Patent Publication Number: US-8526527-B2

Title: Radio communication apparatus and radio communication method

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a MIMO receiving apparatus and a MIMO transmitting apparatus. More particularly, the present invention relates to a MIMO receiving apparatus and MIMO transmitting apparatus in which the transmitting system performs transmission control on a per antenna basis by feedback information from the receiving system. 
     2. Background Art 
     In standardization of 3GPP Long Term Evolution (LTE), PARC (Per Antenna Rate Control) scheme, which is one of MIMO (Multi Input Multi Output) transmission schemes, is discussed. In PARC, modulation and coding schemes are selected according to channel quality (CQI) report values on a per transmission antenna (stream) basis. Patent Document 1 discloses a conventional MIMO PARC scheme. 
       FIG. 1  shows a configuration of the MIMO transmitting apparatus in the MIMO communication system adopting the conventional MIMO PARC scheme. As shown in the figure, the MIMO transmitting apparatus transmits pilot signals on a per antenna basis by using several subcarriers. On the other hand, the receiving apparatus (not shown) measures the received intensity of each pilot signal transmitted from the antennas in the MIMO transmitting apparatus, generates a CQI (channel quality indicator) per antenna based on the channel quality condition for each antenna, and feeds back the CQIs to the MIMO transmitting apparatus. The MIMO transmitting apparatus determines the optimal modulation scheme (QPSK, 16QAM, 64QAM and so on) and coding rate on a per antenna basis based on the CQI information per antenna and transmits substreams from the antennas. In this way, by selecting optimal modulation and coding scheme based on the channel quality condition of each antenna, the maximum peak rate and communication capacity are achieved. Non-patent Document 1: Lucent 3GPP R1-010879 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, the conventional MIMO communication system has a problem of increasing the CQI feedback overhead in proportion to the number of antennas (i.e. streams). Moreover, when the transmitting side performs frequency scheduling, CQI is required per chunk, which is a subcarrier block, and therefore the above problem is further prominent. 
     It is therefore an object of the present invention to provide a MIMO receiving apparatus and MIMO transmitting apparatus that can reduce the amount of feedback information and system traffic. 
     Means for Solving the Problem 
     The MIMO receiving apparatus of the present invention adopts a configuration including: a communication quality measuring section that measures communication quality of individual antennas using pilot signals transmitted from antennas of a transmitting side; a transmitting section that feeds back feedback information based on the communication quality to the transmitting side; a relative value calculating section that calculates relative values of the communication quality for the antennas between the communication quality of a reference antenna and the communication quality of the antennas other than the reference antenna in the antennas in the transmitting side; and a feedback information generating section that generates the feedback information from an absolute value of the communication quality of the reference antenna and the relative values of the communication quality. 
     The MIMO transmitting apparatus of the present invention adopts a configuration including: a receiving section that receives feedback information containing absolute values of communication quality of a reference antenna and relative values of communication quality of antennas other than the reference antenna; a feedback information processing section that calculates communication quality of each antenna from the feedback information; and a transmission control section that controls transmission of substreams via the antennas based on the calculated communication quality. 
     Advantageous Effect of the Invention 
     According to the present invention, a MIMO receiving apparatus and MIMO transmitting apparatus that can reduce the amount of feedback information and system traffic is provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of the conventional MIMO transmitting apparatus; 
         FIG. 2  is a block diagram showing a configuration of the radio communication apparatus of the receiving system according to Embodiment 1; 
         FIG. 3  is a block diagram showing a configuration of the radio communication apparatus of the transmitting system according to Embodiment 1; 
         FIG. 4  explains the feedback information in Embodiment 1; 
         FIG. 5  is a block diagram showing a configuration of the radio communication apparatus of the receiving system according to Embodiment 2; 
         FIG. 6  explains the feedback information in Embodiment 2; 
         FIG. 7  is a block diagram showing a configuration of the radio communication apparatus of the transmitting system according to Embodiment 2; 
         FIG. 8  is a block diagram showing a configuration of the radio communication apparatus of the receiving system according to Embodiment 3; 
         FIG. 9  is a block diagram showing a configuration of the radio communication apparatus of the transmitting system according to Embodiment 3; 
         FIG. 10  explains the feedback information in Embodiment 3; 
         FIG. 11  is a block diagram showing a configuration of the radio communication apparatus of the receiving system according to Embodiment 4; 
         FIG. 12  explains the feedback information in Embodiment 4; 
         FIG. 13  is a block diagram showing a configuration of the radio communication apparatus of the transmitting system according to Embodiment 4; 
         FIG. 14  is a block diagram showing a configuration of the radio communication apparatus of the receiving system according to Embodiment 5; 
         FIG. 15  explains the feedback information in Embodiment 5; 
         FIG. 16  is a block diagram showing a configuration of the radio communication apparatus of the transmitting system according to Embodiment 5; 
         FIG. 17  is a block diagram showing a configuration of the radio communication apparatus of the receiving system according to Embodiment 6; 
         FIG. 18  explains the feedback information in Embodiment 6; and 
         FIG. 19  is a block diagram showing a configuration of the radio communication apparatus of the transmitting system according to Embodiment 6. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In embodiments, the components having the same functions will be assigned the same reference numerals and overlapping descriptions will be omitted. 
