Patent Publication Number: US-2009238290-A1

Title: Transmitting device, receiving device, transmitting method, receiving method and wireless communication system

Description:
TECHNICAL FIELD 
     The present invention relates to a transmitting apparatus, a receiving apparatus, a transmission method, a reception method and a wireless communication system in a MIMO-OFDM system adopting MIMO (Multiple Input Multiple Output) technique and OFDM (Orthogonal Frequency Division Multiplex) technique. 
     BACKGROUND ART 
     In the field of wireless cellular systems, which are represented by, for example, mobile phones, service modes become diverse, and transmitting large capacity data such as still images and movies in addition to voice data is in demand in recent years. On the other hand, a MIMO communication system which has high spectrum efficiency is studied actively. 
     SDM (Space Division Multiplex) scheme is one of techniques to improve transmission rate in MIMO communication systems. SDM scheme refers to transmitting different signals from a plurality of antennas at the same time and demultiplexing the signals at the receiving side. Incidentally, channel information is necessary upon demultiplexing signals. 
     Channel information can be estimated by using pilot symbols which are known information, at the receiving side, but there is a trade-off relationship between data rate and accuracy of channel estimation. That is, if the number of pilot symbols is small, a lot of data can be transmitted, but sufficient accuracy of channel estimation is not expected. In addition, if the number of pilot symbols is great, sufficient accuracy of channel estimation is expected, but data rate decreases accordingly. Consequently, a technique is demanded whereby data rate and accuracy channel of estimation are compatible. 
     As for a technique of being compatible between data rate and accuracy of channel estimation, a method for modulating pilot symbols and carrying information is disclosed in Non-patent document 1. This method performs differential modulation by providing a phase difference between the pilots of neighboring subcarriers at the transmitting side, and detects the phase difference between the pilots of neighboring subcarriers at the receiving side. This determines the end of the pilot period. With this method, if the phase variation between the channels of neighboring subcarriers is less than 180 degrees, this method does not influence channel estimation. 
     Non-patent Document 1: EGASHIRA Yoshimasa et al., “A study on preamble structure for channel estimation of MIMO-OFDM system considering estimation of the number of streams” Society conference of IEICE, 2004, B-5-137 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, in the above-described method disclosed in Non-patent Document 1, the distance between signal points upon differential modulation becomes smaller when information carried upon pilots increases, and, consequently, there are problems that error rate of the information carried upon pilots increases and the accuracy of channel estimation performed using pilots is also deteriorated. 
     For example, if four-bit information is carried upon a pilot, 16 PSK is used for the modulation scheme and the signal point arrangement shown in  FIG. 1  is employed. The phase difference between the signal points is only 22.5 degrees in this case, and, if the phase variation between the channels of neighboring subcarriers exceeds 22.5 degrees due to fast fading fluctuation, information carried upon pilots is not correctly detected. Moreover, a pilot cannot be regarded as a known signal, thereby deteriorating the accuracy of channel estimation. 
     It is therefore an object of the present invention to provide a transmitting apparatus, a receiving apparatus, a transmission method, a reception method and a wireless communication system for improving data rate while maintaining the accuracy of channel estimation or for improving the accuracy of channel estimation while maintaining data rate, in a MIMO-OFDM system. 
     Means for Solving the Problem 
     The transmitting apparatus of the present invention adopts a configuration including: a plurality of transmitting antennas; an antenna information adding section that assigns antenna information to pilot signals transmitted from the plurality of transmitting antennas respectively, the antenna information being attached to the pilot signals to identify the corresponding transmitting antennas; a subcarrier allocating section that allocates the pilot signals assigned the antenna information to subcarriers and combines the antenna information and the subcarriers to which the pilot signals are allocated; and a transmitting section that transmits another piece of information by a combination of the antenna information and the subcarriers to which the pilot signals are allocated. 
