Abstract:
A communication apparatus wherein in a case of reporting a reception quality measured for each of a plurality of subbands, even if the band is widened, the degradation in transmission efficiency can be avoided. In this apparatus, an antenna ( 101 ) receives the pilot signals superimposed on a plurality of subbands in a predetermined band. A quality level calculating unit ( 107 ) uses the received pilot signals to measure the reception qualities of the respective subbands. A CQI selecting unit ( 109 ) selects one of a plurality of CQI values that corresponds to one of the measured reception qualities for each subband. A feedback information generating unit ( 110 ) calculates a first average value of the selected CQI values, calculates a second average value of the CQI values indicating better reception qualities than the first average value, and calculates a difference value between the second average value and each of the CQI values indicating better reception qualities than the second average value. A transmitting unit ( 160 ) transmits, as feedback information, the first and second average values and the difference values to the other end of communication.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a communication apparatus and a method of reporting reception quality. For example, the present invention relates to a communication apparatus and a method of reporting reception quality for transmitting a feedback of a channel quality indicator (CQI), which is a measurement result of reception quality of a downlink radio channel. 
       BACKGROUND ART 
       [0002]    Conventionally, the mobile communication system is known where the result of measurement of reception quality state in a downlink channel is reported as a CQI from a communication terminal apparatus such as a mobile phone to a base station, to perform link adaptation for a downlink channel (for example, transmission power control, adaptive modulation, and adaptive demodulation) or scheduling of packets to transmit to each user (for example, see Patent Literature 1). Here, although a CQI is equivalent to Ec/I0 of the common pilot channel (ratio of received chip energy to interference power), according to the present application, a CQI is not limited to Ec/I0, and also refers to an indicator or feedback information that show the reception quality state of radio channel such as propagation loss, reception power, and the ratio of signal to interference power. 
         [0003]    Further, conventionally, because frequency-selective fading occurs following the trend of broadbandization in a mobile communication system, a mobile communication system for efficiently transmitting data is known where each of a plurality of users use a different frequency band having a good condition. According to this mobile communication system, the whole frequency band to use is divided into a plurality of sub-bands, and a CQI is measured and reported per sub-band. 
         [0004]    Further, in recent years, in the digital radio communication system, high speed transmission has started gaining popularity. Further, in the future mobile communication system, further broadbandization is expected to realize high transmission rate, short delay, and large capacity. 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. 2008-236431 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    However, the conventional mobile communication system has a problem that, in accordance with the trend of the broadbandization, the amount of information required for the report of CQIs increases and the amount of information about positional information of sub-bands increases, lowering the transmission efficiency. 
         [0007]    It is therefore an object of the present invention to provide a communication apparatus and a method of reporting reception quality for making it possible to suppress a decrease in transmission efficiency even when the band is broadened when reporting reception quality that is measured per sub-band. 
       Solution to Problem 
       [0008]    A communication apparatus according to the present invention comprises a reception section that receives a known signal that is superimposed on a plurality of sub-bands in a predetermined band; a reception quality measurement section that measures reception quality per sub-band based on the received known signal; a selection section that selects, from a plurality of report values, a report value corresponding to the measured reception quality, per sub-band; a calculation section that calculates a first average value of the selected report values and calculates a second average value of the selected report values that show better reception quality than the first average value, and calculates difference values between the second average value and the selected report values that show better reception quality than the second average value; and a transmission section that transmits the first average value, the second average value, and the difference values to a communicating party, as feedback information. 
         [0009]    A method of reporting reception quality in a first communication apparatus for reporting reception quality from the first communication apparatus to a second communication apparatus according to the present invention, the method comprising the steps of receiving a known signal that is superimposed on a plurality of sub-bands in a predetermined band; measuring reception quality per sub-band based on the received known signal; selecting, from a plurality of report values, a report value corresponding to the measured reception quality, per sub-band; calculating a first average value of the selected report values and calculates a second average value of the selected report values that show better reception quality than the first average value, and calculates difference values between the second average value and the selected report values that show better reception quality than the second average value; and a transmission section that transmits the first average value, the second average value, and the difference values to the second communication apparatus, as feedback information. 
