PATENT ABSTRACT
Disclosed is a wireless transmitter that can prevent deterioration of the error rate characteristic without reducing the data rate during mobile communications also utilizing THP for FDE. In the device, an equivalent channel matrix computation unit ( 118 ) computes weights to be used for FDE of a transmission block and an equivalent channel matrix indicating equivalent channels that are generated from channel impulse responses, and a decomposition unit ( 119 ) obtains a lower triangular matrix (L), that consists of a diagonal element that includes a high channel quality at the front of the transmitting block and a low channel quality at the rear, so as to indicate the channel quality of the transmission block, and an element indicating interference with the transmission block, and a unitary matrix (Q) by means of LQ decomposition of the equivalent channel matrix. A computation unit ( 120 ) uses the lower triangular matrix (L) and the average channel quality to compute a matrix (B) that minimizes the mean square error of all symbols between the transmission block before precoding and a block received by a wireless receiver. A preceding unit ( 103 ) performs THP of the transmission block using the matrix (B).

PATENT DESCRIPTION
TECHNICAL FIELD  
       [0001]    The present invention relates to a radio transmitting apparatus and a precoding method. 
       BACKGROUND ART  
       [0002]    In recent years, modes of service have diversified in a radio communication system, typically represented by a mobile telephone system, and there is a demand to transmit, in addition to sound/voice data, a large volume of data such as still image data and moving image data, with high speed and high quality, through radio transmission. 
         [0003]    It is well settled that, when high speed wireless transmission is performed in mobile communication, a communication channel will become a frequency selective fading channel that is comprised of a plurality of paths of varying delay times. Consequently, for example, in single-carrier (“SC”) transmission in mobile communication, inter-symbol interference (“ISI”) is produced, in which a preceding channel interferes with a subsequent channel, and the error rate performance is severely deteriorated (see, for example, non-patent literature 1). 
         [0004]    Equalization technology refers to a technique of improving error rate performance by removing the influence of ISI. For example, frequency domain equalization (“FDE”) used in a radio receiving apparatus uses an equalization technology. In FDE, a received block is separated into orthogonal frequency components through the fast Fourier transform (“FFT”), and each frequency component is multiplied by an equalization weight (FDE weight) that is close to the reciprocal of the channel transfer function, and later converted into a time domain signal through the inverse fast Fourier transform (“IFFT”). By means of this FDE, it is possible to correct the spectrum distortion of a received block, and, as a result, reduce ISI and improve error rate performance. 
         [0005]    Now, a mobile communication terminal apparatus such as a mobile telephone basically operates on a battery, so that the power consumption of a radio receiving apparatus to be mounted on that mobile communication terminal apparatus is preferably even lower. Furthermore, a mobile communication terminal apparatus such as a mobile telephone is preferably miniaturized, so that a radio receiving apparatus to be mounted on that mobile communication terminal apparatus is preferably miniaturized even smaller. 
         [0006]    So, as a technique to realize a radio receiving apparatus that removes the influence of ISI and that is formed in a simple configuration, joint THP/transmission FDE to use Tomlinson-Harashima precoding (hereinafter “THP”), which is a precoding technology, and FDE, in combination, is studied (see, for example, non-patent literature 2). That is to say, study is underway to perform THP for a transmission block and perform FDE for the transmission block after THP in a radio transmitting apparatus. In THP, processing to sequentially subtract interference components of a transmission block based on channel information, is performed. By means of this THP, it is possible to cancel interference components added to a transmission block, in advance, reduce ISI and improve error rate performance. For example, even when there is a frequency component with its received level having so significantly lowered due to the influence of frequency selective fading that even FDE cannot completely equalize this frequency component and leaves an interference component (residual ISI), it is still possible to prevent error rate performance deterioration by canceling residual ISI in advance by using FDE and THP in combination. Furthermore, a radio transmitting apparatus performs the entire equalization processing, so that it is possible to realize a mobile communication terminal apparatus having a radio receiving apparatus that is smaller and that consumes less power than heretofore. 
         [0007]    Also, a method to combine THP and received signal detection in a code division multiple access communication system is under study as a technique to realize a radio receiving apparatus that removes the influence of ISI and that is formed in a simple configuration (see, for example, patent literature 1). 
         [0008]    When joint THP/transmission FDE is applied to SC transmission, although ISI is completely removed, channel quality (represented by, for example, the signal-to-noise power ratio (SNR)) becomes poor in symbols near the end of a transmission block after FDE, causing error rate performance deterioration. In order to prevent this deterioration of error rate performance, a conventional radio transmitting apparatus inserts a dummy symbol near the end of a transmission block where the SNR is poor (see, for example, non-patent literature 2). 
       CITATION LIST  
     Patent Literature 
       [0000]    
       
         PTL 1 
         Japanese Patent Application Laid-Open No. 2007-060662 
       
     
       Non-Patent Literature 
       [0000]    
       
         NPL 1 
         W. C. Jakes Jr., Ed., Microwave mobile communications, Wiley, New York, 1974 
         NPL 2: RCS 2007-75, pp. 129-134 (K. Takeda, H. Tomeba, F. Adachi, “Joint THP/pre-FDE for Single-Carrier Transmission,” IEICE Technical Report, RCS 2007-75, pp. 129-134, 2007-8) 
       
     
       SUMMARY OF INVENTION  
     Technical Problem 
       [0014]    When a dummy symbol is inserted near the end of a transmission block like in the conventional art described above, although error rate performance may improve, a data rate decrease to match the length of the dummy symbol is caused. 
         [0015]    It is therefore an object of the present invention to provide a radio transmitting apparatus and a precoding method whereby error rate performance deterioration can be prevented without causing a decrease of data rate, in mobile communication in which FDE and precoding are used in combination. 
       Solution to Problem 
       [0016]    A radio transmitting apparatus according to the present invention employs a configuration having: an operating section that performs an operation of an equalization channel matrix representing an equalization channel formed with a weight to use in equalization processing of a transmission block and a channel impulse response; a decomposing section that acquires lower triangular matrix L and unitary matrix Q by performing LQ decomposition of the equalization channel matrix, lower triangular matrix L comprising diagonal elements representing channel quality of the transmission block including higher channel quality in a first half of the transmission block and lower channel quality in a second half of the transmission block, and elements representing interference of the transmission block; a calculating section that calculates matrix B that minimizes a total of mean square errors of all symbols, between the transmission block prior to precoding and a received block in a radio receiving apparatus, using lower triangular matrix L and average channel quality; a precoding section that performs Tomlinson-Harashima precoding of the transmission block using matrix B; and an equalizing section that performs equalization processing of the transmission block using the weight. 
         [0017]    A precoding method according to the present invention includes: performing an operation of an equalization channel matrix representing an equalization channel formed with a weight to use in equalization processing of a transmission block and a channel impulse response; acquiring lower triangular matrix L and unitary matrix Q by performing LQ decomposition of the equalization channel matrix, lower triangular matrix L comprising diagonal elements representing channel quality of the transmission block including higher channel quality in a first half of the transmission block and lower channel quality in a second half of the transmission block, and elements representing interference of the transmission block; calculating matrix B that minimizes a total of mean square errors of all symbols, between the transmission block prior to precoding and a received block in a radio receiving apparatus, using lower triangular matrix L and average channel quality; and performing Tomlinson-Harashima precoding of the transmission block using matrix B. 
       Advantageous Effects of Invention 
       [0018]    With the present invention, it is possible to prevent error rate performance deterioration without causing a decrease of data rate in mobile communication in which FDE and precoding are used in combination. 
     
    
     
