Abstract:
A system can suppress the degradation of the system&#39;s own throughput, while suppressing the interference with a different communication system sharing a frequency band with the system. In ST 302,  a base station selects a terminal (B) as a relay station. In ST 305,  the base station performs a separation between the subcarrier signals outside an FSS-used band and the subcarrier signals within the FSS-used band, and remaps the separated subcarrier signals within the FSS-used band to the subcarriers outside the FSS-used band. In ST 306,  the separated subcarrier signals outside the FSS-used band and the remapped subcarrier signals outside the FSS-used band are differentially transmitted at the same time. In ST 308,  the terminal (B) remaps signals received from the base station to the subcarriers within the FSS-used band and, in ST 309,  transfers those signals as remapped to a terminal (A). In ST 310 , the terminal (A) combines the signals transferred by the terminal (B) with signals received from the base station for decoding.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a radio communication base station apparatus, a small-scale radio communication base station apparatus, a radio communication terminal apparatus, a radio transmission method, a radio relay method, and a radio reception method capable of reducing interference to a, different radio communication system sharing a frequency band. 
       BACKGROUND ART 
       [0002]    In the World Radio-communication Conference (WRC-07) held in the end of 2007, a new frequency band was allocated for an IMT-Advanced mobile communication service. In the conference, 100 or more countries in the world stated using a frequency band of 3.4 to 3.6 GHz for the IMT-Advanced service. In effect, this frequency band becomes the international mobile communication frequency. 
         [0003]    This frequency band, which is called a C-band, is still utilized for a fixed satellite service (FSS). This frequency band is mainly used as a frequency band for television broadcasting or an emergency frequency band for disasters in the equatorial countries where rain attenuation is severe or the countries with wide territory. In these countries, the FSS is an important communication service. Accordingly, with the IMT-Advanced mobile communication, it is necessary to prevent interference from affecting the FSS when the same frequency as that of the FSS is shared. 
         [0004]    To receive signals from FSS satellite stations, an FSS earth station is configured such that directivity faces the upside. The interference to the FSS is smaller in an uplink (UL) through which radio waves are transmitted from an IMT-Advanced mobile station to an IMT-Advanced base station than in a downlink (DL). The smaller an output transmitted by an IMT-Advanced system is, the smaller the interference to the FSS is. 
         [0005]    For example, Patent Literature 1 discloses a technique for reducing the interference to a different radio communication system when a radio communication system shares a frequency band with the different radio communication system. Patent Literature 1 discloses a method of preventing the interference from affecting a different system by not mapping data to a subcarrier corresponding to a frequency component being used by the different system when the different system has already used a part of a frequency band which is to be used for communication, as shown in  FIG. 1 . 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1 
       Japanese Patent No. 2920131 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    However, when the interference is prevented from affecting the FSS according to the technique disclosed in Patent Literature 1, IMT-Advanced data may not be mapped to the subcarrier corresponding to the frequency component being used for the FSS, thereby deteriorating an IMT-Advanced throughput. 
         [0008]    An object of the present invention is to provide a radio communication base station apparatus, a small-scale radio communication base station apparatus, a radio communication terminal apparatus a radio transmission method, a radio relay method, and radio reception method capable of suppressing deterioration in the throughput of the own communication system while preventing the interference from affecting a different communication system sharing a frequency band. 
       Solution to Problem 
       [0009]    A radio communication base station apparatus according to the present invention includes: a first mapping section that maps transmission data to a predetermined first frequency band; a separation section that separates the mapped transmission data into first transmission data mapped to a second frequency band used by a different radio communication system and second transmission data mapped to a frequency band other than the second frequency band; a second mapping section that remaps the separated first transmission data to the frequency band other than the second frequency band; and a transmission section that distinguishes the remapped first transmission data from the separated second transmission data and simultaneously transmits the remapped first transmission data and the separated second transmission data. 
         [0010]    A radio communication terminal apparatus according to the present invention includes: a transmission control section that receives control information transmitted from a radio communication base station apparatus and switches whether or not the radio communication terminal apparatus operates as a relay station based on the received control information; a mapping section that maps first transmission data, which is transmitted from the radio communication base station apparatus and is used by a different radio communication system and which has been mapped to a frequency band other than a second frequency band, to the second frequency band, when the radio communication terminal apparatus operates as the relay station; a transmission section that transmits the mapped first transmission data; a synthesis section that combines second transmission data transmitted from the radio communication base station apparatus and mapped to a frequency band other than the second frequency band and the first transmission data transmitted by the relay station and mapped to the second frequency band, when the radio communication terminal apparatus does not operate as the relay station; and a decoding section that decodes the combined first and second transmission data. 
