Abstract:
When a terminal ( 200 ) is capable of connecting to two relay devices that are adjacent to the terminal, from among a plurality of relay devices, a receiving unit ( 208 ) receives signals in a first period and a second period for communication among the plurality of relay stations, which are transmitted from the higher order device to the lower order device toward other terminal devices. An interference removal unit ( 209 ) obtains a signal transmitted toward the terminal ( 200 ) from the higher order relay device by employing the signals toward the other terminal devices that are received in the first period and the second period and removing a signal toward other terminal devices that is transmitted in a third period for communication between the plurality of relay devices and the terminal device from the lower order device from a signal that is received in the third period.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a terminal apparatus and an interference removal method in multihop communication. 
       BACKGROUND ART 
       [0002]    In recent years, for the purpose of expanding the coverage areas of base stations, relay transmission techniques have been studied in which a relay apparatus (RN: Relay Node) is installed between a base station and terminals, and communication is performed between the base station and the mobile stations via the relay apparatus. Multihop communication is regarded as a promising means for providing wideband transmission to areas outside macrocell service areas particularly in cellular environments. In the multihop communication, a plurality of relay apparatuses are connected in series, and communication is performed between a base station and terminals. 
         [0003]    Furthermore, in consideration of expansion of use of radio waves not only between, e.g., mobile terminals, but also between various types of apparatuses in the future, a shortage of usable frequencies inevitably occurs. Thus, further enhancement in use efficiency of frequencies or expansion of the usable frequencies to a high-frequency band becomes essential. Multihop communication is a promising communication means also as a means for meeting such demands for, e.g., the enhancement in use efficiency of frequencies and the expansion to a high frequency band. 
         [0004]    More specifically, when a communication distance between a base station and a terminal is the same, a communication distance between the apparatuses in two-hop communication (multihop communication) is a half (½) of a communication distance between the apparatuses in single-hop communication. Here, in consideration of a case where received signal power is inversely proportional to the square of the distance, when the same received signal power is provided in two-hop communication and single-hop communication, the transmission power in two-hop communication can be only ¼ (=(½) 2 ) of the transmission power in the single-hop communication. Furthermore, a frequency reuse distance can be reduced to a half of that in single-hop communication in two-hop communication, and thus, a simultaneous communication density for the same frequency is approximately four times (=2 2 ) that in single-hop communication. However, the transmission timing needs to be divided into two in two-hop communication. Thus, the throughput in this case becomes a half of that in single-hop communication in end-to-end communication (between a base station and a terminal). However, in two-hop communication, an area spectral efficiency, which is provided by the product of a throughput and a simultaneous communication density, is twice (=(½)×4) that in single-hop communication. In other words, employment of multihop communication (here, two-hop communication) enables enhancement in frequency use efficiency as well as enhancement in throughput. 
         [0005]    Furthermore, signals have high linearity and the propagation loss (pathloss) is large in a high-frequency band (high carrier frequency). Thus, when the same transmission power as that in a low-frequency band (low carrier frequency) is used, the received signal power decreases. However, in multihop communication, the propagation loss (pathloss) per hop can be decreased by a further decrease in distance between transmitting and receiving apparatuses. In other words, employment of multihop communication enables flexible support for expansion of usable frequencies to a high frequency band according to the number of hops. 
         [0006]    As an example of multihop communication, a conventional technique is under study, in which a plurality of relay apparatuses perform communication between a base station and terminals using the same fixed frequency (see PLT 1 or the like), for example. 
       CITATION LIST 
     Patent Literature 
     PTL 1 Japanese Translation of a PCT Application Laid-Open No. 2009-533943 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    A specific explanation of the aforementioned conventional technique will be provided with reference to  FIG. 1 , taking multihop communication in downlink from a base station (macrocell base station, which is not illustrated) to terminals (MS 1  to MS 3  in  FIG. 1 ) as an example. 
         [0008]    In the following explanation, one of two adjacent relay apparatuses that is positioned upstream of a signal transfer direction between the base station (macrocell base station) and the terminals is referred to as an upstream RN, and the other one positioned downstream of the signal transfer direction is referred to as a downstream RN. Here, the two adjacent relay apparatuses are of relay apparatuses used in multihop communication (RN 1  to RN 4  in  FIG. 1 ). When a plurality of relay apparatuses are connected in series and placed sequentially from the base station, for example, a relay apparatus closer to the base station (macrocell base station) among two adjacent relay apparatuses is an upstream RN and a relay apparatus farther from the base station is a downstream RN. In RN 1  to RN 4  illustrated in  FIG. 1 , for example, signals transmitted from the base station (macrocell base station) to the terminals are transferred in order of RN 1 , RN 2 , RN 3  and RN 4 . In other words, in  FIG. 1 , RN 1  is the closest to the base station, RN 2  is the second closest to the base station, RN 3  is the third closest to the base station and RN 4  is the farthest from the base station. Accordingly, RN 1  is an upstream RN and RN 2  is a downstream RN between RN 1  and RN 2 . Likewise, RN 2  is an upstream RN and RN 3  is a downstream RN between RN 2  and RN 3 . The same applies to RN 3  and RN 4 . 
         [0009]    Furthermore, in the following explanation, as illustrated in  FIG. 1 , a downlink subframe is formed on a per subframe basis where each subframe includes three periods, i.e., period  1 , period  2  and period  3 . More specifically, the downlink subframe illustrated in  FIG. 1  includes period  1  for communication between a plurality of RNs and terminals, and period  2  and period  3  for communication between the plurality of RNs. 
         [0010]    Furthermore, in  FIG. 1 , RN 1  to RN 4  perform communication using fixed frequency f 1  only. 
         [0011]    Furthermore, in  FIG. 1 , MS 1  exists at a position where a coverage area of RN 1  and a coverage area of RN 2  overlap each other, that is, where MS 1  is connectable to both RN 1  and RN 2 . Likewise, MS 2  exists at a position where the coverage area of RN 2  and a coverage area of RN 3  overlap each other, and MS 3  exists at a position where the coverage area of RN 3  and a coverage area of RN 4  overlap each other. 
         [0012]    First, in  FIG. 1 , each of terminals MS 1  to MS 3  connects to an RN corresponding to a higher received signal strength indicator (RSSI) among RNs to which the terminal is connectable. In  FIG. 1 , MS 1  connects to RN 2 , MS 2  connects to RN 3 , and MS 3  connects to RN 4 . 
         [0013]    Then, in period  1  in the downlink subframe, all of the relay apparatuses (RN 1  to RN 4 ) simultaneously transmit a relay signal of frequency f 1  to terminals connected to the respective relay apparatuses (solid arrows in period  1  illustrated in  FIG. 1 ). 
         [0014]    Next, one of two adjacent relay apparatuses among the plurality of relay apparatuses (RN 1  to RN 4 ) transmits a relay signal to a downstream RN in period  2 , and the other one of the adjacent relay apparatuses transmits a relay signal to a downstream RN in period  3 . For example, the odd-numbered relay apparatuses (RN 1  and RN 3 ) transmit a relay signal of frequency f 1  to the even-numbered relay apparatuses (RN 2  and RN 4 ), which are downstream RNs adjacent to the respective relay apparatuses, in period  2  illustrated in  FIG. 1 . In other words, the even-numbered relay apparatuses (RN 2  and RN 4 ) receive a relay signal from the odd-numbered relay apparatuses (RN 1  and RN 3 ), which are upstream RNs adjacent to the respective relay apparatuses, in period  2  illustrated in  FIG. 1 . Likewise, the even-numbered relay apparatuses transmit a relay signal of frequency f 1  to the odd-numbered relay apparatuses, which are downstream RNs adjacent to the respective relay apparatuses, in period  3  illustrated in  FIG. 1 . In other words, the odd-numbered relay apparatuses receive a relay signal from the even-numbered relay apparatuses, which are upstream RNs adjacent to the respective relay apparatuses, in period  3  illustrated in  FIG. 1 . 
         [0015]    As described above, in the conventional technique, a plurality of relay apparatuses that perform multihop communication (RN 1  to RN 4  illustrated in  FIG. 1 ) use the same frequency (frequency f 1  in  FIG. 1 ). For this reason, there arises a problem that when a relay signal is transmitted from some of the plurality of relay apparatuses to the corresponding terminals (that is, period  1  illustrated in  FIG. 1 ), a terminal located where coverage areas of adjacent relay apparatuses overlap each other is interfered by a signal from a relay apparatus other than a relay apparatus to which the terminal is connected. For example, a signal from RN 2  to which MS 1  is connected (that is, a signal for MS 1  (desired signal)) as shown in  FIG. 1  is interfered by a signal from RN 1  adjacent to RN 2  (that is, a signal for an MS other than MS 1  (interference signal)). The same applies to MS 2  and MS 3  illustrated in  FIG. 1 . 
         [0016]    As described above, when multihop communication is performed among a plurality of relay apparatuses using the same frequency, the terminal cannot avoid interference to a signal from a relay apparatus to which the terminal is connected, by a signal from another relay apparatus. 
         [0017]    An object of the present invention is to provide a terminal apparatus and an interference removal method enabling reduction in interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus, even in a case where multihop communication is performed among a plurality of relay apparatuses using the same frequency. 
       Solution to Problem 
       [0018]    A terminal apparatus according to one aspect of the present invention is a terminal apparatus in a radio communication system in which a plurality of relay apparatuses relay communication between a base station apparatus and terminal apparatuses using the same frequency, on a per-subframe basis where each subframe includes a first period and a second period for communication between the plurality of relay apparatuses and a third period for communication between the plurality of relay apparatuses and the terminal apparatuses, while two adjacent relay apparatuses among the plurality of relay apparatuses perform transmission processing in mutually-different periods, respectively, in the first period and the second period, and the plurality of relay apparatuses simultaneously perform transmission to terminal apparatuses connected to the relay apparatuses, in the third period, the apparatus including: a selection section that selects connection to an upstream relay apparatus positioned upstream in a signal transfer direction between the base station apparatus and the terminal apparatus from among the two relay apparatuses, when the terminal apparatus is connectable to the two relay apparatuses; a receiving section that receives a signal for another terminal apparatus, the signal being transmitted from the upstream relay apparatus to a downstream relay apparatus positioned downstream in the transfer direction among the two relay apparatuses, in the first period or the second period; and a removing section that removes a signal for the other terminal apparatus transmitted from the downstream relay apparatus in the third period from a signal received in the third period, using the signal for the other terminal apparatus received in the first period or the second period, thereby obtaining a signal for the terminal apparatus transmitted from the upstream relay apparatus. 
         [0019]    An interference removal method according to another aspect of the present invention is an interference removal method in a radio communication system in which a plurality of relay apparatuses relay communication between a base station apparatus and terminal apparatuses using the same frequency on a per subframe basis where each subframe includes a first period and a second period for communication between the plurality of relay apparatuses and a third period for communication between the plurality of relay apparatuses and the terminal apparatuses, while two adjacent relay apparatuses among the plurality of relay apparatuses perform transmission processing in mutually-different periods, respectively, in the first period and the second period, and the plurality of relay apparatuses simultaneously perform transmission to terminal apparatuses connected to the relay apparatuses, in the third period, the method including: a selection step of selecting connection for the terminal apparatus to an upstream relay apparatus positioned upstream in a signal transfer direction between the base station apparatus and the terminal apparatus from among the two relay apparatuses, when the terminal apparatus is connectable to the two relay apparatuses; a reception step of receiving a signal for another terminal apparatus, the signal being transmitted from the upstream relay apparatus to a downstream relay apparatus positioned downstream in the transfer direction among the two relay apparatuses, in the first period or the second period; and a removal step of removing a signal for the other terminal apparatus transmitted from the downstream relay apparatus in the third period from a signal received in the third period, using the signal for the other terminal apparatus received in the first period or the second period, thereby obtaining a signal for the terminal apparatus transmitted from the upstream relay apparatus. 
       Advantageous Effects of Invention 
       [0020]    The present invention enables reduction in interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus, even in a case where multihop communication is performed among a plurality of relay apparatuses using the same frequency. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a diagram illustrating a problem to be solved by the present invention; 
           [0022]      FIG. 2  is a block diagram illustrating a configuration of a relay apparatus according to embodiment 1 of the present invention; 
           [0023]      FIG. 3  is a block diagram illustrating a configuration of a terminal according to embodiment 1 of the present invention; 
           [0024]      FIG. 4  is a diagram illustrating connection-destination RN selection processing in the terminal according to embodiment 1 of the present invention; 
           [0025]      FIG. 5  is a diagram illustrating interference removal processing in the terminal according to embodiment 1 of the present invention; 
           [0026]      FIG. 6  is a diagram illustrating a relay signal transmitted between relay apparatuses according to embodiment 1 of the present invention; 
           [0027]      FIG. 7  is a block diagram illustrating a configuration of a relay apparatus according to embodiment 2 of the present invention; 
           [0028]      FIG. 8  is a block diagram illustrating a configuration of a terminal according to embodiment 2 of the present invention; 
           [0029]      FIG. 9  is a diagram illustrating scheduling processing in relay apparatuses according to embodiment 2 of the present invention; 
           [0030]      FIG. 10  is a diagram illustrating scheduling processing in the relay apparatuses according to embodiment 2 of the present invention; 
           [0031]      FIG. 11  is a diagram illustrating interference removal processing in the terminal according to embodiment 2 of the present invention; 
           [0032]      FIG. 12  is a block diagram illustrating a configuration of a relay apparatus according to embodiment 3 of the present invention; 
           [0033]      FIG. 13  is a block diagram illustrating a configuration of a terminal according to embodiment 3 of the present invention; 
           [0034]      FIG. 14  is a diagram illustrating processing in relay apparatuses and terminals according to embodiment 3 of the present invention; 
           [0035]      FIG. 15  is a diagram illustrating interference removal processing in a relay apparatus according to embodiment 4 of the present invention; 
           [0036]      FIG. 16  is a diagram illustrating scheduling processing in relay apparatuses according to embodiment 5 of the present invention; 
           [0037]      FIG. 17  is a diagram illustrating processing in relay apparatuses and terminals according to embodiment 6 of the present invention; 
           [0038]      FIG. 18  is a diagram illustrating a control information notification method according to embodiment 7 of the present invention; 
           [0039]      FIG. 19  is a block diagram illustrating a configuration of a terminal according to embodiment 8 of the present invention; 
           [0040]      FIG. 20  is a diagram illustrating a control information notification method according to embodiment 8 of the present invention (when there are relay signals for terminals); 
           [0041]      FIG. 21  is a diagram illustrating the control information notification method according to embodiment 8 of the present invention (when there are no relay signals for terminals); 
           [0042]      FIG. 22  is a block diagram illustrating a configuration of a relay apparatus according to embodiment 9 of the present invention; 
           [0043]      FIG. 23  is a diagram illustrating a control information notification method according to embodiment 9 of the present invention (when there are relay signals for terminals); 
           [0044]      FIG. 24  is a diagram illustrating a control information notification method according to embodiment 9 of the present invention (when there are no relay signals for terminals); and 
           [0045]      FIG. 25  is a diagram illustrating a sequence of connection-destination RN selection processing in the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0046]    Hereafter, embodiments of the present invention will be described in detail with reference to the drawings. 
       Embodiment 1 
       [0047]    The explanation will be provided below taking multihop communication in downlink as an example. 
         [0048]    Furthermore, the below explanation will be provided for a radio communication system in which a plurality of relay apparatuses relay communication between a base station and terminals in downlink using the same frequency and in subframe (downlink subframes; hereinafter referred to as “DL subframe(s)”) units each including a first period (hereinafter referred to as “period A”) and a second period (hereinafter referred to as “period B”) for communication among the plurality of relay apparatuses (RNs), and a third period (hereinafter referred to as “period C”) for communication among the plurality of relay apparatuses and terminals. 