     The receiving apparatus of the present invention adopts a configuration including: a receiving section that receives pilot signals assigned antenna information, allocated to subcarriers, and transmitted from a plurality of transmitting antennas respectively, the antenna information being attached to the pilot signals to identify the corresponding transmitting antennas; an antenna specifying section that specifies transmitting antennas from which the pilot signals are transmitted from the antenna information; and a converting section that converts combination information of the specified transmitting antennas and the subcarriers to which the pilot signals are allocated, into another piece of information and acquires the another piece of information. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     According to the present invention, it is possible to improve data rate while maintaining the accuracy of channel estimation, or improve the accuracy of channel estimation while maintaining data rate in MIMO-OFDM system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates the pilot signal point arrangement adopting 16PSK according to the technique disclosed in Non-patent document 1; 
         FIG. 2  is a block diagram showing a configuration of the transmitting apparatus according to Embodiment 1 of the present invention; 
         FIG. 3  illustrates a table showing the phase relationships between common pilot signal and dedicated pilot signals; 
         FIG. 4  is a block diagram showing the internal configuration of the pilot arranging section shown in  FIG. 2 ; 
         FIG. 5  illustrates a control information conversion table; 
         FIG. 6  illustrates combinations of transmitting antennas and subcarriers; 
         FIG. 7  is a block diagram showing a configuration of the receiving apparatus according to Embodiment 1 of the present invention; 
         FIG. 8  is a block diagram showing the internal configuration of the pilot analyzing section shown in  FIG. 7 ; 
         FIG. 9  illustrates the correspondence relationships between transmitting antennas and phase differences between common pilot signal and dedicated pilot signals; 
         FIG. 10  illustrates a sequence diagram showing the steps of communications between the transmitting apparatus shown in  FIG. 2  and the receiving apparatus shown in  FIG. 7 ; 
         FIG. 11A  illustrates a state of allocating transmission pilot signals to subcarriers; 
         FIG. 11B  illustrates a state of allocating transmission pilot signals to subcarriers; 
         FIG. 11C  illustrates a state of allocating transmission pilot signals to subcarriers; 
         FIG. 11D  illustrates a state of allocating transmission pilot signals to subcarriers; 
         FIG. 12  illustrates a situation of the multiplexed received signal; 
         FIG. 13  explains the method for specifying transmitting antenna; 
         FIG. 14A  illustrates a state of providing a 0 degree phase difference between neighboring pilot symbols in the frequency domain; 
         FIG. 14B  illustrates a state of providing a 90 degree phase difference between neighboring pilot symbols in the frequency domain; 
         FIG. 14C  illustrates a state of providing a 180 degree phase difference between neighboring pilot symbols in the frequency domain; 
         FIG. 14D  illustrates a state of providing a −90 degree phase difference between neighboring pilot symbols in the frequency domain; 
         FIG. 15  is a block diagram showing a configuration of the transmitting apparatus according to Embodiment 2 of the present invention; 
         FIG. 16  is a block diagram showing the internal configuration of the pilot modulating section shown in  FIG. 15 ; 
         FIG. 17  illustrates a bit information conversion table; 
         FIG. 18  is a block diagram showing a configuration of the receiving apparatus according to Embodiment 2 of the present invention; 
         FIG. 19  is a block diagram showing the internal configuration of the pilot demodulating section shown in  FIG. 18 ; 
         FIG. 20  is a block diagram showing a configuration of the transmitting apparatus according to Embodiment 3 of the present invention; 
         FIG. 21  is a block diagram showing the internal configuration of the pilot modulating section shown in  FIG. 20 ; 
         FIG. 22  illustrates a bit information conversion table; 
         FIG. 23  is a block diagram showing a configuration of the receiving apparatus according to Embodiment 3 of the present invention; and 
         FIG. 24  is a block diagram showing the internal configuration of the pilot demodulating section shown in  FIG. 23 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Embodiments of the present invention will be described presuming a 4×4 MIMO-OFDM system with four transmitting antennas and four receiving antennas. Further, in embodiments, the same components having the same functions will be assigned the same reference numerals and overlapping descriptions will be omitted. 
     Embodiment 1 
       FIG. 2  is a block diagram showing the configuration of transmitting apparatus  100  according to Embodiment 1 of the present invention. In this figure, S/P conversion section  101  converts transmission data as input from a serial signal into parallel signals of four sequences, and outputs the transmission data of the sequences to modulating sections  102 - 1  to  102 - 4 . 