       Advantageous Effects of Invention 
       [0011]    According to the present invention, it is possible to suppress the deterioration in the throughput of a communication system while preventing interference from affecting a different communication system sharing a frequency band. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a diagram illustrating a data mapping method disclosed in Patent Literature 1; 
           [0013]      FIG. 2  is a block diagram illustrating the configuration of a transmission section of an IMT-Advanced base station according to Embodiment 1 of the present invention; 
           [0014]      FIG. 3  is a block diagram illustrating the configuration of an IMT-Advanced terminal according to Embodiment 1 of the present invention; 
           [0015]      FIG. 4  is a diagram illustrating a communication processing sequence between the base station shown in  FIG. 2  and the terminal shown in  FIG. 3 ; 
           [0016]      FIG. 5  is a diagram illustrating a subcarrier mapping method; 
           [0017]      FIG. 6  is a block diagram illustrating another configuration of the transmission section of an IMT-Advanced base station according to Embodiment 1 of the present invention; 
           [0018]      FIG. 7  is a block diagram illustrating another configuration of the IMT-Advanced terminal according to Embodiment 1 of the present invention; 
           [0019]      FIG. 8  is a diagram illustrating still another configuration of the IMT-Advanced terminal according to Embodiment 1 of the present invention; 
           [0020]      FIG. 9  is a schematic diagram illustrating a small-scale base station and a service domain of the small-scale base station; 
           [0021]      FIG. 10  is a block diagram illustrating the configuration of a transmission section of an IMT-Advanced base station according to Embodiment 2 of the present invention; and 
           [0022]      FIG. 11  is a block diagram illustrating the configuration of a transmission section of a small-scale base station according to Embodiment 2 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0023]    Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Throughout the embodiments, the same reference numerals are given to the constituent elements having the same function and the description thereof will not be repeated. 
       Embodiment 1 
       [0024]      FIG. 2  is a block diagram illustrating the configuration of a transmission section of an IMT-Advanced base station (hereinafter, simply referred to as a “base station”) according to Embodiment 1 of the present invention. In the drawing, transmission data generation section  101  generates transmission data and outputs the generated transmission data to error correction coding section  102 . 
         [0025]    Error correction coding section  102  executes error correction coding on the transmission data output from transmission data generation section  101  and outputs the coded data to data modulation section  103 . 
         [0026]    Data modulation section  103  executes primary modulation on the coded data output from error correction coding section  102  and outputs the modulated data to subcarrier mapping section  104 . 
         [0027]    Subcarrier mapping section  104  maps the modulated data output from data modulation section  103  to a predetermined subcarrier (first frequency band) and outputs the mapped data as an OFDM signal to separation section  105 . 
         [0028]    Separation section  105  separates the OFDM signal output from subcarrier mapping section  104  into a subcarrier signal outside an FSS use band and a subcarrier signal inside the FSS use band. The subcarrier signal outside an FSS use band is output to weight multiplication section  107  and the subcarrier signal inside the FSS use band is output to subcarrier remapping section  106 . 
         [0029]    Subcarrier remapping section  106  remaps the subcarrier signal inside the FSS use band output from separation section  105  to the subcarrier outside the FSS use band and outputs the remapped subcarrier signal to weight multiplication section  107 . Here, the remapped subcarrier may overlap the subcarrier signal outside the FSS use band output from separation section  105 . 
         [0030]    Weight multiplication section  107  multiplies each input signal by a weight for which only the subcarrier signal outside the FSS use band output from separation section  105  is received by a communication partner terminal described below and only a signal output from subcarrier remapping section  106  is received by a terminal serving as a relay station. To calculate the weight, it is necessary to acquire the propagation characteristics from a base station to a communication partner terminal and the propagation characteristics from the base station to a relay station or information regarding the direction of each terminal or the like. Here, it is assumed that the propagation characteristics or the information is already acquired. 
         [0031]    Weight multiplication section  107  multiplies two input signals by weights corresponding to respective transmitting antennas and combines the multiplied signals to be transmitted by the respective transmitting antennas. Thereafter, the signal to be transmitted from antenna  111 - 1  is output to IFFT section  108 - 1  and the signal to be transmitted from antenna  111 - 2  is output to IFFT section  108 - 2 . 