       Advantageous Effects of Invention 
       [0010]    According to the present invention, it is possible to suppress a decrease in transmission efficiency even when the band is broadened when reporting reception quality that is measured per sub-band. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a block diagram showing a configuration of a communication apparatus according to Embodiment 1 of the present invention; 
           [0012]      FIG. 2  shows a relationship between the first average value and the CQI values of each sub-band according to Embodiment 1 of the present invention; 
           [0013]      FIG. 3  shows a relationship between the second average value and the CQI values of each sub-band that show better reception quality than the first average value according to Embodiment 1 of the present invention; 
           [0014]      FIG. 4  shows difference values according to Embodiment 1 of the present invention; 
           [0015]      FIG. 5  shows a CQI table according to Embodiment 1 of the present invention; 
           [0016]      FIG. 6  shows the CQI values of each sub-hand that show better reception quality than the first average value according to Embodiment 2 of the present invention; and 
           [0017]      FIG. 7  shows difference values according to Embodiment 2 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0019]      FIG. 1  is a block diagram showing a configuration of communication apparatus  100  according to Embodiment 1 of the present invention. Examples of communication apparatus  100  include a communication terminal apparatus such as a mobile phone. 
         [0020]    Communication apparatus  100  is configured mainly with reception section  150  and transmission section  160 . Further, reception section  150  is configured mainly with antenna  101 , radio processing section  102 , fast Fourier transform (FFT) section  103 , demodulation section  104 , decoding section  105 , channel response estimation section  106 , quality level calculation section  107 , CQI table section  108 , CQI selection section  109 , and feedback information generation section  110 . Further, transmission section  160  is configured mainly with coding section  111 , modulation section  112 , inverse fast Fourier transform section (IFFT) section  113 , radio processing section  114 , and antenna  115 . Each configuration will be described in detail below. 
         [0021]    Antenna  101  receives a reception signal that is transmitted from a communicating party at, for example, a base station (not shown) and includes data superimposed on a plurality of sub-bands in a predetermined band and a pilot signal, a known signal, and outputs the reception signal to radio processing section  102 . 
         [0022]    Radio processing section  102  down-converts the reception signal input from antenna  101  from radio frequency into baseband frequency, and outputs the baseband frequency to FFT section  103 . 
         [0023]    FFT section  103  performs FFT on the reception signal input from radio processing section  102  to convert a frequency domain signal into a time domain signal. Further, FFT section  103  outputs data contained in the converted reception signal to demodulation section  104  and outputs the pilot signal to channel response estimation section  106 . 
         [0024]    Demodulation section  104  demodulates the data input from FFT section  103  and outputs a demodulated signal to decoding section  105 . 
         [0025]    Decoding section  105  decodes the demodulated signal input from demodulation section  104  and outputs the demodulated signal as reception data. 
         [0026]    Channel response estimation section  106  estimates a channel response per sub-band based on the pilot signal input from FFT section  103 . Then, channel response estimation section  106  outputs an estimation result to quality level calculation section  107 . 
         [0027]    Quality level calculation section  107  determines an average value of each sub-band based on the frequency response of the channel per sub-band that is the estimation result input from channel response estimation section  106 , and outputs the average value to CQI selection section  109 . For example, quality level calculation section  107  determines signal to noise plus interference ratio (SINR) as reception quality and determines the average SINR of each sub-band as the reception quality average value of each sub-band. 
         [0028]    CQI table section  108  maintains a CQI table to which CQI indexes (Index: ID), reception qualities, and each parameter of coding scheme and coding rate, for example, are made correspond. The CQI table is maintained in read only memory (ROM). Here, a CQI index corresponds to a CQI value. 
         [0029]    CQI selection section  109  looks up the CQI table maintained in CQI table section  108  to select a CQI index corresponding to the reception quality average value input from quality level calculation section  107 , per sub-band. Specifically, CQI selection section  109  looks up the CQI table stored in CQI table section  108  to select the CQI index corresponding to the reception quality average value input from quality level calculation section  107 , per sub-band. Then, CQI selection section  109  combines the selected CQI index and the CQI value (report value) and outputs the combined CQI index and CQI value to feedback information generation section  110 . 
