Abstract:
Provided are a radio reception device, a radio transmission device, and a feedback method which can uniformly guarantee the feedback accuracy of an average channel quality indicator (CQI) even when the transmission band width is different. A channel estimation unit uses a pilot signal to obtain SINR for each RB. A feedback information generation unit converts SINR of each RB into a corresponding CQI. Moreover, as the transmission band width increases, the number X of the quantization bits is decreased when quantizing the average CQI, thereby generating feedback information. A radio transmission unit transmits feedback information from an antenna.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 of PCT/JP2009/001778 filed Apr. 17, 2009 which is entitled to and claims the benefit of Japanese Application No. JP 2008-109294 filed Apr. 18, 2008, the disclosures of each of which, including the specification, claims, drawings and abstract, are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a radio reception apparatus, radio transmission apparatus and feedback method. 
     BACKGROUND ART 
     As a technology for improving cell throughput in a 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) downlink, there is frequency scheduling (multi-user scheduling). Each terminal feeds back to the base station a CQI (Channel Quality Indicator) that is determined based on an SINR (Signal to Interference and Noise Ratio) for each group of a plurality of subcarriers (hereinafter “RB (Resource Block),” and the base station allocates communication resources to terminals using these CQI&#39;s. 
     The base station allocates a communication resource preferentially to a terminal that feeds back a higher CQI. Consequently, since the number of terminals that feed back a high CQI increases as the number of terminals increases, there is an improvement in cell throughput (peak data rate and frequency utilization efficiency), CQI feedback methods include Best-M reporting. 
       FIG. 1  shows an overview of Best-M reporting. In Best-M reporting, an average CQI (represented by X bits) of an entire transmission band (N RB ), CQI&#39;s corresponding to the top M RB&#39;s with a high CQI level (the CQI of each RB being represented by Y bits) and the positions of selected RB&#39;s (represented by log 2 (N RB C M ) bits) are fed back. By this means, a total of X+YM+log 2 (N RB C M )) bits are fed back. Number of quantization bits Y of the top M CQI&#39;s is represented by a difference value from the average CQI. Also, the average CQI is represented by fixed number of quantization bits X, regardless of the transmission band. 
       FIG. 2  shows the CQI feedback format in Best-M reporting. Here, a case is shown in which X=5 bits, =3 bits, and M=5. The base station demodulates Best-M reporting feedback information, and reproduces the CQI of each RB. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         NPL 1: 3GPP, R1-062954, LG Electronics, “Analysis on DCT based CQI reporting Scheme” 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, if a transmission bandwidth assigned to a terminal varies, the possible range (i.e. fluctuation range) of an average CQI varies too.  FIG. 3  shows relationships between transmission bandwidths and the average CQI fluctuation range.  FIG. 3A  shows a case where the transmission bandwidth is 5 MHz (25 RB&#39;s), and  FIG. 3B  shows a case where the transmission bandwidth is 10 MHz (50 RB&#39;s). The average CQI fluctuation range is represented by the range indicated by dotted lines in the figures, and becomes large when the transmission bandwidth is narrower. 
     That is, even if the average CQI fluctuation range is large, the number of bits to represent the average CQI is limited to X bits, and, consequently, if the average CQI is quantized, the accuracy is reduced. In contrast, in a case where the average CQI fluctuation range is small, if the average CQI is quantized, the accuracy is not reduced extremely. Thus, when the transmission bandwidth varies, the average CQI fluctuation range varies, which causes a difference in the accuracy of average CQI feedback. 
     It is therefore an object of the present invention to provide a radio reception apparatus, radio transmission apparatus and feedback method for equally securing the accuracy of average CQI feedback even in a case where a transmission bandwidth varies. 
     Solution to Problem 
     The radio reception apparatus of the present invention employs a configuration having: a reception section that receives a pilot signal; an estimating section that estimates received quality of a received signal using the received pilot signal; a feedback information generating section that obtains an average channel quality indicator by averaging the received quality over a transmission bandwidth, and generates feedback information by quantizing the obtained average channel quality indicator by a smaller number of quantization bits when the transmission bandwidth is wider; and a transmission section that transmits the feedback information. 