         [0032]    IFFT sections  108 - 1  and  108 - 2  execute reverse Fourier transform on the signals output from weight multiplication section  107 , respectively, and outputs the signals to guard interval (GI) insertion sections  109 - 1  and  109 - 2 , respectively. 
         [0033]    GI insertion sections  109 - 1  and  109 - 2  insert a GI to the transmission data output from IFFT sections  108 - 1  and  108 - 2 , respectively, and output the transmission data to RF transmission sections  110 - 1  and  110 - 2 , respectively. 
         [0034]    RF transmission sections  110 - 1  and  110 - 2  execute predetermined radio transmitting processes, such as a digital-to-analog converting process and an up-converting process to a radio frequency band, on the signals output from GI insertion sections  109 - 1  and  109 - 2  and execute radio transmission from antennas  111 - 1  and  111 - 2 . 
         [0035]    When relay station selection section  112  receives a communication starting request from a terminal or attempts to start communication with a terminal, relay station selection section  112  selects a terminal which serves as a relay station. Specifically, for example, relay station selection section  112  selects a terminal which is present inside the same sector as that of a communication partner terminal and is not executing communication. Alternatively, a base station collects information regarding the position of a terminal using a position information acquiring function (positioning function such as a GPS function) and selects a terminal which is the closest to the communication partner terminal and is not executing communication. Information indicating the selected terminal is output to control information generation section  113 . 
         [0036]    Control information generation section  113  generates control information including information regarding the selection of the relay station communicating with the communication partner terminal and information (information indicating that the signal is mapped from which subcarrier to which subcarrier or resource information such as a radio frequency or a time used for transmission) necessary for the relay, based on the information output from relay station selection section  112 , to transmit the control information to the terminal selected as the relay station. Further, control information generation section  113  generates control information including information regarding start of the communication via the terminal selected as the relay station and information regarding delay occurring in the relay to transmit the control information to the communication partner terminal. Each of the generated control information is output to transmission processing section  114 . 
         [0037]    Transmission processing section  114  executes transmission processes, such as error correction coding, primary modulation on data, and subcarrier mapping, on the signal output from control information generation section  113 . Then, transmission processing section  114  transmits the signal subjected to the transmission process to each terminal via weight multiplication section  107 . Here, when the control information is transmitted, it is assumed that the subcarrier outside an FSS use band is used. When the control information to be transmitted to each terminal may arrive to both terminals (for example, common control information to the terminals), the control information may be input directly to IFFT section  108 - 1  without transmission to weight multiplication section  107  and may be transmitted via single antenna  111 - 1 . 
         [0038]      FIG. 3  is a block diagram illustrating the configuration of an IMT-Advanced terminal (hereinafter, simply referred to as a “terminal”) according to Embodiment 1 of the present invention. In the drawing, transmission data generation section  201  generates transmission data and outputs the transmission data to error correction coding section  202 . 
         [0039]    Error correction coding section  202  executes error correction coding on the transmission data output from transmission data generation section  201  and outputs the coded data to data modulation section  203 . 
         [0040]    Data modulation section  203  executes primary modulation on the coded data output from error correction coding section  202  and outputs the modulated data to first switch section  204 . 
         [0041]    Under the control of transmission control section  215  described below, first switch section  204  connects data modulation section  203  to subcarrier mapping section  205  or connects FFT section  214  to subcarrier mapping section  205  via second switch section  216 . 
         [0042]    Under the control of transmission control section  215  described below, subcarrier mapping section  205  maps the signal output from first switch section  204  to a subcarrier and outputs the signal to IFFT section  206 . 
         [0043]    IFFT section  206  executes reverse Fourier transform on the signal output from subcarrier mapping section  205  and outputs the signal to GI insertion section  207 . 
         [0044]    GI insertion section  207  inserts a GI to the transmission data output from IFFT section  206  and outputs the transmission data to RF transmission section  208 . 
         [0045]    RF transmission section  208  executes predetermined radio transmitting processes, such as a digital-to-analog converting process and an up-converting process to a radio frequency band, on the signals and executes radio transmission from antenna  209 . 
         [0046]    RF reception section  211  receives the signal transmitted from the base station via antenna  210 , executes predetermined radio receiving processes, such as an analog-to-digital converting process and a down-converting process to a baseband, on the signal, and outputs the processed signal to synchronization section  212 . 
         [0047]    Synchronization section  212  synchronizes timing for executing an FFT process on the received signal output from RF reception section  211  and outputs the received signal synchronized in the timing to GI removal section  213 . 
         [0048]    GI removal section  213  removes the GI at the synchronization timing from the received signal output from synchronization section  212  and outputs the data, from which the GI is removed, to FFT section  214 . 