       BRIEF DESCRIPTION OF  DRAWINGS 
         [0019]      FIG. 1  shows a simplified channel according to embodiment 1 of the present invention; 
           [0020]      FIG. 2  shows input/output characteristics of modulo operation according to embodiment 1 of the present invention; 
           [0021]      FIG. 3  shows diagonal elements of lower triangular matrix L according to embodiment 1 of the present invention; 
           [0022]      FIG. 4  shows an error vector to be minimum according to an MMSE criterion, according to embodiment 1 of the present invention; 
           [0023]      FIG. 5  shows error rate performance according to embodiment 1 of the present invention; 
           [0024]      FIG. 6  is a block diagram showing a radio transmitting apparatus according to the present invention; 
           [0025]      FIG. 7  is a block diagram showing an inner configuration of a precoding section according to embodiment 1 of the present invention; 
           [0026]      FIG. 8  is a block diagram showing a radio receiving apparatus according to embodiment 1 of the present invention; 
           [0027]      FIG. 9  is a block diagram showing another radio transmitting apparatus according to embodiment 1 of the present invention; 
           [0028]      FIG. 10  shows diagonal elements of lower triangular matrix L and diagonal elements of matrix B according to embodiment 2 of the present invention; 
           [0029]      FIG. 11  is a block diagram showing a radio transmitting apparatus according to embodiment 2 of the present invention; 
           [0030]      FIG. 12  is a block diagram showing a radio receiving apparatus according to embodiment 3 of the present invention (reporting method 1); 
           [0031]      FIG. 13  is a block diagram showing a radio transmitting apparatus according to embodiment 3 of the present invention (reporting method 1); 
           [0032]      FIG. 14  illustrates a table showing associations between average SNRs and reporting intervals according to embodiment 3 of the present invention; 
           [0033]      FIG. 15  is a block diagram showing a radio receiving apparatus according to embodiment 3 of the present invention (reporting method 2); 
           [0034]      FIG. 16  is a block diagram showing a radio transmitting apparatus according to embodiment 3 of the present invention (reporting method 2); and 
           [0035]      FIG. 17  illustrates a table showing associations between average SNRs and the numbers of reporting bits according to embodiment 3 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0036]    Now, embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0037]    With the present embodiment, a radio transmitting apparatus transmits an SC signal having been subjected to joint THP/transmission FDE, to a radio receiving apparatus. The radio transmitting apparatus also performs THP using matrix B that minimizes the total mean square error of all symbols, between a transmission block prior to THP, and a received block in the radio receiving apparatus. That is to say, with the present embodiment, a radio transmitting apparatus performs THP based on an MMSE (Minimum Mean Square Error) criterion to minimize the total value of the respective mean square errors of a plurality of symbols forming one transmission block. 
         [0038]    First, the principle of joint THP/transmission based on an MMSE criterion according to the present embodiment will be described. 
         [0039]    In joint THP/transmission FDE, a radio transmitting apparatus performs both THP and FDE. In joint THP/transmission FDE, lower triangular matrix L and unitary matrix Q, obtained by performing LQ decomposition of an equalization channel matrix formed with an FDE weight and channel impulse response to use in FDE for a transmission block comprised of N C  symbols, and average channel quality reported from the radio receiving apparatus, are used. 
         [0040]    To be more specific, in THP, a radio transmitting apparatus performs processing, including modulo operation, for a transmission block comprised of N C  symbols, that is, for a data symbol vector obtained by modulating transmission data, using lower triangular matrix L and average channel quality. By this means, a data symbol vector is converted into signal vector x=[x(0), x(1), . . . , x(N C −1)] T . “N C ” is the number of FFT points (the number of IFFT points), and the superscript “T” is the transpose of the vector. Then, a radio transmitting apparatus multiplies signal vector x by Hermitian transposed matrix Q H  of unitary matrix Q and power equalization coefficient for equalizing the power of signal vector x. The superscript H is the Hermitian transpose. 
         [0041]    On the other hand, in transmission FDE, a radio transmitting apparatus performs an N C -point FFT on the signal vector ΩQ H x after the multiplication, and converts the time domain signal into a frequency domain signal. Then, a radio transmitting apparatus multiplies the frequency domain signal by an FDE weight, performs an N C -point IFFT on the frequency domain signal after the multiplication, and converts the frequency domain signal back to a time domain signal. Also, the radio transmitting apparatus transmits the time domain signal by attaching a cyclic prefix (“CP”) to it. 
         [0042]    That is to say, with the present embodiment, as shown in the upper part of  FIG. 1 , signal vector x after THP is transmitted to a radio receiving apparatus via Hermitian transposed matrix Q H  of unitary matrix Q and an equalization channel. With the present embodiment, an equalization channel multiplied by matrix Q H  is used as a simplified channel. That is to say, the channel where signal vector x after THP propagates is formed with matrix Q H , FDE weight to use in FDE and channel impulse response. Here, multiplying the equalization channel by matrix Q H  gives lower triangular matrix L. That is to say, with the present embodiment, as shown in the lower part of  FIG. 1 , signal vector x after THP propagates through a channel represented by lower triangular matrix L and is transmitted to a radio receiving apparatus. 
         [0043]    The radio receiving apparatus removes the CP from the received signal and then processes the received signal sequence, including performing modulo operation, and demodulates the signal after the modulo operation. 
         [0044]    &lt;Transmission Signal&gt; 
         [0045]    A radio transmitting apparatus performs THP for a data symbol vector using lower triangular matrix L obtained by LQ-decomposing an equalization channel matrix, and matrix B calculated from average channel quality, and acquires signal vector x=[x(0), x(1), . . . , x(N C −1)] T  after THP, represented by following equation 1. 
         [0000]    
       
         
           
             
               
                 
                   
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         [0046]    Here, diag( ) represents a diagonal matrix which has given elements (matrix B in equation 1) as diagonal elements and in which all elements besides the diagonal elements are 0&#39;s, and 2 Mz t  represents a modulo operation circuit.  FIG. 2  shows input and output characteristics of a modulo operation circuit. In modulo operation, the real part and the imaginary part of a signal obtained by feedback filter loop processing are converted into an [−M, M] range to stabilize THP output. 2 Mz t is a (N   c ×1) vector, and the real part and imaginary part of z t  are both represented by integers. 
         [0047]    Matrix B to use in THP is given by following equation 2. How matrix B is derived will be described later. 
         [0000]    
       
         
           
             
               
                 
                   
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         [0048]    Here, I is a (N c ×N c ) unit matrix, and E s /N 0  is the signal energy to noise power spectrum density ratio per symbol, which shows average channel quality. Also, L is a lower triangular matrix obtained by LQ-decomposing equalization channel matrix ĥ, and equalization channel matrix ĥ, lower triangular matrix L and unitary matrix Q hold the relationship of equation 3. 
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         [0049]    Equalization channel ĥ is given by following equation 4. 
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         [0050]    Furthermore, element ĥ 1  in above equation 4 is given by following equation 5. 
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         [0000]    Here, H(k) (k=0˜N c −1) is the channel gain of a k-th orthogonal frequency component, and w(k) (k=0˜N c −1) is an FDE weight. It is equally possible to use, for example, a zero forcing (“ZF”) weight, a maximum ratio combining (“MRC”) weight, an equal gain combining (“EGC”) weight, or a minimum mean square error (“MMSE”) weight as an FDE weight. 
         [0051]    In lower triangular matrix L of  FIG. 1  representing a simplified channel, diagonal elements  1   τ,τ  (τ=0˜N c −1) show the received quality (SNR) of signal vector x (that is, a transmission block) after THP, as shown in  FIG. 3 . As shown in  FIG. 3 , diagonal elements  1   τ,τ  of lower triangular matrix L show the SNRs of a transmission block, including the higher SNRs in the first half of the transmission block and the lower SNRs in the second half of the transmission block. That is to say, in the channel of equation 3 represented by lower triangular matrix L, received quality (diagonal elements in lower triangular matrix L) is not fixed between symbols forming a transmission block. 
         [0052]    Also, referring to above equation 3, lower triangular elements in lower triangular matrix L besides the diagonal elements represent residual ISI in the transmission block. To be more specific, in lower triangular matrix L of equation 3,  1   1,0  is an residual ISI component of the symbol of symbol index  1  shown in  FIG. 3 ,  1   2,0  and  1   2,1  are residual ISI components of the symbol of symbol index  2  shown in  FIG. 3 , and  1   3,0  to  1   3,2  are residual ISI components of the symbol of symbol index  3  shown in  FIG. 3 . Likewise,  1   Nc−1,0  to  1   Nc−1,Nc−2  are residual ISI components of the symbol of symbol index N c −1 shown in  FIG. 3 . The same applies to the symbols of symbol indices 4˜N c −2. That is to say, in the channel of equation 3 represented by lower triangular matrix L, in the symbols to form a transmission block, symbols in the second half of the transmission block have more residual ISI components. In other words, residual ISI components are unevenly distributed in a transmission block. 
         [0053]    Next, a radio transmitting apparatus multiples signal vector x by power equalization coefficient Ω and Hermitian transposed matrix Q H  of unitary matrix Q. For example, power equalization coefficient Ω is given by following equation 6 using diagonal element b τ,τ  (τ=0˜N c −1) of matrix B (equation 2) to use in THP. Here, diagonal element b τ,τ  in matrix B shows the received quality (SNR) of each symbol forming a transmission block. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       6 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   Ω 
                   = 
                   
                     
                       
                         N 
                         
                           c 
                            
                           
                               
                           
                         
                       
                       / 
                       
                         
                           ∑ 
                           
                             τ 
                             = 
                             0 
                           
                           
                             
                               N 
                               c 
                             
                             - 
                             1 
                           
                         
                          
                         
                           ( 
                           
                             1 
                             / 
                             
                               
                                  
                                 
                                   b 
                                   
                                     τ 
                                     , 
                                     τ 
                                   
                                 
                                  
                               
                               2 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   6 
                   ] 
                 
               
             
           
         
       
     
         [0054]    Then, a radio transmitting apparatus performs FDE on signal vector ΩQ H x. That is to say, with signal vector ΩQ H x, a radio transmitting apparatus performs an N c -point FFT, a multiplication by FDE weight w(k) and an N c -point IFFT. Now, assume that a transmission data symbol vector after FDE is s′=[s′(0), s′(1), . . . , s′(N C −1)] T . Then, the radio transmitting apparatus attaches a CP to transmission data symbol vector s′ and transmits the result to a radio receiving apparatus. 
         [0055]    &lt;Channel&gt; 
         [0056]    A radio channel is formed with L individual paths, and, assuming that the gain and delay time of path  1  are h 1  and τ 1 , respectively, channel response h(τ) is given by following equation 7. δ(τ) is a delta function. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       7 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     h 
                      
                     
                       ( 
                       τ 
                       ) 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         l 
                         = 
                         0 
                       
                       
                         L 
                         - 
                         1 
                       
                     
                      
                     
                       
                         h 
                         l 
                       
                        
                       
                         δ 
                          
                         
                           ( 
                           
                             τ 
                             - 
                             
                               τ 
                               l 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   7 
                   ] 
                 
               
             
           
         
       
     
         [0057]    &lt;Received Signal&gt; 
         [0058]    Signal vector r=[r(0), r(1), . . . , r(N C −1)] T , which is a received block having propagated through a radio channel represented by equation 7, received by an antenna of a radio receiving apparatus and had the CP removed, is represented by following equation (8). 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       8 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         r 
                         = 
                           
                          
                         
                           
                             
                               
                                 
                                   2 
                                    
                                   
                                     E 
                                     s 
                                   
                                 
                                 
                                   T 
                                   s 
                                 
                               
                             
                              
                             