     Embodiment 1 
     As shown in  FIG. 2 , radio communication apparatus  100  in the MIMO (Multi Input Multi Output) communication system according to Embodiment 1 has a plurality of antennas, receiving section  110 , signal demultiplexing section  120 , received level measuring section  130 , CQI determining section  140 , relative value calculating section  150 , feedback information generating section  160 , transmitting section  170 , demodulating section  175 , decoding section  180  and P/S conversion section  185 . 
     Receiving section  110 , which has the same number of receiving sections  112  as the antennas, receives a space-multiplexed signal, in which signals transmitted from the transmission system in the MIMO communication system are space-multiplexed, and performs radio receiving processing on the received signal. When transmission signals transmitted from the individual antennas of the transmission system form an OFDM signal, which is one kind of multicarrier signal, receiving section  110  performs OFDM receiving processing including FFT processing and P/S conversion processing in addition to normal radio receiving processing (e.g. down-conversion and A/D conversion processing). Moreover, receiving section  110  receives a pilot signal transmitted from each antenna in the transmission system and performs receiving processing. 
     Signal demultiplexing section  120  demultiplexes the signal after radio receiving processing in receiving section  110  into the signals transmitted from the individual antennas of the transmission system (i.e. corresponding to the substreams in the transmission system and therefore hereinafter may be referred to as “substreams”) using methods including MMSE (Minimum Mean Square Error) and so on. Moreover, signal demultiplexing section  120  receives as input the pilot signal after receiving processing in receiving section  110 , and outputs the pilot signals of the individual antennas utilized for transmission in the transmission system (corresponding to the substreams in the transmission system). 
     Received level measuring section  130  measures the received levels of the pilot signals, which are demultiplexed in signal demultiplexing section  120 , of the individual antennas (e.g. SINR: Signal-to-Interference and Noise Power Ratio) and outputs the received levels of the pilot signals to CQI determining section  140 . 
     CQI determining section  140  stores a CQI table and determines the CQI value of each substream based on the received levels of the pilot signals measured in received level measuring section  130 . 
     Relative value calculating section  150  calculates relative CQI values between the CQI value of the reference substream and the CQI values of substreams other than the reference substream. In the present embodiment, the reference substream is determined in advance and fixed. The substreams correspond to the individual antennas of the transmission system respectively, so that the reference substream may be regarded as “the reference antenna,” and relative value calculating section  150  may be construed to calculate relative CQI values between the CQI value of the reference antenna and the CQI values of the antennas other than the reference antenna. 
     Feedback information generating section  160  generates feedback information for the transmission system from the CQI value of the reference substream and the relative CQI values found for the streams other than the reference substream. 
     Transmitting section  170  transmits the feedback information generated in feedback information generating section  160  to the transmission system using at least one of a plurality of antennas provided in radio communication apparatus  100 . That is, transmitting section  170  may transmit the feedback information to the transmission system by a transmission scheme using one antenna or by a multi-antenna communication scheme such as MIMO communication scheme and space-time coding communication scheme. 
     Demodulating section  175 , which has demodulating sections  177  matching the number of the substreams, demodulates each substream demultiplexed in signal demultiplexing section  120 . 
     Decoding section  180 , which has decoding sections  182  matching the number of the substreams, decodes each substream after demodulating processing. 
     P/S conversion section  185  performs parallel-to-serial conversion on the substreams after decoding processing, and outputs the result as a serial data sequence. 
     As shown in  FIG. 3 , radio communication apparatus  200  of the transmission system, has a plurality of antennas, receiving section  210 , feedback information processing section  220 , transmission control section  230 , S/P conversion section  240 , coding section  250 , modulating section  260 , transmitting section  270  and pilot generating section  280 . 
     Receiving section  210  performs radio receiving processing on feedback information, which is from radio communication apparatus  100 , and which is received through at least one of the antennas in radio communication apparatus  200 . To be more specific, receiving section  210  performs receiving processing on feedback information in a reception scheme corresponding to the transmission scheme applied in transmitting section  170  of radio communication apparatus  100 , and outputs the feedback information after receiving processing to feedback information processing section  220 . 
     Feedback information processing section  220  calculates the CQI value of each substream from the feedback information from receiving apparatus  210 . To be more specific, as described above, the feedback information from radio communication apparatus  100  contains the CQI value of the reference substream and the relative CQI values found for the substreams other than the reference substream, so that feedback information processing section  220  calculates the CQI value of each substream from the relative CQI values found between the CQI value of the reference substream and the substreams other than the reference substream. 