     Modulating sections  102 - 1  to  102 - 4  perform modulating processing of the transmission data outputted from S/P conversion section  101  and output the modulated signals to multiplexing sections  108 - 1  to  108 - 4 , respectively. 
     Pilot generating section  103  generates pilot signals and outputs the generated pilot signals to transmitting antenna information adding section  104 . 
     Transmitting antenna information adding section  104  sets the reference phase with the common pilot signal in the pilot signals outputted from pilot generating section  103 , and, with respect to this reference phase, applies a phase rotation, which varies between antennas, to the dedicated pilot signals, as transmitting antenna information. Then, the pilot signals assigned transmitting antenna information, are outputted to pilot arranging section  107 . When the number of antennas is four, the amount of phase rotation, which varies between antennas, can be varied in 90 degree units, as shown in  FIG. 3 , for example. Transmitting antennas  1  to  4  shown in  FIG. 3  correspond to transmitting antennas  110 - 1  to  110 - 4  shown in  FIG. 2 , respectively. 
       FIG. 3  shows that the dedicated pilot signal transmitted from transmitting antenna  1  has the same phase as the common pilot signal, that is, a 0 degree phase rotation is applied, and the dedicated pilot signal transmitted from transmitting antenna  2  is subjected to a 90 degree phase rotation with respect to the common pilot signal. Moreover,  FIG. 3  shows that the dedicated pilot signal transmitted from transmitting antenna  3  is subjected to a 180 degree phase rotation with respect to the common pilot signal, and the dedicated pilot signal transmitted from transmitting antenna  4  is subjected to a −90 degree (270 degree) phase rotation with respect to the common pilot signal. When a transmission pilot signal outputted from pilot generating section  103  is BPSK modulated, the common pilot signal is 1, and, when a transmission pilot signal is QPSK modulated, the common pilot signal is 1+j. 
     Based on the pilot signals transmitted from receiving apparatus  200 , which is a communicating party explained later, received quality measuring section  105  measures received quality such as the SNR (Signal to Noise Ratio), SIR (Signal to Interference Ratio) and SINR (Signal-to-Interference and Noise power Ratio), and outputs measured received quality information to control information generating section  106 . 
     Based on the received quality information outputted from received quality measuring section  105 , control information generating section  106  generates control information such as the number of space-multiplexing, switching information between SDM and diversity, transmitting antenna selection information, user identification information in multi-user environment, and outputs the generated control information to pilot arranging section  107 . 
     Based on the control information outputted from control information generating section  106 , pilot arranging section  107  allocates the transmission pilot signals outputted from transmitting antenna information adding section  104  to subcarriers, and outputs the transmission pilot signals allocated to subcarriers, to multiplexing sections  108 - 1  to  108 - 4 . Pilot arranging section  107  will be explained in detail later. 
     Multiplexing sections  108 - 1  to  108 - 4  multiplex the modulated data outputted from corresponding modulating sections  102 - 1  to  102 - 4  and the transmission pilot signals outputted from pilot arranging section  107 , generate frames (multiplex signals), and outputs the generated multiplex signals to corresponding RF transmitting sections  109 - 1  to  109 - 4 , respectively. RF transmitting sections  109 - 1  to  109 - 4  perform transmission processing such as amplification and up-conversion of the multiplex signals outputted from multiplexing sections  108 - 1  to  108 - 4 , and transmit the multiplex signals after transmission processing to receiving apparatus  200  explained later via corresponding antennas  110 - 1  to  110 - 4 . 
     Pilot arranging section  107  will be explained in detail here.  FIG. 4  is a block diagram showing the internal configuration of pilot arranging section  107  shown in  FIG. 2 . Control information converting section  151  in  FIG. 4 , as shown in  FIG. 5 , for example, has in advance a conversion table showing the correspondence relationships between control information, and transmitting antennas and position information of the subcarriers where the transmission pilot signals are allocated. 