                               hs 
                               ′ 
                             
                           
                           + 
                           n 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               
                                 
                                   2 
                                    
                                   
                                     E 
                                     s 
                                   
                                 
                                 
                                   T 
                                   s 
                                 
                               
                             
                              
                             Ω 
                              
                             
                                 
                             
                              
                             
                               h 
                               ^ 
                             
                              
                             
                                 
                             
                              
                             
                               Q 
                               H 
                             
                              
                             x 
                           
                           + 
                           n 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               
                                 
                                   2 
                                    
                                   
                                     E 
                                     s 
                                   
                                 
                                 
                                   T 
                                   s 
                                 
                               
                             
                              
                             Ω 
                              
                             
                                 
                             
                              
                             
                               
                                 LB 
                                 
                                   - 
                                   1 
                                 
                               
                                
                               
                                 ( 
                                 
                                   s 
                                   + 
                                   
                                     2 
                                      
                                     
                                         
                                     
                                      
                                     
                                       Mz 
                                       t 
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                           + 
                           n 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   8 
                   ] 
                 
               
             
           
         
       
     
         [0000]    Here, E s  is average symbol energy, T s  is the symbol length, and n(=[n(0), n(1), . . . , n(N C −1)] T ) is a noise vector. The elements n(t) of noise vector n are zero-mean complex white Gaussian noise with variance of 2N 0 /T s . N 0  is one-sided noise power spectrum density. Also, h is a (N c ×N c ) cyclic channel impulse response matrix and can be represented by following equation 9. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       9 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   h 
                   = 
                   
                     [ 
                     
                       
                         
                           
                             h 
                             0 
                           
                         
                         
                           0 
                         
                         
                           … 
                         
                         
                           0 
                         
                         
                           
                             h 
                             
                               L 
                               - 
                               1 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             h 
                             1 
                           
                         
                       
                       
                         
                           
                             h 
                             1 
                           
                         
                         
                           
                             h 
                             0 
                           
                         
                         
                           0 
                         
                         
                           
                               
                           
                         
                         
                           ⋱ 
                         
                         
                           ⋱ 
                         
                         
                           ⋮ 
                         
                       
                       
                         
                           ⋮ 
                         
                         
                           
                             h 
                             1 
                           
                         
                         
                           
                             h 
                             0 
                           
                         
                         
                           ⋱ 
                         
                         
                           
                               
                           
                         
                         
                           ⋱ 
                         
                         
                           
                             h 
                             
                               L 
                               - 
                               1 
                             
                           
                         
                       
                       
                         
                           
                             h 
                             
                               L 
                               - 
                               1 
                             
                           
                         
                         
                           ⋮ 
                         
                         
                           
                             h 
                             1 
                           
                         
                         
                           ⋱ 
                         
                         
                           0 
                         
                         
                           
                               
                           
                         
                         
                           0 
                         
                       
                       
                         
                           0 
                         
                         
                           
                             h 
                             
                               L 
                               - 
                               1 
                             
                           
                         
                         
                           ⋮ 
                         
                         
                           ⋱ 
                         
                         
                           
                             h 
                             0 
                           
                         
                         
                           ⋱ 
                         
                         
                           ⋮ 
                         
                       
                       
                         
                           ⋮ 
                         
                         
                           ⋱ 
                         
                         
                           ⋱ 
                         
                         
                           
                               
                           
                         
                         
                           
                             h 
                             1 
                           
                         
                         
                           ⋱ 
                         
                         
                           0 
                         
                       
                       
                         
                           0 
                         
                         
                           … 
                         
                         
                           0 
                         
                         
                           
                             h 
                             
                               L 
                               - 
                               1 
                             
                           
                         
                         
                           ⋮ 
                         
                         
                           ⋱ 
                         
                         
                           
                             h 
                             0 
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   [ 
                   9 
                   ] 
                 
               
             
           
         
       
     
         [0059]    Then, a radio receiving apparatus acquires soft decision symbol vector ŝ represented by following equation 10 by inputting received signal vector r in a modulo operation circuit. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       10 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     s 
                     ^ 
                   
                   = 
                   
                     
                       
                         
                           ( 
                           
                             
                               
                                 2 
                                  
                                 
                                   E 
                                   s 
                                 
                               
                               
                                 T 
                                 s 
                               
                             
                              
                             
                               Ω 
                               2 
                             
                           
                           ) 
                         
                         
                           1 
                           2 
                         
                       
                        
                       r 
                     
                     + 
                     
                       2 
                        
                       
                         Mz 
                         r 
                       
                     
                   
                 
               
               
                 
                   [ 
                   10 
                   ] 
                 
               
             
           
         
       
     
         [0000]    Here, 2 Mz r  is a (N c ×1) vector, and the real part and imaginary part of z r  are represented by integers. 
         [0060]    Then, a radio receiving apparatus demodulates soft decision symbol vector ŝ. 
         [0061]    &lt;Calculation of Matrix B in THP Based on MMSE Criterion&gt; 
         [0062]    In THP based on an MMSE criterion, matrix B to minimize the total mean square error of all symbols, between a transmission block prior to THP, and a received block in a radio receiving apparatus, is used. To be more specific, error vector e between a transmission block prior to THP and a received block in the radio receiving apparatus is used. A correction term (2 Mz t ) is introduced in error vector e, to prevent the error being influenced by the modulo operation in the radio transmitting apparatus. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       11 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   e 
                   = 
                   
                     
                       
                         r 
                         - 
                         
                           
                             
                               2 
                                
                               
                                 
                                   E 
                                   s 
                                 
                                 / 
                                 
                                   T 
                                   s 
                                 
                               
                             
                           
                            
                           
                             C 
                              
                             
                               ( 
                               
                                 s 
                                 + 
                                 
                                   2 
                                    
                                   
                                     Mz 
                                     t 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             2 
                              
                             
                               
                                 E 
                                 s 
                               
                               / 
                               
                                 T 
                                 s 
                               
                             
                           
                         
                          
                         C 
                       
                     
                     ≅ 
                     
                       
                         
                           ( 
                           
                             
                               LB 
                               
                                 - 
                                 1 
                               
                             
                             - 
                             I 
                           
                           ) 
                         
                          
                         s 
                       
                       + 
                       
                         
                           1 
                           
                             
                               
                                 2 
                                  
                                 
                                   
                                     E 
                                     s 
                                   
                                   / 
                                   
                                     T 
                                     s 
                                   
                                 
                               
                             
                              
                             C 
                           
                         
                          
                         n 
                       
                     
                   
                 
               
               
                 
                   [ 
                   11 
                   ] 
                 
               
             
           
         
       
     
         [0000]    Here, C is a constant. 
         [0063]    Then, matrix B to minimize all elements of error vector e, that is, total mean square error e of all symbols (following equation 12), is determined. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       12 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   e 
                   = 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           0 
                         
                         
                           
                             N 
                             c 
                           
                           - 
                           1 
                         
                       
                        
                       
                         E 
                          
                         
                           [ 
                           
                             
                                
                               
                                 e 
                                 i 
                               
                                
                             
                             2 
                           
                           ] 
                         
                       
                     
                     = 
                     
                       tr 
                        
                       
                         [ 
                         
                           E 
                            
                           
                             [ 
                             
                               ee 
                               H 
                             
                             ] 
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   [ 
                   12 
                   ] 
                 
               
             
           
         
       
     
         [0000]    Here, E[ ] is an ensemble average and tr[ ] is a matrix trace. In THP based on an MMSE criterion according to the present embodiment, error vector e, which represents the difference between data symbol vector s (transmission data block prior to THP) and received signal vector r which has propagated through lower triangular matrix L and to which noise vector n is added. A correction term (2 Mz t ) is introduced in error vector e, to prevent the error being influenced by the modulo operation in the radio transmitting apparatus. That is, a radio transmitting apparatus calculates matrix B which suppresses both residual ISI components in the channel represented by lower triangular matrix L, and SNR deterioration due to noise vector n. 
         [0064]    By integrating both sides of above equation 12, following equation 13 is given. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       13 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       ∂ 
                       e 
                     
                     
                       ∂ 
                       
                         B 
                         
                           - 
                           1 
                         
                       
                     
                   
                   = 
                   
                     
                       
                         B 
                         
                           - 
                           H 
                         
                       
                        
                       
                         L 
                         H 
                       
                        
                       L 
                     
                     - 
                     L 
                     + 
                     
                       
                         ( 
                         
                           
                             E 
                             s 
                           
                           
                             N 
                             0 
                           
                         
                         ) 
                       
                        
                       
                         B 
                         
                           - 
                           H 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   13 
                   ] 
                 
               
             
           
         
       
     
         [0000]    In above equation 13, by calculating ∂e/∂B −1 =0, matrix B and inverse matrix B −1  in THP based on an MMSE criterion, are given by following equation 14. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       14 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     B 
                     
                       - 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             [ 
                             
                               
                                 
                                   L 
                                   H 
                                 
                                  
                                 L 
                               
                               + 
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         E 
                                         s 
                                       
                                       
                                         N 
                                         0 
                                       
                                     
                                     ) 
                                   
                                   
                                     - 
                                     1 
                                   
                                 
                                  
                                 I 
                               
                             
                             ] 
                           
                           
                             - 
                             1 
                           
                         
                          
                         
                           L 
                           H 
                         
                       
                       ⇔ 
                       B 
                     
                     = 
                     
                       
                         
                           L 
                           
                             - 
                             H 
                           
                         
                          
                         
                           [ 
                           
                             
                               
                                 L 
                                 H 
                               
                                
                               L 
                             
                             + 
                             
                               
                                 
                                   ( 
                                   
                                     
                                       E 
                                       s 
                                     
                                     
                                       N 
                                       0 
                                     
                                   
                                   ) 
                                 
                                 
                                   - 
                                   1 
                                 
                               
                                
                               I 
                             
                           
                           ] 
                         
                       
                       . 
                     