         [0049]    Furthermore, in period A and period B in a DL subframe, two adjacent relay apparatuses among the plurality of relay apparatuses perform transmission processing in periods different from each other (that is, any one of periods A and B), respectively. Furthermore, in period C in the DL subframe, the plurality of relay apparatuses simultaneously perform transmission to the terminals connected to the respective relay apparatuses. 
         [0050]    Furthermore, in the below explanation, as in  FIG. 1 , among two adjacent relay apparatuses, the relay apparatus positioned upstream in a signal transfer direction (downlink signal) between a base station (macrocell base station) and terminals is referred to as an upstream RN, and the relay apparatus positioned downstream is referred to as a downstream RN. For example, when a plurality of relay apparatuses are connected in series and placed sequentially from the base station, the relay apparatus closer to the base station (macrocell base station) among two adjacent relay apparatuses is an upstream RN and the relay apparatus farther from the base station is a downstream RN. 
         [0051]    Furthermore, in the below explanation, RN number 1 is given to a relay apparatus that directly communicates with a base station (macrocell base station), for example, a relay apparatus closest to the base station (most upstream RN), while RN numbers 2, 3, 4, . . . are sequentially given to the relay apparatuses downstream of the relay apparatus. In other words, the RN numbers of the plurality of relay apparatuses that relay communication between the base station and the terminals include odd numbers and even numbers alternately in order from the most upstream RN. The RN number of the most upstream RN may be given an even number (for example, the RN number is 0), while the relay apparatuses downstream of the relay apparatus with an RN number of 0 are given RN numbers 1, 2, 3, . . . . Hereinafter, a relay apparatus whose RN number is odd is referred to as an odd-numbered RN, and a relay apparatus whose RN number is even is referred to as an even-numbered RN. 
         [0052]    Furthermore, in the below explanation, odd-numbered RNs respectively transmit a relay signal to downstream RNs (that is, even-numbered RNs) in period A, and the even-numbered RNs respectively transmit a relay signal to downstream RNs (that is, the odd-numbered RNs) in period B. In other words, the even-numbered RNs receive a relay signal from the respective upstream RNs (that is, the odd-numbered RNs) in period A, and the odd-numbered RNs receive a relay signal from the respective upstream RNs (that is, the even-numbered RNs) in period B. 
         [0053]    A configuration of relay apparatus  100  according to the present embodiment is illustrated in  FIG. 2 . 
         [0054]    In relay apparatus  100  illustrated in  FIG. 2 , RF receiving section  102  receives a signal transmitted from an upstream apparatus (the base station in the case of the most upstream RN, and an upstream RN in the case of a relay apparatus other than the most upstream RN) via antenna  101 . Then, RF receiving section  102  performs reception processing such as down-conversion and A/D conversion on the received signal. Then, RF receiving section  102  outputs the signal after the reception processing to first memory  103 . It should be noted that a relay signal transmitted from the base station or an upstream RN includes, e.g., a relay signal (data signal and control information) for a terminal connected to relay apparatus  100  (terminal under the control of relay apparatus  100 ) or a relay signal (data signal and control information) for a terminal connected to a relay apparatus downstream of relay apparatus  100  (downstream RN), and a known signal (also referred to as a reference signal or a pilot signal). 
         [0055]    First memory  103  stores (writes in) a signal input from RF receiving section  102  (a signal from the upstream apparatus), and a signal input from transmission processing section  106 , which is described later, (a relay signal for a terminal connected to relay apparatus  100  or a relay signal for a downstream RN), according to instructions from timing control section  109 . Also, first memory  103  outputs (reads out) each of the stored signals to reception processing section  104  or RF transmitting section  107  according to an instruction from timing control section  109 . 
         [0056]    Reception processing section  104  first performs demodulation and decoding of the control information included in the relay signal input from first memory  103 . Here, a mapping position and an MCS (modulation and coding scheme) of the control information are set in advance and known. Also, the control information contains the mapping position and the MCS of the data signal (data directed to the terminal connected to relay apparatus  100  or data directed to a terminal connected to a downstream RN). Then, reception processing section  104  performs demodulation and decoding of the data signal contained in the relay signal input from first memory  103 , based on the mapping position and the MCS contained in the control information. Then, reception processing section  104  outputs the signal after the decoding to second memory  105 . 
         [0057]    Second memory  105  stores (writes in) the signal input from reception processing section  104  (the signal after the decoding), according to an instruction from timing control section  109 . Also, second memory  105  outputs (reads out) each of the stored signals to transmission processing section  106 , according to an instruction from timing control section  109 . 
         [0058]    Transmission processing section  106  performs encoding and modulation of the signal input from second memory  105  (the relay signal for the terminal connected to relay apparatus  100  or the relay signal for the terminal connected to a downstream RN). Then, transmission processing section  106  outputs the signal after the modulation to first memory  103 . 
         [0059]    RF transmitting section  107  performs transmission processing such as D/A conversion, amplification and up-conversion on the signal input from first memory  103 . Then, RF transmitting section  107  transmits the signal after the transmission processing from antenna  101 . 
         [0060]    Odd/even number switching section  108  switches a setting indicating whether relay apparatus  100  is an odd-numbered RN or an even-numbered RN, according to the RN number of relay apparatus  100 . Odd/even number switching section  108  may switch the setting indicating whether relay apparatus  100  is an odd-numbered RN or an even-numbered RN, according to the number of RNs used in multihop communication, which is notified by the base station, for example. Alternatively, odd/even number switching section  108  may switch the setting indicating whether relay apparatus  100  is an odd-numbered RN or an even-numbered RN, according to notification from the base station before the start of communication. Then, odd/even number switching section  108  outputs the setting information indicating whether relay apparatus  100  is an odd-numbered RN or an even-numbered RN (for example, “odd number” or “even number”) to timing control section  109 . 
         [0061]    Timing control section  109  instructs an input/output timing of a relay signal to/from first memory  103  and second memory  105  based on the setting information input from odd/even number switching section  108 . 
         [0062]    If the setting information input from odd/even number switching section  108  indicates “odd number” (if relay apparatus  100  is an odd-numbered RN), timing control section  109  instructs (gives a read instruction to) first memory  103  to output the relay signal for the downstream RN to RF transmitting section  107  in period A, for example. 
         [0063]    Furthermore, in period B, timing control section  109  instructs (gives a write instruction to) first memory  103  to store the relay signal input from RF receiving section  102  (the relay signal for the terminal connected to relay apparatus  100  or the relay signal for the terminal connected to the downstream RN). Furthermore, in period B, when the relay signal is stored in first memory  103 , timing control section  109  instructs (gives a read instruction to) first memory  103  to output the stored relay signal to reception processing section  104 , and instructs (gives a write instruction to) second memory  105  to store the signal input from reception processing section  104  (decoded signal). Furthermore, in period B, when the decoded signal is stored in second memory  105 , timing control section  109  instructs (gives a read instruction to) second memory  105  to output the relay signal (the relay signal for the terminal connected to relay apparatus  100  or the relay signal for the terminal connected to the downstream RN) to transmission processing section  106 , and instructs (gives a write instruction to) first memory  103  to store the relay signal input from transmission processing section  106  (the relay signal for the terminal connected to relay apparatus  100  or the relay signal for the terminal connected to the downstream RN). 
         [0064]    Meanwhile, if the setting information input from odd/even number switching section  108  indicates “even number” (if relay apparatus  100  is an even-numbered RN), timing control section  109  performs processing similar to that performed in period A when the setting information indicates “odd number,” in period B, and performs processing similar to that performed in period B when the setting information indicates “odd number,” in period A. In other words, the processing in period A and the processing in period B in timing control section  109  are interchanged between an odd-numbered RN and an even-numbered RN. 
         [0065]    Furthermore, regardless of the setting information input from odd/even number switching section  108 , timing control section  109  instructs (gives a read instruction to) first memory  103  to output the relay signal for the terminal connected to relay apparatus  100  to RF transmitting section  107  in period C. 
         [0066]    Next, a configuration of terminal  200  according to the present embodiment is illustrated in  FIG. 3 . 
         [0067]    In terminal  200  illustrated in  FIG. 3 , RF receiving section  202  receives a signal transmitted from relay apparatus  100  ( FIG. 2 ), via antenna  201 . Then, RF receiving section  202  performs reception processing such as down-conversion and A/D conversion on the received signal. Then, RF receiving section  202  outputs the signal after the reception processing to first memory  203 . It should be noted that a relay signal transmitted from relay apparatus  100  to which terminal  200  is connected contains a relay signal (data signal and control information) for terminal  200  and a known signal. 
         [0068]    First memory  203  stores (writes in) the relay signal input from RF receiving section  202 , according to an instruction from timing control section  214 . Also, first memory  203  outputs (reads out) the stored signal to known signal detection section  204  and reception processing section  207  according to an instruction from timing control section  214 . 
         [0069]    Known signal detection section  204  performs a correlation calculation between the known signal contained in the relay signal input from first memory  203  and each of all possible known signal patterns. Here, the number of known signal patterns is the number of RNs that may be included in the multihop communication; however, in reality, a maximum of several tens of patterns is sufficient (that is, a maximum of several tens of hops is allowed). Known signal detection section  204  detects the known signal transmitted from relay apparatus  100 , based on the result of the correlation calculation, and outputs the detected known signal to signal strength measuring section  205 . Also, known signal detection section  204  detects a known signal pattern in which a peak appears (that is, a relay apparatus from which the known signal is received), and outputs an RN number corresponding to the detected pattern to selection section  206 . 
         [0070]    Signal strength measuring section  205  measures a received signal strength indicator (RSSI) of the known signal input from known signal detection section  204 . Then, signal strength measuring section  205  outputs the measured received signal strength indicator to selection section  206 . 
         [0071]    Selection section  206  determines a relay apparatus (RN) to which terminal  200  is to be connected, using the RN number input from known signal detection section  204  and the received signal strength indicator (RSSI) of the known signal input from signal strength measuring section  205 . Here, if terminal  200  is connectable to two adjacent relay apparatuses (RNs), selection section  206  selects connection to a relay apparatus positioned upstream in a signal transfer direction (here, downlink signal) between the base station and terminal  200  (a relay apparatus closer to the base station), that is, an upstream RN, from among the two relay apparatuses. In other words, if terminal  200  is connectable to two adjacent relay apparatuses (RNs), selection section  206  selects the upstream RN from among the two relay apparatuses as a serving cell. Then, selection section  206  outputs the RN number of the connection-destination RN (the serving cell) for terminal  200 , which is the result of the selection, to second memory  210  and odd/even number switching section  213 . Details of the connection-destination RN selection processing in selection section  206  will be described later. 
         [0072]    Reception processing section  207  includes receiving section  208  and interference removal section  209 . 
         [0073]    Receiving section  208  of reception processing section  207  performs demodulation and decoding of the relay signal input from first memory  203 . More specifically, if terminal  200  is connectable to two adjacent relay apparatuses (RNs), receiving section  208  performs the following processing. In period A or period B (a period for communication between relay apparatuses), receiving section  208  receives a relay signal transmitted from the upstream RN to the downstream RN of the two relay apparatuses to which terminal  200  is connectable (a relay signal for another terminal) and performs demodulation and decoding of the signal. In other words, receiving section  208  receives the relay signal for another terminal, that is, a signal that may provide interference to terminal  200  in period C (interference signal) in period A or period B. Then, receiving section  208  outputs the relay signal for another terminal (interference signal), which was received in period A or period B, to second memory  210 . Also, receiving section  208  calculates a channel estimation value between the relay apparatus (upstream RN) to which terminal  200  is connected and terminal  200 , using the relay signal for another terminal, and outputs the channel estimation value to second memory  210 . Likewise, receiving section  208  calculates a channel estimation value between the downstream RN and terminal  200  using a relay signal from the downstream RN, and outputs the channel estimation value to second memory  210  as a channel estimation value of the interference signal. 
         [0074]    Interference removal section  209  removes the relay signal for another terminal, which is transmitted from the downstream RN in period C, from the relay signal received in period C, using the relay signal for another terminal (interference signal) and the channel estimation value of the interference signal stored in second memory  210 , which were received in period A or period B. Then, receiving section  208  performs demodulation and decoding of the relay signal which is received in period C (a period for communication between relay apparatuses and terminals) of a DL subframe and from which the interference signal has been removed in interference removal section  209 . Receiving section  208  thereby obtains a relay signal for terminal  200  (desired signal) transmitted from the upstream RN (serving cell for terminal  200 ). Then, receiving section  208  outputs the decoded signal to second memory  210 . Details of the interference removal processing in interference removal section  209  will be described later. 
         [0075]    Second memory  210  stores the result of selection input from selection section  206  (RN number of the serving cell for terminal  200 ). Also, second memory  210  stores the signals input from receiving section  208  of reception processing section  207  (the interference signal and the signal after removal of the interference) according to an instruction from timing control section  214 . Also, second memory  210  outputs the stored signals to reception processing section  207  (interference removal section  209 ) and transmission processing section  211  according to an instruction from timing control section  214 . 
         [0076]    Transmission processing section  211  performs encoding and modulation of a signal containing a terminal ID of terminal  200  and the RN number of the serving cell, which is input from second memory  210 . Then, transmission processing section  211  outputs the modulated signal to RF transmitting section  212  as a response signal. 
         [0077]    RF transmitting section  212  performs transmission processing such as D/A conversion, amplification and up-conversion on the response signal input from transmission processing section  211 . Then, RF transmitting section  212  transmits the response signal after the transmission processing from antenna  201 . Consequently, the relay apparatus corresponding to the serving cell indicated in the response signal recognizes terminal  200  as a terminal to be connected to the relay apparatus itself (terminal under the control of this relay apparatus) and transmits a response signal to terminal  200 . 
         [0078]    Odd/even number switching section  213  performs switching of the setting indicating whether the relay apparatus to which terminal  200  is connected is an odd-numbered RN or an even-numbered RN, according to the RN number of the serving cell input from selection section  206 , as in odd/even number switching section  108  ( FIG. 2 ). Then, odd/even number switching section  213  outputs setting information indicating whether the relay apparatus to which terminal  200  is connected is an odd-numbered RN or an even-numbered RN (“odd number” or “even number”) to timing control section  214 . Odd/even number switching section  213  outputs an indefinite value to timing control section  214  until the RN number of the serving cell (the result of selection in selection section  206 ) is input from selection section  206 . 
         [0079]    As in timing control section  109  ( FIG. 2 ), timing control section  214  gives an instruction to first memory  203  and second memory  210  on input/output timings for a relay signal, based on the setting information input from odd/even number switching section  213 . 
         [0080]    For example, if the setting information input from odd/even number switching section  213  indicates “odd number” (if the serving cell is an odd-numbered RN) timing control section  214  instructs (gives a write instruction to) first memory  203  to store a relay signal for a downstream RN, which is input from RF receiving section  202 , in period A. Also, in period A, when the relay signal for a downstream RN is stored in first memory  203 , timing control section  214  instructs (gives a read instruction to) first memory  203  to output the relay signal for the downstream RN to reception processing section  207 , and instructs (gives a write instruction to) second memory  210  to store an interference signal (a relay signal for another terminal) input from reception processing section  207 , and a channel estimation value between the serving cell and terminal  200 . 
         [0081]    Furthermore, timing control section  214  instructs (gives a write instruction to) first memory  203  to store a relay signal transmitted from the downstream RN among two relay apparatuses to which terminal  200  is connectable, which is input from RF receiving section  202 , in period B. Also, in period B, when the relay signal from the downstream RN is stored in first memory  203 , timing control section  214  instructs (gives a read instruction to) first memory  203  to output the stored relay signal from the downstream RN to reception processing section  207 , and instructs (gives a write instruction to) second memory  210  to store a channel estimation value between the downstream RN and terminal  200 , which is input from reception processing section  207 . 
         [0082]    Meanwhile, if the setting information input from odd/even number switching section  213  indicates an “even number” (if the serving cell is an even-numbered RN), timing control section  214  performs, in period B, processing similar to the processing performed in period A, and performs, in period A, processing similar to the processing performed in period B when the setting information indicates “odd number” in period A. In other words, the processing in period A and the processing in period B in timing control section  214  are interchanged between terminal  200  connected to an odd-numbered RN and terminal  200  connected to an even-numbered RN. 
