Abstract:
The purpose of the present invention is to be able to simultaneously generate three or more sets of CSI within a predetermined time interval, without degrading the accuracy of the CSI, to achieve CoMP control for flexible switching of base stations. At predetermined intervals or at timing coincident with reception of trigger information, a generation unit uses a CSI-RS resource to measure a desired signal component and interference component, and generate CSI. A transmission unit transmits control information including the CSI. During a given interval (for example, during four sub-frames) following reception of trigger information, the generation unit does not measure the interference component, instead using the most recent previously measured interference component, to measure the channel quality.

Description:
TECHNICAL FIELD 
     The present invention relates to a radio communication terminal apparatus, a radio communication base station apparatus, and a CSI generating method, which are compliant with LTE-Advanced. 
     BACKGROUND ART 
     [CSI Generation and Reporting Operation] 
     In order to realize high-speed and large capacity communication between a radio communication base station apparatus (hereinafter, abbreviated as “base station”) and a radio communication terminal apparatus (hereinafter, abbreviated as “terminal (UE: User Equipment)”), 3GPP (3rd Generation Partnership Project) has standardized LTE (Long Term Evolution) and LTE-Advanced (hereinafter, abbreviated as “LTE-A”), and is currently carrying out the standardization for further enhancement. 
     LTE and LTE-A adopt OFDMA (Orthogonal Frequency Division Multiple Access) as a downlink communication scheme and adopt SC-FDMA (Single Carrier Frequency Division Multiple Access) as an uplink communication scheme. 
     For frequency scheduling and link adaptation in OFDMA, a base station instructs each terminal to report CSI (Channel State Information) and allocates appropriate resources using CSI. CSI is information including downlink channel quality (SINR or the like) measured using a desired signal component and an interference component. CSI includes CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator) and RI (Rank Indicator) which indicates a spatial multiplexing number. 
     LTE introduces two operations: operation of periodically reporting CSI (hereinafter referred to as “periodic reporting”) and operation of aperiodically reporting CSI (hereinafter referred to as “aperiodic reporting”). In periodic reporting, a terminal reports CSI by arranging the CSI on an uplink control channel which is a defined uplink resource at predetermined intervals. On the other hand, in aperiodic reporting, a terminal reports CSI using a resource on a common data channel at predetermined timing after receiving an instruction (or request) to report CSI from a base station. Aperiodic reporting is instructed to the terminal when an uplink data channel is allocated using downlink control channel PDCCH. 
     The terminal performs one measurement operation indicated in advance from the base station out of a plurality of measurement operations in one of periodic reporting and aperiodic reporting. This measurement operation is indicated from the base station to the terminal using a message for radio resource control (RRC signaling). Note that the base station can indicate different measurement operations for periodic reporting and aperiodic reporting to the terminal. For example, the base station may instruct the terminal to perform measurement operation to report RI, wideband PMI and wideband CQI in periodic reporting, and may instruct the terminal to perform measurement operation to report RI, wideband PMI, narrow band CQI in aperiodic reporting. In this case, periodic reporting may be used for rough link adaptation which is referenced when transmitting data with low urgency and aperiodic reporting may be used for detailed link adaptation which is referenced when transmitting data with high urgency. 
     The terminal measures channel quality of a measurement target indicated in advance from the base station and reports CSI. LTE-A Release10 has added an operation for a terminal to report CSI for two types of measurement targets indicated in advance in periodic reporting. In addition, LTE-A Release10 has added an operation for a terminal to associate two types of measurement targets indicated in advance with timing at which a base station instructs the terminal to report CSI and for the terminal to report CSI for one of the measurement targets in aperiodic reporting. The two types of measurement targets have different situations of interference components. The two types of measurement targets are indicated to the terminal from the base station using RRC with a bitmap corresponding to 40 continuous subframes. 
     LTE-A Release10 also has introduced a concept of CA (Carrier Aggregation) and increased the number of bits of trigger information (CSI request field) indicating aperiodic reporting from 1 bit to 2 bits. As a result, the base station is enabled to instruct the terminal to report CSI and report one of a plurality of CCs (Component Carriers) or a plurality of CSIs as the CSI to be reported by the terminal. For example, the base station indicates CSIs of two CCs as CSI 1  and CSI 2  using bits of trigger information, “00” indicating that “CSI is not reported,” “01” indicating that “only CSI 1  is reported,” “10” indicating that “only CSI 2  is reported” and “11” indicating that “CSI 1  and CSI 2  are reported” in advance through, for example, RRC signaling. The base station then transmits trigger information with one of the above-described combinations of bits to the terminal, and can thereby indicate aperiodic reporting and also indicate CSI to be reported. 
     Thus, LTE-A Release10 provides a mechanism of simultaneously reporting two CSIs with the introduction of CA. To put it more specifically, in aperiodic reporting, the terminal transmits two CSIs using an uplink data signal after a lapse of a predetermined time (4 subframes) after reception of CSI reporting from the base station. 
     [Coordinated Transmission by Plurality of Base Stations (CoMP)] 
     Meanwhile, in Release 11, which is the next version of LTE-A, CoMP (Coordinated Multi-Point) is being studied whereby a plurality of base stations cooperate to transmit signals to a terminal in a heterogeneous cell network (HetNet: Heterogeneous Network) in which there are a plurality of base stations having cover areas of different scales. HetNet is constructed of a macro cell (cell formed of a base station having large transmission power and coverage) and a pico cell (cell formed of a base station having small transmission power and coverage) within the macro cell. CoMP can reduce inter-cell interference and increase system throughput. 
     As CoMP schemes, 3GPP is studying mainly two CoMP schemes: (1) Coordinated beamforming (CB) and (2) Joint Transmission (JT). 
     CB assumes that data transmitted to a predetermined terminal is possessed by only one cell. In the case of CB, a terminal regards as interference, signals transmitted from a base station of a neighboring cell that possesses no data addressed to the terminal. CB adopts a technique of reducing inter-cell interference by controlling transmission parameters. Examples of specific transmission parameters include precoding, transmission power, modulation scheme and coding rate. By appropriately controlling these parameters, it is possible to weaken signals from the interfering cell addressed to the corresponding terminal while strengthening signals from a desired cell. 