     Transmission control section  230 , which stores a CQI table that is the same as in radio communication apparatus  100 , outputs the coding rates, modulation schemes and so on, associated with the CQI values of the individual substreams calculated in feedback information processing section  220  to coding section  250  and modulating section  260 . 
     S/P conversion section  240  converts inputted transmission data (stream data) from serial to parallel, and divides the transmission data into a plurality of substreams. 
     Coding section  250 , which has coding sections  252  matching the number of the substreams, encodes the individual substreams based on the coding rate of each substream received from transmission control section  230 . 
     Modulating section  260 , which has modulating sections  262  matching the number of the substreams, modulates the substreams based on the modulation scheme of each substream (e.g. QPSK, 16QAM, 64QAM and so on) received from transmission control section  230 . Moreover, modulating section  260  modulates the pilot signals generated in pilot generating section  280 . Further, modulating section  260  performs OFDM modulation processing including S/P conversion processing and IFFT processing when radio communication apparatus  200  transmits OFDM signals from the antennas. 
     Transmitting section  270 , which has transmitting sections  272  matching the number of the substreams, performs radio processing including D/A conversion and up-conversion for the substreams and transmits them from the corresponding antennas. Moreover, transmitting section  270  performs radio processing on the pilot signals modulated in modulating section  260  and transmits them from the corresponding antennas. 
     Next, the operations of radio communication apparatus  100  and radio communication apparatus  200  having the above-described configurations will be explained. 
     In radio communication apparatus  100 , a signal after receiving processing in receiving section  110  is demultiplexed into substreams using methods including MMSE (Minimum Mean Square Error) in signal demultiplexing section  120 . 
     In received level measuring section  130 , the received levels of the pilot signals demultiplexed in signal demultiplexing section  120  are measured per antenna of the transmission system. To be more specific, when the pilot signals are transmitted in the form of OFDM signals from the antennas in radio communication apparatus  200 , received level measuring section  130  measures the received level of each pilot signal on a per chunk basis, and outputs an “average received level,” which is an average of all chunks in one CQI reporting cycle, to CQI determining section  140 . Here, a “chunk” refers to a bundle of consecutive subcarriers in the frequency domain. 
     In CQI determining section  140 , the CQI value of each substream is determined based on the “average received levels” of the pilot signals from received level measuring section  130 . In relative value calculating section  150 , relative CQI values are calculated between the CQI value of the reference substream and the CQI values of substreams other than the reference substream. 
     In feedback information generating section  160 , feedback information for the transmission system is generated from the relative CQI values found between the CQI value of the reference substream and the substreams other than the reference substream. 
     The feedback information generated in this feedback information generating section  160  will be explained with reference to  FIG. 4 . 
     As shown in the figure, as for the reference substream, a CQI value determined based on an “average received level,” which is an average of all chunks (i.e. chunks  1  to  8  in the figure), is fed back to radio communication apparatus  200  every CQI reporting cycle. Moreover, as for substreams other than the reference substream (“other substreams” in the figure), relative CQI values, which are relative to the CQI value determined for the reference substream, are fed back to radio communication apparatus  200  every CQI reporting cycle. 
     In this way, feedback information is generated such that the CQI of the reference substream alone is given in an absolute value and the CQIs of the other substreams are given in relative CQI values with respect to the reference substream, so that it is possible to reduce the amount of feedback information, compared to conventional cases of feeding back the absolute values of the CQI values of all substreams. As a result, it is possible to reduce the traffic in the MIMO communication system. This working effect becomes prominent when the number of antennas mounted in a radio communication apparatus in the MIMO communication system increases. 
     In radio communication apparatus  200 , receiving processing is performed on feedback information in receiving section  210 , and, in feedback information processing section  220 , CQI values of the individual substreams are calculated from the feedback information in receiving section  210 . 
     In transmission control section  230 , coding rates, modulation schemes and so on, associated with the CQI values of the individual substreams calculated in feedback information processing section  220 , are outputted to coding section  250  and modulating section  260 . 
     In coding section  250 , coding processing is performed on the individual substreams based on the coding rate of each substream received from transmission control section  230 . 
     In modulating section  260 , modulating processing is performed on the substreams based on the modulation scheme of each substream (e.g. QPSK, 16QAM, 64QUM and so on) received from transmission control section  230 . 