         [0083]    Furthermore, regardless of the setting information input from odd/even number switching section  213 , timing control section  214  instructs (gives a write instruction to) first memory  203  to store signals from respective RNs, which are input from RF receiving section  202  in period C. In period C, when the signals from the respective RNs are stored in first memory  203 , timing control section  214  instructs (gives a read instruction to) first memory  203  to output the stored signals from the respective RNs, to reception processing section  207 , and instructs (gives a read instruction to) second memory  210  to output, to reception processing section  207 , the interference signal, the channel estimation value between the serving cell and terminal  200  and the channel estimation value between the downstream RN and terminal  200 , which are received in period A and period B. Also, timing control section  214  instructs (gives a write instruction to) second memory  210  to store a signal input from reception processing section  207  (a signal after interference removal). 
         [0084]    Next, details of the connection-destination RN selection processing in selection section  206  ( FIG. 3 ) in terminal  200  according to the present embodiment will be described. 
         [0085]    The below explanation is provided in terms of an MS (terminal  200 ) existing at a position where a coverage area of an odd-numbered RN (with an RN number of, for example, 2n+1) and a coverage area of an even-numbered RN (with a RN number of, for example, 2n+2) overlap each other as illustrated in  FIG. 4 . Furthermore, the odd-numbered RN illustrated in  FIG. 4  transmits a relay signal to the even-numbered RN. In other words, in  FIG. 4 , between two adjacent relay apparatuses (the odd-numbered RN and the even-numbered RN), the odd-numbered RN is an upstream RN and the even-numbered RN is a downstream RN. The odd-numbered RN and the even-numbered RN illustrated in  FIG. 4  each include the configuration of relay apparatus  100  illustrated in  FIG. 2 . 
         [0086]    First, the odd-numbered RN and the even-numbered RN each transmit a known signal to the MS by means of a pre-set resource and pre-set transmission power (step  1  illustrated in  FIG. 4 ). In  FIG. 4 , each of the odd-numbered RN and the even-numbered RN includes its own RN number in the known signal. Also, the known signals from the odd-numbered RN and the even-numbered RN are transmitted in a time-division multiplexed manner. Furthermore, the present invention is not limited to the case where the RN numbers of relay apparatuses are included in their respective known signals. The known signals maybe encoded using codes associated with the RN numbers of the relay apparatuses and then transmitted at the same timing. Here, since no connection-destination RN (serving cell) is selected in the MS (terminal  200 ), an indefinite value is input to timing control section  214  in the MS as setting information from odd/even number switching section  213 . Therefore, timing control section  214  in the MS controls the reception timing (reception window width) to ensure reception of both known signals of the odd-numbered RN and the even-numbered RN illustrated in  FIG. 4 . 
         [0087]    Then, known signal detection section  204  in the MS (terminal  200 ) detects the time-division multiplexed known signals (known signal detection processing in step  2  illustrated in  FIG. 4 ). For example, in  FIG. 4 , known signal detection section  204  performs a correlation calculation of each of the known signals received in step  1  with each possible known signal pattern. Then, as a result of the correlation calculation, known signal detection section  204  detects a peak in a known signal pattern (for example, pattern #2n+1) of the odd-numbered RN (with an RN number of 2n+1) and a peak in a known signal pattern (for example, pattern #2n+2) of the even-numbered RN (with an RN number of 2n+2), thereby detecting the known signals respectively from the odd-numbered RN and the even-numbered RN. 
         [0088]    Next, signal strength measuring section  205  measures a received signal intensity indicator RSSI 2n+1  of the odd-numbered RN and a received signal intensity indicator RSSI 2n+2  of the even-numbered RN using the known signal from the odd-numbered RN and the known signal from the even-numbered RN, which were detected by known signal detection section  204  (signal strength measurement processing in step  2  illustrated in  FIG. 4 ). 
         [0089]    Next, selection section  206  calculates a SIR odd  for the odd-numbered RN illustrated in  FIG. 4  according to, for example, equation 1 below and SIR even  for the even-numbered RN illustrated in  FIG. 4  according to, for example, equation 2 below in the MS (terminal  200 ) in a case where the odd-numbered RN and the even-numbered RN simultaneously transmit a signal. 
         [0000]      [1]SIR odd =10 log 10 (RSSI 2n+1 /RSSI 2n+2 )  (Equation 1)
 
         [0000]      [2]SIR even =10 log 10 (RSSI 2n+2 /RSSI 2n+1 )  (Equation 2)
 
         [0090]    Then, selection section  206  compares calculated SIR odd  and SIR even  with pre-set threshold value α to determine the connection-destination RN, that is, the serving cell for the MS (terminal  200 ). More specifically, selection section  206  selects the serving cell according to conditions (1) to (4) below (selection processing in step  2  illustrated in  FIG. 4 ). 
         [0091]    Condition (1): SIR odd ≧α, SIR even ≧α . . . . Serving cell RN number=2n+1 
         [0092]    Condition (2): SIR odd ≧α, SIR even &lt;α . . . . Serving cell RN number=2n+1 
         [0093]    Condition (3): SIR odd &lt;α, SIR even ≧α . . . . Serving cell RN number=2n+2 
         [0094]    Condition (4): SIR odd &lt;α, SIR even &lt;α . . . . Serving cell RN number=none (cell re-selection) 
         [0095]    In other words, if both of the received signal strength indicators from two RNs (the odd-numbered RN and the even-numbered RN in  FIG. 4 ) are not less than pre-set threshold value α, selection section  206  selects connection to the upstream RN (the odd-numbered RN in  FIG. 4 ) (condition (1)). Also, selection section  206  selects connection to the upstream RN (condition (2)) if the received signal strength indicator from the upstream RN (the odd-numbered RN in  FIG. 4 ) is not less than threshold value α but the received signal strength indicator from the downstream RN (the even-numbered RN in  FIG. 4 ) is less than threshold value α in the two RNs. Also, selection section  206  selects connection to the downstream RN (condition (3)) if the received signal strength indicator from the upstream RN (the odd-numbered RN in  FIG. 4 ) is less than threshold value α but the received signal strength indicator from the downstream RN (the even-numbered RN in  FIG. 4 ) is not less than threshold value α in the two RNs. Meanwhile, if both of the received signal strength indicators from the two RNs are less than threshold value α, selection section  206  selects none of the RNs (none) and makes re-selection of the connection-destination RN (cell re-selection) (condition (4)). 
         [0096]    Here, threshold value α may be either fixed or variable. Also, threshold value α may be different for each RN because of geographic reasons. Furthermore, threshold value α may be determined according to the extent of desired signal components in a dynamic range of an A/D converter generally used in terminal  200 . Alternatively, for threshold value α, an SIR satisfying a required error rate, which is obtained in advance by means of, e.g., a simulation, may be set. Alternatively, threshold value α may be determined using an SIR distribution between adjacent RNs, which is obtained in advance by actual measurements. 
         [0097]    For example, it is assumed that both of SIR odd  and SIR even  calculated in signal strength measuring section  205  in the MS illustrated in  FIG. 4  are not less than threshold value α. In this case, selection section  206  in the MS selects the odd-numbered RN, which is the upstream RN, as the serving cell from among the odd-numbered RN and the even-numbered RN illustrated in  FIG. 4 , according to condition (1). As described above, if there are a plurality of RNs whose SIR is not less than threshold value α, selection section  206  selects the most upstream RN as the serving cell from among the plurality of RNs whose SIR is not less than threshold value α. 
         [0098]    Next, the MS (terminal  200 ) illustrated in  FIG. 4  transmits a response signal containing a terminal ID of the MS and the RN number (here, 2n+1) of the serving cell selected in selection section  206  to the odd-numbered RN and the even-numbered RN (step  3  illustrated in  FIG. 4 ). 
         [0099]    Next, the odd-numbered RN illustrated in  FIG. 4  recognizes the MS (terminal corresponding to the terminal ID contained in the response signal) as a terminal under the control of this relay apparatus because the RN number (2n+1) of the serving cell contained in the response signal transmitted from the MS (terminal  200 ) coincides with the RN number (2n+1) of the relay apparatus. Then, the odd-numbered RN transmits a response signal to the MS (terminal  200 ) (step  4  illustrated in  FIG. 4 ). Meanwhile, the even-numbered RN illustrated in  FIG. 4  does not recognize the MS (terminal corresponding to the terminal ID contained in the response signal) as a terminal under the control of this relay apparatus because the RN number (2n+1) of the serving cell contained in the response signal transmitted from the MS (terminal  200 ) does not coincides with the RN number (2n+2) of the this relay apparatus. 
         [0100]    Next, details of the interference removal processing in interference removal section  209  in terminal  200  according to the present embodiment will be described. 
         [0101]    The below explanation is provided in terms of an MS (terminal  200 ) existing at a position where a coverage area of an odd-numbered RN and a coverage area of an even-numbered RN overlap each other as illustrated in  FIG. 5 , as in  FIG. 4 . Also, as in  FIG. 4 , the odd-numbered RN is an upstream RN and the even-numbered RN is a downstream RN in  FIG. 5 . The odd-numbered RN and the even-numbered RN each illustrated in  FIG. 5  include the configuration of relay apparatus  100  illustrated in  FIG. 2 . 
         [0102]    Also, the MS (terminal  200 ) is connected to the odd-numbered RN in  FIG. 5  in such a manner as described in  FIG. 4 . In other words, the odd-numbered RN is the serving cell for the MS (terminal  200 ). 
         [0103]    As illustrated in  FIG. 5 , the odd-numbered RN transmits a relay signal to the even-numbered RN, which is a downstream RN, in period A of a DL subframe. The relay signal transmitted from the odd-numbered RN in period A illustrated in  FIG. 5  contains signal  11  for a terminal connected to the even-numbered RN (a terminal other than the MS illustrated in  FIG. 5 ) and signal  12  for a terminal connected to an RN positioned downstream of the even-numbered RN. 
         [0104]    Here, the MS (terminal  200 ) illustrated in  FIG. 5  receives the signals transmitted to other terminals (signal  11  and signal  12 ) from the odd-numbered RN (upstream RN) to the even-numbered RN (downstream RN) in period A. More specifically, the signals (signal  11  and signal  12 ) received by RF receiving section  202  are stored in first memory  203  in the MS. Also, still more specifically, a relay signal transmitted between RNs contains a preamble signal, and control information containing, e.g., the mapping position and the MCS of each of signal  11  and signal  12  in the relay signal in addition to signal  11  and signal  12  as illustrated in  FIG. 6  (here, in the case of period A). Therefore, reception processing section  207  (receiving section  208 ) in the MS obtains a channel estimation value between the odd-numbered RN (serving cell) and the MS from the preamble signal included in the relay signal (signal  11  and signal  12 ) in period A and outputs the channel estimation value to second memory  210 . Next, reception processing section  207  (receiving section  208 ) in the MS performs demodulation and decoding of the control information contained in the relay signal (signal  11  and signal  12 ) in period A (information including the mapping position and MCS in the relay signal of the data signal for the signal  11 ). Here, an assumption is made that the preamble signal and the mapping position and MCS in the control information are known to the MS. Then, reception processing section  207  (receiving section  208 ) in the MS performs demodulation and decoding of the data signal contained in signal  11  based on the result of the decoding of the control information (the mapping position and the MCS), and stores the decoded data signal (signal that becomes an interference component in period C (hereinafter referred to as an “interference signal”)) in second memory  210 . Next, interference removal section  209  in the MS performs coding and modulation of the decoded data signal (interference signal) stored in second memory  210  and retains the modulated signal (that is, a replica of the interference signal in period C). 
         [0105]    Next, in period B of the DL subframe illustrated in  FIG. 5 , the even-numbered RN illustrated in  FIG. 5  transmits a relay signal to an odd-numbered RN (not illustrated), which is a downstream RN of the even-numbered RN. As illustrated in  FIG. 5 , the relay signal transmitted from the even-numbered RN contains signal  12  for a terminal connected to the RN positioned further downstream of the even-numbered RN, which is received from the upstream RN (odd-numbered RN) in period A. 
         [0106]    Here, in period B, the MS (terminal  200 ) illustrated in  FIG. 5  receives signal  12  transmitted from the even-numbered RN illustrated in  FIG. 5  to the odd-numbered RN (not illustrated), which is a downstream RN. More specifically, signal  12  received by RF receiving section  202  is stored in first memory  203  in the MS. Then, reception processing section  207  (receiving section  208 ) in the MS calculates a channel estimation value between the even-numbered RN illustrated in  FIG. 5  and the MS (that is, a channel estimation value for the interference signal) using a preamble signal contained in signal  12 , and outputs the channel estimation value to second memory  210 . 
         [0107]    Furthermore, in period B, the odd-numbered RN illustrated in  FIG. 5  receives signal  13  for the MS connected to the odd-numbered RN from a non-illustrated upstream apparatus (macrocell base station in the case of the most upstream RN or an even-numbered RN in the case of an RN other than the most upstream RN). 
         [0108]    Next, in period C of the DL subframe illustrated in  FIG. 5 , the odd-numbered RN illustrated in  FIG. 5  transmits signal  13  for the MS received in period B from the upstream apparatus (not illustrated), and the even-numbered RN illustrated in  FIG. 5  transmits signal  11  for a terminal connected to the even-numbered RN (terminal other than the MS), which was received in period A from the upstream odd-numbered RN. Accordingly, in period C, the MS illustrated in  FIG. 5  receives signal  13  (desired signal for the MS) from the odd-numbered RN (serving cell) and a signal containing signal  11  from the even-numbered RN (interference signal for the MS). 
         [0109]    Then, in period C illustrated in  FIG. 5 , interference removal section  209  in the MS (terminal  200 ) removes signal  11 , which is an interference signal, from the signal received in period C (signal containing signal  13  and signal  11 ), by using signal  11  obtained in period A (replica of the interference signal), the channel estimation value between the odd-numbered RN and the MS obtained in period A (channel estimation value for the desired signal), and the channel estimation value between the even-numbered RN and the MS obtained in period B (channel estimation value for the interference signal), thereby obtaining signal  13  directed to the MS (desired signal). Then, receiving section  208  in the MS performs demodulation and decoding of the signal after the interference removal (that is, signal  13 ), and stores the decoded signal in second memory  210 . 
         [0110]    As described above, in period A and period B of a DL subframe (that is, periods for communication between RNs), terminal  200  obtains a signal that becomes an interference signal in period C, which is subsequent to period A and period B (signal  11  in  FIG. 5 ), and a channel estimation value of the signal that becomes the interference signal in period C. 
         [0111]    Here, as illustrated in  FIG. 5 , in periods for communication between RNs (period A and period B), adjacent RNs perform transmission processing for a relay signal using the same frequency in mutually-different periods, respectively. For example, as illustrated in  FIG. 5 , the odd-numbered RN transmits a relay signal using frequency f 1  in period A, while the even-numbered RN transmits a relay signal using frequency f 1  in period B, which is different from period A. In other words, relay signals from two adjacent RNs are time-divided into period A and period B and thereby orthogonalized. Accordingly, each RN (relay apparatus  100 ) can transmit a relay signal to a downstream RN in either one of period A and period B without interference from an adjacent RN. 
         [0112]    Consequently, terminal  200  (MS illustrated in  FIG. 5 ) connectable to both of adjacent RNs can receive relay signals transmitted by the respective RNs to their downstream RNs without interference in period A and period B illustrated in  FIG. 5 , even if all of the RNs use the same frequency. For example, in  FIG. 5 , the MS (terminal  200 ) can receive only a signal transmitted from the odd-numbered RN (upstream RN) in period A and only a signal transmitted from the even-numbered RN (downstream RN) in period B. 