     On the other hand, JT assumes that data transmitted to a predetermined terminal is possessed by a plurality of cells. Therefore, according to JT, respective base stations of the plurality of cells can simultaneously transmit signals to the corresponding terminal. Thus, unlike a conventional system, the terminal can handle a signal from a neighboring cell not as interference but as a desired signal, and therefore an SINR measured in the terminal is expected to improve. Especially by devising a method of generating precoding weights in a plurality of cells as operation within a network, it is possible to significantly improve the SINR measured in the terminal. 
     For CoMP control, LTE-A Release 11 provides a technique whereby a terminal measures channel quality of downlink to be controlled between a base station (hereinafter referred to as “coordinating base station”) of each cell and the terminal, and reports CSI to the coordinating base stations in cell units. To put it more specifically, in aperiodic reporting, the terminal transmits the same number of CSIs as the coordinating base stations using uplink data signals after a lapse of a predetermined time after reception of an instruction of CSI reporting from the coordinating base station. 
     [Reference Signal] 
     According to LTE-A Release11, a base station can indicate in advance, to a terminal, a resource to be measured to which a reference signal is mapped. As a reference signal, CSI-RS (Channel State Information-Reference Signal) is used. The base station indicates, to the terminal, information on a CSI-RS including a resource to which the CSI-RS is mapped using a message for radio resource control (RRC signaling) before the terminal performs CSI reporting. 
       FIGS. 1A to 1C  are diagrams illustrating configuration examples of resources to which CSI-RSs are mapped. CSI-RSs are defined in 8-port, 4-port and 2-port configurations respectively according to the number of transmitting antenna ports of the base station.  FIG. 1A  illustrates a configuration example when the number of antenna ports is 8,  FIG. 1B  illustrates a configuration example when the number of antenna ports is 4, and  FIG. 1C  illustrates a configuration example when the number of antenna ports is 2. In  FIGS. 1A to 1C , one subframe is made up of two resource blocks (RBs) each bundling  12  subcarriers. In  FIGS. 1A to 1C , #i ( 0  to  19 ) represents a resource (2 REs (Resource Elements)) of two continuous OFDM symbols in the time domain within each subcarrier. In each resource (2 REs), CSI-RSs corresponding to two ports are code-multiplexed. 
     Each terminal acquires CSI-RS-related information from the base station in advance. Examples of the CSI-RS-related information include the number of antenna ports (Antenna Ports Count), CSI-RS configuration number (Resource Config: number # 0  in  FIG. 1  or the like) that identifies subcarriers within a subframe to which CSI-RS is mapped and OFDM symbol position, transmission subframe (Subframe Config) made up of transmission cycle and offset, and power ratio (p-C) between reference signals and data signals. 
     In  FIGS. 1A to 1C , CSI-RS configuration numbers are assigned in order in the time direction and in order in the frequency direction at the same point in time. As shown in  FIGS. 1A to 1C , the same number is assigned to the start position (start position in numbering order) of a resource of each CSI-RS configuration number among CSI-RS configurations corresponding to the respective numbers of antenna ports. As shown in  FIGS. 1A to 1C , a CSI-RS configuration with a small number of antenna ports forms a subset of a CSI-RS configuration with a large number of antenna ports. The same number is assigned to resources with the same start position. This makes it possible to cover all resources to be identified with minimum necessary numbers for each number of ports while using overlapping numbers. For example, CSI-RS config( 0 ) with 2 ports shown in  FIG. 1C  can be identified as only resources (2 REs) corresponding to two ports from the start position of CSI-RS config( 0 ) (8 REs) with 8 ports shown in  FIG. 1A . Resources indicated in this way are resources used to measure desired signal components (hereinafter referred to as “desired signal component measurement resources”) and called “non zero power CSI-RS resources.” 
     LTE-A Release11 also provides a muting technique that causes a coordinating base station in a connected cell to transmit a no transmission signal (signal with amplitude 0) to measure CSI-RS transmitted from a coordinating base station in a peripheral cell. To put it more specifically, of resources with configuration numbers # 0  to # 9  corresponding to four ports, resources to be designated as no transmission signals (resources to be muted) are indicated using a bitmap. Hereinafter, information indicating resources to be designated as no transmission signals will be referred to as “no transmission CSI-RS configuration number list (zeroTxPowerResourceConfigList).” 
     As an example, when configuration numbers (Resource Config) # 1  and # 2  are assumed to be no transmission signals, a no transmission CSI-RS configuration number list becomes {0, 1, 1, 0, 0, 0, 0, 0, 0, 0}. The base station indicates this no transmission CSI-RS configuration number list together with a transmission subframe (zeroTxPowerSubframeConfig) made up of a transmission cycle and offset to the terminal as in the case of the aforementioned CSI-RS, and the terminal can thereby identify resources which become no transmission signals in the corresponding subframe. The positions of the no transmission signals in the subframe corresponding to this example are # 1  and # 2  of CSI-RS shown in  FIG. 2 . 
     By associating a CSI-RS configuration of a coordinating base station of a peripheral cell with one CSI-RS configuration in the no transmission CSI-RS configuration number list, it is possible to avoid interference of a signal from the coordinating base station of the connected cell when measuring an SINR using the signal from the coordinating base station of the corresponding peripheral cell as a desired signal, and thereby improve accuracy of measuring CSI in the terminal. The resources indicated in this way are resources used to measure an interference component (hereinafter referred to as “interference component measurement resources”) and are called “zero power CSI-RS resources.” 
     Each resource of CSI-RS is used to measure one of a desired signal component and an interference component for one CSI report. The base station may indicate only a non zero power CSI-RS resource, indicate only a zero power CSI-RS resource or indicate a combination of a non zero power CSI-RS resource and a zero power CSI-RS resource. Note that the base station may instruct the terminal to use resources used to measure a desired signal component in one CSI report to also measure an interference component in another CSI report. 