                   
                 
               
               
                 
                   [ 
                   14 
                   ] 
                 
               
             
           
         
       
     
         [0065]    As shown with above equation 14, when an average SNR (or E s /N 0 ) is low, B −1  becomes close to (E s /N 0 )L H . That is to say, in THP processing represented by equation 1, an average SNR (E s /N 0 ) and L H  included in matrix B contribute to improving the SNR of signal vector x, so that the SNR characteristic of the channel represented by lower triangular matrix L can be corrected. That is to say, when an average SNR (E s /N 0 ) is low, THP based on an MMSE criterion works to improve the SNR more preferentially than cancelling residual ISI. On the other hand, when an average SNR (E s /N 0 ) is low, B −1  becomes close to L −1 . That is to say, in THP processing represented by equation 1, L −1  included in matrix B cancels the channel represented by lower triangular matrix, so that it is possible to cancel the residual ISI included in the channel represented by lower triangular matrix L completely. That is to say, when an average SNR (E s /N 0 ) is high, THP based on an MMSE criterion works to cancel residual ISI more preferentially than improving the SNR. 
         [0066]    Thus, in THP based on an MMSE criterion, a channel in which residual ISI components are not uniform in a transmission block and in which the SNR is not constant in a transmission block (that is, the channel represented by lower triangular matrix in  FIG. 4 ), and noise (noise vector n shown in  FIG. 4 ), are taken into account. To be more specific, THP is performed based on an MMSE criterion which minimizes the total mean square error of all symbols, between a transmission block and a received block in a radio receiving apparatus. By this means, it is possible to cancel residual ISI that is distributed unevenly in a transmission block and distribute power between symbols in the transmission block, thereby reducing SNR deterioration in the second half of the transmission block shown in  FIG. 3 . 
         [0067]    In a computer simulation conducted by the present inventors, average bit error rate  11  in joint THP/transmission FDE not inserting a dummy symbol near the end of a transmission block, and average bit error rate  12  in joint THP/transmission FDE according to the present embodiment, are as shown in  FIG. 5 . Here, between E s /N 0  and signal energy to noise power spectrum density ratio E b /N 0  per bit, the relationship of E s /N 0 =10 log 10 (M)+E b /N 0  [dB] holds. M is the M-ary modulation value, which shows the number of bits per symbol (for example, M=2 in QPSK and M=4 in 16 QAM). It is clear from this computer simulation result that, whatever E b /N 0  is, average bit error rate  12  shows a better characteristic than average bit error rate  11 . Thus, THP based on an MMSE criterion improves the SNR when an average SNR is low and cancels residual ISI when an average SNR is high, thereby improving error rate performance. 
         [0068]    Next, the configurations of a radio transmitting apparatus and a radio receiving apparatus according to the present embodiment will be described.  FIG. 6  shows a configuration of radio transmitting apparatus  100  according to the present embodiment, and  FIG. 8  shows a configuration of radio receiving apparatus  200  according to the present embodiment. 
         [0069]    First, radio transmitting apparatus  100  will be described. In radio transmitting apparatus  100  shown in  FIG. 6 , coding section  101  encodes transmission data and outputs encoded transmission data to modulating section  102 . 
         [0070]    Modulating section  102  modulates the encoded transmission data received as input from coding section  101 , and generates a data symbol sequence. Then, modulating section  102  outputs the data symbol sequence to precoding section  103 . 
         [0071]    Precoding section  103  divides the data symbol sequence received as input from modulating section  102  into N c  transmission blocks (data symbol vector s), which matches the number of symbols to be subject to the FFT in FFT section  105  described later (FFT block length). Precoding section  103  performs THP based on an MMSE criterion (hereinafter “MMSE-THP”) for a transmission block using matrix B (and matrix B −1 ) of equation 14 received as input from calculating section  120 . 
         [0072]      FIG. 7  is a block diagram showing an internal configuration of precoding section  103 . Multiplying section  131  multiples a transmission block (data symbol vector s) by {diag(B)} −1  using matrix B received as input from calculating section  120 . 
         [0073]    Adder  132  subtracts a signal component received as input from feedback filter  134 , from a transmission block received as input from multiplying section  131 . By means of this subtraction, residual ISI components after transmission FDE are cancelled. 
         [0074]    Modulo operation section  133  applies modulo operation of input and output characteristics shown in  FIG. 2 , to the transmission block after the subtraction. Also, modulo operation section  133  outputs the transmission block after the operation, to feedback filter  134  and multiplying section  104  ( FIG. 6 ). 
         [0075]    Feedback filter  134  multiplies the transmission block received as input from modulo operation section  133 , by {diag(B)} −1 (B−diag(B)). That is to say, by performing filtering processing in feedback filter  134 , only the residual ISI components in the transmission block remain. Then, feedback filter  134  outputs the signal components after the filtering to adder  132 . 
         [0076]    Then, precoding section  103  outputs transmission block x after THP, represented by equation 1, to multiplying section  104 . 
         [0077]    Multiplying section  104  multiplies the transmission block after THP, received as input from precoding section  103 , by Hermitian transposed matrix Q H  of unitary matrix Q (equation 3) received as input from decomposing section  119 , and by power equalization coefficient Ω (equation 6) that is calculated in calculating section  120  as in equation 5 using diagonal elements of matrix B (equation 14). Then, multiplying section  104  outputs transmission block ΩQ H x after the multiplication, to FFT section  105 . 
         [0078]    FFT section  105  performs an N c -point FFT on transmission block ΩQ H x after the multiplication, received as input from multiplying section  104 , and converts a time domain signal having a block length of N c  into a frequency domain signal comprised of N c  frequency components. Then, FFT section  105  outputs the frequency domain signal to FDE section  106 . 
         [0079]    FDE section  106  performs FDE for the frequency domain signal received as input from FFT section  105  using FDE weight w(k) (k=0˜N c −1) received as input from weight calculating section  117 . To be more specific, FDE section  106  multiplies the frequency components of the frequency domain signal by FDE weight w(k). Then, FDE section  106  outputs the frequency domain signal after FDE, to IFFT section  107 . 
         [0080]    IFFT section  107  performs an IFFT on the frequency domain signal received as input from FDE section  106  per block, that is, performs an N c -point FFT, and converts the frequency domain signal into a transmission block, which is a time domain signal. Then, IFFT section  107  outputs the transmission block after the IFFT (transmission data symbol vector s′) to multiplexing section  108 . 
         [0081]    Multiplexing section  108  multiplexes the transmission block received as input from IFFT section  107  and a pilot signal, and outputs the transmission block after the multiplexing to CP adding section  109 . 
         [0082]    CP adding section  109  attaches an end portion of the transmission block received as input from multiplexing section  108  to the beginning of that transmission block as a CP. 
         [0083]    Radio transmitting section  110  performs radio transmission processing of the transmission block with a CP, including D/A conversion, amplification and up-conversion, and transmits the result to radio receiving apparatus  200  ( FIG. 8 ) from antenna  111 . That is to say, radio transmitting section  110  transmits an SC signal with a CP to radio receiving apparatus  200 . 
         [0084]    On the other hand, radio receiving section  112  receives the signal transmitted from radio receiving apparatus  200  ( FIG. 8 ) and performs radio receiving processing of the received signal including down conversion and A/D conversion. Then, radio receiving section  112  outputs the signal after radio receiving processing to demodulating section  113 . 
         [0085]    The received signal includes a data signal and a control signal which contains SNR information that shows an average SNR and CIR information that shows the CIR. 
         [0086]    Demodulating section  113  demodulates the received signal received as input from radio receiving section  112  and outputs the demodulated signal to decoding section  114 . 
         [0087]    Decoding section  114  decodes the signal received as input from demodulating section  113 . Then, decoding section  114  outputs the decoded data signal as received data and outputs the decoded control signal to extracting section  115 . 
         [0088]    Extracting section  115  extracts the SNR information and CIR information from control signal received as input from decoding section  114 . Then, extracting section  115  outputs the extracted SNR information and CIR information to dequantizing section  116 . 
         [0089]    Dequantizing section  116  dequantizes the CIR information and SNR information received as input from extracting section  115  and finds the CIR and average SNR. Then, dequantizing section  116  output the CIR to weight calculating section  117  and equalization channel matrix operation section  118 , and outputs the average SNR to calculating section  120 . 
         [0090]    Weight calculating section  117  calculates FDE weight w(k) (k=0˜N c −1) to use in FDE for a transmission block using the CIR received as input from dequantizing section  116 . Then, weight calculating section  117  outputs FDE weight w(k) to equalization channel matrix operation section  118  and FDE section  106 . 
         [0091]    Equalization channel matrix operation section  118  calculates an equalization channel matrix representing an equalization channel formed with the FDE weight received as input from weight calculating section  117  and the CIR received as input from dequantizing section  116 . To be more specific, equalization channel matrix operation section  118  calculates each element ĥ 1  of equalization channel matrix ĥ using FDE weight w(k), and channel gain H(k) by applying the FFT to the CIR, and generates equalization channel matrix ĥ represented by equation 4. Then, equalization channel matrix operation section  118  outputs equalization channel matrix ĥ to decomposing section  119 . 
         [0092]    As represented by equation 3, decomposing section  119  acquires lower triangular matrix L and unitary matrix Q by LQ decomposing equalization channel matrix ĥ received as input from equalization channel matrix operation section  118 . As explained earlier, lower triangular matrix L is comprised of diagonal elements that represent the SNRs of a transmission block, including the higher SNRs in the first half of the transmission block and the lower SNRs in the second half of the transmission block, and elements that represent the residual ISI of the transmission block. Then, decomposing section  119  outputs lower triangular matrix L to calculating section  120  and unitary matrix Q to multiplying section  104 . 