     The radio transmission apparatus of the present invention employs a configuration having: a reception section that receives feedback information including an average channel quality indicator obtained by averaging received quality over a transmission bandwidth; and a feedback information demodulating section that demodulates the feedback information based on a smaller number of quantization bits when the transmission bandwidth is wider. 
     The feedback method of the present invention includes: receiving a pilot signal; estimating received quality of a received signal using the received pilot signal; obtaining an average channel quality indicator by averaging the received quality over a transmission bandwidth, and generating feedback information by quantizing the obtained average channel quality indicator by a smaller number of quantization bits when the transmission bandwidth is wider; and transmitting the feedback information. 
     The feedback method of the present invention includes: receiving pilot signals transmitted from a plurality of antennas, via a plurality of antennas; estimating received quality of a received signal for each stream, using the received pilot signals; obtaining an average channel quality indicator by averaging the received quality of each stream over a transmission bandwidth; generating feedback information by quantizing the obtained average channel quality indicator of each stream by a smaller number of quantization bits when the transmission bandwidth is wider; and transmitting the feedback information. 
     Advantageous Effects of Invention 
     According to the present invention, even in a case where a transmission bandwidth varies, it is possible to equally secure the accuracy of average CQI feedback. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an overview of Best-M reporting; 
         FIG. 2  shows a CQI feedback format according to Best-M reporting; 
         FIG. 3  shows relationships between transmission bandwidths and the average CQI fluctuation range; 
         FIG. 4  is a block diagram showing the configuration of a reception apparatus according to Embodiment 1 of the present invention; 
         FIG. 5  shows a feedback table according to Embodiment 1 of the present invention; 
         FIG. 6  shows a state where SINR&#39;s are converted to CQI&#39;s; 
         FIG. 7  is a block diagram showing the configuration of a transmission apparatus according to Embodiment 1 of the present invention; 
         FIG. 8  is a block diagram showing the configuration of a reception apparatus according to Embodiment 2 of the present invention; 
         FIG. 9  shows a feedback table according to Embodiment 2 of the present invention; and 
         FIG. 10  is a block diagram showing the configuration of a transmission apparatus according to Embodiment 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 4  is a block diagram showing the configuration of a reception apparatus according to Embodiment 1 of the present invention. Radio reception section  102  down-converts a signal received via antenna  101  to a baseband signal, outputs the pilot signal in the received signal to channel estimating section  103 , and outputs the data signal in the received signal to data demodulating section  104 . 
     Channel estimating section  103  obtains the channel estimation value and SINR for each RB, using the pilot signal outputted from radio reception section  102 , and outputs the obtained channel estimation value to data demodulating section  104  and the SINR to feedback information generating section  107 . 
     Data demodulating section  104  corrects the phase distortion of the data signal outputted from radio reception section  102  using the channel estimation value outputted from channel estimating section  103 , converts the modulation symbol of the corrected phase distortion to soft decision bits, and outputs these bits to data decoding section  105 . Data decoding section  105  decodes the soft decision bits outputted from data decoding section  104  and restores transmission data. 
     Transmission band information storage section  106  stores a transmission bandwidth assigned to the subject apparatus and reports the stored transmission bandwidth to feedback information generating section  107 . The transmission bandwidth is reported by, for example, a broadcast channel. 
     Feedback information generating section  107  converts the SINR of each RB outputted from channel estimating section  103 , to a corresponding CQI. Further, feedback information generating section  107  generates feedback information by the number of quantization bits determined based on the transmission bandwidth reported from transmission band information storage section  106 , and outputs this information to radio transmission section  108 . Feedback information generating section  107  will be described later in detail. 
     Radio transmission section  108  up-converts the feedback information outputted from feedback information generating section  107  and transmits the result from antenna  101 . 
     Next, generation of feedback information in above feedback information generating section  107  will be explained in detail. Assume that feedback information generating section  107  has a feedback table as shown in  FIG. 5 . In this feedback table, number of quantization bits X for an average CQI is reduced when the transmission bandwidth is wider. Here, assume that the number of quantization bits is equal in 20 MHz (100 RB&#39;s) or more. 