     [Number of CSI Reports] 
     As described above, LTE-A Release10 provides the mechanism for simultaneously reporting two CSIs. On the other hand, a terminal simultaneously reports a plurality of CSIs to realize CoMP in LTE-A Release11 as well. In LTE-A Release11, unlike LTE-A Release10, the number of CSIs simultaneously generated is not limited to 2. For example, a base station of a macro cell, as a base station corresponding to a desired signal component, causes a terminal located in the vicinity of two pico cells within the macro cell area to measure SINRs of signals transmitted from three cells: a macro cell (TP-a), pico cell 1 (TP-b) and pico cell 2 (TP-c) and report the three CSIs. Thus, it is possible to transmit a signal from a base station having the best channel quality among the three cells, and thereby realize data transmission of high quality. 
     However, as the number of simultaneously reported CSIs increases, the amount of processing required to generate CSI for updating the information thereof increases. For example, in the case where the terminal is caused to simultaneously report three CSIs, the amount of processing required to generate CSIs becomes at least 1.5 times compared to a case where two CSIs are simultaneously generated. For this reason, the terminal may not be able to complete processing of CSI reporting within a predetermined time (4 subframes) in aperiodic reporting. Thus, a technique for handling this increase in the amount of processing is necessary. 
     A first conventional technique for handling the increase in the amount of processing may be to limit to a maximum of 2, the number of CSIs to be reported in one reporting unit of aperiodic reporting which is indicated by the base station using RRC signaling. It is thereby possible to make the amount of processing required to generate CSI equivalent to that in the related art. 
     Moreover, as a second conventional technique for handling the increase in the amount of processing may be to lessen the allowable value of the processing time (see NPL 1). To put it more specifically, although CSI is conventionally reported after a lapse of 4 subframes after reception of an instruction of CSI reporting, CSI may be reported after a lapse of 6 subframes. This makes it possible to complete processing of CSI reporting without increasing the amount of processing per unit time. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         NPL 1 
         R1-122350, Renesas Mobile Europe Ltd., “On CSI feedback processing complexity in CoMP” 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, according to the above-described first technique, the reporting operation is limited to a set value by RRC signaling, and so a base station as a reporting target can be switched only about one time every several seconds, which means that CSI is set quasi-statically, which diminishes the effect of CoMP that switching between base stations can be performed flexibly at intervals of several ms. 
     According to the above-described second technique, the time from an instruction of CSI reporting to actual CSI reporting is extended. According to the above-described second technique, timing of CSI reporting is different between a Release10 compliant terminal and a Release11 compliant terminal, and therefore scheduling in the base station becomes complicated. 
     An object of the present invention is to provide a radio communication terminal apparatus, a radio communication base station apparatus and a CSI generating method capable of generating a plurality of CSIs within a period defined in Release10 without deteriorating accuracy of CSI and realizing CoMP control whereby switching between base stations can be performed flexibly. 
     Solution to Problem 
     As described above, a radio communication terminal apparatus according to an aspect of the present invention includes: a generation section that generates CSI (Channel State Information) using a desired signal component and an interference component; and a transmitting section that transmits the CSI, in which when receiving trigger information that requests a CSI report and generating the CSI, the generation section uses an interference component measured before receiving the trigger information. 
     A radio communication base station apparatus according to an aspect of the present invention includes: a transmitting section that transmits resource information indicating a resource to which a reference signal is mapped and trigger information requesting a CSI report; and a receiving section that receives CSI (Channel State Information) generated based on a desired signal component and an interference component measured using the resource for the trigger information, in which the CSI is generated based on an interference component measured before transmitting the trigger information. 
     A CSI generating method according to an aspect of the present invention includes: measuring a desired signal component and an interference component; and generating CSI (Channel State Information) using the desired signal component and the interference component, in which, when trigger information requesting a CSI report is received and the CSI is generated, an interference component measured before receiving the trigger information is used. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to generate a plurality of CSIs within a period defined in Release10 without deteriorating accuracy of CSI and realize CoMP control whereby switching between base stations can be performed flexibly. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A to 1C  illustrate configuration examples of CSI-RS resources; 
         FIG. 2  illustrates a configuration example of CSI-RS resources; 
         FIG. 3  is a block diagram illustrating a main configuration of a base station according to Embodiment 1 of the present invention; 
         FIG. 4  is a block diagram illustrating a main configuration of a terminal according to Embodiment 1 of the present invention; 
         FIG. 5  is a block diagram illustrating a configuration of the base station according to Embodiment 1 of the present invention; 
         FIG. 6  is a block diagram illustrating a configuration of the terminal according to Embodiment 1 of the present invention; 
         FIG. 7  illustrates an example of a communication system according to Embodiment 1 of the present invention; 
         FIG. 8  illustrates a method of generating CSI by the terminal according to Embodiment 1 of the present invention; 
         FIG. 9  illustrates a method of generating CSI by a terminal according to Embodiment 2 of the present invention; and 
         FIG. 10  illustrates a method of generating CSI by a terminal according to Embodiment 3 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Since a desired signal component follows instantaneous variations such that narrow band signals corresponding to subband CQI or the like tend to have lower time correlation or that it is necessary to observe a complex signal component for PMI calculation according to an instantaneous fading value, the desired signal component has a small allowable delay. On the other hand, since an interference component follows shadowing and traffic load such as an average power value of components that can be received as interference, the interference component has a large allowable delay. In this way, allowable control delays vary depending on the nature of channel information. 
     Focusing attention on this aspect, the present invention is based on a concept that regarding an interference component, the accuracy of CSI would not significantly deteriorate even by using values measured in advance for resources transmitted in the past corresponding to one to several transmissions at CSI-RS transmission intervals. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Embodiment 1 
     System Configuration 
     A communication system according to Embodiment 1 of the present invention includes base station  100  (see  FIGS. 3 and 5 ) and terminal  200  (see  FIGS. 4 and 6 ). Base station  100  is an LTE-A base station and terminal  200  is an LTE-A terminal. LTE-A-compliant radio communication is carried out between base station  100  and terminal  200 . 
