obtains a frequency domain signal by performing a discrete Fourier transform (DFT) on the multiplexed transmission data output from channel multiplexing section  125 . DFT-s-OFDM section  126  maps the frequency domain signal on a transmission subcarrier, performs an inverse fast Fourier transform (IFFT) on the mapped frequency domain signal to obtain a transmission data sequence, and outputs the obtained transmission data sequence to CP adding section  127 . 
         [0045]    CP adding section  127  adds a CP to the transmission data sequence output from DFT-s-OFDM section  126  by duplicating the data in the end of a frame and inserting the duplicated data in the head of the frame, in each frame of the transmission data sequence, and outputs the transmission data sequence with a CP as the baseband signal, to radio transmission section  128 . 
         [0046]    Radio transmission section  128  converts the frequency with respect to the baseband signal output from CP adding section  127  into radio frequency bandwidth to obtain a transmission signal, and transmits the obtained transmission signal via an antenna. 
         [0047]      FIG. 2  is a block diagram showing an internal configuration of coding rate setting section  122  according to the present embodiment. 
         [0048]    Rank information offset obtaining section  1221  stores rank information offset table  1222  inside, and obtains rank offset ΔRANKoffset from rank information table  1222  corresponding to the data CH rank indication. Rank information offset table  1222  will be explained later. Rank information offset obtaining section  1221  outputs the obtained rank offset ΔRANKoffset to coding rate calculating section  1223 . 
         [0049]    Coding rate calculating section  1223  sets control information coding rate R′ control  based on user data coding rate R data , PUSCH offset ΔPUSCHoffset and rank offset ΔRANKoffset, corresponding to the data CH rank indication, based on equation 4. 
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         [0000]    where ┌x┐ is an integer not greater than x, and max(x,y) is the value of the greater one of x and y. 
         [0050]    In equation 4, R′1 is a coding rate that is set based on user data coding rate R data , PUSCH offset per control information which is defined as ΔPUSCHoffset, and rank offset corresponding to the data CH rank indication which is defined as ΔRANKoffset. R2′ is the lower limit value of control information coding rate R′ control . A case will be described below where coding rate R′1 is greater than lower limit value R′2, and control information coding rate R control  is set as coding rate R′1. 
         [0051]    Further, in equation 4, O is the number of control information bits and Q′ is the number of coded symbols of control information. The number of coded symbols of control information Q′ is represented by equation 5. 
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         [0000]    where ┌x┐ is an integer not greater than x, and min(x,y) is the value of the smaller one of x and y. As is obvious in equation 4, according to the present embodiment, by correcting user data coding rate R data  using PUSCH offset ΔPUSCHoffset, corresponding to a type of control information and rank offset ΔRANKoffset, corresponding to a data CH rank indication, it is possible to set the corrected user data coding rate as control information coding rate R′ control . In other words, by setting the user data coding rate R data , to be adaptively set according to the user CQI, as a reference value, and by correcting the reference value based on PUSCH offset ΔPUSCHoffset, corresponding to the type of control information, and rank offset ΔRANKoffset, corresponding to the data CH rank indication, it is possible to set the corrected reference value as control information coding rate R′ control . 
         [0052]    As PUSCH offset ΔPUSCHoffset corresponding to the type of control information, ΔHARQ-ACK is used when control information is HARQ-ACK, ΔRI is used when control information is RI, and ΔCQI is used when control information is CQI, for example. An offset corresponding to the type of control information such as ΔHARQ-ACK, ΔRI, and ΔCQI is reported from a base station via a higher layer (see Non-Patent Literature 1). 
         [0053]      FIG. 3  shows an example of rank information offset table  1222  stored inside the rank information offset obtaining section  1221 . According to the present embodiment, rank information offset table  1222  stores rank offset, ΔRANKoffset, of a greater value for a data CH rank indication of a greater value. For example, in rank information offset table  1222  in  FIG. 3 , rank offsets ΔRANKoffset, are set at from a to z in ascending order of data CH rank indications, and ΔRANKoffset values of from a to z are set to satisfy z&gt; . . . &gt;b&gt;a. 
         [0054]    As described above, by setting rank offset ΔRANKoffset of a greater value for the data CH rank indication of a greater value, it is possible to correct control information coding rate R′ control , to be obtained based on equation 4, to become higher when the data CH rank indication is greater. 
         [0055]    Generally, the influence of interference between streams becomes greater when a rank indication is greater. Therefore, when a data CH rank indication is large, in adaptive modulation, user data MCS is lowered to ensure reception quality. That is, in adaptive modulation, user data coding rate R data  is set lower, when a data CH rank indication is greater and the influence of interference between streams is greater. 