         [0113]    Furthermore, when terminal  200  can be connected to a plurality of adjacent RNs, terminal  200  selects an upstream RN (RN positioned upstream in the signal transfer direction between the base station and the terminals; that is, an RN closest to the base station in downlink) among the plurality of adjacent RNs (two RNs in  FIG. 5 ) as a serving cell. 
         [0114]    Here, the signals received by the MS (terminals  200 ) in period A and period B illustrated in  FIG. 5  (signals transmitted between RNs) are signals directed to terminals connected to RNs positioned downstream of the odd-numbered RN illustrated in  FIG. 5  (serving cell for the MS), that is, signals directed to terminals other than the MS. In other words, the signals received by the MS (terminal  200 ) in period A and period B illustrated in  FIG. 5  are signals that may be interference signals for the MS. Consequently, terminal  200  can recognize in advance the signals that may be interference signals for terminal  200 , at times before a period for communication between the plurality of RNs and the terminals (period C illustrated in  FIG. 5 ). 
         [0115]    Accordingly, terminal  200  can remove the interference signals from signals transmitted from the plurality of RNs, using the interference signals recognized in advance and the channel estimation values of the interference signals. Incidentally, various interference cancellation techniques are known, and examples of such techniques include JD (joint detection) in which MLD (maximum likelihood detection) processing is performed on each of a desired signal (signal  13  in  FIG. 5 ) and an interference signal (signal  11  in  FIG. 5 ). It is known that in JD, interference can be removed with good precision if the channel estimation value of the desired signal and the channel estimation value of the interference signal are obtained. Meanwhile, since not only the channel estimation value of the desired signal and the channel estimation value of the interference signal but also the interference signal itself is known to terminal  200  in advance, even where the SIR is low, the interference signal can be removed with good precision, thus making it possible to obtain the desired signal. 
         [0116]    As described above, according to the present embodiment, even when multihop communication is performed among a plurality of relay apparatuses using the same frequency, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reduced. 
         [0117]    The present embodiment has been described of a case where there is a RN positioned downstream of a different RN to which a terminal is connected. Here, there is no RN positioned downstream of the most downstream RN (RN farthest from a base station) among a plurality of RNs used in multihop communication. Thus, no interference owing to a signal transmitted from an RN other than the most downstream RN occurs in an MS that can be connected only to the most downstream RN. Accordingly, the MS connected to the most downstream RN only needs to receive a signal directed to the MS, which is transmitted from the most downstream RN, in period C without doing anything in period A and period B. Furthermore, since there is no RN positioned downstream of the most downstream RN among the plurality of RNs used in multihop communication, the most downstream RN does not transmit a relay signal for a downstream RN. 
         [0118]    Furthermore, the present embodiment has been described taking a case where an odd-numbered RN is an upstream RN and an even-numbered RN is a downstream RN as an example in  FIG. 4  and  FIG. 5 . However, the present invention is also applicable to a case where an even-numbered RN is an upstream RN and an odd-numbered RN is a downstream RN. More specifically, as in condition (1) described above, if both of the received signal strengths from two RNs (an even-numbered RN (upstream RN) and an odd-numbered RN (downstream RN)) are not less than pre-set threshold value α, a terminal may select connection to the even-numbered RN, which is an upstream RN. Then, upon connection of the terminal to the even-numbered RN, which is an upstream RN, the terminal may perform the processing performed in period A illustrated in  FIG. 5  in period B and the processing performed in period B illustrated in  FIG. 5  in period A. 
       Embodiment 2 
       [0119]    The present embodiment is similar to embodiment 1 in that, if a certain terminal is connectable to two relay apparatuses, the terminal selects connection to an upstream RN from among the two relay apparatuses. The present embodiment will be described of a case where the upstream RN further generates control information (performs scheduling) for a terminal connected to the downstream RN, using control information for the terminal connected to this relay apparatus. 
         [0120]    A specific explanation of the present embodiment will be provided below.  FIG. 7  is a block diagram illustrating a configuration of a relay apparatus according to the present embodiment. In relay apparatus  300  illustrated in  FIG. 7 , components that are the same as those of embodiment 1 ( FIG. 2 ) are provided with reference numerals that are the same as those of embodiment 1 and explanation of the components will be omitted. 
         [0121]    In relay apparatus  300  illustrated in  FIG. 7 , upon input of a relay signal for a terminal connected to relay apparatus  300  (terminal under the control of relay apparatus  300 ), scheduling section  301  extracts control information contained in the relay signal (that is, control information for the terminal under the control of relay apparatus  300 ). The control information contains, e.g., a mapping position and an MCS used when relay apparatus  300  relays data to the terminal in period C. Then, scheduling section  301  performs scheduling (determination of, e.g., a mapping position and an MCS) for a terminal connected to a relay apparatus (downstream RN) positioned downstream of relay apparatus  300  (terminal under the control of the downstream RN), using the control information for the terminal under the control of relay apparatus  300 . 
         [0122]    More specifically, scheduling section  301  determines a mapping position of a relay signal for the terminal under the control of the downstream RN, using the mapping position of the relay signal for the terminal under the control of relay apparatus  300  contained in the control information for the terminal under the control of relay apparatus  300 . For example, scheduling section  301  may determine a result of adding a fixed offset to the mapping position of the relay signal for the terminal under the control of relay apparatus  300 , as a mapping position of a relay signal for the terminal under the control of the downstream RN. Consequently, the terminal under the control of relay apparatus  300  identifies the mapping position of the relay signal for the terminal, enabling identification of a mapping position where an interference signal (relay signal for the terminal under the control of the downstream RN) is mapped. Alternatively, scheduling section  301  determines a mapping position where line quality is favorable among mapping positions for a relay signal for the terminal under the control of relay apparatus  300 , as a mapping position for a relay signal for the terminal under the control of the downstream RN, and can avoid determining a mapping position where line quality is poor, as a mapping position for a relay signal for the terminal under the control of the downstream RN. Consequently, the terminal under the control of relay apparatus  300  can identify a mapping position where an interference signal is mapped. Furthermore, since no interference signal is mapped in a mapping position with a poor line quality, the terminal under the control of relay apparatus  300  can receive a desired signal without a considerable decrease in reception quality due to an effect of interference in a mapping position with a poor line quality. 
         [0123]    Furthermore, scheduling section  301  determines an MCS of a relay signal for the terminal under the control of the downstream RN using the MCS of the relay signal for the terminal under the control of relay apparatus  300  contained in the control information for the terminal under the control of relay apparatus  300 . For example, scheduling section  301  may determine an MCS that is the same as the MCS of the relay signal for the terminal under the control of relay apparatus  300  as the MCS for a relay signal for the terminal under the control of the downstream RN. Consequently, the terminal under the control of relay apparatus  300  identifies the MCS of the relay signal for the relevant terminal, enabling identification of an MCS for an interference signal (relay signal for the terminal under the control of the downstream RN), too. Alternatively, scheduling section  301  may determine an MCS that provides multilevel modulation with low transfer rate for a mapping position with a favorable line quality among mapping positions for relay signals for the terminal under the control of relay apparatus  300 , and an MCS that provides multilevel modulation with high transfer rate for a mapping position with a poor line quality, as an MCS for a relay signal for the terminal under the control of the downstream RN. Consequently, the terminal under the control of relay apparatus  300  can increase contribution to interference removal processing for a known interference signal, enabling enhancement in precision of estimation of a desired signal. 
         [0124]    Then, scheduling section  301  outputs the control information for the terminal under the control of relay apparatus  300  and the control information for the terminal under the control of the downstream RN to second memory  105 . 
         [0125]    Transmission processing section  302  performs encoding and modulation of the relay signal for the terminal under the control of relay apparatus  300  and the control information for the terminal under the control of relay apparatus  300  input from second memory  105 , based on the control information for the terminal under the control of relay apparatus  300  input from second memory  105 . Also, transmission processing section  302  performs pre-set encoding and modulation of the relay signal for the terminal under the control of the downstream RN and the control information for the terminal under the control of the downstream RN, which are input from second memory  105 . 
         [0126]    Timing control section  303  gives an instruction to first memory  103  and second memory  105  about timings for inputting/outputting the control information for the terminal under the control of relay apparatus  300  and the control information for the terminal under the control of the downstream RN, in addition to the processing performed by timing control section  109  in embodiment 1. 
         [0127]    For example, if setting information input from odd/even number switching section  108  indicates “odd number” (if relay apparatus  300  is an odd-numbered RN), in period B, timing control section  303  instructs (gives a write instruction to) second memory  105  to store a scheduling result input from scheduling section  301  (the control information for the terminal under the control of relay apparatus  300  and the control information for the terminal under the control of the downstream RN), in addition to processing similar to that in timing control section  109 . Furthermore, in period B, when the decoded signal (relay signal) is stored in second memory  105 , timing control section  303  instructs (gives a read instruction to) second memory  105  to output the control information for the terminal under the control of relay apparatus  300  and the control information for the terminal under the control of the downstream RN to transmission processing section  302 , in addition to processing similar to that in timing control section  109 . 
         [0128]    Meanwhile, if the setting information input from odd/even number switching section  108  indicates “even number” (if relay apparatus  300  is an even-numbered RN), timing control section  303  performs, in period A, the above-described processing performed in period B when the setting information indicates “odd number.” In other words, period A and period B in timing control section  303  are interchanged between an odd-numbered RN and an even-numbered RN. 
         [0129]    Next, a terminal according to the present embodiment will be described.  FIG. 8  is a block diagram illustrating a configuration of the terminal according to the present embodiment. In terminal  400  illustrated in  FIG. 8 , components that are the same as those of embodiment 1 ( FIG. 3 ) are provided with reference numerals that are the same as those of embodiment 1, and explanation of the components will be omitted. 
         [0130]    In terminal  400  illustrated in  FIG. 8 , pointer generation section  401  generates a pointer for each storage address of control information for terminal  400  and of control information for a terminal under the control of a relay apparatus that is an RN positioned downstream of a serving cell (upstream RN) for terminal  400  using a DL subframe number input from timing control section  402 . 
         [0131]    It is assumed that the number of RNs that may be included in multihop communication, which is notified in advance, is N, the RN number of the serving cell for terminal  400  is L and a DL subframe number input from timing control section  402  is m, for example. Also, it is assumed that setting information in odd/even number switching section  213  is “odd number.” In this case, in period A in DL subframe m, pointer generation section  401  outputs a pointer indicating storage address [m−L] for the control information for terminal  400  and a pointer indicating storage address [m−L] for the control information for the terminal under the control of the downstream RN to timing control section  402 . Next, in period A, pointer generation section  401  outputs a pointer indicating storage address [m−N+1] for the control information for the terminal under the control of the downstream RN to timing control section  402 . Also, in period C in DL subframe m, pointer generation section  401  outputs a pointer indicating storage address [m−N+1] for the control information for terminal  400  to timing control section  402 . 
         [0132]    Timing control section  402  outputs a DL subframe number at the present time (for example, DL subframe number m) to pointer generation section  401 . Also, timing control section  402  gives an instruction to first memory  203  and second memory  210  about timings for inputting/outputting the control information for terminal  400  and the control information for the terminal under the control of the downstream RN using the pointers input from pointer generation section  401 , in addition to the processing performed by timing control section  214  ( FIG. 3 ) in embodiment 1. 
         [0133]    For example, if the setting information input from odd/even number switching section  213  indicates “odd number” (if the serving cell is an odd-numbered RN), in period A in DL subframe m, timing control section  402  instructs (gives a write instruction to) second memory  210  to store the control information for terminal  400  (storage address [m−L]) and the control information for the terminal under the control of the downstream RN (storage address [m−L]), in addition to the processing performed by timing control section  214 . Also, in period A, when an interference signal (relay signal for another terminal) is input from reception processing section  207  to second memory  210 , timing control section  402  instructs (gives a read instruction to) second memory  210  to output the control information for the downstream RN (storage address [m−N+1]) to reception processing section  207  (interference removal section  209 ), in addition to the processing performed by timing control section  214 . Consequently, interference removal section  209  performs encoding and modulation of the interference signal stored in second memory  210  based on the control information for the terminal under the control of the downstream RN (storage address [m−N+1]), and retains the interference signal after the modulation (replica of the interference signal in period C). Furthermore, in period C in DL subframe m, timing control section  402  instructs (gives a read instruction to) second memory  210  to output the control information for terminal  400  (storage address [m−N+1]) to reception processing section  207 , in addition to the processing in timing control section  214 . 
         [0134]    Meanwhile, if the setting information input from odd/even number switching section  213  indicates “even number” (if the serving cell is an even-numbered RN), timing control section  402  performs, in period B, the processing performed in period A when the setting information indicates “odd number.” In other words, the processing in period A and the processing in period B in timing control section  402  are interchanged between terminal  400  connected to an odd-numbered RN and terminal  400  connected to an even-numbered RN. 
         [0135]    Next, details of the scheduling processing in relay apparatus  300  according to the present embodiment will be described. 
         [0136]    The below explanation will be provided for a case where multihop communication is performed by four relay apparatuses RN# 1  to RN# 4  as illustrated in  FIG. 9  and  FIG. 10 . In  FIG. 9  and  FIG. 10 , RN# 1  is the most upstream RN and RN# 4  is the most downstream RN. RN# 1  to RN# 4  illustrated in  FIG. 9  and  FIG. 10  each include the configuration of relay apparatus  300  illustrated in  FIG. 7 . 
         [0137]    Also, in  FIG. 10 , for example, a scheduling result (control information) for a terminal under the control of an RN having a RN number of α is represented by “SCHEDULING FOR #α.” Also, in  FIG. 9  and  FIG. 10 , a storage address for control information for a terminal under the control of RN# 1  received by RN# 1  (odd-numbered RN) from an upstream apparatus (macrocell base station MeNB in  FIG. 10 ) in DL subframe [β] is represented by “[β].” Also, a storage address for control information for a terminal under the control of a downstream RN generated based on the control information in storage address [β] is represented by [β]. For example, control information for a terminal under the control of an RN with an RN number of 3, which is generated based on the control information received by RN# 1  in DL subframe [β] (SCHEDULING FOR # 1  [β]) is “SCHEDULING FOR # 3  [β].” Also, a terminal under the control of an RN with an RN number of α is represented by “TERMINAL#α.” 
         [0138]    Also, in  FIG. 10 , transmission processing is represented by “TX” and reception processing is represented by “RX.” 
         [0139]    Also, here, in  FIG. 9  and  FIG. 10 , an explanation will be provided focusing on processing from reception of control information for terminal# 1  under the control of RN# 1  (SCHEDULING FOR # 1  [m]) by RN# 1  (odd-numbered RN) in DL subframe [m] to processing to reflect the control information in the terminal. 
         [0140]    In DL subframe [m] illustrated in  FIG. 9  and  FIG. 10 , RN# 1  receives control information for terminal# 1  under the control of RN# 1  from the apparatus positioned upstream of RN# 1  (MeNB in  FIG. 10 ). More specifically, in period B in DL subframe [m] illustrated in  FIG. 10 , RN # 1  receives control information for terminal# 1  under the control of RN# 1  (SCHEDULING FOR # 1  [m] illustrated in  FIG. 10 ) from the upstream apparatus (MeNB) of RN# 1 . Then, scheduling section  301  in RN# 1  performs scheduling processing for terminal# 2  under the control of RN# 2 , which is a downstream RN of RN# 1 , using the control information for terminal# 1  under the control of RN# 1  (SCHEDULING FOR # 1  [m] illustrated in  FIG. 10 ). Consequently, scheduling section  301  in RN# 1  obtains control information for terminal# 2  under the control of RN# 2  (SCHEDULING FOR # 2  [m] illustrated in  FIG. 10 ). In other words, in DL subframe [m], as illustrated in  FIG. 9 , RN# 1  obtains scheduling results for terminal# 1  under the control of RN# 1  and terminal# 2  under the control of RN# 2 . 