     [Main Configuration of Base Station] 
       FIG. 3  is a block diagram illustrating a main configuration of a base station according to Embodiment 1 of the present invention. Base station  100  shown in  FIG. 3  is mainly constructed of control section  120 , transmitting section  130  and receiving section  140 . 
     Control section  120  generates information indicating positions or the like of desired signal component measurement resources and interference component measurement resources of CSI-RS (hereinafter referred to as “measurement resource information”). Control section  120  requests that CSI should be reported in aperiodic reporting and also generates trigger information for identifying CSI to be reported by a terminal (hereinafter referred to as “reporting target”). Control section  120  also generates information indicating a reporting target identified by trigger information (hereinafter referred to as “CSI reporting information”). For example, the CSI reporting information is information indicating the association between bits of trigger information and one set of one or a plurality of CSIs as a reporting target. Control section  120  performs scheduling and link adaptation based on CSI or the like. 
     Transmitting section  130  transmits data signals and CSI-RSs to terminal  200  in subframe units. Transmitting section  130  indicates CSI reporting information and measurement resource information to terminal  200  in advance. When requesting aperiodic reporting, transmitting section  130  transmits trigger information to terminal  200 . 
     Receiving section  140  receives data signals from terminal  200  in subframe units. Receiving section  140  receives CSI reported from terminal  200  at predetermined intervals or after a lapse of a certain period (e.g., after 4 subframes) after transmitting trigger information. 
     Here, control section  120  performs scheduling and link adaptation assuming that a measured value of the received interference component of CSI will not be updated for a certain period after transmitting CSI-RS using interference component measurement resources or that the received interference component of CSI is measured for CSI-RS transmitted using interference component measurement resources several transmissions (CSI-RS other than the last transmitted CSI-RS) before. To put it more specifically, control section  120  sets MCS (Modulation and Coding Scheme) by taking into account a possibility that a propagation environment may change for a period after the interference component is measured until CSI is generated. 
     Base station  100  indicates the CSI reporting information and measurement resource information to terminal  200  using, for example, RRC signaling. Base station  100  may also indicate the CSI reporting information and measurement resource information included in a CSI-RS-Config message. Base station  100  may set whether reporting is periodic reporting or aperiodic reporting for terminal  200  which is a CSI reporting target and indicate the set information included in a CQI-ReportConfig message. 
     [Main Configuration of Terminal] 
       FIG. 4  is a block diagram illustrating a main configuration of a terminal according to Embodiment 1 of the present invention. Terminal  200  shown in  FIG. 4  is mainly constructed of receiving section  220 , generation section  230  and transmitting section  240 . 
     Receiving section  220  receives data signals and CSI-RS from base station  100  in subframe units. Before performing CSI reporting, receiving section  220  receives CSI reporting information and measurement resource information in advance from base station  100 . Before performing aperiodic reporting, receiving section  220  receives trigger information from base station  100 . 
     After receiving a predetermined interval or trigger information, generation section  230  measures a desired signal component and interference component using CSI-RS resources indicated in the measurement resource information and generates CSI indicated in the CSI reporting information corresponding to the bits of trigger information using the CSI-RS resources indicated in the measurement resource information. 
     Here, generation section  230  does not measure any interference component for a certain period after receiving trigger information (e.g., for 4 subframes) and measures channel quality using an already measured interference component. For example, generation section  230  measures channel quality using the last measured interference component. 
     Transmitting section  240  transmits data signals to base station  100  in subframe units. Transmitting section  240  transmits the generated CSI to base station  100 . 
     [Configuration of Base Station] 
       FIG. 5  is a block diagram illustrating a configuration of the base station according to the present embodiment. As shown in  FIG. 5 , base station  100  includes setting section  151 , coding and modulation sections  152  and  153 , transmission processing section  154 , radio transmission processing sections  155 - 1  and  155 - 2 , antennas  156 - 1  and  156 - 2 , radio reception processing sections  157 - 1  and  157 - 2 , reception processing section  158 , demodulation and decoding sections  159  and  160  and scheduling section  161 . 
     Note that control section  120  in  FIG. 3  corresponds to setting section  151  and scheduling section  161  in  FIG. 5 . Transmitting section  130  in  FIG. 3  corresponds to coding and modulation sections  152  and  153 , transmission processing section  154  and radio transmission processing sections  155 - 1  and  155 - 2  in  FIG. 5 . Receiving section  140  in  FIG. 3  corresponds to radio reception processing sections  157 - 1  and  157 - 2 , reception processing section  158  and demodulation and decoding sections  159  and  160  in  FIG. 5 . 
     Setting section  151  generates measurement resource information. As described above, each resource of CSI-RS is used to measure one of a desired signal component and an interference component for one CSI report. Information on a non zero power CSI-RS resource in the measurement resource information includes parameters such as the number of antenna ports (Antenna Ports Count), CSI-RS configuration number (Resource Config) that identifies subcarrier and OFDM symbol positions in a subframe to which CSI-RS is mapped, transmission subframe (Subframe Config) made up of a transmission cycle and an offset. Information on the zero power CSI-RS resource includes parameters such as a no transmission CSI-RS configuration number list and a transmission subframe. 
     Setting section  151  generates CSI reporting information. Information for identifying CSI which is a reporting target is set in the CSI reporting information. For example, the CSI reporting information indicates association between the bits of trigger information and one set of one or a plurality of CSIs as a reporting target. Setting section  151  sets CSI reporting information so as to report a plurality of CSIs to each terminal  200  to perform CoMP. 
     The measurement resource information and CSI reporting information are indicated from base station  100  to terminal  200  using, for example, RRC signaling and shared between base station  100  and terminal  200 . 
     When requesting aperiodic reporting, setting section  151  requests a CSI report, also generates trigger information for identifying a reporting target and outputs the trigger information to coding and modulation section  152  and demodulation and decoding section  160 . 