         [0056]    Therefore, in the case where user data coding rate R data  is set lower in adaptive modulation, when the control information coding rate is set using only PUSCH offset, ΔPUSCHoffset, per control information, based on equation 3, for example, the control information coding rate is set further lower than user data coding rate R data . Accordingly, there is a possibility that control information is encoded at an excessively low coding rate. 
         [0057]    In contrast, according to the present embodiment, the control information coding rate is set by equation 4 using rank offset, ΔRANKoffset, of a greater value for a data CH rank indication of a greater value, in addition to an offset per control information. By this means, the control information coding rate is corrected higher when the data CH rank indication is greater, and it is possible to prevent the control information coding rate from being set excessively low. In this way, according to the present embodiment, it is possible to obtain the control information coding rate by correcting the user data coding rate, based on the difference of the influence of interference between streams that a data CH suffers and the influence of interference between streams that a control CH suffers. 
         [0058]    As described above, according to the present embodiment, coding rate setting section  122  corrects the value of the user data coding rate to be adaptively set according to a channel quality indicator of a user, based on the type of control information to be time-multiplexed with user data and the rank indication of a data CH in which user data is transmitted, and sets the corrected value of the coding rate as the control information coding rate. That is, coding rate setting section  122  sets the user data coding rate to be adaptively set according to a channel quality indicator of a user, as a reference value, corrects the reference value based on the type of control information to be time-multiplexed with user data and the rank indication of a data CH in which user data is transmitted, and sets the corrected reference value as the control information coding rate. For example, coding rate setting section  122  sets control information coding rate R′ control  to be time-multiplexed with user data, based on user data coding rate R data , PUSCH offset ΔPUSCHoffset, per control information, and rank offset ΔRANKoffset, corresponding to a data CH rank indication, based on equation 4. 
         [0059]    In this way, according to the present embodiment, the value of the user data coding rate is corrected based on the type of control information and the data CH rank indication, and the corrected value of the coding rate is set as the control information coding rate. By this means, even when the rank indication of a data CH in which user data is transmitted is greater and the user data coding rate is set lower in adaptive modulation, it is possible to prevent the control information coding rate from being set excessively low and suppress the decrease in the efficiency of control information transmission. 
         [0060]    Further, by correcting the control information coding rate to become higher when a data CH rank indication is greater, it is possible to correct the value of the user data coding rate, based on the difference of the influence of interference between streams that the data CH suffers and the influence of interference between streams that a control CH suffers, so as to set the user data coding rate as the control information coding rate. As a result of this, even when the user data coding rate is extremely low, it is possible to prevent the control information coding rate from being set excessively low and suppress the decrease in the efficiency of control information transmission. 
         [0061]    A case has been described with the above embodiment as an example where rank information offset obtaining section  1221  stores rank information offset table  1222 , in which the rank offset is defined separately for each rank indication, for example, from a to z. Rank information offset obtaining section  1221 , however, may not store rank information offset table  1222 , and may calculate rank offset ΔRANKoffset based on the equation shown as equation 6. 
         [0000]      ΔRANKoffset=(rank indication−1)× a ( a  is a constant)  (Equation 6)
 
         [0062]    Further, it is not necessary to define the rank offset at a different value for each rank indication, and it is possible to define the same rank offset for a plurality of rank indications. For example, it is possible to divide data channel rank indications into a plurality of groups by comparing the data channel rank indications with a predetermined threshold value, and define a rank offset so that the control information coding rate is set higher when a data CH rank indication in each group is greater. As shown in  FIG. 4 , for example, it is possible to define all rank offsets at a(a&gt;0) for the rank indication of 2 or greater. 
       Embodiment 2 
       [0063]    A case has been described with Embodiment 1 where, when a data CH rank indication is transmitted, the control information coding rate is set based on a rank offset corresponding to the data CH rank indication. A case will be described here with the present embodiment where, when a data CH rank indication and a control CH rank indication (the number of a rand for a control CH) are transmitted, the control information coding rate is set based on the rank offset based on the combination of the data CH rank indication and the control CH rank indication. 
         [0064]      FIG. 5  is a block diagram showing a main configuration of a terminal according to the present embodiment. In a terminal according to the present embodiment in  FIG. 5 , parts that are the same as in  FIG. 1  will be assigned the same reference numerals as in  FIG. 1  and overlapping explanations will be omitted. In  FIG. 5 , terminal  100   a  is provided with decoding section  116   a  and coding rate setting section  122   a  instead of decoding section  116  and coding rate setting section  122  in terminal  100  in  FIG. 1 . 