     In  FIG. 5 , five bits are provided for the average CQI in 5 MHz (25 RB&#39;s), four bits are provided for the average CQI in 10 MHz (50 RB&#39;s), three bits are provided for the average CQI in 20 MHz (100 RB&#39;s) and three bits are provided for the average CQI in 40 MHz (200 RB&#39;s). These values are set because, since the number of samples (the number of RB&#39;s in this case) to be averaged increases when the transmission bandwidth is wider, the frequency diversity effect increases and the average CQI fluctuation range becomes small. Here, number of CQI&#39;s M to feed back is five and number of quantization bits Y of top M CQI&#39;s is three bits. 
     As shown in  FIG. 6 , feedback information generating section  107  converts SINR&#39;s averaged per RB to CQI&#39;s, according to the numbers of quantization bits in the feedback table shown in  FIG. 5 . Also, feedback information generating section  107  obtains the average SINR in the entire transmission band from the SINR per RB, and performs CQI conversion of the average SINR according to the numbers of quantization bits in the feedback table of  FIG. 5 . Then, feedback information is generated. 
       FIG. 7  is a block diagram showing the configuration of a transmission apparatus according to Embodiment 1 of the present invention. Radio reception section  202  receives feedback information fed back from the reception apparatus via antenna  201 , down-converts the received feedback information to a baseband signal and outputs this signal to feedback information demodulating section  203 . 
     Feedback information demodulating section  203  has the same feedback table as the feedback table provided in feedback information generating section  107  of the reception apparatus shown in  FIG. 4 , demodulates the feedback information outputted from radio reception section  202  based on the feedback table and obtains a CQI (channel coding rate and modulation level). Here, feedback information demodulating section  203  has transmission bandwidth information assigned to the communicating reception apparatus. The obtained channel coding rate is outputted to encoding section  204 , and the modulation level is outputted to modulating section  205 . Feedback information demodulating section  203  will be described later in detail. 
     Encoding section  204  encodes each input transmission data by the channel coding rate outputted from feedback information demodulating section  203 , and outputs encoded data to modulating section  205 . Modulating section  205  modulates the encoded data outputted from encoding section  204  by the modulation level outputted from feedback information demodulating section  203 , and outputs the modulation symbol to radio transmission section  206 . 
     Radio transmission section  206  up-converts the modulation symbol outputted from modulating section  205  and transmits the result from antenna  201 . 
     Next, demodulation of feedback information in above feedback information demodulating section  203  will be explained in detail. Feedback information demodulating section  203  has the feedback table shown in  FIG. 5 . 
     The number of quantization bits for an average CQI varies between transmission bandwidths. Consequently, with reference to the feedback table, feedback information demodulating section  203  obtains number of quantization bits X for the average CQI, number of CQI&#39;s M to feed back, and number of quantization bits Y for the CQI&#39;s, according to transmission bandwidth information shared between the reception apparatus and the transmission apparatus. Feedback information demodulating section  203  demodulates feedback information based on obtained X, M and Y, and obtains a transmission weight and CQI (channel coding rate and modulation level). According to the feedback table shown in  FIG. 5 , X=3 to 5, M=5 and Y=3. 
     Thus, according to Embodiment 1, by reducing the number of quantization bits for an average CQI when the transmission bandwidth is wider, the number of quantization bits is decreased when the fluctuation range of the average CQI is narrower, so that, regardless of the transmission bandwidth, it is possible to equally secure the accuracy of average CQI feedback. Further, it is possible to reduce the amount of feedback. 
     Embodiment 2 
     Although a case of SISO (Single Input Single Output) has been described with Embodiment 1, a case of MIMO (Multiple Input Multiple Output) will be explained with Embodiment 2 of the present invention. 