     Setting section  151  generates downlink resource allocation information which is information indicating resource allocation of PDSCH (Physical Downlink Shared Channel) for each terminal stored in PDCCH (Physical Downlink Control Channel) and outputs the downlink resource allocation information to transmission processing section  154 . Setting section  151  also generates uplink resource allocation information which is information indicating PUCCH (Physical Uplink Control Channel) resources and outputs the uplink resource allocation information to coding and modulation section  152  and demodulation and decoding section  160 . 
     Coding and modulation section  152  performs modulation processing on CSI-RS and outputs the modulated CSI-RS to transmission processing section  154 . Coding and modulation section  152  performs coding processing and modulation processing on control information such as uplink resource allocation information, trigger information, generates PDCCH and outputs the generated PDCCH to transmission processing section  154 . Coding and modulation section  153  performs coding processing and modulation processing on transmission data according to the control of scheduling section  161  and outputs the transmission data to transmission processing section  154 . 
     Transmission processing section  154  maps PDSCH based on the downlink resource allocation information. Transmission processing section  154  maps PDCCH. Transmission processing section  154  then forms a transmission signal through the mapping processing. When the transmission signal is an OFDM signal, transmission processing section  154  maps the modulated signal to resources indicated by the downlink resource allocation information, performs inverse fast Fourier transform (IFFT) processing to transform the modulated signal into a frequency-domain signal, adds a CP (Cyclic Prefix) thereto and thereby forms an OFDM signal. 
     Radio transmission processing sections  155 - 1  and  155 - 2  performs radio transmission processing (up-conversion, digital/analog conversion or the like) on the transmission signal and transmits the transmission signal to terminal  200  via antennas  156 - 1  and  156 - 2 . 
     Radio reception processing sections  157 - 1  and  157 - 2  perform radio reception processing (down-conversion, analog/digital conversion or the like) on radio signals received via antennas  156 - 1  and  156 - 2 , and outputs the received signals obtained to reception processing section  158 . 
     Reception processing section  158  extracts PUSCH (Physical Uplink Shared Channel), PUCCH, SRS (Sounding Reference Signal) or the like mapped to resources of the received signals based on the uplink resource allocation information. Reception processing section  158  outputs PUSCH to demodulation and decoding section  159 , outputs PUCCH to demodulation and decoding section  160 , and outputs SRS to scheduling section  161 . 
     When the received signal is a spatially multiplexed signal, that is, a signal transmitted with a plurality of codewords (CWs), reception processing section  158  demultiplexer the received signal into CWs. On the other hand, when the received signal is an OFDM signal, reception processing section  158  deletes a CP from the received signal, performs fast Fourier transform (FFT) processing on the received signal to transform the signal into a time-domain signal. 
     Demodulation and decoding section  159  performs demodulation processing and decoding processing on PUSCH and obtains received data and CSI corresponding to aperiodic reporting. Demodulation and decoding section  159  extracts CSI corresponding to aperiodic reporting in a subframe 4 subframes after the subframe in which trigger information is transmitted. 
     Demodulation and decoding section  160  performs demodulation processing and decoding processing on PDCCH and obtains control information including CSI corresponding to periodic reporting and ACK/NACK. Demodulation and decoding section  160  extracts CSI corresponding to periodic reporting in a defined subframe. 
     Scheduling section  161  measures receiving quality of the uplink based on SRS, performs scheduling and link adaptation on the uplink and downlink respectively based on the measurement result, CSI and ACK/NACK, and controls coding and modulation section  153 . 
     Here, scheduling section  161  performs scheduling and link adaptation assuming that the measured value of an interference component of the received CSI is not updated for a certain period after transmitting CSI-RS using an interference component measurement resource or that an interference component of the received CSI has been measured with respect to CSI-RS transmitted using an interference component measurement resource several transmissions before (CSI-RS other than the last transmitted CSI-RS). To put it more specifically, scheduling section  161  sets MCS (Modulation and Coding Scheme) by taking into account a possibility that a propagation environment may change for a period after an interference component is measured until CSI is generated. 
     Note that the present embodiment has adopted the configuration in which a macro cell and a pico cell are formed by a single base station, but a macro cell and a pico cell may be formed of a plurality of base stations and both cells may be made to operate in coordination by sharing appropriate signals. 
     In the present embodiment, of the plurality of radio transmission processing sections  155 - 1  and  155 - 2 , antennas  156 - 1  and  156 - 2  and radio reception processing sections  157 - 1  and  157 - 2 , it is possible to use, for example, radio transmission processing section  155 - 1 , radio reception processing section  157 - 1  and antenna  156 - 1  to form a macro cell and use radio transmission processing section  155 - 2 , radio reception processing section  157 - 2  and antenna  156 - 2  to form a pico cell. 
     [Configuration of Terminal] 
       FIG. 6  is a block diagram illustrating a configuration of the terminal according to the present embodiment. As shown in  FIG. 6 , terminal  200  includes antenna  251 , radio reception processing section  252 , reception processing section  253 , demodulation and decoding sections  254  and  255 , CSI generating section  256 , transmission control section  257 , coding and modulation sections  258  and  259 , transmission processing section  260  and radio transmission processing section  261 . 
     Note that receiving section  220  in  FIG. 4  corresponds to radio reception processing section  252 , reception processing section  253  and demodulation and decoding sections  254  and  255  in  FIG. 6 . Generation section  230  in  FIG. 4  corresponds to CSI generating section  256  and transmission control section  257  in  FIG. 6 . Transmitting section  240  in  FIG. 4  corresponds to coding and modulation sections  258  and  259 , transmission processing section  260  and radio transmission processing section  261  in  FIG. 6 . 
     Radio reception processing section  252  performs radio reception processing (down-conversion, analog/digital conversion or the like) on a radio signal received via antenna  251  and outputs the received signal obtained to reception processing section  253 . 