         [0049]    FFT section  214  executes Fourier transform on the data output from GI removal section  213  and outputs the processed data to second switch section  216 . 
         [0050]    When the terminal operates as a relay station, transmission control section  215  controls first switch section  204  and second switch section  216  such that second switch section  216  connects FFT section  214  to subcarrier mapping section  205  and controls subcarrier mapping section  205  such that subcarrier mapping section  205  remaps the data from FFT section  214  to the subcarrier inside the FFS use band based on the control information transmitted from the base station. On the contrary, when the terminal does not operate as the relay station, transmission control section  215  controls first switch section  204  such that first switch section  204  connects data modulation section  203  to subcarrier mapping section  205  and controls second switch section  216  such that second switch section  216  connects FFT section  214  to subcarrier demapping section  217  based on the control information transmitted from the base station. 
         [0051]    Under the control of transmission control section  215 , second switch section  216  connects FFT section  214  to subcarrier demapping section  217  or connects FFT section  214  to subcarrier mapping section  205  via first switch section  204 . 
         [0052]    Subcarrier demapping section  217  executes parallel-to-serial conversion on the signal output from second switch section  216  and outputs the processed signal to data demodulation section  218 . Here, when the control information transmitted from the base station is input from an upper layer (not shown), subcarrier demapping section  217  temporarily stores the signal output from second switch section  216  and directly arriving from the base station, executes a time matching process and a synthesizing process on the stored signal and the signal output from second switch section  216  and arriving from the relay station, and executes parallel-to-serial conversion based on information, which is included in the control information, regarding the delay occurring in the relay. Here, the directly arriving signal refers to a signal which is transmitted from the base station and is received without passing through the relay station. The signal directly arriving from the base station and the signal arriving from the relay station are distinguished from each other by determining whether the signal is the subcarrier signal inside the FSS use band. Here, since a communication scheme such as the OFDM of using the FFT or the DFT is supposed to be used, the delay occurring in the relay is an integer multiple of a time unit at which the DFT or the FFT such as an OFDM symbol is executed. 
         [0053]    Data demodulation section  218  demodulates the signal output from subcarrier demapping section  217  and outputs the demodulated signal to error correction decoding section  219 . The synthesizing process of executing the time matching process on the signal directly arriving from the base station and the signal arriving from the relay station may be executed on the signal demodulated by data demodulation section  218 . 
         [0054]    Error correction decoding section  219  executes error correction decoding on the signal output from data demodulation section  218 . 
         [0055]    Next, referring to  FIG. 4 , a communication processing sequence will be described when there are a plurality of terminals under a base station and a terminal communicating with the base station is referred to as terminal A and a terminal relaying communication with terminal A is referred to as terminal B. In  FIG. 4 , in ST 301 , terminal A that attempts to communicate with the base station gives a communication starting request to the base station. Here, when the base station attempts to communicate with terminal A, this process is substituted by a process of replying a communication request from the base station. In ST 302 , when the base station receives the communication starting request (or response) from terminal A, relay station selection section  112  selects a relay station. Here, terminal B, which is located near terminal A (for example, within the same sector as that of terminal A) and is not executing communication, is selected as the relay station. 
         [0056]    In ST 304 , the base station transmits to terminal A control information including information regarding start of the communication via terminal B selected as the relay station and information regarding delay occurring in the relay, and transmits to terminal B control information including information regarding the selection of the relay station communicating with terminal A and information (information indicating that the signal is mapped from which subcarrier to which subcarrier). 
         [0057]    In ST 304 , transmission control section  215  of terminal B switches a mode to a relay mode and executes a setting process of relaying a signal which is transmitted from the base station and is to be transmitted to terminal A. In ST 305 , as shown in  FIG. 5A , the separation section  105  of the base station separates the signal into the subcarrier signal outside the FFS use band and the subcarrier signal inside the FSS use band and subcarrier remapping section  106  remaps the separated subcarrier signal inside the FFS use band to the subcarrier outside the FFS use band. 
         [0058]    In ST 306 , the subcarrier signal outside the FSS use band separated in ST 305  and the signal remapped in ST 305  are simultaneously transmitted. Here, since the signal transmitted from the base station does not include the frequency component inside the FSS use band, it is possible to prevent interference from affecting an FSS earth station. 