     In this way, according to Embodiment 1, radio communication apparatus  100  has: received level measuring section  130  as a communication quality measuring means for measuring communication quality (e.g. SINR) of individual antennas (corresponding to the substreams) using the pilot signals transmitted from the antennas of the transmitting side (radio communication apparatus  200 ); transmitting section  170  that feeds back feedback information based on the communication quality, to the transmitting side; relative value calculating section  150  as a relative value calculating means for calculating relative values of communication quality between a reference antenna and individual antennas other than the reference antenna, from communication quality of the reference antenna (corresponding to the reference substream) and communication quality of the antennas other than the reference antenna in the transmitting antennas; and feedback information generating section  160  as a feedback generating means for generating the feedback information from the absolute value of communication quality of the reference antenna and the relative values of communication quality. 
     By this means, the feedback information is generated such that the communication quality of the reference antenna alone is given in an absolute value and the communication quality of other antennas is given in the relative values of the communication quality with respect to the reference antenna, so that it is possible to reduce the amount of feedback information, compared to conventional cases of feeding back the absolute values of the CQI values of all antennas. As a result, it is possible to reduce the amount of overhead of control information channels and interference power by the amount in the MIMO communication system. This working effect becomes prominent when the number of antennas mounted in a radio communication apparatus in the MIMO communication system increases. 
     Moreover, radio communication apparatus  100  has: received level measuring section  130  that measures the received levels of the individual pilot signals transmitted from the antennas of the transmitting side (radio communication apparatus  200 ); CQI determining section  140  that determines the CQI value of each transmitting antenna based on the received levels; relative value calculating section  150  that calculates relative CQI values showing the relative values of the CQI values between the reference antenna and the antennas other than the reference antenna, from the CQI value determined for the reference antenna and the CQI values determined for the antennas other than the reference antenna, in the transmitting antennas by CQI determining section  140 ; and feedback information generating section  160  that generates feedback information for the transmitting side including the CQI value of the reference antenna and the relative CQI values. 
     By this means, feedback information is generated such that the CQI of the reference antenna alone is given in an absolute value and the CQIs of the other antennas are given in the relative values of the CQI with respect to the reference antenna, so that it is possible to reduce the amount of feedback information, compared to conventional cases of feeding back the absolute values of the CQI values of all antennas. As a result, it is possible to reduce the amount of overhead of control information channels and interference power in the MIMO communication system. This working effect becomes prominent when the number of antennas mounted in a radio communication apparatus in the MIMO communication system increases. Moreover, by using the CQI values used in conventional systems to generate feedback information, the present invention can be applicable for conventional systems. 
     Moreover, according to Embodiment 1, radio communication apparatus  200  has: receiving section  210  as a receiving means for receiving feedback information containing the absolute value of communication quality (e.g. CQI values) of the reference antenna (corresponding to the reference substream) and the relative values of communication quality of the antennas other than the reference antenna; feedback information processing section  220  as a calculating means for calculating communication quality of each antenna from the feedback information; and transmission control section  230  as a transmission control means for controlling the transmission of the substreams via the antennas based on the calculated communication quality. 
     By this means, it is possible to control to transmit substreams transmitted from the antennas and reduce the amount of overhead of control information channels and interference power in the MIMO communication system. 
     Embodiment 2 
     In Embodiment 1, the CQI value of each substream is fed back. By contrast with this, in Embodiment 2, a MIMO communication scheme of transmitting multicarrier signals (e.g. OFDM signals) from the individual antennas of the transmission system is presumed, and the CQI values of individual chunks related to substreams are fed back. The embodiments are the same in that feedback is carried out using the absolute value of the CQI value with respect to the reference substream and relative CQI values with respect to substreams other than the reference substream. In this way, by feeding back CQI values of individual chunks related to the substreams, what is commonly referred to as “frequency scheduling” for controlling subcarriers used in the transmission system can be carried out efficiently. 
     As shown in  FIG. 5 , radio communication apparatus  300  according to Embodiment 2 has received level measuring section  330 , CQI determining section  340 , relative value calculating section  350  and feedback information generating section  360 . 
     Received level measuring section  330  measures the received levels (e.g. SINRs) of the individual chunks, for the pilot signals demultiplexed in signal demultiplexing section  120  of the individual antennas of the transmission system. 
     CQI determining section  340  determines the CQI values of the individual chunks related to the substreams based on the received levels per chunk related to the pilot signals from received level measuring section  330 . 
     Relative value calculating section  350  calculates relative CQI values of the individual chunks (hereinafter may be referred to as “relative chunk CQI values”) between the CQI value of the reference substream and the CQI values of substreams other than the reference substream. In the present embodiment, the reference substream is determined in advance and fixed. 
     Feedback information generating section  360  generates feedback information (see  FIG. 6 ) for the transmission system from the CQI value of each chunk related to the reference substream and the relative chunk CQI values found for the streams other than the reference substream. 
     As shown in  FIG. 7 , radio communication apparatus  400  of the transmission system has feedback information processing section  420  and transmission control section  430 . 