         [0093]    Using lower triangular matrix L received as input from decomposing section  119  and an average SNR received as input from dequantizing section  116 , calculating section  120  calculates matrix B that minimizes the total mean square error of all symbols, between a transmission block prior to THP and a received block in radio receiving apparatus  200 , and inverse matrix B −1  of matrix B. To be more specific, calculating section  120  calculates matrix B and matrix B −1  represented by equation  14  using lower triangular matrix L and average SNR (E s /N 0 ). Furthermore, calculating section  120  calculates power equalization coefficient Ω represented by equation 6 using diagonal elements b τ,τ  (τ=0˜N c −1) of calculated matrix B. Calculating section  120  outputs matrix B and matrix B −1  to precoding section  103 , and outputs power equalization coefficient Ω to multiplying section  104 . 
         [0094]    Next, radio receiving apparatus  200  will be described. In radio receiving apparatus  200  shown in  FIG. 8 , radio receiving section  202  receives an SC signal transmitted from radio transmitting apparatus  100  ( FIG. 6 ), that is to say, receives a block-unit symbol sequence, via antenna  201 , and performs radio receiving processing of the symbol sequence including down conversion and A/D conversion. 
         [0095]    CP removing section  203  removes the CP from the symbol sequence after the radio receiving processing, and outputs the symbol sequence without a CP (received signal vector r represented by equation  8 ) to modulo operation section  204 , channel estimating section  207  and SNR estimating section  210 . 
         [0096]    Modulo operation section  204  applies modulo operation to the symbol sequence received as input from CP removing section  203 , and outputs the symbol sequence after the operation (soft decision symbol vector represented by equation 10) to demodulating section  205 . 
         [0097]    Demodulating section  205  demodulates the symbol sequence received as input from modulo operation section  204 , and outputs the demodulated data signal to decoding section  206 . 
         [0098]    Decoding section  206  acquires the received data by decoding the data signal received as input from demodulating section  205 . 
         [0099]    Channel estimating section  207  extracts the pilot signal multiplexed upon the symbol sequence received as input from CP removing section  203 , and estimates the CIR using the extracted pilot signal. Then, channel estimating section  207  outputs the estimated CIR to quantizing section  208  and SNR estimating section  210 . 
         [0100]    Quantizing section  208  quantizes the CIR received as input from channel estimating section  207  and outputs the quantized CIR (bit sequence) to generating section  209 . 
         [0101]    Generating section  209  generates CIR information representing the quantized CIR received as input from quantizing section  208 . Generating section  209  outputs the generated CIR information to coding section  213 . 
         [0102]    SNR estimating section  210  extracts the pilot signal multiplexed upon the symbol sequence received as input from CP removing section  203  and estimates average SNR (E s /N 0 ) using the extracted pilot signal and the CIR received as input from channel estimating section  207 . Then, SNR estimating section  210  output estimated average SNR (E s /N 0 ) to quantizing section  211 . 
         [0103]    Quantizing section  211  quantizes the average SNR received as input from SNR estimating section  210  and outputs the quantized average SNR (bit sequence) to generating section  212 . 
         [0104]    Generating section  212  generates SNR information, which represents the quantized average SNR received as input from quantizing section  211 . Then, generating section  212  outputs the generated SNR information to coding section  213 . 
         [0105]    Coding section  213  encodes transmission data and a control signal including the CIR information received as input from generating section  209  and the SNR information received as input from generating section  212 , and outputs the coded signal to modulating section  214 . 
         [0106]    Modulating section  214  modulates the signal received as input from coding section  213  and outputs the modulated signal to radio transmitting section  215 . 
         [0107]    Radio transmitting section  215  performs radio transmission processing of the signal received as input from modulating section  214 , including D/A conversion, amplification and up-conversion, and transmits the result to radio transmitting apparatus  100  ( FIG. 6 ) from antenna  201 . 
         [0108]    Thus, in mobile communication in which a channel represented by lower triangular matrix L ( FIG. 3 ) is subject to radio communication, radio transmitting apparatus  100  performs MMSE-THP to cancel residual ISI and improve the SNR based on an average SNR and CIR reported from radio receiving apparatus  200 . To be more specific, MMSE-THP improves the SNR more preferentially when average SNR is low. On the other hand, when an average SNR is high, MMSE-THP cancels residual ISI more preferentially. That is, by using MMSE-THP, it is possible to achieve both a residual ISI suppression effect and an SNR improvement effect based on average SNR fluctuation. 
         [0109]    By this means, with the present embodiment, a radio transmitting apparatus performs THP based on an MMSE-criterion which minimizes the total mean square error of all symbols, between a transmission block and a received block in a radio receiving apparatus. By using MMSE-THP, it is possible to cancel residual ISI after FDE, and, furthermore, by improving the SNR, prevent error rate performance deterioration in the second half of a transmission block due to the use of FDE and THP in combination. Then, with the present embodiment, in mobile communication combining FDE and THP, it is possible to prevent error rate performance deterioration without causing a decrease of data rate. 
         [0110]    Furthermore, with the present embodiment, a radio transmitting apparatus calculates matrix B using the CIR and average SNR reported from a radio receiving apparatus. That is to say, a radio receiving apparatus has only to report the CIR and average SNR to a radio transmitting apparatus, so that it is possible to improve transmission efficiency. 
         [0111]    Furthermore, with the present embodiment, a radio transmitting apparatus calculates a power equalization coefficient using diagonal elements of matrix B as represented by equation 6. By this means, by using accurate power equalization coefficient Ω, the radio transmitting apparatus is able to perform transmission power control processing for a transmission block having been subjected to THE using matrix B. 
         [0112]    A case has been described with the present embodiment where FDE, which performs transmission equalization processing in the frequency domain, and MMSE-THP, are used in combination. However, with the present invention, it is equally possible to use a configuration to use time-domain transmission equalization processing and MMSE-THP in combination.  FIG. 9  shows a configuration of radio transmitting apparatus  300  to use time domain transmission equalization processing and MMSE-THP in combination. Parts in  FIG. 9  that are the same as in  FIG. 6  will be assigned the same reference codes as in  FIG. 6 , and their explanations will be omitted. Parts that differ between  FIG. 9  and  FIG. 6  include that processing of calculating a time domain transmission equalization weight is added in weight calculating section  117  in  FIG. 6 , and that FFT section  105 , FDE section  106  and IFFT section  107  are replaced by cyclic convolution operation section  301 . To be more specific, weight calculating section  117  of radio transmitting apparatus  300  shown in  FIG. 9  calculates FDE weight w(k) (k=0˜N c −1) to use in FDE for a transmission block, using the CIR received as input from dequantizing section  116  (or CIR and average SNR). Then, by performing an IFFT upon FDE weight w(k), weight calculating section  117  converts FDE weight w(k) into a time domain component and calculates a time domain transmission equalization weight. Then, weight calculating section  117  outputs the time domain transmission equalization weight to cyclic convolution operation section  301  and outputs FDE weight w(k) to equalization channel matrix operation section  118 . Cyclic convolution operation section  301  equalizes a transmission block in the time domain by performing a cyclic convolution operation of transmission block ΩQ H x received as input from multiplying section  104  and the time domain transmission equalization weight received as input from weight calculating section  117 . Then, cyclic convolution operation section  301  outputs the transmission block after the cyclic convolution operation (transmission data symbol vector s′), to multiplexing section  108 . By this means, it is possible to use time domain transmission equalization processing and MMSE-THP in combination and achieve the same effect as by the present embodiment. 
         [0113]    Furthermore, a case has been described with the present embodiment where a radio transmitting apparatus performs THP using matrix B that minimizes the total mean square error of all symbols, between a transmission block prior to THP, and a received block in a radio receiving apparatus. However, with the present invention, a radio transmitting apparatus may assign weights to the mean square errors of symbols, between a transmission block prior to THP and a received block in a radio receiving apparatus, and perform THP using matrix B that minimizes the total of the weighted mean square errors of all symbols. For example, it is possible to define total average square error e of all symbols represented by following equation using weighting coefficients α i  (i=0˜N c −1) for the mean square errors of symbols in a transmission block. 
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         [0114]    By this means, a radio transmitting apparatus achieves both a residual ISI suppression effect and an SNR improvement effect more efficiently by, for example, assigning weighting coefficients α i  (i=0˜N c −1) to each symbol&#39;s mean square error according to the significance of each symbol&#39;s mean square error in a transmission block. 
         [0115]    For example, upon assigning a weight to the mean square error of each symbol in a transmission block, a radio transmitting apparatus sets weighting coefficients α i  (i=0˜N c −1) according to the scale of diagonal elements in lower triangular matrix L. For example, when a diagonal element of lower triangular matrix L is big (that is, when channel quality is high), an error in the channel has little impact on symbols in a transmission block, whereas, when a diagonal element in lower triangular matrix L is small (that is, when channel quality is low), an error in the channel has significant impact on transmission blocks in a transmission block. That is to say, when a diagonal element of lower triangular matrix L is smaller (that is, when channel quality is lower), the significance of the mean square error of the symbol corresponding to that diagonal element becomes higher. Consequently, when a diagonal element of lower triangular matrix L is smaller (that is, when channel quality is lower), it is possible to increase the value of weighting coefficient α i  (i=0˜N c −1). By this means, it is possible to make the mean square error of each symbol in a transmission block reflect the influence of diagonal elements showing symbol-specific channel quality (for example, SNR) in a transmission block, thereby achieving a better SNR improvement effect. 