         [0059]    In ST 307 , as shown in  FIG. 5B , subcarrier mapping section  205  of terminal B remaps the signal transmitted from the base station to terminal .B to the subcarrier inside the FFS use band and transmits the remapped signal to terminal A in ST 308 . The radio frequency used for the transmission is the same as that of the signal transmitted from the base station to terminal A. Here, the signal transmitted from terminal B to terminal A includes a frequency component inside the FSS use band. However, the transmission from terminal B is the same as the uplink transmission and there is substantially no interference in the FSS earth station configured such that directivity faces the upside. Further, since terminal A is located near terminal B, the output of terminal B may be small. Thus, the interference to the FSS earth station can be further reduced. 
         [0060]    By the processing given above, as shown in  FIG. 5C , the signal transmitted from the base station to terminal A and the signal transmitted from terminal B to terminal A are combined, and the combined signal is received at the antenna of terminal A. 
         [0061]    In ST 309 , subcarrier demapping section  217  of terminal A temporarily stores the signal transmitted from the base station. 
         [0062]    In ST 310 , subcarrier demapping section  217  of terminal A combines the signal transmitted from terminal B and the signal stored in ST 309  (synchronizes a delay time caused in the relay), and then data demodulation section  218  and error correction decoding section  219  decode the combined signal. 
         [0063]    Although not shown in the drawing, before the communication starts, it is necessary to execute a process of acquiring information regarding the position of each terminal, a process of estimating the propagation characteristics from the base station to each terminal, or a process of estimating the direction of each terminal. 
         [0064]    Since the communication can be realized using the entire band including the FSS use band while preventing the interference from affecting the FSS by executing the above-described communication processing sequence, it is possible to suppress the deterioration in the throughput. Further, the frequency can be shared only through the process executed on the IMT side without executing a process on the FSS side. 
         [0065]    To appropriately combine the signal directly arriving from the base station and the signal arriving from terminal B serving as the relay station in terminal A, the system may be designed such that the delay occurring in the relay process in terminal B may be inserted into the GI. In this ease, it is not necessary to execute the synthesizing process in consideration of the delay occurring in the relay. Further, the signal arriving from terminal B is configured to be normally delayed only by n×OFDM symbol (where n is a positive integer) compared to the signal directly arriving from the base station and is received by terminal A. 
         [0066]    According to Embodiment 1, the base station separates the signal into the subcarrier signal outside the FSS use band and the subcarrier signal inside the FSS use band, remaps the separated subcarrier signal inside the FSS use band to the subcarrier outside the FSS use band, transmits the separated subcarrier signal outside the FSS use band to a first terminal which is a communication partner, transmits the remapped subcarrier signal outside the FSS use band to a second terminal selected as the relay station, transmits the remapped subcarrier signal outside the FSS use band to the second terminal selected as the relay station, remaps the subcarrier signal received by the second terminal to the inside of the FSS band, transmits the subcarrier signal remapped to the inside of the FSS band to the first terminal, combines the signal transmitted from the first terminal to the second terminal and the signal directly transmitted from the base station, and decodes the combined signal. In this way, since the communication can be realized using the FSS use band while preventing the interference from affecting the FSS, it is possible to suppress the deterioration in the throughput. 
         [0067]    In this embodiment, subcarrier demapping section  217  of the terminal serves as the synthesis section that combines the signal directly arriving from the base station and the signal arriving from the relay station. However, data demodulation section  218  may serve as the synthesis section. 
         [0068]    In this embodiment, when the signals are simultaneously transmitted from the base station to terminal A (the first terminal) and terminal B (the second terminal), the signals are spatially separated and transmitted. However, the signals may not be spatially separated in the base station, but may be transmitted as a separate stream of MIMO. 
         [0069]    When the signals are simultaneously transmitted from the base station to terminal A (the first terminal) to terminal B (the second terminal), the signals may be transmitted using different radio frequencies. In this case, when the radio signal transmitted to terminal B (the second terminal) does not include the frequency component of the FSS use band, subcarrier remapping section  106  does not remap the subcarrier signal. Here, the signals up-converted to the two different radio frequencies may be simultaneously transmitted to terminal A (the first terminal) intentionally without passing through the relay station. However, RF reception sections need to be prepared by two radio frequencies in order for terminal A to demodulate the signals. It is not preferable that the terminal includes the plurality of RF reception sections since the cost of the terminal is increased and the power consumption is increased. Therefore, the same radio frequency as that used to transmit the signal from terminal B (the second terminal) to terminal A (the first terminal) may be used to transmit the signal from terminal B (the second terminal) to terminal A (the first terminal) using a radio frequency separated from the radio frequency of the signal transmitted from the base station to terminal B (the second terminal) and the radio frequency of the signal transmitted from the base station to terminal A (the first terminal). In this way, the cost of the terminal can be reduced and the power consumption can be reduced. 