         [0141]    Next, in DL subframe [m+1] illustrated in  FIG. 9  and  FIG. 10 , RN# 1  transmits the control information for terminal# 2  under the control of RN# 2  (SCHEDULING FOR # 2  [m] illustrated in  FIG. 10 ) in period A and RN# 2  receives the control information for terminal# 2  under the control of RN# 2 . Then, scheduling section  301  in RN# 2  performs scheduling processing for terminal# 3  under the control of RN# 3 , which is a downstream RN of RN# 2 , using the control information for terminal# 2  under the control of RN# 2  (SCHEDULING FOR # 2  [m] illustrated in  FIG. 10 ). Consequently, scheduling section  301  in RN# 2  obtains control information for terminal# 3  under the control of RN# 3  (SCHEDULING FOR # 3  [m] illustrated in  FIG. 10 ). In other words, in DL subframe [m+1], RN# 2  obtains scheduling results for terminal# 2  under the control of RN# 2  and terminal# 3  under the control of RN# 3  as illustrated in  FIG. 9 . 
         [0142]    Also, in DL subframe [m+2] illustrated in  FIG. 9  and  FIG. 10 , as in RN# 1  and RN# 2 , RN# 3  performs scheduling processing for # 4  terminal under the control of RN# 4 , which is a downstream RN of RN# 3 , using the control information for terminal# 3  under the control of RN# 3  received in period B from RN# 2  (SCHEDULING FOR # 3  [m] illustrated in  FIG. 10 ). Then, RN# 3  transmits control information for terminal# 4  under the control of RN# 4  (SCHEDULING FOR # 4  [m] illustrated in  FIG. 10 ) to RN# 4  in period A in DL subframe [m+3]. 
         [0143]    Then, in period C in DL subframe [m+3] illustrated in  FIG. 9  and  FIG. 10 , all of the RNs, i.e., RN# 1  to RN# 4 , simultaneously transmit relay signals for the terminals under the control of the respective RNs (TERMINALS# 1  to # 4  in  FIG. 10 ) based on the scheduling results determined in DL subframes [m] to [m+2] (SCHEDULING FOR # 1  TO # 4  [m] illustrated in  FIG. 9 ) to reflect the scheduling results in the terminals. More specifically, as illustrated in  FIG. 10 , RN# 1  transmits a relay signal for terminal# 1  under the control of RN# 1  in period C (TERMINAL# 1 @SCHEDULING [m] TX illustrated in  FIG. 10 ) using the control information for terminal# 1  obtained in DL subframe [m] (SCHEDULING FOR # 1  [m] illustrated in  FIG. 10 ). Likewise, as illustrated in  FIG. 10 , RN# 2  transmits a relay signal for terminal# 2  under the control of RN# 2  in period C (TERMINAL# 2 @SCHEDULING [m] TX illustrated in  FIG. 10 ) using the control information for terminal# 2  obtained in DL subframe [m+1] (SCHEDULING FOR # 2  [m] illustrated in  FIG. 10 ). The same applies to RN/13 and RN# 4 . 
         [0144]    Next, details of the interference removal processing in terminal  400  according to the present embodiment will be described. 
         [0145]    The below explanation will be provided for a case where multihop communication is performed by four relay apparatuses RN# 1  to RN# 4  (RN count N=4) as in  FIG. 9  and  FIG. 10 . However, in  FIG. 11 , two RN# 1  and RN# 2  among RN# 1  to RN# 4  will be illustrated. Furthermore, as in  FIG. 9  and  FIG. 10 , RN# 1  is the most upstream RN and RN# 4  is the most downstream RN. In other words, in RN# 1  and RN# 2  in  FIG. 11 , RN# 1  is an upstream RN and RN# 2  is a downstream RN. Also, in  FIG. 11 , terminal# 1  is connected to RN# 1  and terminal# 2  is connected to RN# 2 . RN# 1  and RN# 2  illustrated in  FIG. 11  each include the configuration of relay apparatus  300  illustrated in  FIG. 7 , and terminal# 1  and terminal# 2  each include the configuration of terminal  400  illustrated in  FIG. 8 . 
         [0146]    Also, in  FIG. 11 , a relay signal for terminal# 1  under the control of RN# 1 , which is received by RN/41 (with an RN number L of 1) in DL subframe [β] from an upstream apparatus (MeNB in  FIG. 11 ) is represented by “FOR TERMINAL# 1  [β].” Also, a storage address for control information for terminal# 1  contained in the relay signal (for terminal# 1  [β]) is represented by “[β],” and a storage address for control information for a terminal under the control of a downstream RN generated based on the control information in storage address [β] is represented by [β]. Also, in  FIG. 11 , a relay signal transmitted by an RN with an RN number of a to a terminal under the control of the RN with an RN number of a in period C in DL subframe [β] is represented by “TERMINAL#a@[β−N+1].” This means a relay signal transmitted based on control information for a terminal (storage address [β−N+1]). 
         [0147]    Also, in  FIG. 11 , signal transmission processing is represented by “TX” and signal reception processing is represented by “RX.” 
         [0148]    First, an operation of terminal  400  in periods A to C in DL subframe m illustrated in  FIG. 11  will be described. The below explanation will be provided taking an operation of a terminal under the control of an odd-numbered RN whose RN number L is an odd number (# 1  terminal under the control of RN # 1  (L=1) in  FIG. 11 ) as an example. For processing in a terminal under the control of an even-numbered RN whose RN number L is an even number (terminal# 2  under the control of RN# 2  (L=2) in  FIG. 11 ), the later-described processing in period B for the terminal under the control of the odd-numbered RN may be performed in period A and the processing in period A for the terminal under the control of the odd-numbered RN may be performed in period B. 
         [0149]    In period A in DL subframe [m] illustrated in  FIG. 11 , terminal  400  (terminal under the control of an RN with an RN number of L) receives a signal from RN# 1  to RN# 2 , thereby receiving a relay signal for terminal  400  and a relay signal (storage address [m−L]) for a terminal under the control of a downstream RN. For example, in period A in DL subframe [m] illustrated in  FIG. 11 , terminal# 1  under the control of RN# 1  (with an RN number L of 1) receives a relay signal for terminal# 1  and a relay signal for terminal# 2  (FOR TERMINALS# 1  AND # 2  [m−1] in  FIG. 11 ). Here, control information for terminal# 1  (FOR TERMINAL# 1  [m−1]) contained in FOR TERMINALS# 1  AND # 2  [m−1] is control information received by RN# 1  from MeNB in non-illustrated DL subframe [m−1]. Also, control information for terminal# 2  (FOR TERMINAL# 2  [m−1]) is control information generated by RN# 1  in non-illustrated DL subframe [m−1] using the control information for terminal# 1 . 
         [0150]    Then, as in embodiment 1, terminal# 1  obtains a channel estimation value between terminal# 1  and RN# 1  (channel estimation value for a desired signal) from a preamble signal contained in the relay signal, and outputs the channel estimation value to second memory  210 . Also, terminal# 1  demodulates and decodes the control information contained in the respective relay signals (FOR TERMINALS# 1  AND # 2  [m−1]) to obtain the control information for terminal# 1  (storage address [m−1]) and the control information for terminal# 2  (storage address [m−1]), and stores the control information for terminal# 1  and the control information for terminal# 2  in second memory  210 . Then, terminal# 1  demodulates and decodes an interference signal (FOR TERMINAL# 2  [m−1]) using control information contained in a relay signal between RNs in period A (control information containing a mapping position of the interference signal in the relay signal and an MCS: For example, the control information illustrated in  FIG. 6 ) and a channel estimation value between terminal# 1  and RN# 1 . Then, in terminal# 1 , the decoded interference signal, the control information for terminal# 1  (storage address [m−1]) and the control information for terminal# 2  (storage address[m−1]) are stored in second memory  210 . 
         [0151]    Furthermore, in period A, when an interference signal is stored in second memory  210 , terminal  400  outputs the interference signal and control information for a terminal under the control of a downstream RN (storage address [m−N+1]), which are stored in second memory  210 , to interference removal section  209 . For example, terminal# 1  illustrated in  FIG. 11  outputs the interference signal (that is, the relay signal for terminal# 2 ) and the control information for terminal# 2  under the control of RN# 2  (storage address [m−3]) to interference removal section  209 . Then, interference removal section  209  in terminal# 1  encodes and modulates the interference signal using the control information for terminal# 2  (storage address [m−3]), and retains the modulated interference signal (replica of the interference signal in period C in DL subframe [m]). 
         [0152]    In period Bin DL subframe [m] illustrated in  FIG. 11 , terminal  400  (terminal under the control of an odd-numbered RN) performs processing similar to that performed by terminal  200  in embodiment 1 in period B. For example, terminal# 1  illustrated in  FIG. 11  receives a relay signal for terminal# 2  and a relay signal for the # 3  terminal (FOR TERMINALS# 2  AND # 3  [m−2] in  FIG. 11 ) transmitted from RN# 2  to RN# 3 . Using a preamble signal contained in the relay signal, terminal# 1  illustrated in  FIG. 11  obtains a channel estimation value between RN# 2  and terminal# 1  (channel estimation value for an interference signal). 
         [0153]    In period C in DL subframe [m] illustrated in  FIG. 11 , terminal  400  (terminal under the control of an odd-numbered RN) outputs a channel estimation value between the upstream RN and terminal  400  (calculated in period A) and the previously-received control information for terminal  400  (storage address [m−N+1]), which are stored in second memory  210  to interference removal section  209 . For example, in period A in DL subframe [m] illustrated in  FIG. 11 , terminal# 1  under the control of RN # 1  outputs the channel estimation value between RN# 1  and terminal# 1  and the control information for terminal# 1  (storage address [m−3]) to reception processing section  207 . Then, in period C, interference removal section  209  in terminal# 1  removes the relay signal for terminal# 2  (TERMINAL# 2 @[m−3] illustrated in  FIG. 11 ), which is an interference signal from RN# 2 , from the signal received in period C, using the channel estimation value between RN# 1  and terminal# 1 , the channel estimation value between RN# 2  and terminal# 1 , the replica of the interference signal and the control information for terminal# 1  (storage address [m−3]), thereby obtaining the relay signal for terminal# 1  (TERMINAL# 1 @[m−3] illustrated in  FIG. 11 ), which is a desired signal from RN# 1 . 
         [0154]    Next, an explanation will be provided with reference to  FIG. 11 , focusing on processing from RN# 1  (odd-numbered RN)&#39;s reception of the relay signal for terminal# 1  under the control of RN# 1  (FOR TERMINAL# 1  [m]) in DL subframe [m] to RN# 1  (odd-numbered RN)&#39;s transmission of the relay signal to terminal# 1 . 
         [0155]    As illustrated in  FIG. 9  and  FIG. 10 , upon reception of the relay signal for terminal# 1  (FOR TERMINAL# 1  [m]) in period B in DL subframe [m] illustrated in  FIG. 11 , RN# 1  (scheduling section  301 ) generates control information for terminal# 2  under the control of the downstream RN (storage address [m]) using the control information for terminal# 1  contained in the relay signal for terminal# 1  (FOR TERMINAL# 1  [m]). 
         [0156]    Then, in period A in DL subframe [m+1], RN# 1  transmits a relay signal containing the control information for terminal# 1  and the control information for terminal# 2  (FOR TERMINALS# 1  AND # 2  [m] illustrated in  FIG. 11 ) to RN# 2 . At this time, terminal# 1  receives the relay signal (FOR TERMINALS# 1  AND # 2  [m] illustrated in  FIG. 11 ) transmitted from RN# 1  to RN# 2 . Then, as described above, terminal# 1  obtains the interference signal (relay signal for terminal# 2 ), the channel estimation value between RN# 1  and terminal# 1 , the control information for terminal# 1  and the control information for terminal# 2 , using the relay signal (FOR TERMINALS# 1  AND # 2  [m] illustrated in  FIG. 11 ). Also, terminal# 1  encodes and modulates the interference signal using the control information for terminal# 2  (storage address [m−2]) and the interference signal to generate a replica of the interference signal in period C in DL subframe [m+1]. 
         [0157]    Also, upon receipt of the relay signal (FOR TERMINALS# 1  AND # 2  [m] illustrated in  FIG. 11 ) in period A in DL subframe [m+1], RN# 2  generates control information for terminal# 3  (not illustrated) (storage address [m]) under the control of RN# 3  (not illustrated), which is a downstream RN, using the control information for terminal# 2  contained in the relay signal. 
         [0158]    Then, in period B in DL subframe [m+2], RN# 2  transmits a relay signal containing the control information for terminal# 2  and the control information for terminal# 3  (FOR TERMINALS# 2  AND # 3  [m] illustrated in  FIG. 11 ) to RN# 3  (not illustrated). At this time, terminal# 1  receives the relay signal transmitted from RN# 2  to RN# 3  (FOR TERMINALS# 2  AND # 3  [m] illustrated in  FIG. 11 ). Then, as described above, terminal# 1  obtains a channel estimation value between RN# 2  and terminal# 1  using the relay signal (FOR TERMINALS# 2  AND # 3  [m] illustrated in  FIG. 11 ). 
         [0159]    Then, in period C in DL subframe [m+3], RN# 1  transmits the relay signal for terminal# 1  (TERMINAL# 1 @[m] illustrated in  FIG. 11 ) to terminal# 1 , and RN# 2  transmits the relay signal for terminal# 2  (TERMINAL# 2 @[m] illustrated in  FIG. 11 ) to terminal# 2 . Accordingly, the signal received by terminal# 1  contains the relay signal for terminal# 1  (TERMINAL# 1 @[m] illustrated in  FIG. 11 ) and the relay signal for terminal# 2  (TERMINAL# 2 @[m] illustrated in  FIG. 11 ). 
         [0160]    Therefore, as illustrated in  FIG. 11 , terminal# 1  removes the relay signal for terminal# 2  (TERMINAL# 2 @[m] illustrated in  FIG. 11 , that is, interference signal) from the signal received by terminal# 1  in period C, using the interference signal (replica of the interference signal in period C), the channel estimation value between RN# 1  and terminal# 1  and the control information for terminal# 1 , which were obtained in period A in DL subframe [m+3], and the channel estimation value between RN# 2  and the # 1  terminal obtained in period B, thereby obtaining a relay signal for terminal# 1  (TERMINAL# 1 @[m] illustrated in  FIG. 11 , that is, a desired signal). 
         [0161]    As described above, in the present embodiment, the upstream RN (relay apparatus  300 ) performs scheduling processing for a terminal under the control of a downstream RN based on scheduling for a terminal under the control of this relay apparatus. Then, during communication between RNs (in period A or period B), the upstream RN (relay apparatus  300 ) transmits a relay signal containing control information for the terminal under the control of this relay apparatus and control information for the terminal under the control of the downstream RN to the downstream RN. Consequently, in period A or period B, terminal  400  connected to the upstream RN can receive control information for terminal  400  and the control information for the terminal under the control of the downstream RN without interference. 
         [0162]    Consequently, terminal  400  can recognize not only a mapping position and an MCS of a relay signal for terminal  400  (desired signal) but also a mapping position and an MCS of a relay signal for another terminal (interference signal) before a time when terminal  400  actually receives the relay signal that becomes an interference signal (period C). Accordingly, terminal  400  can start preparation for interference removal processing (for example, processing for generating a replica of an interference signal or processing for selecting an interference removal method) at a point of time when terminal  400  obtains a signal that becomes the interference signal in period C (period A or period B), enabling a decrease in time required for reception processing for obtaining a desired signal. 
         [0163]    As described above, according to the present embodiment, even in a case where multihop communication is performed between a plurality of relay apparatuses using the same frequency, as in embodiment 1, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reduced. Furthermore, according to the present embodiment, a terminal can reliably obtain control information relating to an interference signal for removing the interference signal. Thus, it is made possible to ensure reduction in interference to a signal from a relay apparatus to which the terminal is connected, by a signal from another relay apparatus. 