     Feedback information processing section  420  calculates the CQI values of the individual chunks related to the substreams from the feedback information from receiving apparatus  210 . To be more specific, the feedback information from radio communication apparatus  300  contains the CQI value of each chunk related to the reference substream and the relative chunk CQI values found for the substreams other than the reference substream, so that feedback information processing section  420  calculates the CQI values of the individual chunks related to the substreams from the CQI value of each chunk related to the reference substream and the relative chunk CQI values found for the substreams other than the reference substream. 
     Transmission control section  430  performs frequency scheduling for the individual substreams based on the CQI values of the individual chunks related to the substreams from feedback information processing section  420 , and outputs frequency scheduling information for each substream to modulating section  260 . 
     Modulating section  260  sequentially changes the subcarriers per substream based on the frequency scheduling information from transmission control section  430 . 
     In this way, according to Embodiment 2, radio communication apparatus  300  has: received level measuring section  330  that measures the received levels of the individual pilot signals transmitted from the antennas of the transmitting side (radio communication apparatus  400 ); CQI determining section  340  that determines the CQI value of each transmitting antenna based on the received levels; relative value calculating section  350  that calculates relative CQI values showing the relative values of the CQI values between the reference antenna and the antennas other than the reference antenna, from the CQI value determined for the reference antenna and the CQI values determined for the antennas other than the reference antenna, in the transmitting antennas by CQI determining section  340 ; and feedback information generating section  360  that generates feedback information for the transmitting side including the CQI values of the reference antenna and the relative CQI values, and received level measuring section  330  measures the received levels per chunk formed with a plurality of subcarriers; CQI determining section  340  determines the CQI value of each chunk related to the transmitting antennas based on the received levels; relative value calculating section  350  calculates relative chunk CQI values showing relative CQI values of the individual chunks between the CQI value of the chunk determined for the reference antenna and the CQI values of the individual chunks determined for the antennas other than the reference antenna; and feedback information generating section  360  generates feedback information including the CQI value of the chunk of the reference substream and the relative chunk CQI values. 
     By this means, CQI values of individual chunks related to the antennas are fed back, so that what is commonly referred to as “frequency scheduling” for controlling subcarriers used in the transmission system can be carried out efficiently. 
     Embodiment 3 
     In Embodiment 1, the reference substream is fixed. By contrast with this, in Embodiment 3, the substream of the best communication quality every reporting cycle, is selected as the reference substream. The embodiments are the same in that feedback is carried out using the absolute value of the CQI value with respect to the reference substream and relative CQI values with respect to substreams other than the reference substream. In this way, the substream of the best communication quality is selected as the reference substream, and, by feeding back the absolute value of communication quality of the reference substream and the relative values of the substreams other than the reference substream, the reliability of CQI feedback information of the substream of the best channel communication quality especially improves. As a result, the transmission system receiving the feedback information can perform transmission control based on reliable feedback information, thereby improving system throughput. 
     As shown in  FIG. 8 , radio communication apparatus  500  according to Embodiment 3 has reference determining section  510 , relative value calculating section  550  and feedback information generating section  560 . 
     Reference determining section  510  receives as input the CQI values for the substreams from CQI determining section  140  and determines the reference substream. To be more specific, reference determining section  510  selects the substream associated with the CQI value of the highest received level as the reference substream every CQI reporting cycle. That is, reference determining section  510  selects the reference substream based on the received level. Then, reference determining section  510  outputs information specifying the reference substream (hereinafter may be referred to as “the reference substream information”) to relative value calculating section  550  and feedback information generating section  560 . 
     Relative value calculating section  550  calculates relative CQI values between the CQI value of the reference substream selected in reference determining section  510  and the CQI values of substreams other than the reference substream. 
     Feedback information generating section  560  generates feedback information for the transmission system from the CQI value of the reference substream, the relative CQI values found for the streams other than the reference substream and the reference substream information (e.g. stream index information identifying the reference substream). 
     As shown in  FIG. 9 , radio communicating apparatus  600  has feedback information processing section  620 . 
     Feedback information processing section  620  calculates the CQI value of each substream from the feedback information from receiving apparatus  210 . To be more specific, the feedback information from radio communication apparatus  500  contains the CQI value of the reference substream, the relative CQI values found for the substreams other than the reference substream and the reference substream information (e.g. stream index information identifying the reference substream), so that feedback information processing section  620  calculates the CQI value of each substream from the CQI value of the reference substream and the relative CQI values found for the substreams other than the reference substream specified from the reference substream information. 
     Next, the operations of radio communication apparatus  500  and radio communication apparatus  600  having the above-described configurations will be explained. 
     In reference determining section  510 , the CQI values for the substreams from CQI determining section  140  are received as input, and the reference substream is determined. To be more specific, in reference determining section  510 , the substream associated with the CQI value of the highest received level is selected as the reference substream every CQI reporting cycle. That is, in reference determining section  510 , the reference substream is selected based on the received level. 