         [0070]    As several methods have been described, the separated subcarrier signal outside the FSS use band and the remapped subcarrier signal outside the FSS use band may be simultaneously transmitted so as to be distinguished from each other. 
         [0071]    In this embodiment, the transmission section of the base station has the configuration shown in  FIG. 2 , but may have a configuration shown in  FIG. 6 . In the configuration shown in  FIG. 6 , the base station does not spatially separate the transmission signal to be transmitted to terminal A and the transmission signal to be transmitted to terminal B, but transmits the signal by MIMO. 
         [0072]    Here, the radio frequencies of two RF transmission sections are the same as each other. The transmission signal to be transmitted to terminal A and the transmission signal to be transmitted to terminal B are transmitted from different antennas. As a consequence, each terminal receives the signal where the transmission signal to be transmitted to terminal A and the transmission signal to be transmitted to terminal B coexist. Therefore, it is necessary to provide two or more antennas and execute a predetermined separating process of separating extracting only the signal for the own terminal. Further, when information to be transmitted to each terminal may arrive to both terminals (for example, when control information common to the terminals is transmitted), a common control information signal may be input to IFFT section  108 - 1  and may be transmitted using single antenna  111 - 1 . 
         [0073]    In this embodiment, the terminal has the configuration shown in  FIG. 3 , but may have a configuration shown in  FIG. 7  or  8 . In the configuration shown in  FIG. 7 , when the terminal operates as the relay station, transmission control section  215  controls first switch section  204  and second switch section  216  such that the output of subcarrier demapping section  217  is input to subcarrier mapping section  205 . Transmission control section  215  controls subcarrier demapping section  217  such that subcarrier demapping section  217  extracts the data mapped only to a specific subcarrier outside the FSS use band. Further, transmission control section  215  controls subcarrier mapping section  205  such that subcarrier mapping section  205  maps the input data to the subcarrier inside the FSS use band. 
         [0074]    On the contrary, when the terminal does not operate as the relay station, transmission control section  215  controls second switch section  216  such that the output of subcarrier demapping section  217  is input to data demodulation section  218 . Further, transmission control section  215  controls first switch section  204  such that the output of data modulation section  203  is input to subcarrier mapping section  205 . 
         [0075]    In the configuration shown in  FIG. 8 , when the terminal operates as the relay station, transmission control section  215  controls first switch section  204  and second switch section  216  such that the output of error correction decoding section  219  is input to error correction coding section  202 . Transmission control section  215  controls subcarrier demapping section  217  such that subcarrier demapping section  217  extracts the data mapped, only to a specific subcarrier outside the FSS use band. Further, transmission control section  215  controls subcarrier mapping section  205  such that subcarrier mapping section  205  maps the input data to the subcarrier inside the FSS use band. 
         [0076]    On the contrary, when the terminal does not operate as the relay station, transmission control section  215  controls first switch section  204  such that the output of transmission data generation section  201  is input to error correction coding section  202 . Further, transmission control section  215  controls second switch section  216  such that the output of error correction decoding section  219  becomes output data. 
       Embodiment 2 
       [0077]    In Embodiment 2 of the present invention, the case has hitherto been described in which a very small-scale base station with a coverage area of several meters to several tens of meters is installed in a household or the like. Here, the small-scale base station refers to a base station that realizes a pico cell, a femto cell, a small-scale cell such as Home eNode B or a Rely Node which has a cell radius and is installed in a spot manner in a building, a moving object (vehicle), or a large-scale cell. The coverage area (small-scale cell) of a small-scale base station is very small, as shown in  FIG. 9 . Therefore, even when the FSS use band is used in DL in the small-scale cell, there is substantially no interference to the FSS earth station and all system bands can be used. That is, it is not necessary to use the relay scheme described in Embodiment 1. 
         [0078]    Hereinafter, a case will be described in which the terminal being executing communication by the relay scheme (hereinafter, simply referred to as a “relay scheme”) described in Embodiment 1 executes soft handover to a small-scale cell out of the area of the small-scale cell or executes soft handover to a different IMT-Advanced base station executing the relay scheme from the small-scale cell. The terminal being executing the communication by the relay scheme receives the signal of the FSS use band passing through the terminal operating as the relay station. This signal is delayed by the n×OFDM symbol compared to the signal directly arriving from the IMT-Advanced base station, when the signal arrives to the terminal. When the terminal executes the soft handover, the IMT-Advanced base station and the small-scale base station synchronize with each other. Therefore, the signal of the FSS use band passing through the terminal operating as the relay station is delayed by the n×OFDM symbol compared to the signal directly arriving from the base station, when the signal arrives. For this reason, when soft handover is executed between the small-scale cell and the cell using the relay scheme, it is necessary to efficiently process the signal inside the FSS use band which is delayed by the n×OFDM symbol when the signal arrives to the terminal. 