         [0164]    In the present embodiment, an explanation has been given, with reference to  FIG. 11 , of a case where terminal  400  under the control of an odd-numbered RN obtains control information for terminal  400  in period A (period B in the case of terminal  400  under the control of an even-numbered RN) and uses the control information in period C. However, the present invention is not limited to the case shown in  FIG. 11 . Terminal  400  may obtain control information for terminal  400  transmitted from an upstream RN in period C and use the control information. Likewise, in the present embodiment, an explanation has been given of a case where terminal  400  under the control of an odd-numbered RN obtains a channel estimation value between the odd-numbered RN and terminal  400  in period A and uses the channel estimation value in period C. However, the preset invention is not limited to this case. Terminal  400  may obtain a channel estimation value from a relay signal for terminal  400  transmitted from an upstream RN in period C and use the channel estimation value. 
         [0165]    Also, the present embodiment has been described of a case where there is an RN positioned downstream of an RN to which a terminal is connected. However, since there is no downstream RN for the most downstream RN (RN farthest from a base station) among a plurality of RNs used in multihop communication, there occurs no interference due to a signal transmitted from an RN other than the most downstream RN in a terminal connectable only to the downstream RN. Accordingly, the terminal connected to the most downstream RN may receive a relay signal for the terminal transmitted from the most downstream RN in period C without doing anything in period A or period B. Then, the terminal may demodulate and decode the relay signal (data signal) in period C using a channel estimation value between the most downstream RN and the terminal, which is calculated using a preamble signal contained in the relay signal, and a mapping position and an MCS contained in control information contained in the relay signal. Also, the most downstream RN among the plurality of RNs used in multihop communication has no RN positioned downstream of this RN and thus, does not transmit a relay signal for a downstream RN. 
         [0166]    Also, the present embodiment has been described of a case where an upstream RN among two adjacent RNs performs scheduling for a terminal under the control of a downstream RN. However, among a plurality of RNs performing multihop communication, the most upstream RN (or a macrocell base station) may perform scheduling for terminals under the control of all of the RNs (that is, all of the RNs positioned downstream). 
       Embodiment 3 
       [0167]    The present embodiment is similar to embodiment 2 in that a terminal performs interference removal processing using control information for the terminal itself and control information for another terminal (control information on an interference signal), but different from embodiment 2 in the method for providing notification of control information used by the terminal. 
         [0168]    In general, in a plurality of relay apparatuses (RN) included in multihop communication as described above are provided with a guard time for switching between transmission processing and reception processing. 
         [0169]    An explanation will be given of case where an odd-numbered RN (upstream RN) and an even-numbered RN (downstream RN) adjacent to each other perform communication in period A to period C in a certain DL subframe, for example. In this example, the odd-numbered RN transmits a relay signal to the downstream RN in period A and receives a relay signal from an upstream apparatus in period B. Meanwhile, the even-numbered RN receives a relay signal from the upstream RN in period A and transmits a relay signal to a downstream RN in period B. In other words, the transmission processing and the reception processing are switched between period A and period B in the odd-numbered RN and the even-numbered RN (that is, all of the RNs). Accordingly, each of the RNs needs to have a guard time between period A and period B. 
         [0170]    Also, the odd-numbered RN and the even-numbered RN transmit a relay signal to terminals under the control of the respective RNs in period C. Accordingly, between period B and period C, transmission processing and reception processing are switched in the odd-numbered RN while the even-numbered RN continues transmission processing. Accordingly, the odd-numbered RN needs to have a guard time between period B and period C. Meanwhile, the even-numbered RN does not need to have a guard time between period B and period C. In other words, in a period corresponding to a guard time between period B and period C, the odd-numbered RN cannot transmit a signal because of the switching between transmission/reception processing, while the even-numbered RN can transmit a signal because the even-numbered RN continues transmission processing. 
         [0171]    As described above, in a guard time provided for the switching between transmission/reception processing in one RN (odd-numbered RN in the above example) among a plurality of adjacent RNs (a plurality of RNs to which a certain terminal is connectable), another RN (even-numbered RN in the above example) can transmit a signal to a terminal without interference owing to a signal from the one RN. 
         [0172]    Also, in a radio communication system according to the present embodiment, downlink and uplink are alternately switched on a per subframe basis. In other words, immediately after (or immediately before) a DL subframe, an uplink subframe (hereinafter referred to as UL subframe) exists. More specifically, an UL subframe exists after period C among period A to period C in the above-described DL subframe. 
         [0173]    Thus, in a plurality of relay apparatuses (RNs) included in multihop communication, a guard time is provided also when downlink and uplink are switched. For example, after the above-described DL subframe (in other words, after period C), a guard time is provided. Then, during the guard time, the plurality of RNs perform no transmission/reception processing. 
         [0174]    Accordingly, in a guard time provided between downlink and uplink, only one RN (for example, an odd-numbered RN) among a plurality of adjacent RNs (RNs to both of which a certain terminal is connectable) transmits a signal, thereby enabling transmission of the signal to the terminal without interference owing to a signal from another RN (for example, an even-numbered RN). 
         [0175]    Therefore, in the present embodiment, one relay apparatus among two adjacent relay apparatuses to both of which a certain terminal is connectable in a plurality of relay apparatuses (RNs) included in multihop communication transmits control information for a terminal under the control of the one relay apparatus in a guard time provided for switching between transmission/reception processing in the other relay apparatus, and the other relay apparatus transmits control information for a terminal under the control of the other relay apparatus in a guard time provided between downlink and uplink. 
         [0176]    A more specific explanation of the present embodiment will be provided below. The present embodiment will be described for a radio communication system in which downlink and uplink are switched on a per subframe basis, a guard time (first guard time) is provided between a DL subframe and a UL subframe, and a guard time (second guard time) is provided between period B and period C in DL subframe m. 
         [0177]      FIG. 12  is a block diagram illustrating a configuration of a relay apparatus according to the present embodiment. In relay apparatus  500  illustrated in  FIG. 12 , components that are the same as those of embodiment 1 ( FIG. 2 ) are provided with reference numerals that are the same as those of embodiment 1, and explanation of the components will be omitted. 
         [0178]    In relay apparatus  500  illustrated in  FIG. 12 , timing control section  501  provides a guard time between period A and period B in each DL subframe, provides a guard time between period B and period C, and also provides a guard time between a DL subframe and a UL subframe, in addition to the processing performed by timing control section  109  in embodiment 1. 
         [0179]    However, timing control section  501  controls input/output timings for first memory  103  and second memory  105  so as to transmit control information for a terminal under the control of relay apparatus  500  in either one of the guard time between period B and period C and the guard time between downlink and uplink. 
         [0180]    For example, if setting information input from odd/even number switching section  108  indicates “odd number” (if relay apparatus  500  is an odd-numbered RN), timing control section  501  instructs (gives a read instruction to) second memory  105  to output the control information for the terminal under the control of relay apparatus  500  to transmission processing section  106  and instructs (gives a read instruction to) first memory  103  to output the control information for the terminal under the control of relay apparatus  500  to RF transmitting section  107  after period C, that is, a period corresponding to the guard time between downlink and uplink (hereinafter referred to as period post-C), in addition to processing similar to that in timing control section  109 . 
         [0181]    Meanwhile, if the setting information input from odd/even number switching section  108  indicates “even number”, timing control section  501  instructs (gives a read instruction to) second memory  105  to output the control information for the terminal under the control of relay apparatus  500  to transmission processing section  106  and instructs (gives a read instruction to) first memory  103  to output the control information for the terminal under the control of relay apparatus  500  to RF transmitting section  107  in a period corresponding to the guard time between period B and period C (hereinafter referred to as period pre-C), in addition to processing similar to that in timing control section  109 . 
         [0182]    Next, a terminal according to the present embodiment will be described.  FIG. 13  is a block diagram illustrating a configuration of a terminal according to the present embodiment. In terminal  600  illustrated in  FIG. 13 , components that are the same as those of embodiment 1 ( FIG. 3 ) are provided with reference numerals that are the same as those of embodiment 1 and explanation of the components will be omitted. 
         [0183]    In terminal  600  illustrated in  FIG. 13 , timing control section  601  controls input/output timings for first memory  203  and second memory  210  so as to receive control information for terminal  600  in either one of two periods, i.e., period pre-C corresponding to the guard time between period B and period C and period post-C corresponding to the guard time between downlink and uplink, and receive control information for a terminal under the control of a downstream RN in the other period, in addition to the processing in timing control section  214  ( FIG. 3 ) in embodiment 1. 
         [0184]    For example, a case where setting information input from odd/even number switching section  213  indicates “odd number” (if a serving cell is an odd-numbered RN) will be described. In this case, timing control section  601  instructs (gives a write instruction to) first memory  203  to store the control information for the terminal under the control of the downstream RN, which is input from RF receiving section  202  (that is, control information on an interference signal) in a period corresponding to the guard time between period B and period C (period pre-C). Also, in period pre-C, when the control information for the terminal under the control of the downstream RN is stored in first memory  203 , timing control section  601  instructs (gives a read instruction to) first memory  203  to output the control information for the terminal under the control of the downstream RN to reception processing section  207 , and instructs (gives a write instruction to) second memory  210  to store the control information for the terminal under the control of the downstream RN, which is input from reception processing section  207 . Also, in period pre-C, when a decoded signal (signal that becomes an interference signal in period C) is stored in second memory  210 , timing control section  601  instructs (gives a read instruction to) second memory  210  to output the interference signal (relay signal for the terminal under the control of the downstream RN) and the control information for the terminal under the control of the downstream RN to reception processing section  207  (interference removal section  603 ). 
         [0185]    Also, in the period corresponding to the guard time between downlink and uplink (period post-C), timing control section  601  instructs (gives a write instruction to) first memory  203  to store the control information for terminal  600 , which is input from RF receiving section  202 . Also, in period post-C, upon the control information for terminal  600  being stored in first memory  203 , timing control section  601  instructs (gives a read instruction to) first memory  203  to output the control information for terminal  600  to reception processing section  207  (receiving section  602 ) and instructs (gives a write instruction to) second memory  210  to store the control information for terminal  600  input from reception processing section  207  (receiving section  602 ). 
         [0186]    Meanwhile, if the setting information input from odd/even number switching section  213  indicates “even number” (if the serving cell is an even-numbered RN), timing control section  601  performs the processing performed in period pre-C where the setting information indicates “odd number” in period post-C, and performs the processing performed in period post-C where the setting information indicates “odd number” in period pre-C. In other words, the processing in period pre-C and the processing in period post-C in timing control section  601  are interchanged between an odd-numbered RN and an even-numbered RN. 
         [0187]    In period pre-C or period post-C, upon the control information for the terminal for the downstream RN (another terminal) being input from first memory  203 , receiving section  602  of reception processing section  207  demodulates and decodes the control information for the terminal under the control of the downstream RN in addition to the processing in receiving section  208  in embodiment 1. Consequently, receiving section  602  obtains, e.g., a mapping position and an MCS of an interference signal (relay signal for the terminal under the control of the downstream RN). Then, receiving section  602  outputs the control information for the terminal under the control of the downstream RN after the decoding to second memory  210 . Furthermore, in period pre-C or period post-C, upon the control information for terminal  600  being input from first memory  203 , receiving section  602  demodulates and decodes the control information for terminal  600 . Consequently, receiving section  602  obtains, e.g., a mapping position and an MCS of a relay signal for terminal  600  (desired signal). Then, receiving section  602  outputs the control information for terminal  600  after the decoding to second memory  210 . 
         [0188]    As in interference removal section  209  according to embodiment 1, in period pre-C or period post-C, upon the interference signal (relay signal for the terminal under the control of the downstream RN) and the control information for the terminal under the control of the downstream RN being input from second memory  210 , interference removal section  603  of reception processing section  207  encodes and modulates the interference signal using the control information for the terminal under the control of the downstream RN. Then, interference removal section  603  retains the interference signal after the modulation (replica of the interference signal in period C). Then, as in embodiment 1, interference removal section  603  removes the interference signal from the signal received in period C, using the interference signal after the modulation, a channel estimation value between an upstream RN and terminal  600 , a channel estimation value between the downstream RN and terminal  600  and the control information for terminal  600  (the mapping position and the MCS of the desired signal), thereby obtaining a relay signal for terminal  600  (desired signal). 
         [0189]    Next, details of processing in relay apparatus  500  and terminal  600  according to the present embodiment will be described. 
         [0190]    The below explanation will be provided in terms of a case where multihop communication is performed by three or more RNs. However, in  FIG. 14 , only two RNs  1  and  2  among the three or more RNs are illustrated. Also, RN 1  is an upstream RN and RN  2  is a downstream RN between RN 1  and RN 2  illustrated in  FIG. 14 . Furthermore, in  FIG. 14 , MS 1  is connected to RN 1 , and MS 2  is connected to RN 2 . RN 1  and RN 2  illustrated in  FIG. 14  each include the configuration of relay apparatus  500  illustrated in  FIG. 12 , and MS 1  and MS 2  each include the configuration of terminal  600  illustrated in  FIG. 13 . 
         [0191]    Also, in  FIG. 14 , transmission processing is represented by “TX,” and reception processing is represented by “RX.” 
         [0192]    Here, an explanation will be provided focusing on interference removal processing in MS 1  connected to RN 1  (MS 1  under the control of RN 1 ). 
         [0193]    In period A in the DL subframe illustrated in  FIG. 14 , RN 1  transmits a relay signal for a terminal (MS 2 ) under the control of RN 2 , which is a downstream RN of RN 1 , to RN 2 , and RN 2  receives the relay signal for the terminal (MS 2 ) under the control of RN 2 . At this time, MS 1  (terminal under the control of RN 1 ) positioned between RN 1  and RN 2  receives the relay signal for the terminal (MS 2 ) under the control of RN 2  transmitted from RN 1  to RN 2 . Consequently, as in embodiment 1, MS 1  obtains the relay signal for MS 2  (signal that becomes an interference signal in period C) and a channel estimation value between RN 1  and MS 1 . 
         [0194]    Next, RN 1  and RN 2  (timing control section  501 ) provide a guard time between period A and period B illustrated in  FIG. 14 . 
         [0195]    Next, in period B in the DL subframe illustrated in  FIG. 14 , RN 1  receives a relay signal for MS 1  under the control of RN 1  from an upstream apparatus (MeNB in  FIG. 14 ). Meanwhile, RN 2  transmits a relay signal for MS 3  (not illustrated) under the control of RN 3 , which is a downstream RN of RN 2 , to RN 3 . At this time, MS 1  receives the relay signal for MS 3  under the control of RN 3  transmitted from RN 2  to RN 3 . Consequently, MS 1  obtains a channel estimation value between RN 2  and MS 1  (channel estimation value for the interference signal in period C) as in embodiment 1. 
         [0196]    Next, RN 1  (timing control section  501 ) provides a guard time (period pre-C) between period B and period C illustrated in  FIG. 14 . Meanwhile, in period pre-C corresponding to the guard time provided by RN 1 , RN 2  transmits control information for MS 2  under the control of RN 2  to MS 2 . At this time, MS 1  receives the control information for MS  2  (control information on the interference signal in period C) transmitted from RN 2  to MS 2 . 
         [0197]    Here, in period pre-C illustrated in  FIG. 14 , RN 1  does nothing because of the switching between transmission/reception processing between period B (reception processing) and period C (transmission processing) (provides a guard time). Meanwhile, in period pre-C illustrated in  FIG. 14 , RN 2  can transmit a signal even in period pre-C because both period B and period C relate to transmission processing. Accordingly, in period pre-C illustrated in  FIG. 14 , MS 1  can receive a signal (control information of the interference signal) from RN 2  without interference owing to a signal from RN  1 . Then, in period pre-C, MS 1  (interference removal section  603 ) encodes and modulates the interference signal (relay signal for MS  2 ) obtained in period A, using the control information of the interference signal obtained in period pre-C, thereby obtaining the demodulated interference signal (replica of the interference signal in period C). 