     In relative value calculating section  550 , relative CQI values are calculated between the CQI value of the reference substream selected in reference determining section  510  and the CQI values of substreams other than the reference substream. 
     In feedback information generating section  560 , feedback information for the transmission system is generated from the CQI value of the reference substream, the relative CQI values found for the streams other than the reference substream and the reference substream information. 
     The feedback information generated in this feedback information generating section  560  will be explained with reference to  FIG. 10 . In the figure, for ease of the explanation, the case is shown where the number of substreams is two. 
     As shown in the figure, the substream associated with the CQI value of the highest received level is selected as the reference substream every reporting cycle. Then, as for the reference substream of each CQI reporting cycle, a CQI value determined based on an “average received level,” which is an average of all chunks (i.e. chunks  1  to  8  in the figure) on a per CQI reporting cycle basis, is fed back to radio communication apparatus  600 . Moreover, as for the substreams other than the reference substream, relative CQI values, which are relative to the CQI value determined for the reference substream on a per CQI reporting cycle basis, are fed back to radio communication apparatus  600 . In the figure, substream  1  is selected as the reference substream in the first and second CQI reporting cycles, and substream  2  is selected as the reference substream in the third CQI reporting cycle. Then, as described above, the reference substream information (not shown in the figure) in the CQI reporting cycles is also fed back. 
     Incidentally, in what is referred to as a “2×2 MIMO communication system” in which the transmission system and the reception system each have two antennas, one bit is necessary for the reference substream information (e.g. stream index information identifying the reference substream), and, in a 4×4 MIMO communication system, only two bits are necessary. 
     In radio communication apparatus  600 , in feedback information processing section  620 , CQI values of the individual substreams are calculated from the feedback information from receiving section  210 . To be more specific, the feedback information from radio communication apparatus  500  contains the CQI value of the reference substream, the relative CQI values found for the substreams other than the reference substream and the reference substream information, so that feedback information processing section  620  calculates the CQI value of each substream from the relative CQI values found between the CQI value of the reference substream specified from the reference substream information and the substreams other than the reference substream. 
     In this way, according to Embodiment 3, radio communication apparatus  500  has reference determining section  510  that selects the reference antenna (corresponding to the reference substream) from the antennas of the transmitting side (radio communication apparatus  600 ) based on the CQI values determined by CQI determining section  140 , and relative value calculating section  550  calculates relative CQI values between the CQI value determined for the reference antenna selected in reference determining section  510  and the CQI values determined for the antennas other than the reference antenna. Especially, reference determining section  510  selects the antenna of the highest CQI value as the reference antenna. 
     By this means, the antenna of the best communication quality (e.g. SINR) is selected as the reference antenna, and, by feeding back the absolute value of communication quality of the reference antenna (the absolute value of the CQI value) and the relative values of the antennas other than the reference antenna (relative CQI values), the reliability of CQI feedback information of the substream of the best channel communication quality especially improves. As a result, the transmission system receiving the feedback information can perform transmission control based on reliable feedback information, thereby improving system throughput. 
     Embodiment 4 
     In Embodiment 2, the reference substream is fixed between all chunks. By contrast with this, in Embodiment 4, the substream of the best communication quality is selected as the reference substream on a per chunk basis. The embodiments are the same in that feedback is carried out using the absolute value of the CQI value with respect to the reference substream and relative CQI values with respect to substreams other than the reference substream. In this way, the substream of the best communication quality is selected as the reference substream per chunk, and by feeding back the absolute value of communication quality of the reference substream and the relative values of the substreams other than the reference substream, so that the reliability of feedback information improves. Moreover, by feeding back communication quality of individual chunks related to the substreams, frequency scheduling can be carried out efficiently in the transmission system. As a result, the transmission system receiving the feedback information can perform transmission control based on the feedback information, which is reliable and which contains communication quality per chunk, thereby improving system throughput. 
     As shown in  FIG. 11 , radio communication apparatus  700  according to Embodiment 4 has reference determining section  710 , relative value calculating section  750  and feedback information generating section  760 . 
     Reference determining section  710  receives as input the CQI values of the individual chunks related to the substreams from CQI determining section  340  and determines the reference substream of each chunk. To be more specific, reference determining section  710  selects the substream associated with the CQI value of the highest received level as the reference substream on a per chunk basis. That is, reference determining section  710  selects the reference substream per chunk based on the received level of each chunk. Then, reference determining section  710  outputs information specifying the reference substream of each chunk (hereinafter may be referred to as “the reference chunk substream information”) to relative value calculating section  750  and feedback information generating section  760 . 
     Relative value calculating section  750  calculates relative chunk CQI values, which are the CQI values of the individual chunks, between the CQI value of the reference substream selected in reference determining section  710  and the CQI values of substreams other than the reference substream. 