         [0030]    Feedback information generation section  110  determines an average value of the CQI values for the whole band (hereinafter referred to as “first average value”) using the CQI values of each sub-band in the whole band that are input from CQI selection section  109 . Further, feedback information generation section  110  selects a sub-band having the CQI value that shows the better reception quality than the first average value out of the CQI values of each sub-band. Further, feedback information generation section  110  determines an average CQI value (hereinafter referred to as “second average value”) using the CQI value of the selected sub-band. Further, feedback information generation section  110  selects a sub-band having a CQI value that shows the better reception quality than the determined second average value, and determines a difference value between the CQI value of the selected sub-band and the second average value. Then, feedback information generation section  110  outputs the determined first average value, second average value, and difference value to coding section  111  as feedback information. The specific method of generating feedback information will be described later. 
         [0031]    Coding section  111  encodes a transmission signal including the feedback information and transmission data input from feedback information generation section  110 , and outputs the coded signal to modulation section  112 . 
         [0032]    Modulation section  112  modulates the coded signal input from coding section  111  and outputs a modulated signal to IFFT section  113 . 
         [0033]    IFFT section  113  performs IFFT on the modulated signal input from modulation section  112  to convert a time domain signal to a frequency domain signal. Then, IFFT section  113  outputs the converted signal to radio processing section  114 . 
         [0034]    Radio processing section  114  up-converts the signal input from IFFT section  113 , from the base band frequency into the radio frequency, and outputs the signal to antenna  115 . 
         [0035]    Antenna  115  transmits the signal input from radio processing section  114  to a communicating party such as a base station (not shown). 
         [0036]    Next, a method of generating feedback information will be described below using  FIGS. 2 to 5 .  FIG. 2  shows a relationship between the first average value and the CQI values of each sub-band.  FIG. 3  shows a relationship between the second average value and the CQI values of each sub-band that show better reception quality than the first average value.  FIG. 4  shows difference values.  FIG. 5  shows a CQI table. In  FIG. 5 , although the CQI table stores the reception quality that is associate with the CQI index, the description will be omitted. 
         [0037]    First, feedback information generation section  110  determines first average value # 201  of the CQI values in the whole band. That is, first average value # 201  is obtained by adding CQI values of sub-bands in the whole band including sub-bands n 1  to n 13  to determine a sum value and dividing the sum value by the number of sub-bands in the whole band (see  FIG. 2 ). 
         [0038]    Further, feedback information generation section  110  selects sub-bands having a CQI value that shows better reception quality than first average value # 201 , that is, sub-bands having a greater CQI value than first average value # 201 . In  FIG. 2 , feedback generation section  110  selects six sub-bands, n 3 , n 4 , n 9 , n 10 , n 11 , and n 12 , having a greater CQI value than first average value # 201  (see  FIG. 2 ). 
         [0039]    Further, feedback information generation section  110  determines second average value # 301  that is the average value of each CQI value of selected sub-bands n 3 , n 4 , n 9 , n 10 , n 11 , and n 12 . That is, second average value # 301  can be determined by adding the CQI values of sub-bands n 3 , n 4 , n 9 , n 10 , n 11 , and n 12  to obtain a sum value, and dividing the obtained sum value by the number of sub-bands of 6 (see  FIG. 3 ). 
         [0040]    Further, feedback information generation section  110  selects the sub-bands having a CQI value that shows better reception quality than second average value # 301 , that is, sub-bands n 3 , n 9 , n 10 , n 11 , and n 12 , having a greater CQI value than second average value # 301  (see  FIG. 3 ). 
         [0041]    Further, feedback information generation section  110  determines a difference value between the CQI values of selected sub-bands n 3 , n 9 , n 10 , n 11 , and n 12  and second average value # 301  (see  FIG. 4 ). That is, the difference value can be determined by subtracting second average value # 301  from each CQI value of sub-bands n 3 , n 9 , n 10 , n 11 , and n 12 . 
         [0042]    Here, in feedback information, five bits are allocated to first average value # 201 . Further, by allocating five bits to first average value # 201 , it is possible to specify first average value # 201  from one of the 32 types of CQI values corresponding to CQI indexes 0 to 31 (see  FIG. 5 ). 