     Incidentally, in  FIG. 5 , Tx 1  to Tx 4  show transmitting antennas  110 - 1  to  110 - 4 , and f a  to f d  show subcarriers where pilot symbols per transmitting antenna are arranged, respectively. Moreover, there are control information  1  to  4  as control information, items of combination information of transmitting antenna information and subcarrier position information (hereinafter simply “combination information”) and respective items of control information correspond to one-to-one. In this connection, although  FIG. 5  shows only four combination patterns of transmitting antennas and subcarriers, if there are four transmitting antennas and the number of subcarriers where transmission pilot signals are allocated is four, there are twenty four patterns as shown in  FIG. 6 . 
     Based on this conversion table, control information converting section  151  converts control information outputted from control information generating section  106  into combination information, and outputs the subcarrier position information in the combination information to subcarrier allocating sections  152 - 1  to  152 - 4 . 
     Subcarrier allocating sections  152 - 1  to  152 - 4  allocate the transmission pilot signals outputted from transmitting antenna information adding section  104  to the subcarriers according to subcarrier position information outputted from control information converting section  151 . By this means, transmission pilot signals are allocated to different subcarriers for every transmitting antenna. The transmission pilot signals allocated to the subcarriers are outputted to multiplexing sections  108 - 1  to  108 - 4 . 
       FIG. 7  is a block diagram showing the configuration of receiving apparatus  200  according to Embodiment 1 of the present invention. In this figure, RF receiving sections  202 - 1  to  202 - 4  respectively receive signals transmitted from transmitting apparatus  100  shown in  FIG. 2  via antennas  201 - 1  to  201 - 4 , perform predetermined radio receiving processing including down-conversion of the received signals, and extract the received pilot signals from the received signals. RF receiving sections  202 - 1  to  202 - 4  output the data signals in the received signals subjected to radio receiving processing and the extracted received pilot signals to pilot analyzing section  203 . 
     Based on the phase differences between the common pilot signal and the dedicated pilot signals of the received pilot signals outputted from RF receiving sections  202 - 1  to  202 - 4 , pilot analyzing section  203  specifies the antennas used to transmit the dedicated pilot signals and acquires the control information based on the combination of the transmitting antennas and the subcarriers used to transmit the dedicated pilots. The acquired control information is outputted to receiving processing section  205 . Moreover, the received pilot signals are outputted to channel estimating section  204 . Pilot analyzing section  203  will be described in detail later. 
     Channel estimating section  204  performs a channel estimation based on the received pilot signals outputted from pilot analyzing section  203  and outputs channel estimation information to receiving processing section  205 . 
     Based on the control information outputted from pilot analyzing section  203 , receiving processing section  205  performs receiving processing of the data signals outputted from RF receiving sections  202 - 1  to  202 - 4  and outputs the signals after receiving processing to demodulating sections  206 - 1  to  206 - 4 . Receiving processing here, for example, refers to MIMO signal separating processing using channel estimation information or diversity receiving processing. 
     Demodulating sections  206 - 1  to  206 - 4  demodulate the signals outputted from receiving processing section  205 , and output the demodulated signals to P/S conversion section  207 . By converting the parallel signals of four sequences outputted from demodulating sections  206 - 1  to  206 - 4  into a serial signal of one sequence, P/S conversion section  207  acquires the received data. 
     Here, pilot analyzing section  203  shown in  FIG. 7  will be explained in detail below.  FIG. 8  is a block diagram showing the internal configuration of pilot analyzing section  203  shown in  FIG. 7 . In  FIG. 8 , phase difference detecting section  251  detects the phase difference between the common pilot signal and the dedicated pilot signal for each subcarrier where the received pilot symbols outputted from RF receiving sections  202 - 1  to  202 - 4  are allocated, and outputs phase difference information to transmitting antenna specifying section  252 . Phase difference information φ (f i ) (f i =f a ˜f d ) is represented by the following equation 1. 
     [1] 
       φ( f   i )=|arg{ P   common ( f   i )}−arg{ P   dedicate ( f   i )}|  (Equation 1) 
     Incidentally, f a ˜f d  are subcarriers where pilot symbols are allocated, P common (f i ) is a common pilot signal for all subcarriers, and P dedicate (f i ) is a dedicated pilot signal. 