         [0198]    Next, in period C in DL subframe illustrated in  FIG. 14 , RN 1  transmits the relay signal for MS 1  under the control of RN 1  to MS 1 , and RN 2  transmits the relay signal for MS 2  under the control of RN 2  to MS 2 . Accordingly, as illustrated in  FIG. 14 , MS 1  receives a signal containing the relay signal for MS 1  from RN 1  (desired signal) and the relay signal for MS 2  from RN 2  (interference signal). 
         [0199]    Next, after period C illustrated in  FIG. 14 , that is period post-C corresponding to the guard time between the DL subframe and a UL subframe (not illustrated), RN 1  transmits the control information for the MS 1  under the control of RN 1  to MS 1 . Then, MS 1  receives the control information for MS 1  transmitted from RN 1  to MS 1  (control information on the desired signal). Meanwhile, RN 2  (timing control section  501 ) provides a guard time (period post-C) between the DL subframe illustrated in  FIG. 14  and the UL subframe (not illustrated). 
         [0200]    Here, in period post-C illustrated in  FIG. 14 , RN 2  does nothing (provides a guard time) because of switching between downlink and uplink. Meanwhile, in period post-C illustrated in  FIG. 14 , RN 1  transmits the control information for the terminal under the control of RN 1 . Accordingly, as in period pre-C, in period post-C illustrated in  FIG. 14 , MS 1  can receive the signal from RN 1  (control information on the desired signal) without interference owning to the signal from RN 2 . 
         [0201]    Then, as in embodiment 1, MS 1  (interference removal section  603 ) illustrated in  FIG. 14  removes the interference signal (relay signal for MS 2 ) transmitted by RN 2  in period C from the signal received in period C, using the interference signal (interference signal modulated in period pre-C) obtained in period A, the channel estimation value between RN 1  and MS 1  (channel estimation value of the desired signal) obtained in period A, the channel estimation value between RN 2  and MS 1  (channel estimation value for the interference signal) obtained in period B and control information on the desired signal (control information for MS 1 ) obtained in period post-C, thereby obtaining the desired signal (relay signal for MS 1 ). 
         [0202]    Here, the explanation has been provided for terminal  600  (MS 1 ) under the control of an odd-numbered RN (RN 1 ). Meanwhile, in the case of terminal  600  (MS 2 ) under the control of an even-numbered RN (RN 2 ), the processing in period A and the processing in period pre-C in the terminal under the control of the odd-numbered RN may be performed in period B and period post-C, the processing in period B and the processing in period post-C in the terminal under the control of the odd-numbered RN may be performed in period A and period pre-C. 
         [0203]    For example, in period A, MS 2  under the control of RN 2  illustrated in  FIG. 14  (even-numbered RN) receives a relay signal for a terminal under the control of RN 4  transmitted from RN 3  (not illustrated), and obtains a channel estimation value between RN 3  and MS 2  (channel estimation value for an interference signal). Also, in period B, MS 2  receives a relay signal for MS 3  under the control of RN  3 , which is transmitted from RN 2 , and obtains an interference signal for MS 2  and a channel estimation value between RN 2  and MS 2  (channel estimation value for a desired signal). Also, in period pre-C, MS 2  obtains control information for MS 2  (control information on the desired signal) transmitted from RN 2 . Also, in period post-C, MS 2  obtains control information for MS 3  (control information on the interference signal) transmitted from RN 3  (not illustrated). Consequently, as in a terminal under the control of an odd-numbered RN (MS 1  in  FIG. 14 ), a terminal under the control of an even-numbered RN (MS 2  in  FIG. 14 ) removes an interference signal from a signal received in period C, thereby obtaining a desired signal. 
         [0204]    As described above, in the present embodiment, relay apparatus  500  (every RN) transmits control information for a terminal under the control of relay apparatus  500  in either one of a guard time between period B and period C (guard time provided for switching between transmission/reception processing (period pre-C)) and a guard time between downlink and uplink (guard time provided for switching between downlink and uplink (period post-C)). Then, in the guard time between period B and period C or the guard time between downlink and uplink, terminal  600  receives control information for terminal  600  (control information on a desired signal) transmitted from an upstream RN and control information for another terminal (control information on an interference signal) transmitted from a downstream RN. 
         [0205]    More specifically, in the guard time between period B and period C, terminal  600  can receive control information from a relay apparatus not needing switching between transmission/reception processing (even-numbered RN in  FIG. 14 ), without interference owing to a signal from a relay apparatus needing switching between transmission/reception processing (odd-numbered RN in  FIG. 14 ). 
         [0206]    Likewise, in the guard time between downlink and uplink, terminal  600  can receive control information from one relay apparatus among two adjacent relay apparatuses to which terminal  600  is connectable (that is, a relay apparatus needing to provide a guard time between period B and period C; the odd-numbered RN in  FIG. 14 ), without interference owing to a signal from the other relay apparatus (the even-numbered RN in  FIG. 14 ). 
         [0207]    As described above, according to the present embodiment, even if multihop communication is performed between a plurality of relay apparatuses using the same frequency, as in embodiment 1, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reduced. Furthermore, according to the present embodiment, a terminal can reliably obtain control information on an interference signal, using a guard time for switching between transmission/reception processing in a relay apparatus or a guard time for switching between downlink and uplink for communication of control information. Thus, in the present embodiment, as in embodiment 2, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can reliably be reduced. 
         [0208]    The present embodiment has been described for a case where, for example, in period pre-C and period post-C illustrated in  FIG. 14 , control information (e.g., a mapping position and an MCS) for a desired signal and control information on an interference signal are transmitted. However, for example, in period pre-C and period post-C illustrated in  FIG. 14 , not only control information such as a mapping position and an MCS but also other data may be transmitted. Examples of information transmitted in period pre-C and period post-C can include information providing notification of change in configuration of a multihop communication network (number of RNs after the change or an RN number of an newly-added RN), information indicating a data type of the relay signal, notification of handover, a known signal for performing channel estimation and information indicating an interference level. 
       Embodiment 4 
       [0209]    While embodiments 1 to 3 have been described for multihop communication in downlink, the present embodiment will be described for multihop communication in uplink. 
         [0210]    As illustrated in  FIG. 15 , the below explanation will be provided for a radio communication system in which communication in uplink is performed by a base station and terminals via a plurality of relay apparatuses in a unit of a subframe (UL subframe) including period A′ for communication between the plurality of relay apparatuses and the terminals and period B′ and period C′ for communication between the plurality of relay apparatuses, and with the same frequency. 
         [0211]    Also, in period B′ and period C′ in the UL subframe illustrated in  FIG. 15 , as in period A and period B in a DL subframe, two adjacent relay apparatuses in the plurality of relay apparatuses perform transmission processing at mutually-different periods (that is, either period B′ or period C′), respectively. Also, in period A′ in the UL subframe illustrated in  FIG. 15 , the terminals simultaneously perform transmission to the respective relay apparatuses, which are serving cells. 
         [0212]    Also, in the below explanation, among two adjacent relay apparatuses, the relay apparatus positioned upstream in a signal (uplink signal) transfer direction between a terminal and a base station (macrocell base station) is referred to as an upstream RN and the relay apparatus positioned downstream is referred to as a downstream RN. For example, in a case where a plurality of relay apparatuses are connected in series and sequentially placed from a base station, among two adjacent relay apparatuses, the relay apparatus farther from the base station (macrocell base station) is an upstream RN and the relay apparatus closer to the base station is a downstream RN. In other words, between downlink and uplink, the upstream RN and the downstream RN are interchanged. For example, as illustrated in  FIG. 15 , among two adjacent relay apparatuses RN 1  and RN 2 , RN 2  positioned upstream in an uplink signal transfer direction (base station is an upstream RN, and RN 1  positioned downstream in the signal transfer direction is a downstream RN). 
         [0213]    Also, in the below explanation, as in embodiment 1, an RN number of a relay apparatus that directly communicates with a base station, for example, a relay apparatus closest to the base station (most downstream RN) is 1 (odd number) and RN numbers of relay apparatuses upstream of the relay apparatus with an RN number of 1 are 2, 3, 4, in order. In other words, in the RN numbers of a plurality of relay apparatuses that relay communication between the base station and terminals, odd numbers and even numbers are alternately provided in order from the most downstream RN. The RN number of the most downstream RN may be set to an even number (for example, the RN number is 0); and RN numbers of the relay apparatuses upstream of the relay apparatus with the RN number of 0 may be set to 1, 2, 3, in order. 
         [0214]    Also, in the below explanation, odd-numbered RNs (RN 1  and RN 3  in  FIG. 15 ) transmit a relay signal to respective downstream RNs (or a macrocell base station) in period B′, and even-numbered RNs (RN 2  in  FIG. 15 ) transmit a relay signal to respective downstream RNs in period C′. In other words, the even-numbered RNs receive a relay signal from the respective upstream RNs in period B′, and the odd-numbered RNs receive a relay signal from the respective upstream RNs in period C′. 
         [0215]    In the radio communication system, as in embodiment 1, if a terminal (for example, a selection section) according to the present embodiment is connectable to both of adjacent RNs, the terminal selects (that is, selects as a serving cell) an upstream RN from among the plurality of adjacent RNs (two RNs in  FIG. 15 ) (RN positioned upstream in a signal transfer direction between a base station and the terminal, i.e., an RN farther from the base station). For example, as illustrated in  FIG. 15 , MS 1  is connectable to both of RN 1  and RN 2 . Also, RN 1  is a downstream RN and RN 2  is an upstream RN between RN 1  and RN 2 . Therefore, MS 1  selects connection to RN 2  positioned upstream among RN 1  and RN 2 . The same applies to MS 2  illustrated in  FIG. 15 . 
         [0216]    Then, each terminal according to the present embodiment transmits a signal to the base station to the relay apparatus selected as a serving cell, in period A′ in an UL subframe. 
         [0217]    Meanwhile, each relay apparatus (for example, a receiving section) according to the present embodiment receives the signals transmitted from the respective terminals, in period A′. However, the signals include not only a signal from a terminal under the control of this node (desired signal) but also a signal from a terminal under the control of an upstream RN of this relay apparatus (interference signal). Also, in period B′ or period C′, each relay apparatus (for example, a receiving section) receives a relay signal transmitted from the upstream RN to the relay apparatus (signal to the base station transmitted from a terminal other than the terminal under the control of the relay apparatus). In other words, in period B′ or period C′ (communication between relay apparatuses), each relay apparatus receives a relay signal containing a signal that becomes an interference signal for the relevant node in period A′. 
         [0218]    Then, each relay apparatus (for example, an interference removal section) removes the signal transmitted from the terminal under the control of the upstream RN in period A′ (interference signal) from the signal received in period A′ using the relay signal (signal to the base station transmitted from the terminal under the control of the upstream RN) (that is, the interference signal in period A′) received in period B′ or period C′, and control information for the terminal under the control of the relay apparatus, thereby obtaining a signal transmitted from the terminal under the control of the relay apparatus (desired signal). It should be noted that each relay apparatus provides notification of control information for a terminal under the control of the relay apparatus to the terminal under the control of this relay apparatus (that is, the control information for the terminal under the control of the relay apparatus is known). Also, each relay apparatus provides notification of control information for a terminal under the control of an upstream RN to the upstream RN. 
         [0219]    Next, details of the processing in relay apparatuses and terminals according to the present embodiment will be described. 
         [0220]    As described above, in  FIG. 15 , MS 1  is connected to RN 2  and MS 2  is connected to RN 3 . 
         [0221]    Here, the explanation will be provided focusing on interference removal processing in RN 2  illustrated in  FIG. 15 . 
         [0222]    As illustrated in  FIG. 15 , in period A′ of a UL subframe, MS 1  transmits signal  11  to a base station to RN 2 , which is a serving cell, and MS 2  transmits signal  12  to the base station to RN 3 , which is a serving cell. Accordingly, in period A′, RN 2  receives a signal containing signal  11  from MS 1  (desired signal) and signal  12  from MS 2  (interference signal). 
         [0223]    Next, as illustrated in  FIG. 15 , in period B′ in the DL subframe, RN 1  and RN 3  (odd-numbered RNs) transmit a relay signal to respective downstream apparatuses (macrocell base station for RN 1 , and RN 2  for RN 3 ). As illustrated in  FIG. 15 , the relay signal transmitted from RN 3  contains signal  12  transmitted in period A′ from MS 2  connected to RN 3  and signal  13  to the base station, which has been transmitted from a terminal connected to an RN (not illustrated) positioned upstream of RN 3 . 
         [0224]    Here, in period B′, RN 2  illustrated in  FIG. 15  receives the relay signal containing signal  12  that becomes an interference signal in period A′ (signal  12  and signal  13 ). Therefore, as in a terminal according to embodiment 1, RN 2  demodulates and decodes a data signal contained in signal  12 , using control information (for example, the control information illustrated in  FIG. 6 ) contained in the relay signal (signal  12  and signal  13 ), thereby obtaining the decoded signal (interference signal in period A′). Next, RN 2  performs encoding and modulation of the decoded interference signal to generate the modulated interference signal (that is, a replica of the interference signal in period A′). Then, RN 2  removes signal  12 , which is the interference signal, from the signal received in period A′ (signal containing signal  11  and signal  12 ), using the replica of the interference signal generated in period B′ and control information for MS 1  (known information), thereby obtaining signal  11  transmitted from MS 1  under the control of RN 2 . 
         [0225]    Then, in period C′ of the UL subframe illustrated in  FIG. 15 , RN 2  (even-numbered RN) transmits a relay signal to RN 1 , which is a downstream RN. As illustrated in  FIG. 15 , the relay signal transmitted from RN 2  contains signal  12  and signal  13  received in period B′ from RN 3 , which is an upstream RN, and signal  11  obtained in period B′ (signal  11  after interference removal). 
         [0226]    As described above, if a terminal according to the present embodiment is connectable to both of adjacent RNs, the terminal selects as a serving cell the upstream RN (RN positioned upstream in the signal transfer direction between the base station and terminals, i.e., the RN farthest from the base station in uplink) among the plurality of adjacent RNs (two RNs in  FIG. 15 ). Consequently, a signal received by each RN (signal communicated between RNs) in period B′ and period C′ illustrated in  FIG. 15  is a signal to the base station from terminals under the control of RNs positioned upstream of each RN, that is, a signal to terminals other than the terminal under the control of each RN. In other words, a signal received by each RN in period B′ and period C′ illustrated in  FIG. 15  contains a signal that may become an interference signal for each RN in period A′. For example, RN 2  illustrated in  FIG. 15  obtains signal  12  that becomes an interference signal in period A′, in period B′ of the UL subframe. 
         [0227]    Here, as in embodiment 1 (DL subframe), in a UL subframe, as illustrated in  FIG. 15 , in periods for communication between RNs (period B′ and period C′), adjacent RNs perform relay signal transmission processing in mutually-different periods and with the same frequency, respectively. For example, as illustrated in  FIG. 15 , odd-numbered RNs (RN 1  and RN 3 ) transmit a relay signal using frequency f 1  in period B′, while even-numbered RNs (RN 2 ) transmit a relay signal using frequency f 1  in period C′, which is different from period B′. In other words, two adjacent RNs time-divide their relay signals into period B′ and period C and thereby orthogonalize the relay signals. Accordingly, each RN can transmit a relay signal to a downstream RN in either one of period B′ and period C′ without interference from an adjacent RN. 
         [0228]    Consequently, each RN receives a signal for a base station transmitted from a terminal under the control of an upstream RN (signal  12  for RN 2  in  FIG. 15 ), which becomes an interference signal in period A′, without interference in period B′ or period C′. In other words, a terminal selects connection to an upstream RN from among an upstream RN and a downstream RN to which the terminal is connectable, and the downstream RN can receive a signal that is an interference signal for the downstream RN (signal to a base station from a terminal under the control of the upstream RN) as a relay signal from the upstream RN without interference. 
         [0229]    Accordingly, a relay apparatus according to the present embodiment can recognize an interference signal for the relay apparatus at a time (period B′ or period C′) other than a period for communication between a plurality of RNs and terminals (period A′ illustrated in  FIG. 15 ). Consequently, the relay apparatus can remove the interference signal from a signal received in period A′, using the recognized interference signal. 