         [0043]    Further, in feedback information, two bits are allocated to second average value # 301 . Further, by allocating only 2 bits to second average value # 301 , which is smaller than first average value # 201 , second average value # 301  needs to be specified based on one CQI value from four types of CQI values out of CQI indexes 0 to 31. However, because the CQI value that is used to determine second average value # 301  is a CQI value that shows better reception quality than first average value # 201 , it is possible to specify second average value # 301  based on four types of CQI values. 
         [0044]    Further, in feedback information, one bit is allocated to the difference value per sub-band. Further, by allocating only one bit to the difference value, which is smaller than first average value # 201  and second average value # 301 , the difference value needs to be specified based on one CQI value from two types of CQI values out of CQI indexes 0 to 31. However, because the difference value is a difference between second average value # 301  and a CQI value that shows better reception quality than second average value # 301 , it is possible to specify the difference value based on two types of CQI values. 
         [0045]    As described above, feedback information generation section  110  generates first average value # 201  of five bits, second average value # 301  of two bits, and a one-bit difference per sub-band wherein the difference value is calculated, as feedback information. In the case of  FIGS. 2 to 4 , feedback information generation section  110  generates feedback information of 12 bits, from “first average value # 201  (five bits)+second average value # 301  (two bits)+the difference value (one bit)×the number of sub-bands wherein the difference value are calculated=12 bits.” Further, feedback information includes positional information of the sub-bands wherein the difference value are calculated. 
         [0046]    As described above, according to the present embodiment, only by reporting the first average value and the second average value to a communicating party and allocating only an amount of information of one bit, per sub-band, to a difference value, which needs to be transmitted for the number of sub-bands, it is possible to suppress the amount of feedback information, suppressing a decrease in transmission efficiency even when the band is broadened. 
         [0047]    Further, although a case has been described with the present embodiment where feedback information is formed with the first average value, the second average value, and the difference value, the present embodiment is by no means limited to this, and feedback information may include other parameters as long as at least the first average value, the second average value, and the difference value are included. Further, although a case has been described with the present embodiment where five bits are allocated to the first average value, two bits are allocated to the second average value, and one bit is allocated to the difference value, the present embodiment is by no means limited to this, and it is equally possible to allocate an arbitrary number of bits to the first average value, the second average value, and the difference value. 
       Embodiment 2 
       [0048]      FIG. 6  shows the CQI values of each sub-band that show better reception quality than the first average value. Further,  FIG. 7  shows difference values. 
         [0049]    The communication apparatus according to the present embodiment is configured with the same functions as  FIG. 1  and is different only in processing in feedback information generation section  110  from the above Embodiment 1, and therefore the overlapping explanations for the functions of the communication apparatus will be omitted. Further, in the explanation for the present embodiment below, the same reference numerals as in  FIG. 1  will be used. 
         [0050]    A method of generating feedback information according to the present embodiment will be described below using  FIGS. 6  and  7 . Further, the present embodiment is the same as Embodiment 1 up to the selection of sub-bands using the first average value,  FIG. 2  will be used for the explanation. Further, according to the present Embodiment, the CQI table in  FIG. 5  is used. 
         [0051]    First, feedback information generation section  110  determines first average value # 201  of CQI values for the whole band. That is, first average value # 201  can be determined by adding the CQI values of sub-bands in the whole band including sub-bands n 1  to n 13  to determine a sum value, and dividing the determined sum value by the number of sub-bands in the whole band (see  FIG. 2 ). 
         [0052]    Further, feedback information generation section  110  selects sub-bands having a CQI value that shows the better reception quality than first average value # 201 , that is, sub-bands having a greater CQI value than first average value # 201 . In  FIG. 2 , feedback information generation section  110  selects six sub-bands n 3 , n 4 , n 9 , n 10 , n 11 , and n 12 , having a CQI value that shows better reception quality than first average value # 201  (see  FIG. 2 ). 