         [0065]    As is the case with Embodiment 1, the control information coding rate can be set either at a base station or at a terminal. A case will be described below where the control information coding rate is set at a terminal. 
         [0066]    Decoding section  116   a  obtains a decoded signal by correcting errors with respect to a demodulated signal output from demodulation section  115 . Then, decoding section  116   a  extracts, from the obtained decoded signal, information including an information data sequence, the number of bits per block K r , the number of subcarriers per subframe M sc , the number of symbols per subcarrier N symb , the PUSCH offset, the data CH rank indication, and the control CH rank indication. 
         [0067]    Decoding section  116   a  outputs the extracted information on K r , M sc , and N symb  to coding rate setting section  121 , and outputs information on the PUSCH offset, the data CH rank indication and the control CH rank indication to coding rate setting section  122   a.    
         [0068]    Coding rate setting section  122   a  sets control information coding rate R′ control  based on information on user data coding rate R data , the PUSCH offset, and the combination of the data CH rank indication and the control CH rank indication. The internal configuration of coding rate setting section  122  and the method of setting control information coding rate R′ control  will be explained later. Coding rate setting section  122   a  outputs the set control information coding rate R′ control  to coding modulation section  124 . 
         [0069]      FIG. 6  is a block diagram showing an internal configuration of coding rate setting section  122   a  according to the present embodiment. 
         [0070]    Rank information offset obtaining section  1221   a  stores rank information offset table  1222   a  inside, and obtains a rank offset ΔRANKoffset, corresponding to the combination of the data CH rank indication and the control CH rank indication, from rank information table  1222   a . Rank information offset table  1222   a  will be explained later. Rank information offset obtaining section  1221   a  outputs the obtained rank offset ΔRANKoffset, to coding rate calculating section  1223   a.    
         [0071]    Coding rate calculating section  1223   a  sets control information coding rate R′ control  based on user data coding rate R data , PUSCH offset ΔPUSCHoffset, and rank offset ΔRANKoffset, corresponding to the combination of the data CH rank indication and the control CH rank indication, based on equation 4. 
         [0072]      FIG. 7  shows an example of rank information offset table  1222   a  stored inside the rank information offset obtaining section  1221   a .  FIG. 7  shows a case where the maximum rank indication is 2. According to the present embodiment, rank information offset table  1222   a  stores rank offsets ΔRANKoffset, corresponding to the combinations of a data CH rank indication and a control CH rank indication. The relationship between rank offsets ΔRANKoffset and the combinations of a data CH rank indication and a control CH rank indication will be described below. 
         [0073]    As shown in case #1 in  FIG. 7 , when both the data CH rank indication and the control CH rank indication are 1, both the data CH and the control CH do not suffer interference between streams. Therefore, when obtaining the control information coding rate by correcting the user data coding rate, it is not necessary to consider the difference of the influence of interference between streams that the data CH suffers and the influence of interference between streams that the control CH suffers. Accordingly, as shown in case #1, when both the data CH rank indication and the control CH rank indication are 1, rank offset ΔRANKoffset is set at 0. When rank offset ΔRANKoffset is 0, the control information coding rate coincides with the coding rate that is set based on equation 3. 
         [0074]    As shown in case #2 in  FIG. 7 , when the data CH rank indication is 1 and the control CH rank indication is 2, only control information suffers reception quality deterioration due to interference between streams. In this case, rank offset ΔRANKoffset is set at a (a&lt;0). By setting ΔRANKoffset smaller than 0, it is possible to set the control information coding rate obtained based on equation 4 lower than the control information coding rate obtained based on equation 3. By this means, it is possible to enhance the capability of error correction of control in formation. 
         [0075]    As shown in case #3 in  FIG. 7 , when the data CH rank indication is 2 and the control CH rank indication is 1, only user data suffers reception quality deterioration due to interference between streams. In this case, rank offset ΔRANKoffset is set at b (b&gt;0). By setting ΔRANKoffset greater than 0, it is possible to set the control information coding rate obtained based on equation 4 higher than the control information coding rate obtained based on equation 3. By this means, it is possible to prevent control information from being encoded at an excessively low coding rate and suppress the decrease in the efficiency of control information transmission. 
         [0076]    As shown in case #4 in  FIG. 7 , when the data CH rank indication and the control CH rank indication are 2, both the data CH and the control CH suffer interference between streams. In this case, the influence of interference between streams is considered to be approximately equal between user data and control information. Accordingly, as shown in case #4, when both the data CH rank indication and the control CH rank indication are 2, the value (c), corresponding to the slight difference of the influence of interference between streams that the data CH suffers and the influence of interference between streams that the control CH suffers in the communication status between a base station and a terminal, is set as rank offset ΔRANKoffset. When the influence of interference between streams that a data CH suffers and the influence of interference between streams that a control CH suffers are equal, rank offset ΔRANKoffset may be set at 0, as is the case with case #1. 