         [0116]    Furthermore, when diagonal elements in lower triangular matrix L show the channel quality (for example, the SNR) of a transmission block including higher channel quality (for example, the SNR) in the first half of the transmission block and lower channel quality (for example, the SNR) in the second half of the transmission block, a radio transmitting apparatus may set a greater value for weighting coefficient α i  (i=N c −1) for a symbol in the second half of a transmission block. By this means, it is possible to make the mean square error of each symbol in a transmission block reflect the influence of diagonal elements in lower triangular matrix L and achieve a better SNR improvement effect. 
       Embodiment 2 
       [0117]    A case will be described with the present embodiment where point-to-multipoint communication (for example, downlink transmission from a base station to a plurality of mobile communication terminals) is performed or multipoint-to-point communication (for example, uplink transmission from a plurality of mobile communication terminal to a base station) is performed. 
         [0118]      FIG. 10  shows diagonal elements (solid line) of matrix B to use in THP based on an MMSE criterion according to the present invention, and diagonal elements (dotted line) of lower triangular matrix. As shown in  FIG. 10 , the characteristics of diagonal elements of matrix B (that is to say, the received quality of each symbol forming a transmission block) vary according to E b /N 0 . For example, as shown in  FIG. 10 , when E b /N 0 =0 dB, the values of diagonal elements in matrix B become significantly bigger near the end of a transmission block. Furthermore, when E b /N 0 =5 dB, diagonal elements of matrix B in a transmission block are substantially fixed. 
         [0119]    When E b /N 0  is high (for example, when E b /N 0 =20), that is, when the distance between a radio transmitting apparatus and a radio receiving apparatus is short, the radio transmitting apparatus transmits a transmission block to the radio receiving apparatus by making the transmission power lower by transmission power control. In this case, even in a mobile communication system where a plurality of radio communication apparatuses including a radio transmitting apparatus and a radio receiving apparatus use the same frequency, a transmission block that is transmitted from a radio transmitting apparatus interferes little with a different radio communication apparatus. On the other hand, when E b /N 0  is low (for example, when E b /N 0 =0), that is, when the distance between a radio transmitting apparatus and a radio receiving apparatus is long, the radio transmitting apparatus transmits a transmission block to the radio receiving apparatus by making the transmission power higher by transmission power control. In this case, in a mobile communication system where a plurality of radio communication apparatuses use the same frequency, a transmission block that is transmitted from a radio transmitting apparatus interferes with a different radio communication apparatus (for example, a radio communication apparatus having a shorter distance to the radio transmitting apparatus than a radio receiving apparatus). In particular, in the case of E b /N 0 =0 as shown in  FIG. 10 , the transmission power of a symbol near the end of a transmission block becomes even greater than the transmission power of symbols other than symbols near the end of the transmission block. Consequently, a different radio communication apparatus is subject to varying magnitudes of interference per symbol in a transmission block. 
         [0120]    Each radio communication apparatus performs adaptive modulation and channel coding (“AMC”) control to select a modulation and channel coding scheme (“MCS”) set according to received quality, based on received signal power and also based on interference power. Consequently, when interference is produced in varying degrees in a transmission block, each radio communication apparatus is unable to select an optimal MCS set and therefore is unable to perform accurate AMC control. Consequently, the system throughput of the mobile communication system is deteriorated. Here, by exchanging information about interference between varying radio communication apparatuses, a control to minimize the interference against a plurality of radio communication apparatuses that use the same frequency, may be possible. However, when performing such control, it is necessary to perform complex control processing and calculation processing. Now, when E b /N 0  is high (for example, when E b /N 0 =20), that is, when the distance between a radio transmitting apparatus and a radio receiving apparatus is short, the radio transmitting apparatus transmits a transmission block to the radio receiving apparatus by making the transmission power lower by transmission power control. In this case, even in a mobile communication system where a plurality of radio communication apparatuses including a radio transmitting apparatus and a radio receiving apparatus use the same frequency, a transmission block that is transmitted from a radio transmitting apparatus interferes little with a different radio communication apparatus. On the other band, when E b /N 0  is low (for example, when E b /N 0 =0), that is, when the distance between a radio transmitting apparatus and a radio receiving apparatus is long, the radio transmitting apparatus transmits a transmission block to the radio receiving apparatus by making the transmission power higher by transmission power control. In this case, in a mobile communication system where a plurality of radio communication apparatuses use the same frequency, a transmission block that is transmitted from a radio transmitting apparatus interferes with a different radio communication apparatus (for example, a radio communication apparatus having a shorter distance to the radio transmitting apparatus than a radio receiving apparatus). In particular, in the case of E b /N 0 =0 as shown in  FIG. 10 , the transmission power of a symbol near the end of a transmission block becomes even greater than the transmission power of symbols other than symbols near the end of the transmission block. Consequently, a different radio communication apparatus is subject to varying magnitudes of interference per symbol in a transmission block. 
         [0121]    So, with the present embodiment, a radio transmitting apparatus calculates matrix B using average SNR (E s /N 0 ), which adds an offset to average SNR (E s /N 0 ) and lower triangular matrix L. 
         [0122]    This will be described in detail below.  FIG. 11  shows the configuration of radio transmitting apparatus  400  according to the present embodiment. Parts in  FIG. 11  that are the same as in  FIG. 6  will be assigned the same reference codes as in  FIG. 6 , and their explanations will be omitted. 
         [0123]    Deciding section  401  of radio transmitting apparatus  400  shown in  FIG. 11  decides whether or not to add an offset to an average SNR (E s /N 0 ) based on an average SNR (E s /N 0 ) received as input from dequantizing section  116 . For example, when an average SNR (E s /N 0 ) received as input from dequantizing section  116  is lower than a predetermined threshold and diagonal elements of matrix B calculated from that average SNR (E s /N 0 ) fluctuate significantly in a transmission block (for example, when E b /N 0 =0 dB as shown in  FIG. 10 ), deciding section  401  decides to add an offset to the average SNR (E s /N 0 ). Then, deciding section  401  commands calculating section  120  to given an offset to the average SNR (E s /N 0 ). 
         [0124]    Calculating section  120 , when commanded by deciding section  401  to give an offset to an average SNR (E s /N 0 ), gives an offset to an average SNR (E s /N 0 ) received as input from dequantizing section  116 . Then, calculating section  120  calculates matrix B represented by equation 14 using an average SNR (E s /N 0 ) with an offset, and lower triangular matrix L. That is to say, calculating section  120  calculates matrix B using an average SNR that is different from the actual average SNR, when interference applied against a different radio communication apparatus is significant and the magnitude of interference fluctuates significantly in a transmission block. 
         [0125]    To be more specific, first, calculating section  120  sets E b /N 0  offset value Δ b . Then, calculating section  120  calculates matrix B represented by equation 14 using an average SNR (E s /N 0 =10 log 10 (M)+E b /N 0 +Δ b  [dB]), which adds offset value Δ b  to an average SNR (E s /N 0 =10 log 10 (M)+E b /N 0  [dB]). 
         [0126]    For example, in the event E b /N 0 =0 dB where diagonal elements of matrix B fluctuate significantly in a transmission block, calculating section  120  sets offset value Δ b =5 dB. By this means, calculating section  120  calculates matrix B represented by equation 14 using an average SNR (E s /N 0 =10 log 10 (M)+0+5 [dB]), which adds offset value Δ b =5 dB to an average SNR (E s /N 0 =10 log 10 (M)+0 [dB]). That is to say, when E b /N 0 =0 dB, calculating section  120  calculates matrix B of when E b /N 0 =5 dB shown in  FIG. 10 . As shown in  FIG. 10 , the received quality of diagonal elements of matrix B of when E b /N 0 =5 dB is substantially fixed in a transmission block. 
         [0127]    Thus, radio transmitting apparatus  400  can suppress the fluctuation of received quality in a transmission block by performing MMSE-THP by giving an offset to an average SNR, even when diagonal elements of matrix B fluctuate significantly in a transmission block, such as when E b /N 0 =0 dB, as shown in  FIG. 10 . By this means, significant fluctuation of interference applied against a different radio communication apparatus is suppressed in a transmission block, so that the different radio communication apparatus is able to perform accurate AMC control. Consequently, it is possible to prevent the system throughput of a mobile communication system from deteriorating. 
         [0128]    With the present embodiment, calculating section  120  adds an offset to an average SNR and calculates matrix B using an average SNR that is different from the actual average SNR. That is to say, referring to equation 14, E s /N 0  that is different from the actual value is used, and, consequently, MMSE-THP using calculated matrix B cannot achieve an optimal SNR improvement effect. However, even when calculating section  120  gives an offset to an average SNR, lower triangular matrix L is acquired using the actual CIR, so that the ISI suppression effect does not deteriorate significantly. 
         [0129]    Thus, with the present embodiment, diagonal elements of matrix B fluctuate significantly in a transmission block, a radio transmitting apparatus calculates matrix B using an average SNR which adds an offset to an average SNR. By this means, the received quality in a transmission block is smoothed. That is to say, interference given from a different radio communication apparatus does not fluctuate significantly in a transmission block. Consequently, with the present embodiment, even when a plurality of radio communication apparatuses communicate at the same time using the same frequency, each radio communication apparatus is still able to perform accurate AMC control, so that the system throughput of a mobile communication system can be prevented from deteriorating. 