     Reception processing section  253  extracts PDCCH mapped to resources of the received signal. Note that when the received signal is an OFDM signal, reception processing section  253  also performs CP removing processing and FFT processing. Reception processing section  253  extracts PDSCH mapped to resources of the received signal based on the downlink resource allocation information. Reception processing section  253  outputs PDSCH to demodulation and decoding section  254  and outputs PDCCH to demodulation and decoding section  255  and CSI generating section  256 . 
     Demodulation and decoding section  254  performs demodulation processing and decoding processing on PDSCH and obtains received data. Demodulation and decoding section  254  performs error detection processing on the received data and outputs ACK/NACK corresponding to the error detection result to coding and modulation section  258 . 
     Demodulation and decoding section  255  performs demodulation processing and decoding processing on PDCCH and obtains control information such as uplink resources allocation control information and trigger information. Demodulation and decoding section  255  outputs the trigger information to CSI generating section  256  and outputs the uplink resources allocation control information to transmission control section  257 . 
     After a predetermined interval or reception of trigger information, CSI generating section  256  measures a desired signal component of a non zero power CSI-RS resource and an interference component of a zero power CSI-RS resource indicated in measurement resource information and measures channel quality (e.g., SINR) based on the desired signal component and the interference component. Upon receiving trigger information, in order to generate CSI indicated in CSI reporting information corresponding to the trigger information bit, CSI generating section  256  measures a desired signal component of a non zero power CSI-RS resource indicated in the measurement resource information and an interference component of the zero power CSI-RS resource, and measures channel quality (e.g., SINR) based on the desired signal component and the interference component. CSI generating section  256  generates CSI based on the measurement result, outputs CSI corresponding to periodic reporting to coding and modulation section  258  and outputs CSI corresponding to aperiodic reporting to coding and modulation section  259 . 
     Here, CSI generating section  256  does not measure any interference component for a certain period (e.g., for 4 subframes) after receiving the trigger information and measures channel quality from the measured interference component using an already measured interference component, for example, resources transmitted in the past corresponding to one transmission at a CSI-RS transmission interval. 
     Transmission control section  257  identifies a resource to which the transmission signal is mapped based on the uplink resources allocation control information and outputs mapping resource information indicating this resource to transmission processing section  260 . Transmission control section  257  also outputs MCS information included in the uplink resources allocation control information to coding and modulation section  259 . 
     Coding and modulation section  258  performs coding processing and modulation processing on ACK/NACK and CSI corresponding to periodic reporting and outputs PUCCH to transmission processing section  260 . Coding and modulation section  259  performs coding processing and modulation processing on the transmission data and CSI corresponding to aperiodic reporting based on the MCS information and outputs PUSCH to transmission processing section  260 . 
     Transmission processing section  260  maps PUSCH, PUCCH and SRS based on the mapping resource information and forms a transmission signal. Here, when the transmission signal is an OFDM signal, the transmission processing section maps the modulated signal to a resource indicated in the downlink resource allocation information, performs IFFT processing to transform the signal into a frequency-domain signal, and adds a CP to thereby form an OFDM signal. In the case of non-MIMO transmission, the transmission processing section generates a transmission signal using one codeword (CW) and in the case of MIMO transmission, the transmission processing section generates a transmission signal using two codewords. 
     Radio transmission processing section  261  performs radio transmission processing (up-conversion, digital/analog conversion or the like) on the transmission signal and transmits a radio signal to base station  100  via antenna  251 . 
     [Specific Example of CSI Generating Method] 
     Next, a specific example of the method for generating CSI by terminal  200  according to the present embodiment will be described with reference to  FIG. 7  and  FIG. 8 . An example in  FIG. 7  illustrates a case where a terminal (UE) is communicating with three base stations (TP-b, TP-c and TP-d) according to CoMP. In  FIG. 7 , a desired signal component measurement resource of base station TP-b is represented by NZP-b, a desired signal component measurement resource of base station TP-c is represented by NZP-c, and a desired signal component measurement resource of base station TP-d is represented by NZP-d. In  FIG. 7 , an interference component measurement resource of a base station not included in CoMP is represented by ZP-a. 
       FIG. 8  illustrates subframes (eNB tx) transmitted by coordinating base stations (TP-b, TP-c and TP-d), a CQI generation process (UE processing) performed by a terminal (UE) and subframes (UE tx) transmitted by the terminal (UE). 
     In the case of  FIG. 8 , subframe  301  includes at least ZP-a and subframe  303  includes NZP-b, NZP-c, NZP-d and ZP-a. ZP-a is not included in subframes  302  and  304 . The coordinating base stations (TP-b, TP-c and TP-d) transmit trigger information for instructing the terminal (UE) to report all CSIs (CSI 1 , CSI 2  and CSI 3 ) in subframe  303 . Note that CSI 1  is CSI corresponding to base station TP-b, CSI 2  is CSI corresponding to base station TP-c, and CSI and CSI 3  are CSIs corresponding to base station TP-d. 
     In this case, in a stage in which the terminal (UE) receives subframe  301 , the terminal (UE) measures an interference component using ZP-a in advance. Furthermore, in subframe  303 , the terminal (UE) does not measure any interference component for a certain period (4 subframes up to subframe  311  in  FIG. 8 ) after receiving trigger information. 
     Upon receiving the trigger information, the terminal (UE) measures a desired signal component using NZP-b, NZP-c and NZP-d, measures channel quality using these resources and the interference component measured in advance, generates CSIs (CSI 1 , CSI 2  and CSI 3 ) indicating the measurement result and reports the CSIs in subframe  311 . After that, the terminal (UE) measures the interference component using ZP-a included in subframe  303 . 
     As a result, the present embodiment can reduce the amount of processing required to generate one CSI compared to Release10 and reduce the time to generate each CSI. The present embodiment can also advance the timing of starting pipeline processing to generate CSI, and can thereby advance the completion of the processing all the more for CSIs generated in later stages of the pipeline. In  FIG. 8 , the amount of processing (time) to generate CSI in CoMP is shown by a solid line arrow and the amount of processing (time) to generate CSI in Release10 is shown by a dotted line arrow. 
     By this means, the present embodiment can process three or more CSIs for a period (4-subframe period) defined in Release10. 