     Feedback information generating section  760  generates feedback information (see  FIG. 12 ) for the transmission system from the CQI value of the reference substream of each chunk, the relative chunk CQI values found for streams other than the reference substream per chunk and the reference chunk substream information. 
     As shown in  FIG. 13 , radio communicating apparatus  800  has feedback information processing section  820 . 
     Feedback information processing section  820  calculates the CQI value of each chunk related to the substream from the feedback information from receiving apparatus  210 . To be more specific, the feedback information from radio communication apparatus  700  contains the CQI value of the reference substream of each chunk, the relative chunk CQI values found for the substreams other than the reference substream per chunk and the reference chunk substream information, so that feedback information processing section  820  calculates the CQI values of the individual chunks related to the substreams from the CQI value of the reference substream per chunk and the relative chunk CQI values found for the substreams other than the reference substream specified from the reference chunk substream information. 
     In this way, according to Embodiment 4, radio communication apparatus  700  has reference determining section  710  that selects the reference antenna from the antennas of the transmitting side (radio communication apparatus  800 ) on a per chunk basis based on the CQI values of the individual chunks related to the transmitting antennas determined by CQI determining section  340 , relative value calculating section  750  calculates relative chunk CQI values of the individual chunks between the reference antenna and the antennas other than the reference antenna, from the CQI value of the reference antenna per chunk and the CQI values of the antennas other than the reference antenna, and feedback information generating section  760  generates feedback information containing the CQI value of the reference antenna of each chunk, the relative chunk CQI values and the identification information of the reference antenna per chunk. Especially, reference determining section  710  selects the antenna of the highest CQI value on a per chunk basis as the reference antenna. 
     By this means, the antenna of the best communication quality (e.g. SINR) for each chunk is selected as the reference antenna, and by feeding back the absolute value of communication quality of the reference antenna (the absolute value of the CQI value) and the relative values of the antennas other than the reference antenna (relative chunk CQI values), the reliability of CQI feedback information of the substream of the best channel communication quality per chunk especially improves. Moreover, by feeding back communication quality per chunk related to the antennas, frequency scheduling can be carried out efficiently in the transmission system. As a result, the transmission system receiving the feedback information can perform transmission control based on the feedback information, which is reliable and which contains communication quality per chunk, thereby improving system throughput. 
     Embodiment 5 
     In Embodiment 1, the reference substream is fixed. By contrast with this, in Embodiment 5, the reference substream changes every reporting cycle according to a predetermined pattern. The embodiments are the same in that feedback is carried out using the absolute value of the CQI value with respect to the reference substream and relative CQI values with respect to substreams other than the reference substream. In this way, by changing the reference substream every predetermined cycle according to a predetermined cycle and by feeding back the absolute value of communication quality of the reference substream and the relative values of the substreams other than the reference substream, the reliability of the feedback information can be kept in good balance. As a result, the transmission system receiving the feedback information can perform transmission control based on reliable feedback information, thereby improving system throughput. 
     As shown in  FIG. 14 , radio communication apparatus  900  according to Embodiment 5 has relative value calculating section  950 . 
     Relative value calculating section  950  changes the reference substream every CQI reporting cycle according to the predetermined pattern and calculates relative CQI values between the CQI value of the reference substream and the CQI values of substreams other than the reference substream. 
     In feedback information generating section  160 , feedback information for the transmission system is generated from the relative CQI values between the CQI value of the reference substream per CQI reporting cycle and substreams other than the reference substream per CQI reporting cycle. 
       FIG. 15  shows the feedback information when the reference substream alternately changes between substream  1  and substream  2  every CQI reporting cycle. 
     As shown in  FIG. 16 , radio communication apparatus  1000  in Embodiment 5 has feedback information processing section  1020 . 
     Feedback information processing section  1020  calculates the CQI value of each substream from the feedback information from receiving apparatus  210 . To be more specific, as described above, the feedback information from radio communication apparatus  900  contains the CQI value of the reference substream per CQI reporting cycle and the relative CQI values found for the substreams other than the reference substream per CQI reporting cycle, so that feedback information processing section  1020  calculates the CQI value every CQI reporting cycle related to the substreams from the CQI value of the reference substream per CQI reporting cycle and the relative CQI values found for the substreams other than the reference substream per CQI reporting cycle. 
     Feedback information processing section  1020  needs to specify the reference substream in order to calculate the CQI values, and the CQI values of the substreams can be calculated if feedback information processing section  1020  acquires the change pattern of the reference substream in advance in relative value calculating section  950  of radio communication apparatus  900 . If the change pattern of the reference substream is determined in advance between transmitting side and receiving side, signaling for reporting the reference substream is not necessary. 
     In this way, according to Embodiment 5, relative value calculating section  950  of radio communication apparatus  900  sequentially changes the reference antenna according to the predetermined change pattern of the reference antenna and calculates relative CQI values. 