         [0077]      FIG. 8  shows another example of rank information offset table  1222   a  stored inside the rank information offset obtaining section  1221   a .  FIG. 8  shows a case where the maximum rank indication is 4. The relationship between rank offset values ΔRANKoffset and the combinations of a data CH rank indication and a control CH rank indication will be described below. The explanation for cases #1 to 4 in  FIG. 8  are the same as for cases #1 to 4 in  FIG. 7 , therefore the explanation will be omitted. 
         [0078]    As shown in cases #5 and 9 in  FIG. 8  and as is the case with case #2 in  FIG. 7 , when the control CH rank indication is greater than the data CH rank indication, control information reception quality deteriorates more severely than user data reception quality, due to the difference of the influence of interference between streams. In this case, rank offset ΔRANKoffset is set smaller than 0. By setting ΔRANKoffset smaller than 0, it is possible to set the control information coding rate obtained based on equation 4 lower than the control information coding rate obtained based on equation 3. By this means, it is possible to enhance the capability of error correction of control information. In this case, for example, when the greater absolute value of rank offset ΔRANKoffset is set as the data CH rank indication is smaller than the control CH rank indication, the control information coding rate becomes lower as the data CH rank indication is smaller than the control CH rank indication. Therefore, it is possible to prevent the control information reception quality from being deteriorated. 
         [0079]    As shown in cases #6, 7, and 10-12 in  FIG. 8  and as is the case with case #3 in  FIG. 7 , when the data CH rank indication is greater than the control CH rank indication, the user data reception quality deteriorates more severely than the control information reception quality due to the difference of the influence of interference between streams. In this case, rank offset ΔRANKoffset is set greater than 0. By setting ΔRANKoffset greater than 0, it is possible to set the control information coding rate obtained based on equation 4 higher than the control information coding rate obtained based on equation 3. By this means, it is possible to prevent control information from being encoded at an excessively low coding rate and suppress the decrease in the efficiency of control information transmission. In this case, for example, when the greater absolute value of rank offset ΔRANKoffset is set as the data CH rank indication is greater than the control CH rank indication, the control information coding rate becomes higher as the data CH rank indication is greater than the control CH rank indication. As a result of this, it is possible to prevent control information from being encoded at an excessively low coding rate and suppress the decrease in the efficiency of control information transmission. 
         [0080]    As shown in cases #8 and 13 in  FIG. 8  and as is the case with case #4 in  FIG. 7 , when the data CH rank indication and the control CH rank indication are equal, the influence of interference between streams that the data CH suffers and the influence of interference between streams that the control CH suffers are considered to be approximately equal. In this case, as shown in case #4, when both the data CH rank indication and the control CH rank indication are equal, the value (g and l), corresponding to the slight difference of the influence of interference between streams that a data CH suffers and the influence of interference between streams that a control CH suffers in the communication status between a base station and a terminal, is set as rank offset ΔRANKoffset. When the influence of interference between streams that the data CH and the influence of interference between streams that the control CI suffers are equal, rank offset ΔRANKoffset may be set at 0, as is the case with case #1. 
         [0081]      FIG. 9  shows yet another example of rank information offset table  1222   a  stored inside rank information offset obtaining section  1221   a . In  FIG. 9 , an identical rank offset ΔRANKoffset is defined for a plurality of combinations of a data CH rank indication and a control CH rank indication at rank information offset obtaining section  1221   a . More specifically, an identical rank offset ΔRANKoffset is set for the combination where the data CH rank indication and the control CHI rank indication are equal. The relationship between the combinations of a data CH rank indication and a control CHI rank indication and rank offset ΔRANKoffset will be described below.  FIG. 9  shows a case where the maximum rank indication is 4, as is the case with  FIG. 8 . 
         [0082]    As shown in case #1 in  FIG. 9 , when both the data CH rank indication and the control CH rank indication are 1, both the data CH and the control CH do not suffer interference between streams. Further, when both the data CH rank indication and the control CH rank indication are equal and are 2 or greater, the influence of interference between streams that the data CH suffers and the influence of interference between streams that the control CH suffers are considered to be approximately equal. 
         [0083]    In this case, when the data CH rank indication and the control CH rank indication are equal, rank offset ΔRANKoffset is set at 0 assuming that the influence of interference between streams is equal between the data CH and the control CH. 