     Based on the phase difference information outputted from phase difference detecting section  251 , transmitting antenna specifying section  252  specifies from which transmitting antennas the received pilot signals have been transmitted. If transmitting apparatus  100  gives the phase differences shown in  FIG. 3  to the common pilot signal and the dedicated pilot signals, transmitting antenna specifying section  252  specifies the transmitting antennas based on the correspondence relationships shown in  FIG. 9 . 
     Then, transmitting antenna specifying section  252  generates combination information of the subcarriers and the transmitting antennas used to transmit the dedicated pilot signals, outputs the generated combination information to control information converting section  253  and the received pilot signals to channel estimating section  204 . 
     Control information converting section  253  has in advance the conversion table shown in  FIG. 5 , and, based on this conversion table, converts the combination information outputted from transmitting antenna specifying section  252 , to control information. The control information is outputted to receiving processing section  205 . 
     Next, the operations of transmitting apparatus  100  and receiving apparatus  200  having the above-described configurations will be explained.  FIG. 10  illustrates a sequence diagram showing the steps of communications between transmitting apparatus  100  shown in  FIG. 2  and receiving apparatus  200  shown in  FIG. 7 . In  FIG. 10 , in step (hereinafter abbreviated as “ST”)  901 , receiving apparatus  200  transmits a pilot signal to transmitting apparatus  100 . 
     In ST 902 , received quality measuring section  105  of transmitting apparatus  100  measures received quality such as the SNR, SIR and SINR using the pilot signal transmitted from receiving apparatus  200 , and, in ST 903 , based on the received quality measured in ST 902 , control information generating section  106  generates control information. 
     In ST 904 , pilot generating section  103  of transmitting apparatus  100  generates a transmission pilot signal, and, in ST 905 , transmitting antenna information adding section  104  gives the dedicated pilot signal a phase rotation such that the phase difference between the dedicated pilot signal of the transmission pilot signal generated in ST 904  and the common pilot signal varies per transmitting antenna. 
     In ST 906 , pilot arranging section  107  of transmitting apparatus  100  converts the control information generated in ST 903  into combination information and allocates the transmission pilot signals to the subcarriers according to the subcarrier position information of the combination information. 
     Here,  FIGS. 11A to 11D  show the states of allocating the transmission pilot signal to the subcarriers. Here, all transmitting antennas allocate the common pilot symbol in the first symbol and the dedicated pilot symbol in the fourth symbol. Moreover, in a MIMO system, to prevent pilot signals transmitted from antennas from interfering with each other, the subcarrier where one antenna allocates the common pilot or dedicated pilot is a null subcarrier for the other antennas, as shown in  FIGS. 11A to 11D . Incidentally, as explained earlier, it depends on control information that, to which subcarriers pilot signals assigned which transmitting antenna information are arranged. Moreover, as shown in  FIGS. 11A to 11D , each dedicated pilot signal is given a phase rotation that varies between transmitting antennas with respect to the reference phase of the common pilot signal. In  FIGS. 11A to 11D , the blank symbols represent data symbols. 
     Referring to  FIG. 10  again, in ST 907 , multiplexing sections  108 - 1  to  108 - 4  multiplex the transmission data and the pilot signals allocated to the subcarriers in ST 906  and generate frames, and, in ST 908 , transmit the generated frames to receiving apparatus  200 . 
     In ST 909 , RF receiving sections  202 - 1  to  202 - 4  of receiving apparatus  200  receive the frames transmitted from transmitting apparatus  100  and demultiplex the received frames to the pilot signals and the data signals. As shown in  FIG. 12 , in the signals which RF receiving sections  202 - 1  to  202 - 4  receive, even though the data symbols (the blank symbols in the drawings) are space-multiplexed, the common pilot signals and the dedicated pilot signals are not space-multiplexed. The reason is that the subcarrier where one antenna in transmitting apparatus  100  allocates the common pilot or the dedicated pilot is a null subcarrier for the other antennas. Consequently, the subcarriers where the pilot symbols are allocated are associated with the transmitting antennas in one-to-one. 