         [0130]    With the present embodiment, a case has been described where calculating section  120  gives an offset to an average SNR (E s /N 0 ) using E b /N 0  offset value Δ b . However, with the present invention, calculating section  120  may given an offset to an average SNR (E s /N 0 ) or E s /N 0  using average SNR offset value Δ SNR  or E s /N 0  offset value Δ S . For example, calculating section  120  may calculate matrix B using average SNR+Δ SNR  [dB], which adds average SNR offset value Δ SNR  to an average SNR (E s /N 0 ), and lower triangular matrix L, or may calculate matrix B using E s /N 0 +Δ S  [dB], which adds E s /N 0  offset value Δ s  to E s /N 0 , and lower triangular matrix L. By this means, the same effects as by the present embodiment can be achieved. 
         [0131]    Furthermore, with the present embodiment, it is possible to change an MCS set to select in AMC control, based on an offset value. To be more specific, when a radio transmitting apparatus mounted on a radio communication base station apparatus (hereinafter “base station”) performs MMSE-THP transmission with a radio communication apparatus mounted on a given radio communication mobile station apparatus (hereinafter “mobile station”) using matrix B calculated using an average SNR, which adds an offset to an average SNR, the base station may switch to and use for that mobile station an MCS set of lower data transmission speed when the absolute value of the offset value given to that average SNR increases. For example, when the absolute value of an offset value increases, the base station may change an MCS set of a modulation scheme of 16 QAM and a coding rate of ½, to an MCS set of a modulation scheme of QPSK and a coding rate of ⅓, and lower the transmission speed. By this means, it is possible to achieve the same effect as with the present embodiment and also correct the deterioration of received quality due to the use of matrix B calculated using E b /N 0  (or E s /N 0 , average SNR, etc.) that is different from the actual channel. 
         [0132]    With the present embodiment, the range of offset value fluctuation may be changed on an adaptive basis based on the number of radio communication apparatuses (or the volume of traffic) in a communication system. For example, when the number of radio transmitting apparatuses (for example, radio communication apparatuses having established communication with that radio transmitting apparatus) in a communication system (or the volume of traffic) is decided to be greater than a predetermined threshold, a radio transmitting apparatus mounted on a base station may control the range of offset value fluctuation on an adaptive basis by making the range of offset value fluctuation bigger. Also, when a radio transmitting apparatus is mounted on a mobile station and a base station decides that the number of radio communication apparatuses (for example, radio communication apparatuses having established communication with that base station) in a communication system (or the volume of traffic) is decided to be greater than a predetermined threshold, the base station may control the range of offset value fluctuation on an adaptive basis by commanding the mobile station to make the range of offset value fluctuation smaller. By this means, it is possible to reduce the fluctuation of interference against a different radio communication apparatus in a transmission block when the number of radio communication apparatuses (or the volume of traffic) in a radio communication system is large. Also, when the number of radio communication apparatuses (or the volume of traffic) in a communication system is small, even if a different radio communication apparatus is unable to perform accurate AMC control, this has little impact on the system as a whole. Consequently, by making the range of offset value fluctuation small and using an average SNR that is close to the actual average SNR, it is possible to suppress MMSE-THP performance deterioration in the radio transmitting apparatus, that is, prevent the SNR improvement effect and residual ISI suppression effect of the radio transmitting apparatus from deteriorating. Thus, it is possible to suppress system throughput deterioration by changing the range of offset value fluctuation on an adaptive basis according to the number of radio communication apparatuses (or the volume of traffic) in a communication system. 
         [0133]    Furthermore, with the present embodiment, it is equally possible to change the transmission power of an entire transmission block based on an offset value. For example, when a radio transmitting apparatus mounted on a base station apparatus performs MMSE-THP transmission with a radio communication apparatus mounted on a given mobile station using matrix B calculated using an average SNR, which adds an offset to an average SNR (E s /N 0 ), the base station may increase the transmission power to give to all symbols in a transmission block for that mobile station on an constant basis when the absolute value of an offset value increases. By this means, it is possible to achieve the same effect as with the present embodiment and also correct the deterioration of received quality due to the use of matrix B calculated using E b /N 0  (or E s /N 0 , average SNR, etc.) that is different from actual E b /N 0  of the channel. 
       Embodiment 3 
       [0134]    Referring to equation 14, when an average SNR (E s /N 0 ) is low, B −1  comes close to (E s /N 0 )L H  (or B comes close to (E s /N 0 ) −1 L −H ), or, when an average SNR (E s /N 0 ) is high, B −1  comes close to L −1  (or B comes close to L). That is, in MMSE-THP, when an average SNR (E s /N 0 ) is higher, the significance of an average SNR (E s /N 0 ) becomes lower, in other words, in MMSE-THP, when an average SNR (E s /N 0 ) is lower, the significance of average SNR (E s /N 0 ) becomes higher. 
         [0135]    Thus, MMSE-THP according to the present invention operates to provide an ISI suppression effect or an SNR improvement effect depending on an average SNR, the significance of report information to be reported from a radio receiving apparatus also changes depending on an average SNR. That is to say, the significance of CIR information that is necessary to acquire lower triangular matrix L and the significance of SNR information that is necessary to acquire an average SNR (E s /N 0 ), change depending on an average SNR. 
         [0136]    Whatever an average SNR (E s /N 0 ) is, lower triangular matrix L has significant impact on the calculation of matrix B. The change of significance based on average SNR is greater with an average SNR (E s /N 0 ) than with lower triangular matrix L. 
         [0137]    With the present embodiment, the method of reporting an average SNR (that is, SNR information) from a radio receiving apparatus to a radio transmitting apparatus, is switched according to an average SNR. 
         [0138]    Now, average SNR reporting methods 1 and 2 according to the present embodiment will be described. 
         [0139]    (Reporting Method 1) 
         [0140]    With this reporting method, the period of reporting an average SNR is made longer when an average SNR is higher. 
         [0141]    The configurations of a radio transmitting apparatus and a radio receiving apparatus according to the present reporting method will be described.  FIG. 12  shows the configuration of radio receiving apparatus  500  according to the present reporting method, and  FIG. 13  shows the configuration of radio receiving apparatus  600  according to the present reporting method. Parts in  FIG. 12  and  FIG. 13  that are the same as in  FIG. 6  and  FIG. 8  will be assigned the same reference codes as in  FIG. 6  and  FIG. 8 , and their explanations will be omitted. 
         [0142]    In radio receiving apparatus  500  shown in  FIG. 12 , control section  501  receives as input an average SNR from SNR estimating section  210 . Control section  501  controls the period of reporting an average SNR based on an average SNR. To be more specific, with reference to the table of  FIG. 14  showing associations between average SNRs and SNR reporting periods, control section  501  determines the interval of reporting an average SNR. Here, in  FIG. 14 , reporting interval T SNR ( 0 ) is the shortest and reporting interval T SNR ( 9 ) is the longest. Also, reporting intervals T SNR ( 0 ) to T SNR ( 9 ) are set in ascending order from the shortest reporting interval. That is to say, reporting intervals T SNR ( 0 ) to T SNR ( 9 ) hold the relationship of: reporting interval T SNR (i)≦reporting interval T SNR (i=0˜8). That is to say, according to the associations between average SNRs and average SNR reporting intervals shown in  FIG. 14 , a longer average SNR reporting interval is used when an average SNR is higher. That is to say, the average SNR reporting period becomes longer when average SNR is higher. Then, control section  501  outputs a determined reporting interval to generating section  212 . 
         [0143]    Generating section  212  generates SNR information at an interval received as input from control section  501  and outputs SNR information to coding section  213 . 
         [0144]    Radio transmitting section  215  transmits SNR information showing average SNR to radio transmitting apparatus at in a reporting period determined in control section  501 . 
         [0145]    Radio receiving section  112  of radio transmitting apparatus  600  shown in  FIG. 13  receives SNR information report showing an average SNR, from radio receiving apparatus  500  ( FIG. 12 ). Here, the SNR information reporting period is longer when an average SNR is higher. 
         [0146]    Control section  601  holds the same table as the table ( FIG. 14 ) held in control section  501  of radio receiving apparatus  500 . Then, control section  601  outputs, for example, the minimum reporting interval T SNR ( 0 ) amongst the reporting intervals shown in the table of  FIG. 14 , to extracting section  115 . 
         [0147]    Extracting section  115  extracts the SNR information included in a control signal received as input from decoding section  114 , at a reporting interval received as input from control section  601 . To be more specific, extracting section  115  performs blind detection of control information at minimum reporting interval T SNR ( 0 ) and extracts SNR information. By this means, at whatever interval SNR information is reported from radio receiving apparatus  500 , extracting section  115  is able to extract SNR information reliably. 
         [0148]    By this means, when an average SNR (E s /N 0 ) is lower (that is to say, when matrix B −1  comes close to (E s /N 0 )L H ), radio transmitting apparatus  600  receives an average SNR (E s /N 0 ) in a shorter reporting period. Consequently, radio transmitting apparatus  600  is able improve MMSE-THP performance by calculating matrix B using a newer average SNR (E s /N 0 ), that is to say, using an average SNR (E s /N 0 ) that reflects the channel condition at that time. 
         [0149]    By contrast with this, an average SNR (E s /N 0 ) is higher (that is to say, when matrix B −1  comes close to L −1 ), radio transmitting apparatus  600  receives an average SNR (E s /N 0 ) in a longer reporting period. Here, when an average SNR (E s /N 0 ) is higher, an average SNR (E s /N 0 ) has less impact on the calculation of matrix B. Consequently, radio transmitting apparatus  600  is able to reduce the amount of reporting for reporting an average SNR (that is, the number of bits required to report an average SNR), without causing MMSE-THP performance deterioration. 
         [0150]    Thus, with the present reporting method, when an average SNR is higher, the average SNR reporting period is made longer. By this means, a radio transmitting apparatus is able to reduce the amount of control information to be reported from a radio receiving apparatus without causing MMSE-THP performance deterioration. 