         [0079]    A terminal according to Embodiment 2 of the present invention has the same configuration shown in  FIG. 3 ,  7 , or  8  of Embodiment 1. The configuration will be described with reference to, for example,  FIG. 3 . In  FIG. 3 , subcarrier demapping section  217  receives the control information transmitted by the IMT-Advanced base station or the small-scale base station from an upper layer (not shown). 
         [0080]    When the received control information indicates that the relay scheme is not applied, subcarrier demapping section  217  executes parallel-to-serial conversion on the signal output from FFT section  214  via second switch section  216  and outputs the processed signal to data demodulation section  218  without delaying the signal. On the contrary, when the received control information indicates that the relay scheme is not applied or indicates an instruction to execute the handover to the IMT-Advanced base station using the relay scheme, subcarrier demapping section  217  adds a delay amount (n×OFDM symbol) occurring in the relay to the signal outside the FSS use band in the signal output from FFT section  214  via second switch section  216 , executes parallel-to-serial conversion, and outputs the processed signal to data demodulation section  218 . 
         [0081]    Further, when the control information transmitted by the IMT-Advanced base station or the small-scale base station indicates application of the relay scheme or indicates the handover to the 
         [0082]    IMT-Advanced base station using the relay scheme, the control information may indicate that the transmission data mapped to the FSS use band is remapped to a band other than the FSS use band. 
         [0083]      FIG. 10  is a block diagram illustrating the configuration of the transmission section of the IMT-Advanced base station according to Embodiment 2 of the present invention.  FIG. 10  is different from  FIG. 2  in that handover execution determination section  501  and inter-base station communication section  502  are further provided. 
         [0084]    Handover execution determination section  501  acquires information regarding the reception qualities of the own cell and a peripheral cell transmitted from the terminal and determines whether the handover of the terminal is executed based on the acquired information regarding the reception qualities. When handover execution determination section  501  determines that the handover is executed, handover execution determination section  501  determines a cell to which the terminal executes the handover. When handover execution determination section  501  determines that the handover is executed, handover execution determination section  501  reports a handover destination cell to inter-base station communication section  502  and control information generation section  113 . At this time, when the terminal selected as the relay station is reported from relay station selection section  112 , handover execution determination section  501  also reports application of the relay scheme to inter-base station communication section  502  of. Here, the information regarding the reception quality acquired from the terminal may be reported to a different base station apparatus or a different base station control apparatus (not shown), and then the different base station apparatus or the different base station control apparatus may determine whether the handover is executed and may determine a handover destination. In this case, the different base station apparatus or the different base station control apparatus reports to the base stations the handover destination and the handover source of the intention via inter-base station communication section  502 . 
         [0085]    Further, when inter-base station communication section  502  reports to handover execution determination section  501  the fact that a terminal executing the handover from another cell is present, handover execution determination section  501  reports to inter-base station communication section  502  the fact that the relay scheme is applied. 
         [0086]    Control information generation section  113  generates control information used to report to the terminal the handover destination cell reported from handover execution determination section  501 . 
         [0087]    Inter-base station communication section  502  reports to the handover destination base station the handover destination cell connected to the different IMT-Advanced base station and the different small-scale base station and reported from handover execution determination section  501  and the fact that the relay scheme is applied. When it is reported to inter-base station communication section  502  the fact that there is a terminal executing the handover from a connected different IMT-Advanced base station or a connected different small-scale base station, inter-base station communication section  502  reports the intention to handover execution determination section  501 . As a consequence, when the fact that the relay scheme is applied is reported from handover execution determination section  501 , the intention is reported to the IMT-Advanced base station or the small-scale base station of the handover source. 
         [0088]      FIG. 11  is a block diagram illustrating the configuration of the transmission section of the small-scale base station according to Embodiment 2 of the present invention.  FIG. 11  is different from  FIG. 2  in that there are provided inter-base station communication section  601 , control section  602 , and delay section  603  and there are not provided subcarrier remapping section  106 , weight multiplication section  107 , IFFT section  108 - 2 , GI insertion section  109 - 2 , RF transmission section  110 - 2 , relay station selection section  112 , control information generation section  113 , and transmission processing section  114 . 