     In ST 910 , pilot analyzing section  203  detects the amounts of phase rotation with the pilot signals demultiplexed in ST 909  and specifies from which transmitting antenna each pilot signal has been transmitted. With the present embodiment, as explained earlier, the correspondence relationships between subcarriers and transmitting antennas are not fixed, and control information is transmitted by changing these correspondence relationships. For this reason, receiving apparatus  200  needs to specify from which transmitting antennas the received pilot signals have been transmitted. Here, this specifying method will be explained using  FIG. 13 . 
     Transmitting apparatus  100  gives the dedicated pilot signal a phase rotation, which varies between antennas with respect to the reference phase of the common pilot signal. For this reason, by detecting the phase difference between the dedicated pilot and the reference phase of the common pilot, receiving apparatus  200  can specify from which transmitting antennas the received pilots have been transmitted. 
     Referring to  FIG. 13 , if the common pilot symbol is received in the first quadrant and a dedicated pilot symbol is received in the first quadrant, the dedicated pilot symbol is specified as the pilot signal transmitted from transmitting antenna  1 . Moreover, if a dedicated pilot symbol is received in the second quadrant, the dedicated pilot symbol is specified as the pilot signal transmitted from transmitting antenna  2 . Moreover, if a dedicated pilot symbol is received in the third quadrant, the dedicated pilot symbol is specified as the pilot signal transmitted from transmitting antenna  3 . In addition, if a received dedicated pilot symbol is received in the fourth quadrant, the dedicated pilot symbol is specified as the pilot signal transmitted from transmitting antenna  4 . 
     Referring to  FIG. 10  again, in ST 911 , pilot analyzing section  203  of receiving apparatus  200  generates combination information of the subcarrier and the transmitting antenna used to transmit the pilot signal, and acquires control information based on the generated combination information. 
     In ST 912 , channel estimating section  204  of receiving apparatus  200  performs a channel estimation using the received pilot signals, and, in ST 913 , based on the control information acquired in ST 911 , receiving processing section  205  performs MIMO signal demultiplexing processing using the channel estimation information estimated in ST 912  or diversity receiving processing. Then, demodulating sections  206 - 1  to  206 - 4  perform demodulation on the signals after receiving processing, P/S conversion section  207  performs P/S conversion on the signals after demodulation, and received data is acquired. 
     In this way, according to Embodiment 1, the transmitting apparatus and the receiving apparatus have in advance tables that associate control information with combination information of transmitting antennas and subcarriers used to transmit pilot signals, the transmitting apparatus gives the dedicated pilot signals phase rotations such that the phase difference between the common pilot signal and the dedicated pilot signal varies between transmitting antennas, and the receiving apparatus specifies the antennas used to transmit the pilot signals from the phase differences between the received common pilot signal and the received dedicated pilot signals and acquires control information based on combination information of subcarriers and transmitting antennas used to transmit the pilot signals, so that, control information can be transmitted using the pilot signals, thereby allocating more data by reducing the amount of control information allocated in frames, and, consequently, improving data rate while maintaining the accuracy of channel estimation. In addition, it is also possible to allocate more pilot signals by reducing the amount of control information allocated in frames, and consequently improve the accuracy of channel estimation while maintaining data rate. 
     Incidentally, although the present embodiment has been described above to assign transmitting antenna information by providing phase differences between the common pilot signal and the dedicated pilot signals arranged in the time domain, the present invention is not limited to this, and, as shown in  FIGS. 14A to 14D , transmitting antenna information may be added by way of providing phase differences varying between transmitting antennas between neighboring pilot symbols in the frequency domain. Incidentally, in  FIGS. 14A to 14D , the blank symbols show data symbols. 
     Embodiment 2 
     A case has been described above with Embodiment 1 where control information is transmitted using pilot signals by associating control information with combination information of the transmitting antennas and subcarriers used to transmit the pilot signals. Now, a case will be described with Embodiment 2 of the present invention where data is transmitted using pilot signals by associating data with combination information between the transmitting antennas and subcarriers used to transmit the pilot signals. 