       FIG. 8  is a block diagram showing the configuration of a reception apparatus according to Embodiment 2 of the present invention. Here, a case will be explained where two antennas are provided. However, the same components as in  FIG. 4  of Embodiment 1 will be assigned the same reference numerals as in  FIG. 4 , and overlapping explanation will be omitted. Here, when blocks having the same function overlap by providing two antennas, although branch numbers are assigned to these blocks, there is no difference between these branch numbers unless explained otherwise. 
     Radio reception sections  102 - 1  and  102 - 2  down-convert signals received via corresponding antennas  101 - 1  and  101 - 2  to baseband signals, output data signals in the received signals to MIMO demodulating section  303 , and output pilot signals in the received signals to channel estimating section  301 . 
     Channel estimating section  301  obtains the channel estimation value and SINR per RB in each stream, using the pilot signals outputted from radio reception sections  102 - 1  and  102 - 2 , and outputs the obtained SINR to feedback information generating section  302  and the channel estimation value to MIMO demodulating section  303 . 
     Feedback information generating section  302  converts the SINR per RB outputted from channel estimating section  301 , to the CQI corresponding to each stream. Further, feedback information generating section  302  generates CQI feedback information by the number of quantization bits determined based on a transmission bandwidth reported from transmission band information storage section  106 , and outputs this information to radio transmission section  108 . Feedback information generating section  302  will be described later in detail. 
     MIMO demodulating section  303  demultiplexes the data signals outputted from radio reception sections  102 - 1  and  102 - 2  for each stream, using the channel estimation values outputted from channel estimating section  301 . The demultiplexed streams are outputted to data demodulating sections  104 - 1  and  104 - 2 , respectively. 
     Next, generation of feedback information in above feedback information generating section  302  will be explained in detail. As shown in  FIG. 9 , feedback information generating section  302  has a feedback bit table in which, as for the first stream, number of quantization bits X for the average CQI is reduced when the transmission bandwidth is wider, and in which, as for a second stream, the average CQI is represented by the difference from the average CQI in the first stream and number of bits Xd representing the difference is reduced when the transmission bandwidth is wider. Here, the same number of quantization bits is provided for the average CQI in the first stream in 20 MHz (100 RB&#39;s) or more, and 0 bit is provided for the average CQI in the second stream in 20 MHz (100 RB&#39;s). 
     In  FIG. 9 , as for the first stream, five bits are provided for the average CQI in 5 MHz (25 RB&#39;s), four bits are provided for the average CQI in 10 MHz (50 RB&#39;s), three bits are provided for the average CQI in 20 MHz (100 RB&#39;s), and three bits are provided for the average CQI in 40 MHz (200 RB&#39;s). Also, as for the second stream, three bits are provided for the difference in 5 MHz (25 RB&#39;s), and two bits are provided for the difference in 10 MHz (50 RB&#39;s). These values are set because, since the number of samples (the number of RB&#39;s in this case) to be averaged increases when the transmission bandwidth is wider, the frequency diversity effect improves and the difference between average CQI&#39;s in streams becomes small. Here, number of CQI&#39;s M to feed back is five and number of quantization bits Y of top M CQI&#39;s is three bits. 
     Based on the feedback table shown in  FIG. 9 , feedback information generating section  302  obtains the number of quantization bits for the average CQI in the first stream based on the transmission bandwidth and obtains the number of quantization bits for the difference in the second stream based on the transmission bandwidth. Further, for each stream, feedback information generating section  302  obtains the average SINR in the entire transmission band from the SINR per RB, and converts the average SINR and SINR&#39;s of top M RB&#39;s to CQI&#39;s by the obtained number of quantization bits. Then, feedback information is generated. 
       FIG. 10  is a block diagram showing the configuration of a transmission apparatus according to Embodiment 2 of the present invention. Here, a case will be explained where two antennas  201 - 1  and  201 - 2  are provided. However, the same components as in  FIG. 7  of Embodiment 1 will be assigned the same reference numerals as in  FIG. 7 , and overlapping explanation will be omitted. Here, when blocks having the same function overlap by providing two antennas, although branch numbers are assigned to these blocks, there is no difference between these branch numbers unless explained otherwise. 