         [0053]    Further, feedback information generation section  110  selects the smallest CQI value out of the CQI values of selected sub-bands n 3 , n 4 , n 9 , n 10 , n 11 , and n 12 . In the case of  FIG. 2 , because the CQI value of sub-band n 4  is the smallest, feedback information generation section  110  selects the CQI value of sub-band n 4  as the smallest CQI. 
         [0054]    Further, feedback information generation section  110  determines difference values of from r 1  to r 5  between the smallest CQI and the CQI values of each sub-band n 3 , n 9 , n 10 , n 11 , and n 12  excluding sub-band n 4  (see  FIG. 6 ). That is, the difference values of from r 1  to r 5  can be determined by subtracting the smallest CQI from the CQI values of each sub-band n 3 , n 9 , n 10 , n 11 , and n 12  excluding sub-band n 4 . 
         [0055]    Here, in feedback information, five bits are allocated to first average value # 201 . Further, by allocating five bits to first average value # 201 , it is possible to specify first average value # 201  from one of the 32 types of CQI values corresponding to CQI indexes 0 to 31 (see  FIG. 5 ). 
         [0056]    Further, in feedback information, two bits are allocated to the smallest CQI. Further, by allocating only two bits to the smallest CQI, which is fewer than to first average value # 201 , the smallest CQI needs to be specified based on one CQI value from four types of CQI values out of CQI indexes 0 to 31. However, because the CQI values that are used to determine the smallest CQI are CQI values that show better reception quality than first average value # 201 , it is possible to specify the smallest CQI from four types of CQI values. 
         [0057]    Further, in feedback information, one bit is allocated to the difference value per sub-band. Further, by allocating only one bit to the difference value, which is smaller than first average value # 201  and the smallest CQI, the difference value needs to be specified based on one CQI value from two types of CQI values out of CQI indexes 0 to 31. However, because the difference value is a difference between the smallest CQI value that shows better reception quality than first average value # 201  and the CQI value that shows better reception quality than first average value # 201  excluding the smallest CQI value, it is possible to specify the difference value from two types of CQI values. 
         [0058]    As described above, feedback information generation section  110  generates first average value # 201  of five bits, the smallest CQI of two bits, and the difference value of one bit per sub-band wherein the difference value is calculated, as feedback information. For example, feedback information generation section  110  generates feedback information of 12 bits, from “first average value # 201  (five bits)+the smallest CQI (two bits)+the difference value (one bit)×the number of sub-bands wherein the difference value is calculated=12 bits.” Further, feedback information includes positional information of the sub-bands wherein the difference value is calculated. 
         [0059]    As described above, according to the present embodiment, only by reporting the first average value and the smallest CQI to a communicating party and allocating only an amount of information of one bit, per sub-band, to a difference value, which needs to be transmitted for the number of sub-bands, it is possible to suppress the amount of feedback information, suppressing a decrease in transmission efficiency even when the band is broadened. 
         [0060]    Further, although a case has been described with the present embodiment where feedback information is formed with the first average value, the smallest CQI, and the difference value, the present embodiment is by no means limited to this, and t 6  feedback information may include other parameters as long as at least the first average value, the smallest CQI, and the difference value are included. Further, although a case has been described with the present embodiment where five bits are allocated to the first average value, two bits are allocated to the smallest CQI, and one bit is allocated to the difference value, the present embodiment is by no means limited to this, and it is equally possible to allocate an arbitrary number of hits to the first average value, the smallest CQI, and the difference value. 
         [0061]    Although cases have been described with the above Embodiments 1 and 2 where reception quality is reported using the CQI, the present invention is by no means limited to this, and it is equally possible to report reception quality using arbitrary parameters other than the CQI as long as the parameter indicates reception quality. Further, although cases have been described with the above Embodiment 1 and 2 where reception quality is measured using a pilot signal, the present invention is by no means limited to this, and it is equally possible to measure reception quality using a known arbitrary signal. 
         [0062]    The disclosure of Japanese Patent Application No. 2009-28432 filed on Feb. 10, 2009, including the specification, drawings, and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0063]    A communication apparatus and a method of reporting reception quality according to the present invention is suitable, for example, to send a feedback of a CQI, which is a measurement result of reception quality of a downlink radio channel.