       FIG. 15  is a block diagram showing the configuration of transmitting apparatus  300  according to Embodiment 2 of the present invention.  FIG. 15  is different from  FIG. 2  in that received quality measuring section  105  and control information generating section  106  are removed and pilot arranging section  107  is changed to pilot modulating section  301 . 
       FIG. 16  is a block diagram showing the internal configuration of pilot modulating section  301  shown in  FIG. 15 . Referring to  FIG. 16 , transmitting data converting section  351  has in advance a conversion table, as shown in  FIG. 17 , for example, showing the correspondence relationships between data and the position information of subcarriers where the transmission pilot signals are allocated. 
     Incidentally, in  FIG. 17 , Tx 1  to Tx 4  are transmitting antennas  110 - 1  to  110 - 4  and f a  to f d  are subcarriers where pilot symbols per transmitting antenna are arranged, respectively. Moreover, there are two values of BPSK, four values of QPSK, sixteen values of 16QAM as data, and items of combination information of transmitting antenna information and subcarrier position information and bit values per symbol in modulation schemes correspond to one-to-one. Incidentally, if there are four transmitting antennas and four subcarriers where transmission pilot signals are allocated, there are twenty four patterns as shown in  FIG. 6 , so that the two values of BPSK, four values of QPSK, and sixteen values of 16QAM, total twenty two values, can be associated with combination information of transmitting antennas and subcarriers. 
     Based on this conversion table, transmission data converting section  351  converts transmission data into combination information and outputs the subcarrier position information of the combination information to subcarrier allocating sections  152 - 1  to  152 - 4 . 
       FIG. 18  is a block diagram showing the configuration of receiving apparatus  400  according to Embodiment 2 of the present invention.  FIG. 18  is different from  FIG. 7  in that pilot analyzing section  203  is changed to pilot demodulating section  401 . 
       FIG. 19  is a block diagram showing the internal configuration of pilot demodulating section  401  shown in  FIG. 18 . Referring to  FIG. 19 , transmission data converting section  451  has in advance the conversion table shown in  FIG. 17 , and, based on this conversion table, converts the combination information outputted from transmission antenna specifying section  252  into demodulated data. The demodulated data is outputted to P/S conversion section  207 . 
     When four-bit data is transmitted using a pilot signal, the accuracy of symbol decision specifying the transmitting antennas is the same as QPSK, so that the accuracy of data detection improves more than 16 QAM modulation, thereby improving received quality. 
     In this way, according to Embodiment 2, it is possible to transmit data using pilot signals by associating data with combination information of transmitting antennas and subcarriers used to transmit pilot signals, so that it is possible to transmit more data and consequently improve data rate more while maintaining the accuracy of channel estimation. 
     Embodiment 3 
     A case has been described above with Embodiment 2 where data is transmitted using pilot signals by associating data with combination information of the transmitting antennas and subcarriers used to transmit the pilot signals. Now, a case will be described below with Embodiment 3 where redundancy information is transmitted using pilot signals by associating the redundancy information with combination information of the transmitting antennas and subcarriers used to transmit the pilot signals. 
       FIG. 20  is a block diagram showing the configuration of transmitting apparatus  500  according to Embodiment 3 of the present invention.  FIG. 20  is different from  FIG. 15  in that coding section  501  and modulating section  502  are added and pilot modulating section  301  is changed to pilot modulating section  503 . 
     Coding section  501  performs coding processing such as turbo coding of transmission data and generates information bits and redundancy bits. The generated information bits are outputted to modulating section  502  and the redundancy bits are outputted to pilot modulating section  503 . Modulating section  502  performs modulating processing of the information bits outputted from coding section  501  and outputs the modulated signal to S/P conversion section  101 . 
     Based on the redundancy bits outputted from coding section  501 , pilot modulating section  503  allocates transmission pilot signals outputted from transmitting antenna information adding section  104  to the subcarriers, and outputs the transmission pilot signals allocated to the subcarriers to multiplexing sections  108 - 1  to  108 - 4 . 