     Feedback, information demodulating section  401  has the same feedback bit table as the feedback bit table provided in feedback information generating section  302  of the reception apparatus shown in  FIG. 8 , demodulates feedback information outputted from radio reception section  202  based on the feedback table, and obtains transmission weights and CQI&#39;s (channel coding rates and modulation levels). The obtained channel coding rates are outputted to encoding sections  204 - 1  and  204 - 2 , and the modulation levels are outputted to modulating sections  205 - 1  and  205 - 2 . Also, feedback information demodulating section  401  will be described later in detail. 
     MIMO multiplexing section  402  converts modulation symbols outputted from modulating sections  205 - 1  and  205 - 2  to transmission streams, multiplexes all transmission streams and outputs the result to radio transmission sections  206 - 1  and  206 - 2 . 
     Next, demodulation of feedback information in above feedback information demodulating section  401  will be explained in detail. Feedback information demodulating section  401  has the feedback bit table shown in  FIG. 9 . 
     The number of quantization bits for the average CQI in each stream varies between transmission bandwidths. Consequently, with reference to the feedback table, feedback information demodulating section  401  obtains number of quantization bits X for the average CQI in the first stream, number of quantization bits Xd for the difference in the second stream, number of CQI&#39;s M to feed back, and number of quantization bits Y for the CQI&#39;s. Feedback information demodulating section  401  demodulates feedback information based on the number of quantization bits obtained, and obtains transmission weights and CQI&#39;s (channel coding rates and modulation levels). 
     Thus, according to Embodiment 2, by reducing the number of quantization bits for an average CQI when the transmission bandwidth is wider, the number of quantization bits is decreased when the average CQI fluctuation range is narrower, so that, regardless of the transmission bandwidth, it is possible to equally secure the accuracy of average CQI feedback. Further, it is possible to reduce the amount of feedback. 
     Also, although a case has been described above with the present embodiment where the number of antennas is two, the present invention is not limited by the number of antennas. 
     Also, cases have been described above with embodiments where the reception apparatus receives and obtains a broadcast channel including transmission bandwidth information as a method of obtaining a transmission bandwidth. However, in a system in which the transmission bandwidth is variable during communication, it may be possible to obtain the transmission bandwidth by a control channel in shorter transmission intervals (10 msec or below). Also, in a system in which the transmission bandwidth is determined in advance between the transmission apparatus and the reception apparatus, reporting by signaling is not particularly necessary. 
     Also, although cases have been described with embodiments where Best-M reporting is used as an example of a CQI feedback method and an average CQI is used as an index to represent the quality of the entire transmission band, the present invention is not limited to this. For example, it is equally possible to use DCT reporting as a CQI feedback method and use a DC component as an index to represent the quality of the entire transmission band. 
     Also, although cases have been described above with embodiments where the number of RB&#39;s (i.e. the number of samples to represent channel quality) increases when the transmission bandwidth is wider, it is equally possible to change the number of RB&#39;s even when the transmission band is fixed. For example, it may be possible to group a plurality of RB&#39;s and change the number of samples in the entire transmission band. 
     Although example cases have been described with the above embodiments where the present invention is implemented with hardware, the present invention can be implemented with software. 
     Furthermore, each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. “LSI” is adopted here but this may also be referred to as “IC,” “system LSI,” “super LSI,” or “ultra LSI” depending on differing extents of integration. 
     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 in an LSI can be regenerated 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. 
     Although the present invention has been described above with embodiments using antennas, the present invention is equally applicable to antenna ports. 
     An antenna port refers to a theoretical antenna comprised of one or a plurality of physical antennas. That is, an antenna port does not necessarily represent one physical antenna, and may represent an array antenna comprised of a plurality of antennas. 
     For example, 3 GPP LTE does not define how many physical antennas an antenna port is formed with, but defines that an antenna port is the minimum unit for transmitting different reference signals in a base station. 
     Also, an antenna port may be defined as the minimum unit upon multiplication of weighting of a precoding vector. 
     INDUSTRIAL APPLICABILITY 
     The radio reception apparatus, radio transmission apparatus and feedback method according to the present invention are applicable to, for example, a mobile communication system.