         [0151]    A case has been described above with the present reporting method where, when an average SNR is higher, the average SNR reporting period is made longer. However, with the present invention, it is equally possible to make the average SNR reporting period longer and make the CIR reporting period shorter when an average SNR is higher. By this means, when a radio transmitting apparatus or a radio receiving apparatus is moving fast, the radio transmitting apparatus is able to acquire CIR, which also fluctuates fast, with high accuracy. By this means, the radio transmitting apparatus is able to perform optimal MMSE-THP without increasing the amount of information to report, in a fast-moving environment. 
         [0152]    Also, a case has been described with the present reporting method where radio receiving apparatus  500  transmits SNR information showing an average SNR at a reporting interval determined in control section  501 , and where radio transmitting apparatus  600  extracts SNR information showing an average SNR by performing control signal blind detection at the minimum reporting interval amongst a plurality of reporting intervals. However, with the present invention, radio receiving apparatus  500  may report a reporting period index (for example, reporting period indices  0  to  9  shown in  FIG. 14 ) showing a reporting interval determined in control section  501 , to radio transmitting apparatus  600  as control information. By this means, control section  601  of radio transmitting apparatus  600  is able to specify a reporting interval based on a reporting period index received. Then, extracting section  115  extracts SNR information showing an average SNR per reporting interval specified by control section  601 . By this means, radio transmitting apparatus  600  is able to acquire an average SNR without performing blind detection. 
         [0153]    (Reporting Method 2) 
         [0154]    With the present reporting method, the amount of SNR reporting information is reduced when an average SNR is higher. 
         [0155]    The configurations of a radio transmitting apparatus and radio receiving apparatus according to the present reporting method will be described.  FIG. 15  shows a configuration of radio receiving apparatus  700  according to the present reporting method, and  FIG. 16  shows a configuration of radio transmitting apparatus  800  according to the present reporting method. Parts in  FIG. 15  and  FIG. 16  that are the same as in  FIG. 6  and  FIG. 8  will be assigned the same reference codes as in  FIG. 6  and  FIG. 8  and their explanations will be omitted. 
         [0156]    In radio receiving apparatus  700  shown in  FIG. 15 , control section  701  receives an average SNR as input from SNR estimating section  210 . Control section  701  controls the amount of SNR reporting information, that is, the number of bits necessary to report an average SNR, based on an average SNR. To be more specific, control section  701  determines the number of average SNR reporting bits with reference to the table of  FIG. 17  showing associations between average SNRs and the numbers of average SNR reporting bits. In  FIG. 17 , number of reporting bits N SNR ( 0 ) is the maximum and number of reporting bits N SNR ( 9 ) is the minimum. Furthermore, numbers of reporting bits N SNR ( 0 ) to N SNR ( 9 ) are set in descending order from the maximum number of reporting bits. That is to say, numbers of bits N SNR ( 0 ) to N SNR ( 9 ) hold the relationship of: number of reporting bits N SNR (i)≧number of reporting bits N SNR (i+1) (i=0˜8). That is to say, in the associations between average SNRs and the numbers of average SNR reporting bits in  FIG. 17 , the number of average SNR reporting bits becomes smaller when an average SNR is higher. Then, control section  701  outputs the determined number of reporting bits to quantizing section  211 . 
         [0157]    Quantizing section  211  quantizes an average SNR received as input from SNR estimating section  210  using the number of reporting bits received as input from control section  701 . 
         [0158]    Radio transmitting section  215  transmits SNR average information, which shows an average SNR of the number of bits determined in control section  701 , to radio transmitting apparatus  800 . 
         [0159]    Meanwhile, radio receiving section  112  of radio transmitting apparatus  800  shown in  FIG. 16  receives SNR information report, which shows an average SNR, from radio receiving apparatus  700  ( FIG. 15 ). The amount of average SNR information represented by SNR information (the number of reporting bits) is smaller when an average SNR is higher. 
         [0160]    Control section  801  holds the same table as the table ( FIG. 17 ) held in control section  701 . Then, control section  801  outputs all or a predetermined number of numbers of reporting bits, amongst the reporting intervals shown in the table of  FIG. 17 , to dequantizing section  116 . 
         [0161]    Dequantizing section  116  dequantizes SNR information using the number of reporting bits received as input from control section  801 , and acquires an average SNR. To be more specific, dequantizing section  116  dequantizes SNR information using different numbers of reporting bits until SNR information is accurately dequantizes. 
         [0162]    By this means, when an average SNR (E s /N 0 ) is lower (that is to say, when matrix B comes close to (E s /N 0 )L H ), radio transmitting apparatus  800  receives an average SNR (E s /N 0 ) quantized by a greater number of reporting bits. By this means, radio transmitting apparatus  800  can improve MMSE-THP performance by calculating matrix B using a more accurate average SNR (E s /N 0 ). 
         [0163]    By contrast with this, when an average SNR (E s /N 0 ) is higher (that is to say, when matrix B −1  comes close to L −1 ), radio transmitting apparatus  800  receives an average SNR (E s /N 0 ) quantized by a smaller number of reporting bits. Similar to reporting method 1, when an average SNR (E s /N 0 ) is higher, an average SNR (E s /N 0 ) has less impact on the calculation of matrix B. Consequently, radio transmitting apparatus  800  is able to reduce the amount of reporting for reporting an average SNR (that is, the number of bits required to report an average SNR), without causing MMSE-THP performance deterioration. 
         [0164]    Thus, according to the present reporting method, when an average SNR is higher, the amount of SNR reporting information is made smaller. By this means, similar to reporting method 1, a radio transmitting apparatus is able to reduce the amount of control information to report from a radio receiving apparatus without causing MMSE-THP performance deterioration. 
         [0165]    A case has been described with the present reporting method where the number of average SNR reporting bits is made smaller when an average SNR is higher. However, with the present invention, it is equally possible to make the number of average SNR reporting bits smaller and also make the number of CIR reporting bits bigger when an average SNR is higher. By this means, when an average SNR (E s /N 0 ) is higher (that is to say, when matrix B −1  comes close to L −1 ), a radio transmitting apparatus is able to acquire CIR, which is more significant information than an average SNR (E s /N 0 ), with high accuracy. Consequently, a radio transmitting apparatus is able to improve MMSE-THP performance without increasing the amount of information to report. 
         [0166]    Furthermore, a case has been described above with the present reporting method where radio receiving apparatus  700  quantizes an average SNR by the number of reporting bits determined in control section  701 , and radio transmitting apparatus  800  dequantizes SNR information using a plurality of numbers of reporting bits in order from a given number of reporting bits. However, with the present invention, radio receiving apparatus  700  may report a number-of-reporting-bits index (for example, number-of-reporting-bits indices  0  to  9  shown in  FIG. 17 ) showing the number of reporting bits determined in control section  701 , to radio transmitting apparatus  600  as control information. By this means; control section  801  of radio transmitting apparatus  800  is able to specify the number of reporting bits based on the number-of-reporting-bits index received. Then, dequantizing section  116  dequantizes SNR information using the number of reporting bits specified in control section  801 . By this means, radio transmitting apparatus  800  is able to acquire an average SNR without dequantizing a plurality of numbers of reporting bits in order. 
         [0167]    Average SNR reporting methods 1 and 2 according to the present embodiment have been described above. 
         [0168]    With the present embodiment, thus, by changing the method of reporting an average SNR according to an average SNR, it is possible to achieve the same effect as by embodiment 1 and furthermore reduce the amount of control signal information to report from a radio receiving apparatus to a radio transmitting apparatus. 
         [0169]    Although a case has been described above with the present embodiment where the method of reporting an average SNR is changed based on an average SNR, it is equally possible to change the method of reporting CIR based on an average SNR. As explained earlier, when an average SNR is lower, MMSE-THP operates to achieve an SNR improvement effect more than an ISI suppression effect. That is to say, when an average SNR (E s /N 0 ) is lower, lower triangular matrix L is less significant than lower triangular matrix L is when an average SNR (E s /N 0 ) is higher. Then, for example, it is possible to make the CIR reporting period longer when an average SNR is lower. It is also possible to make the number of CIR reporting bits smaller when an average SNR is lower. By this means, it is possible to reduce the amount of CIR reporting information without causing MMSE-THP performance deterioration. 
         [0170]    Although a case has been described above with the present embodiment where transmission PDE and MMSE-THP are used in combination, is equally possible to adopt above reporting methods 1 and 2 when transmission signal processing is performed based on an MMSE criterion (that is, when, for example, transmission equalization is performed based on an MMSE criterion). By this means, it is possible to reduce the amount of control signal information to report from a radio receiving apparatus to a radio transmitting apparatus without causing performance deterioration of transmission signal processing based on an MMSE criterion. 
         [0171]    Embodiments of the present invention have been described above. 
         [0172]    The radio transmitting apparatus and radio receiving apparatus of the present invention are suitable for use in, for example, a radio communication mobile station apparatus and radio communication base station apparatus to use in a mobile communication system. It is possible to provide a radio communication mobile station apparatus and a radio communication base station apparatus of the same operations and effects as described above, by mounting a radio transmitting apparatus and a radio receiving apparatus of the present invention on a radio communication mobile station apparatus and a radio communication base station apparatus. 
         [0173]    Also, 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. 
         [0174]    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. 
         [0175]    Further, the method of circuit integration is not limited to LSITs, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible. 
         [0176]    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 also possible. 
         [0177]    The disclosure of Japanese Patent Application No. 2008-234979, filed on Sep. 12, 2008, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY  
       [0178]    The present invention is applicable to a communication system.