     [Effects] 
     As described above, according to the present embodiment, it is possible to generate a plurality of (3 or more in the present embodiment) CSIs within a period predefined in Release10 by using an interference component measured in advance and thereby realize CoMP control that flexibly switches between base stations. Since the interference component has a large allowable delay, using an interference component measured in advance will not cause the accuracy of CSI to significantly deteriorate. 
     According to the present embodiment, since the base station knows that the terminal generates CSI using an interference component measured in advance, it is possible to set MCS by taking into account the possibility that the propagation environment may change for a period after an interference component is measured until CSI is generated. 
     Embodiment 2 
     Overview 
     Embodiment 2 will describe a method of generating CSI when there is a constraint that only up to two non zero power CSI-RS resources can be arranged in one subframe with reference to  FIG. 7  and  FIG. 9 . The configurations of a base station and a terminal in the present embodiment are the same as those shown in  FIG. 3  to  FIG. 6 . 
     As in the case of  FIG. 8 ,  FIG. 9  illustrates subframes (eNB tx) transmitted by coordinating base stations (TP-b, TP-c, TP-d), a CQI generation process (UE processing) executed by a terminal (UE) and subframes (UE tx) transmitted by the terminal (UE). 
     In the case of  FIG. 9 , subframes  301  and  303  include NZP-b, NZP-f and ZP-a and subframes  302  and  304  include NZP-c, NZP-d and ZP-e. In subframe  303 , coordinating base stations (TP-b, TP-c and TP-d) transmit trigger information for instructing the terminal (UE) to report all CSIs (CSI 1 , CSI 2  and CSI 3 ). ZP-e and NZP-f are resources used in other terminals. The terminal (UE) need not measure any desired signal component or interference component using ZP-e and NZP-f. 
     In this case, in the stage of receiving subframe  301 , the terminal (UE) measures an interference component in advance using ZP-a. In subframe  303 , the terminal (UE) does not measure any interference component for a certain period (4 subframes up to subframe  311  in  FIG. 8 ) after receiving trigger information. 
     In the stage of receiving subframes  301  and  303 , the terminal (UE) measures a desired signal component using NZP-b and then measures an interference component using ZP-a. Upon receiving trigger information, the terminal (UE) measures channel quality using a desired signal component newly measure using NZP-b at the timing and an interference component measured in advance and generates CSI 1 . 
     In the stage of receiving subframes  302  and  304 , the terminal (UE) measures a desired signal component using NZP-c and NZP-d, measures channel quality using this desired signal component and an interference component measured in advance and generates CSI 2  and CSI 3 . Upon receiving trigger information, the terminal (UE) uses CSI 2  and CSI 3  generated in the stage of receiving subframe  302  and reports CSI 1 , CSI 2  and CSI 3  in subframe  311 . 
     Thus, in the present embodiment, even when there is a constraint that only up to two non zero power CSI-RS resources can be arranged in one subframe, three or more CSIs can be simultaneously processed within a period (4-subframe period) defined in Release10. 
     [Effects] 
     As described above, according to the present embodiment, even when there is a constraint on non zero power CSI-RS resources (up to two resources in the present embodiment) that can be arranged in one subframe, a plurality of (three or more in the present embodiment) CSIs can be generated within a period defined in Release10, and it is thereby possible to realize CoMP control that flexibly switches between base stations. When reporting CSI, the present embodiment can substitute some of CSIs with those generated in advance, and can thereby reduce the amount of calculation compared to Embodiment 1. Note that the desired signal component used to generate CSIs as substitutes is measured within a range of allowable delays. For this reason, even when a desired signal component is measured in advance, this will not cause the accuracy of CSI to deteriorate significantly. 
     Embodiment 3 
     Specific Example of CSI Generating Method 
     Depending on a propagation environment or traffic situation, occupying resources possessed by all coordinating base stations by one terminal may not always be the best. Transmitting a signal from some of the coordinating base stations to another terminal may result in an improved throughput of the entire cell or satisfy the allowable delay in the base stations. 
     In view of this aspect, Embodiment 3 will describe a method of generating CSI when a base station instructs a terminal to use resources used to measure a desired signal component in reporting of one CSI to also measure an interference component in reporting of other CSIs with reference to  FIG. 7  and  FIG. 10 . That is, in the present embodiment, resources used to measure a desired signal component of CSI and resources used to measure an interference component of another CSI are the same. The configurations of a base station and a terminal in the present embodiment are the same as those shown in  FIG. 3  to  FIG. 6 . In the present embodiment, as in the case of Embodiment 2, there is a constraint that only up to two non zero power CSI-RS resources can be arranged in one subframe. 
     As in the case of  FIG. 8  and  FIG. 9 ,  FIG. 10  shows subframes (eNB tx) transmitted by coordinating base stations (TP-b, TP-c and TP-d), CQI generation process (UE processing) executed by a terminal (UE) and subframes (UE tx) transmitted by the terminal (UE). 
     In the case of  FIG. 10  as in the case of  FIG. 9 , subframes  301  and  303  include NZP-b, NZP-f and ZP-a and subframes  302  and  304  include NZP-c, NZP-d and ZP-e. The coordinating base stations (TP-b, TP-c and TP-d) transmit trigger information for instructing the terminal (UE) to report all CSIs (CSI 1 , CSI 2  and CSI 3 ) in subframe  303 . 
     In  FIG. 10 , the coordinating base stations (TP-b, TP-c and TP-d) instruct the terminal (UE) to use NZP-b to measure a desired signal component in CSI 1  and to measure an interference component in CSI 3 . 
     In this case, upon reception of subframe  301 , the terminal (UE) measures an interference component using ZP-a and NZP-b in advance. The terminal (UE) does not measure any interference component for a certain period (4 subframes up to subframe  311  in  FIG. 8 ) after receiving trigger information in subframe  303 . 
     In the stage of receiving subframes  301  and  303 , the terminal (UE) measures a desired signal component using NZP-b and then measures an interference component. Upon receiving trigger information, the terminal (UE) measures channel quality using a desired signal component newly measured using NZP-b at the timing and the interference component measured using ZP-a in advance, and generates CSI 1 . 