       FIG. 21  is a block diagram showing the internal configuration of pilot modulating section  503  shown in  FIG. 20 . Referring to  FIG. 21 , redundancy bit converting section  551  has in advance the conversion table shown in  FIG. 17 , for example. Incidentally, redundancy bit converting section  551  may also have the conversion table shown in  FIG. 22  and in that case would implement even more accurate error correction. 
     Based on the conversion table shown in  FIG. 17 , redundancy bit converting section  551  converts the redundancy bits into combination information and outputs the subcarrier position information of the combination information to subcarrier allocating sections  152 - 1  to  152 - 4 . 
       FIG. 23  is a block diagram showing the configuration of receiving apparatus  600  according to Embodiment 3 of the present invention.  FIG. 23  is different from  FIG. 18  in that pilot demodulating section  401  is changed to pilot demodulating section  601  and demodulating section  602  and decoding section  603  are added. 
     Based on the phase differences between the common pilot signal and the dedicated pilot signals of the received pilot signals outputted from RF receiving sections  202 - 1  to  202 - 4 , pilot demodulating section  601  specifies the antennas used to transmit the dedicated pilot signals and acquires the redundancy bits based on the combinations of the transmitting antennas and the subcarriers used to transmit the dedicated pilots. The acquired redundancy bits are outputted to decoding section  603 . 
     Demodulating section  602  performs demodulation processing of the signal outputted from P/S conversion section  207 , generates a demodulated signal and outputs the generated demodulated signal to decoding section  603 . Decoding section  603  performs decoding processing such as turbo decoding using redundancy bits outputted from pilot demodulating section  601 , of the demodulated signal outputted from demodulating section  602 , and acquires decoded data, that is, received data. 
       FIG. 24  is a block diagram showing the internal configuration of pilot demodulating section  601  shown in  FIG. 23 . Referring to  FIG. 24 , redundancy bit converting section  651  has in advance the conversion table shown in  FIG. 17  and, based on the conversion table, converts the combination information outputted from transmitting antenna specifying section  252  into redundancy bits. The redundancy bits are outputted to decoding section  603 . 
     In this way, according to Embodiment 3, redundancy bits can be transmitted using pilot signals by associating the redundancy bits with combination information of the transmitting antennas and subcarriers used to transmit the pilot signals, so that it is possible to improve error correction capacity while maintaining the accuracy of channel estimation and consequently improve received quality. Moreover, if received quality is fixed, it is possible to transmit more data and consequently improve data rate. 
     Moreover, although a case has been described with the present embodiment where coding is performed before MIMO stream is separated at the transmitting apparatus, coding may be performed individually for each MIMO stream. 
     Moreover, it is also possible to combine the present embodiment and Embodiment 2 and improve system throughput by transmitting transmission data by pilot signals to improve data rate if received states are good and by transmitting redundancy bits by pilot signals to improve received quality if received states are poor. 
     Embodiments of the present invention have been described. 
     Moreover, with the embodiments described above, it is possible to apply the transmitting apparatuses to the base station apparatuses and the receiving apparatuses to the mobile station apparatuses, conversely, it is possible to apply the transmitting apparatuses to the mobile station apparatuses and the receiving apparatuses to the base station apparatuses. 
     Although cases have been described with the embodiments here where the number of transmitting antennas and the number of receiving antennas are both four and the number of subcarriers where transmission pilot signal is allocated is four, the present invention is not limited to this, and the number of transmitting antennas, the number of receiving antennas and the number of subcarriers may be two or more. 
     Moreover, although cases have been described with the embodiments above where the present invention is configured by hardware, the present invention may be implemented by software. 
     Each function block employed in the description of the aforementioned embodiment 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. 
     Further, the method of circuit integration is not limited to LSI&#39;s, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an 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. 
     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. 
     The present application is based on Japanese Patent Application No. 2005-314621, filed on Oct. 28, 2005, the entire content of which is expressly incorporated by reference herein. 
     INDUSTRIAL APPLICABILITY 
     The transmitting apparatus, the receiving apparatus, the transmission method, the reception method and the wireless communication system have an advantage of improving both data rate and the accuracy of channel estimation in MIMO-OFDM system and are applicable to, for example, mobile phones, base stations, and wireless cellular systems.