         [0089]    When it is reported to inter-base station communication section  601  the fact that there is a terminal connected to the IMT-Advanced base station and executing the handover from the connected IMT-Advanced base station and the terminal applies the relay scheme, inter-base station communication section  601  reports the intention to control section  602 . Further, when control section  602  reports to inter-base station communication section  601  the fact that there is a terminal executing the handover to the connected IMT-Advanced base station, inter-base station communication section  601  reports the intention to the connected IMT-Advanced base station. As a consequence, when the fact that the relay scheme is applied is reported from the IMT-Advanced base station, the intention is reported to control section  602 . 
         [0090]    When inter-base station communication section  601  reports to control section  602  the fact that a base station of the handover partner applies the relay scheme, control section  602  allows separation section  105  to separate the OFDM signal output from subcarrier mapping section  104  into the subcarrier signal outside the FSS use band and the subcarrier signal inside the FSS use band and outputs the separated subcarrier signal inside the FSS use band to delay section  603 . Further, control section  602  controls delay section  603  such that delay section  603  delays the subcarrier signal inside the FSS use band output from separation section  105  by the delay amount (n×OFDM symbol) occurring in the relay. IFFT section  108 - 1  combines the subcarrier signal outside the FSS use band containing no delay and the subcarrier signal inside the FSS use band containing delay and executes reverse Fourier transform. 
         [0091]    On the other hand, when inter-base station communication section  601  does not report to control section  602  the fact that a base station of the handover partner applies the relay scheme, control section  602  allows separation section  105  not to separate the OFDM signal output from subcarrier mapping section  104  and outputs the OFDM signal only to IFFT section  108 - 1 . 
         [0092]    According to Embodiment 2, when the soft handover is executed between the IMT-Advanced base station and the small-scale base station using the relay scheme, the small-scale base station delays and transmits the subcarrier signal inside the FSS use band by the delay amount (n×OFDM symbol) occurring in the relay. Thus, the terminal executing the soft handover can synchronize with the subcarrier signal inside the FSS use band passing through the terminal operating as the relay station and can receive the subcarrier signal inside the FSS use band from the small-scale base station. 
         [0093]    In the above-described embodiments, the common frequency is shared between the IMT-Advanced system and the FSS system. However, the present invention is not limited to the systems. When a communication system shares a frequency with a different communication system, the frequency used by the different communication system is not included in a signal which is widely transmitted as in DL of a cellular system, thereby preventing interference according to the present invention. In relay transmission, the frequency used by the different communication system is used. However, when the communication system is close to a relay terminal being communicating with the relay terminal, the transmission output at the relay time may be small. Therefore, the interference to the different system can be reduced. 
         [0094]    The disclosures of Japanese Patent Application No. 2009-189992 filed on Aug. 19, 2009, and Japanese Patent Application No. 2010-004119 filed on Jan. 12, 2010, including the specifications, drawings and abstracts, are incorporated herein by reference in their entirety. 
       INDUSTRIAL APPLICABILITY 
       [0095]    The radio communication base station apparatus, the small-scale radio communication base station apparatus, the radio communication terminal apparatus, the radio transmission method, the radio relay method, and the radio reception method according to the present invention are applicable to a case where a frequency needs to be shared with a different radio communication system such as an IMT-Advanced system. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           101 ,  201  Transmission data generation section 
           102 ,  202  Error correction coding section 
           103 ,  203  Data modulation section 
           104 ,  205  Subcarrier mapping section 
           105  Separation section 
           106  Subcarrier remapping section 
           107  Weight multiplication section 
           108 - 1 ,  108 - 2 ,  206  IFFT section 
           109 - 1 ,  109 - 2 ,  207  GI insertion section 
           110 - 1 ,  110 - 2 ,  208  RF transmission section 
           111 - 1 ,  111 - 2 ,  209 ,  210  Antenna 
           112  Relay station selection section 
           113  Control information generation section 
           114  Transmission processing section 
           204  First switch section 
           211  RF reception section 
           212  Synchronization section 
           213  GI removal section 
           214  FFT section 
           215  Transmission control section 
           216  Second switch section 
           217  Subcarrier demapping section 
           218  Data demodulation section 
           219  Error correction decoding section 
           401  Weight multiplication section 
           501  Handover execution determination section 
           502 ,  601  Inter-base station communication section 
           602  Control section 
           603  Delay section