     In the stage of receiving subframes  302  and  304 , the terminal (UE) measures a desired signal component using NZP-c and measures channel quality using the interference component measured using ZP-a in advance, and generates CSI 2 . In the stage of receiving subframes  302  and  304 , the terminal (UE) measures a desired signal component using NZP-d and measures channel quality using this desired signal component and the interference component measured using ZP-a and NZP-b in advance, and generates CSI 3 . Upon receiving trigger information, the terminal (UE) reports CSI 1 , CSI 2  and CSI 3  in subframe  311  using CSI 2  and CSI 3  measured in the stage of receiving subframe  302 . 
     Thus, in the present embodiment, even in a case where the terminal is instructed to use resources used to measure a desired signal component in reporting of one CSI to also measure an interference component in reporting of another CSI, it is possible to simultaneously process three or more CSIs within a period (4-subframe period) defined in Release10. 
     [Effects] 
     As described above, according to the present embodiment, even in a case where the terminal is instructed to use resources used to measure a desired signal component in reporting of one CSI to also measure an interference component in reporting of another CSI, it is possible to simultaneously process a plurality of (three or more in the present embodiment) CSIs within a period defined in Release10 and realize CoMP control that flexibly switches between base stations as in Embodiments 1 and 2. According to the present embodiment, when generating CSI, it is possible to substitute some of desired signal components with those measured in advance, and thereby reduce the amount of calculation compared to Embodiment 1. Note that since the desired signal component measured in advance is measured when receiving the last CSI-RS, channel quality is measured within a range of allowable delays of the desired signal component. For this reason, even when the desired signal component is measured in advance, this will not cause the accuracy of CSI to deteriorate significantly. 
     Each embodiment of the present invention has been described thus far. 
     In the foregoing embodiments, the present invention is configured with hardware by way of example, but the invention may also be provided by software in cooperation with hardware. 
     In addition, the functional blocks used in the descriptions of the embodiments are typically implemented as LSI devices, which are integrated circuits. The functional blocks may be formed as individual chips, or a part or all of the functional blocks may be integrated into a single chip. The term “LSI” is used herein, but the terms “IC,” “system LSI,” “super LSI” or “ultra LSI” may be used as well depending on the level of integration. 
     In addition, the circuit integration is not limited to LSI and may be achieved by dedicated circuitry or a general-purpose processor other than an LSI. After fabrication of LSI, a field programmable gate array (FPGA), which is programmable, or a reconfigurable processor which allows reconfiguration of connections and settings of circuit cells in LSI may be used. 
     Should a circuit integration technology replacing LSI appear as a result of advancements in semiconductor technology or other technologies derived from the technology, the functional blocks could be integrated using such a technology. Another possibility is the application of biotechnology and/or the like. 
     As described above, a radio communication terminal apparatus according to the embodiments includes: a generation section that generates CSI (Channel State Information) using a desired signal component and an interference component; and a transmitting section that transmits the CSI, in which when receiving trigger information that requests a CSI report and generating the CSI, the generation section uses an interference component measured before receiving the trigger information. 
     In the radio communication terminal apparatus according to the embodiments, when receiving the trigger information and generating the CSI, the generation section uses a desired signal component measured after receiving the trigger information. 
     In the radio communication terminal apparatus according to the embodiments, the generation section measures a desired signal component and an interference component using a resource indicated by resource information, in which the resource information indicates a resource to which a reference signal is mapped. 
     In the radio communication terminal apparatus according to the embodiments, when no resource exists for measuring a desired signal component of CSI to be reported in a subframe received at timing at which the trigger information is received, the generation section uses a desired signal component of CSI to be reported that is measured before receiving the trigger information. 
     In the radio communication terminal apparatus the embodiments, when a resource used to measure a desired signal component of CSI and a resource used to measure an interference component of another CSI are the same, the generation section measures a desired signal component using the resource after receiving the trigger information and measures an interference component using the interference component measured using the resource before receiving the trigger information. 
     A radio communication base station apparatus according to the embodiments includes: a transmitting section that transmits resource information indicating a resource to which a reference signal is mapped and trigger information requesting a CSI report; and a receiving section that receives CSI (Channel State Information) generated based on a desired signal component and an interference component measured using the resource for the trigger information, in which the CSI is generated based on an interference component measured before transmitting the trigger information. 
     In the radio communication base station apparatus according to the embodiments, the CSI is generated based on a desired signal component measured after transmitting the trigger information. 
     A CSI generating method according to the embodiments includes: measuring a desired signal component and an interference component; and generating CSI (Channel State Information) using the desired signal component and the interference component, in which, when trigger information requesting a CSI report is received and the CSI is generated, an interference component measured before receiving the trigger information is used. 
     The disclosure of the specification, drawings and abstract in Japanese Patent Application No. 2012-173036 filed on Aug. 3, 2012 is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a mobile communication system which performs CoMP and in which a radio communication terminal apparatus reports CSI to a radio communication base station apparatus. 
     REFERENCE SIGNS LIST 
     
         
           100  Base station 
           120  Control section 
           130  Transmitting section 
           140  Receiving section 
           151  Setting section 
           152 ,  153  Coding and modulation section 
           154  Transmission processing section 
           155 - 1 ,  155 - 2  Radio transmission processing section 
           156 - 1 ,  156 - 2  Antenna 
           157 - 1 ,  157 - 2  Radio reception processing section 
           158  Reception processing section 
           159 ,  160  Demodulation and decoding section 
           161  Scheduling section 
           200  Terminal 
           220  Receiving section 
           230  Generation section 
           240  Transmitting section 
           251  Antenna 
           252  Radio reception processing section 
           253  Reception processing section 
           254 ,  255  Demodulation and decoding section 
           256  CSI Generating section 
           257  Transmission control section 
           258 ,  259  Coding and modulation section 
           260  Transmission processing section 
           261  Radio transmission processing section