         [0084]    As shown in cases #2-6 in  FIG. 9 , when the data CH rank indication is greater than the control CH rank indication, the user data reception quality deteriorates more severely than the control information reception quality due to the difference of the influence of interference between streams. In this case, rank offset ΔRANKoffset is set greater than 0. By setting ΔRANKoffset greater than 0, it is possible to set the control information coding rate obtained based on equation 4 higher than the control information coding rate obtained based on equation 3. By this means, it is possible to prevent control information from being encoded at an excessively low coding rate and suppress the decrease in the efficiency of control information transmission. 
         [0085]    In this case, rank offset ΔRANKoffset of a greater value is set when the ratio of the data CH rank indication to the control CH rank indication (the data CH rank indication/the control CH rank indication) is greater. For example, in  FIG. 9 , when the relationship p&gt;n&gt;m&gt;o&gt;q holds, the control information coding rate becomes higher as the data CH rank indication is greater than the control CH rank indication. Accordingly, it is possible to prevent control information from being encoded at an excessively low coding rate and suppress the decrease in the efficiency of control information transmission. 
         [0086]    As described above, according to the present embodiment, coding rate setting section  122   a  corrects the value of the user data coding rate to be adaptively set according to a channel quality indicator of a user, based on the type of control information to be time-multiplexed with user data and the combination of the data CH rank indication and the control CH rank indication, and sets the corrected value of the coding rate as the control information coding rate. That is, coding rate setting section  122   a  sets the user data coding rate to be adaptively set according to a channel quality indicator of a user as a reference value, corrects the reference value based on the type of control information to be time-multiplexed with user data and the combination of the data CH rank indication and the control CH rank indication, and sets the corrected reference value as the control information coding rate. For example, control information coding rate, R′ control , to be time-multiplexed with user data is set based on user data coding rate R data . PUSCH offset ΔPUSCHoffset per control information, and rank offset, ΔRANKoffset, corresponding to the combination of the data CH rank indication and the control CH rank indication, based on equation 4. 
         [0087]    Further, by correcting the control information coding rate to be higher when the data CH rank indication is greater than the control CH rank indication, it is possible to correct the user data coding rate based on the difference of the influence of interference between streams that a data CH suffers and the influence of interference between streams that a control CH suffers, and set the control information coding rate. As a result of this, even when the user data coding rate is low, it is possible to prevent the control information coding rate from being set excessively low and suppress the decrease in the efficiency of control information transmission. 
         [0088]    Although cases have been described above as examples where the control information coding rate is set at a terminal, the present invention is by no means limited to this, and it is equally possible that a base station sets the control information coding rate and reports the set control information coding rate to a terminal, so that the terminal can obtain the reported control information coding rate. 
         [0089]    Further, it is also possible that a base station sets rank offset ΔRANKoffset instead of the control information coding rate, and report the set rank offset ΔRANKoffset to a terminal so that the terminal can obtain the control information coding rate using the reported rank offset ΔRANKoffset. 
         [0090]    Further, it is also possible that a base station reports a rank information offset table to a terminal via a higher layer. 
         [0091]    Further, the present invention is not limited to a data CH and a control CH, and is also applicable to other two channels having the different reception qualities required for the present invention. 
         [0092]    Although cases have been described with the above embodiment as examples where the present invention is configured by hardware, the present invention can also be realized by software in combination with hardware. 
         [0093]    Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. LSI is adopted here but this may also be referred to as “IC”, “system LSI”, “super LSI”, or “ultra LSI” depending on differing extents of integration. 
         [0094]    Further, the method of circuit integration is not limited to LSI&#39;s, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of a programmable field programmable gate array (FPGA) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible. 
         [0095]    Further, if integrated circuit technology comes out to replace LSI&#39;s as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application of biotechnology is possible, for example. 
         [0096]    The disclosure of Japanese Patent Application No. 2008-307658, filed on Dec. 2, 2008, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0097]    The present invention is useful as a coding rate setting method and a radio communication apparatus used for the radio communication system using adaptive modulation and MIMO technology. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100 ,  100   a  Terminal 
           110  Receiving section 
           111  Radio receiving section 
           112  CP removing section 
           113  FFT section 
           114  Propagation path estimation section 
           115  Demodulation section 
           116 ,  116   a  Decoding section 
           120  Transmission section 
           121 ,  122 ,  122   a  Coding rate setting section 
           123 ,  124  Coding modulation section 
           125  Channel multiplexing section 
           126  DFT-s-OFDM section 
           127  CP adding section 
           128  Radio transmission section 
           1221 ,  1221   a  Rank information offset obtaining section 
           1222 ,  1222   a  Rank information offset table 
           1223 ,  1223   a  Coding rate calculating section