     By this means, by changing the reference antenna according to the predetermined pattern and by feeding back the absolute value of communication quality of the reference antenna (the absolute value of the CQI value) and the relative values (relative CQI values) of the antennas other than the reference antenna, the reliability of the feedback information can be kept in good balance. As a result, the transmission system receiving the feedback information can perform transmission control based on reliable feedback information, thereby improving system throughput. 
     Embodiment 6 
     In Embodiment 2, the reference substream is fixed between all chunks. By contrast with this, in Embodiment 6, the reference substream changes on a per chunk basis according to a predetermined pattern. The embodiments are the same in that feedback is carried out using the absolute value of the CQI value with respect to the reference substream and relative CQI values with respect to substreams other than the reference substream. In this way, by changing the reference substream on a per chunk basis according to the predetermined pattern and by feeding back the absolute value of communication quality of the reference substream and the relative values of the substreams other than the reference substream, the reliability of the feedback information can be kept in good balance. Moreover, by feeding back communication quality per chunk related to the substreams, frequency scheduling can be carried out efficiently in the transmission system. As a result, the transmission system receiving the feedback information can perform transmission control based on the feedback information, which is kept reliability and which contains communication quality per chunk, thereby improving system throughput. 
     As shown in  FIG. 17 , radio communication apparatus  1100  according to Embodiment 6 has relative value calculating section  1150 . 
     Relative value calculating section  1150  changes the reference substream according to the predetermined pattern on a per chunk basis and calculates relative chunk CQI values, which are the CQI values per chunk, between the CQI value of the reference substream and the CQI values of substreams other than the reference substream. 
     In feedback information generating section  360 , feedback information for the transmission system is generated from the relative CQI values between the CQI value of each chunk for reference substream and substreams other than the reference substream of each chunk. 
       FIG. 18  shows the feedback information when the reference substream alternately changes between substream  1  and substream  2  on a per chunk basis. 
     As shown in  FIG. 19 , radio communication apparatus  1200  in Embodiment 6 has feedback information processing section  1220 . 
     Feedback information processing section  1220  calculates the CQI value of each chunk for the substreams from the feedback information from receiving apparatus  210 . To be more specific, as described above, the feedback information from radio communication apparatus  1100  contains the CQI value of each chunk for the reference substream and the relative chunk CQI values found for the substreams other than the reference substream of each chunk, so that feedback information processing section  1220  calculates the CQI values of the individual chunks related to the substreams from the CQI value of each chunk for the reference substream and the relative chunk CQI values found for the substreams other than the reference substream of each chunk. 
     Feedback information processing section  1220  needs to specify the reference substream of each chunk in order to calculate the CQI values, and CQI values of individual chunks related to the substreams can be calculated if feedback information processing section  1220  acquires the change pattern of the reference substream in advance in relative value calculating section  1150  of radio communication apparatus  1100 . If the change pattern of the reference substream is determined in advance between transmitting side and receiving side, signaling for reporting the reference substream is not necessary. 
     In this way, according to Embodiment 6, radio communication apparatus  1100  has: received level measuring section  330  that measures the received levels of the individual pilot signals transmitted from the antennas of the transmitting side (radio communication apparatus  1200 ); CQI determining section  340  that determines the CQI value of each transmitting antenna based on the received levels; relative value calculating section  1150  that calculates relative CQI values showing the relative values of the CQI values between the reference antenna and the antennas other than the reference antenna, from the CQI value determined for the reference antenna and the CQI values determined for the antennas other than the reference antenna, in the transmitting antennas by CQI determining section  340 ; and feedback information generating section  360  that generates feedback information for the transmitting side including the CQI values of the reference antenna and the relative CQI values. Received level measuring section  330  measures the received levels of the individual chunks formed with a plurality of subcarriers, CQI determining section  340  determines the CQI value of each chunk related to the transmitting antennas based on the received levels, and relative value calculating section  1150  changes the reference antenna according to the predetermined pattern per chunk and calculates relative chunk CQI values showing the relative values of the CQI values of the individual chunks between the reference antenna and the antennas other than the reference antenna. 
     By this means, by changing the reference antenna on a per chunk basis according to the predetermined pattern and by feeding back the absolute value of communication quality of the reference antenna (the absolute value of the CQI value) and the relative values of the antennas other than the reference antenna (the relative chunk CQI values), the reliability of the feedback information can be kept in good balance. Moreover, by feeding back communication quality per chunk related to the antennas, frequency scheduling can be carried out efficiently in the transmission system. As a result, the transmission system receiving the feedback information can perform transmission control based on the feedback information, which is kept reliability and which contains communication quality per chunk, thereby improving system throughput. 
     INDUSTRIAL APPLICABILITY 
     The MIMO receiving apparatus and the MIMO transmitting apparatus of the present invention are suitable for use in reducing an amount of feedback information and system traffic.