         [0230]    Consequently, according to the present embodiment, also in uplink, as in embodiment 1, even if multihop communication is performed between the plurality of relay apparatuses using the same frequency, interference to a signal from a terminal connected to a relay apparatus, by a signal from a terminal connected to another relay apparatus can be reduced. 
       Embodiment 5 
       [0231]    The present embodiment will be described for a case where a certain terminal is connectable to two relay apparatuses in uplink, and the downstream RN among the two relay apparatuses generates control information (performs scheduling) for a terminal connected to the upstream RN using control information for a terminal connected to the downstream relay apparatus, as in embodiment 2. 
         [0232]    A specific explanation of the present embodiment will be provided below. 
         [0233]    In downlink, a relay apparatus (for example, a scheduling section) according to the present embodiment performs scheduling processing for a terminal under the control of a downstream RN (that is, an RN farther from a base station relative to this relay apparatus) in downlink based on scheduling for a terminal under the control of this relay apparatus as in embodiment 2. Meanwhile, in uplink, a relay apparatus (for example, a scheduling section) performs scheduling processing for a terminal under the control of an upstream RN (that is, an RN farther from the base station relative to this relay apparatus) in uplink based on scheduling for the terminal under the control of this relay apparatus. In other words, in either downlink or uplink, a relay apparatus (for example, a scheduling section) generates control information for a terminal under the control of a relay apparatus farther from a base station relative to the relay apparatus (a relay apparatus to be a downstream RN in downlink and an upstream RN in uplink), using control information for the terminal under the control of this relay apparatus. 
         [0234]    Then, during communication between RNs in downlink (for example, period A or period B illustrated in  FIG. 9 ), the relay apparatus transmits a relay signal containing control information for a terminal under the control of the relevant node in downlink and uplink and control information for a terminal under the control of another relay apparatus in downlink and uplink (a downstream RN in downlink and an upstream RN in uplink). 
         [0235]    As in embodiment 1 and embodiment 4, in downlink and uplink, if there are a plurality of RNs to which a terminal (for example, a selection section) according to the present embodiment is connectable, the terminal selects connection to an upstream RN (relay apparatus positioned upstream in a signal transfer direction). For example, in downlink, the terminal selects connection to a relay apparatus closer to a base station (relay apparatus positioned upstream in the downlink signal transfer direction) from among the plurality of relay apparatuses to which the terminal is connectable. Meanwhile, in uplink, the terminal selects connection to a relay apparatus farther from the base station (relay apparatus positioned upstream in the uplink signal transfer direction) from among the plurality of relay apparatuses to which the terminal is connectable. 
         [0236]    Also, as in embodiment 2, during communication between RNs in downlink (for example, period A or period B illustrated in  FIG. 9 ), a terminal (for example, timing control section) according to the present embodiment controls input/output timings so as to receive a relay signal containing control information for the relevant terminal for downlink and uplink and control information for another terminal for downlink and uplink. 
         [0237]    Next, details of the scheduling processing in a relay apparatus according to the present embodiment will be described. 
         [0238]    The below explanation will be provided for a case where multihop communication is performed by four relay apparatuses RN# 1  to RN# 4  as illustrated in  FIG. 16 . Also, in  FIG. 16 , RN# 1  is the closest to a macrocell base station and the RN# 4  is the farthest from the macrocell base station. Accordingly, as illustrated in  FIG. 16 , a downlink signal transfer direction is a direction from RN# 1  to RN# 4 , and an uplink signal transfer direction is a direction from RN# 4  to RN# 1 . In other words, in downlink, RN# 1  is the most upstream RN, and RN# 4  is the most downstream RN. Also, in uplink, RN# 4  is the most upstream RN and RN# 1  is the most downstream RN. 
         [0239]    Accordingly, in  FIG. 16 , in downlink, MS 1  is connected to RN# 1 , which is the upstream RN in downlink among RN# 1  and RN# 2  to which MS 1  is connectable. Likewise, in downlink, MS 2  is connected to RN# 2 , which is the upstream RN in downlink among RN# 2  and RN# 3  to which MS 2  is connectable. The same applies to MS 0 , MS 3  and MS 4 . 
         [0240]    Meanwhile, in  FIG. 16 , in uplink, MS 1  is connected to RN# 2 , which is the upstream RN in uplink among RN# 1  and RN# 2  to which MS 1  is connectable. Likewise, in uplink, MS 2  is connected to RN# 3 , which is the upstream RN in uplink among RN# 2  and RN# 3  to which MS 2  is connectable. The same applies to MS 0  and MS 3 . In uplink, there is no RN positioned upstream of RN# 4  illustrated in  FIG. 16  (no RN farther from the base station as compared to RN 4 ), and thus, MS 4  is connected to RN# 4 . 
         [0241]    Here, in  FIG. 16 , the explanation will be provided focusing on processing from reception by RN# 1  (odd-numbered RN) in DL subframe [m] of control information for MS 1  under the control of RN# 1  in downlink (DL) (DL control information) and control information for MS 0  under the control of RN# 1  in uplink (UL) (UL control information) to reflection of the control information in a terminal. 
         [0242]    In  FIG. 16 , scheduling processing in a relay apparatus in downlink is similar to that in embodiment 2. In other words, in subframe [m] illustrated in  FIG. 16 , RN# 1  generates DL control information for MS 2  under the control of RN# 2  using DL control information for MS 1  under the control of RN# 1 . Likewise, in subframe [m+1] illustrated in  FIG. 16 , RN# 2  generates DL control information for MS 3  under the control of RN# 3  using DL control information for MS 2  under the control of RN# 2 . The same applies to RN# 4  in subframe [m+2] illustrated in  FIG. 16 . 
         [0243]    Meanwhile, scheduling processing in a relay apparatus in uplink is described below. More specifically, in subframe [m] illustrated in  FIG. 16 , RN# 1  receives UL control information for MS 0  under the control of RN# 1  from a macrocell base station. Therefore, RN# 1  performs scheduling processing for MS 1  under the control of RN# 2 , which is an upstream RN for RN# 1  in uplink, using the UL control information for MS 0  under the control of RN# 1 . Consequently, RN# 1  obtains UL control information for MS 1  under the control of RN# 2 . Likewise, in subframe [m+1] illustrated in  FIG. 16 , RN# 2  generates UL control information for MS 2  under the control of RN# 3 , which is an upstream RN for RN# 2  in uplink, using the UL control information for MS 1  under the control of RN# 2 , which is transmitted from RN# 1 . The same applies to RN# 3  in subframe [m+2] illustrated in  FIG. 16 . 
         [0244]    Then, in subframe [m+3] illustrated in  FIG. 16 , all of the RNs, i.e., RN# 1  to RN# 4 , perform communication with terminals under the control of the respective RNs (MS 0  to MS 4  in  FIG. 16 ) based on the scheduling results determined in subframes [m] to [m+2], respectively, thereby reflecting the scheduling results on the terminals. 
         [0245]    As described above, in the present embodiment, a relay apparatus performs scheduling processing for a terminal under the control of an adjacent relay apparatus farther from a base station as compared with the relay apparatus (a downstream RN in downlink and an upstream RN in uplink) based on scheduling for a terminal under the control of the relay apparatus. 
         [0246]    Consequently, in downlink, as in embodiment 2, a terminal can receive not only a mapping position and an MCS of a relay signal for this terminal (desired signal) but also a mapping position and an MCS of a relay signal for another terminal (interference signal) without interference before a time when the terminal actually receives a relay signal that becomes an interference signal (for example, period C illustrated in  FIG. 9 ). Accordingly, the terminal can start preparation for interference removal processing at a point of time when the terminal obtains in advance the signal that becomes an interference signal (for example, processing for generating a replica of the interference signal or processing for selecting an interference removal method), enabling reduction in reception processing time required for obtaining a desired signal. 
         [0247]    Also, in uplink, a relay apparatus generates control information for a terminal under the control of an upstream RN in uplink. Consequently, the relay apparatus can recognize control information for a terminal that transmits a signal that becomes an interference signal for the relay apparatus. For example, RN# 2  illustrated in  FIG. 16  generates control information for MS 2  connected to RN# 3 , which is an upstream RN in uplink. Consequently, RN# 2  illustrated in  FIG. 16  can reliably obtain an interference signal when receiving a signal from MS 1  under the control of RN# 2 , that is, control information on a signal from MS 2 . 
         [0248]    As described above, according to the present embodiment, in downlink, as in embodiment 2, a terminal can reliably obtain control information on an interference signal to remove the interference signal, and thus, interference to a signal from a relay apparatus to which the terminal is connected, by a signal from another relay apparatus can reliably be reduced. Furthermore, according to the present embodiment, in uplink, a relay apparatus generates control information for a terminal that transmits a signal that becomes an interference signal for this relay apparatus. Thus, according to the present embodiment, a relay apparatus can reliably reduce interference to a signal transmitted from a terminal under the control of the relay apparatus by a signal transmitted from a terminal under the control of another relay apparatus. 
         [0249]    The present embodiment has been described taking a case where scheduling in downlink and scheduling in uplink are performed in downlink and uplink, respectively, as an example. However, the present invention is not limited to this case, and for example, both scheduling for a following uplink and scheduling for a following downlink may simultaneously be performed in a downlink, and both scheduling for a following downlink and scheduling for a following uplink may simultaneously be performed in an uplink. 
       Embodiment 6 
       [0250]    The present embodiment will be described for a case where, in multihop communication in uplink as in embodiment 4, a terminal provides notification of control information for the terminal (control information on an interference signal for a notification destination relay apparatus) to a relay apparatus other than a serving cell as in embodiment 3. 
         [0251]    In the below explanation, as in embodiment 4, in period A′ to period C′ in an UL subframe, odd-numbered RNs transmit a relay signal to respective downstream RNs (or a macrocell base station) in period B′ and even-numbered RNs transmit a relay signal to respective downstream RNs in period C′. 
         [0252]    Also, as in a DL subframe, a plurality of relay apparatuses (RNs) included in multihop communication are provided with a guard time for switching between transmission processing and reception processing in a UL subframe. 
         [0253]    For example, here, the odd-numbered RNs transmit a relay signal to respective downstream apparatuses in period B′ and receive a relay signal from respective upstream RNs in period C′. Meanwhile, the even-numbered RNs receive a relay signal from respective upstream RNs in period B′, and transmit a relay signal to respective downstream apparatuses in period C′. In other words, between period B′ and period C′, transmission processing and reception processing are switched in the odd-numbered RNs and the even-numbered RNs (that is, all of the RNs). Accordingly, each of the RNs needs to be provided with a guard time between period B′ and period C. 
         [0254]    Also, the odd-numbered RNs and the even-numbered RNs receive a signal (relay signal) to a base station, which is transmitted in period A′ from terminals under the control of the respective RNs. Accordingly, between period A′ and period B′, reception processing and transmission processing are switched in the odd-numbered RNs while the even-numbered RNs continue reception processing. Accordingly, the odd-numbered RNs need to provide a guard time between period A′ and period B′. Meanwhile, the even-numbered RNs do not need to provide a guard time between period A′ and period B′. In other words, in a period corresponding to a guard time between period A′ and period B′, the odd-numbered RNs can receive no signal because of switching between transmission/reception processing, while the even-numbered RNs continue reception processing and thus can receive a signal. 
         [0255]    In other words, in a guard time provided for the switching between transmission/reception processing in one RN (odd-numbered RN in the above example) among a plurality of adjacent RNs (a plurality of RNs to which a certain terminal is connectable), another RN can receive not only a signal from a terminal under the control of the relay apparatus, but also a signal from a terminal under the control of an RN other than this relay apparatus. 
         [0256]    Also, as described in embodiment 3, in a radio communication system according to the present embodiment, downlink and uplink are alternately switched on a per subframe basis. Thus, a plurality of relay apparatuses (RNs) included in multihop communication are provided with a guard time also when downlink and uplink are switched. In other words, there is a DL subframe immediately after (or immediately before) the above-described UL subframe, and for example, before period A′ in period A′ to period C in the UL subframe, a guard time for switching to the DL subframe is provided. 
         [0257]    Accordingly, as in embodiment 3, it is possible that in the guard time provided between downlink and uplink, some RNs among a plurality of adjacent RNs (a plurality of RNs to which a certain terminal is connectable) receive a signal from respective terminals. 
         [0258]    Therefore, in the present embodiment, in a plurality of relay apparatuses (RNs) included in multihop communication, a terminal under the control of one relay apparatus among terminals under the control of two adjacent relay apparatuses transmits control information for the terminal in a guard time provided for switching between transmission/reception processing in the relay apparatus to which the terminal is connected, and a terminal under the control of the other relay apparatus transmits control information for this terminal at a guard time provided between downlink and uplink. 
         [0259]    Also, in a plurality of relay apparatuses (RNs) included in multihop communication, one relay apparatus among two adjacent relay apparatuses receives control information from a terminal under the control of the other relay apparatus at a guard time provided for switching between transmission/reception processing in the other relay apparatus, and the other relay apparatus receives control information from a terminal under the control of the one relay apparatus at a guard time provided between downlink and uplink. 
         [0260]    A more specific explanation of the present embodiment will be provided below. The present embodiment will be described for a radio communication system in which downlink and uplink are switched on a per subframe basis, a guard time is provided between a DL subframe and a UL subframe and a guard time is provided between period A′ and period B′ in a UL subframe. 
         [0261]    In the radio communication system, a relay apparatus according to the present embodiment provides a guard time between period A′ and period B′ (period post-A′) and between period B′ and period C′ in each UL subframe, provides a guard time between a DL subframe and a UL subframe (period pre-A′) in addition to the processing in a relay apparatus in embodiment 4. However, the relay apparatus receives control information from a terminal under the control of an upstream RN (that is, control information on an interference signal) in either one of the guard time between period A′ and period B′ (period post-A′) and the guard time between downlink and uplink (period pre-A′). The relay apparatus notifies a terminal under the control of this relay apparatus of control information for the terminal (UL control information) (in other words, the control information for the terminal under the control of the relay apparatus is known). Also, the relay apparatus notifies an upstream RN of control information for a terminal under the control of the upstream RN. 
         [0262]    Then, the relay apparatus demodulates and decodes the control information from the terminal under the control of the upstream RN, which is received in period pre-A′ or period post-A′ (control information on an interference signal). Consequently, the relay apparatus obtains, e.g., a mapping position and an MCS of an interference signal (relay signal from the terminal under the control of the upstream RN). In the relay apparatus, the control information for the terminal under the control of the relay apparatus (control information on a desired signal) is known, and thus, the relay apparatus recognizes, e.g., a mapping position and an MCS of a desired signal (relay signal transmitted from the terminal under the control of the relevant node). Accordingly, as in embodiment 4, the relay apparatus encodes and modulates an interference signal contained in a relay signal received in period B′ or period C′, using the control information from the terminal under the control of the upstream RN, which is received in period pre-A′ or period post-A′. Then, the relay apparatus removes the interference signal from the signal received in period A′, using the modulated interference signal (replica of the interference signal) and the control information for the terminal under the control of the relay apparatus (control information on a desired signal), thereby obtaining a relay signal transmitted from the terminal under the control of this relay apparatus (desired signal). 
         [0263]    A terminal according to the present embodiment transmits control information for the relevant terminal in either one of two periods, i.e., a period corresponding to the guard time between period A′ and period B′ (hereinafter referred to as period post-A′) and a period immediately before period A′, that is, a period corresponding to the guard time between downlink and uplink (hereinafter referred to as period pre-A′), in addition to the processing in a terminal in embodiment 4. For example, if a serving cell provides a guard time in period post-A′, the terminal transmits the control information for the terminal in period post-A′. Also, if the serving cell provides no guard time in period post-A′, the terminal transmits the control information for the terminal in period pre-A′. Each terminal is notified by the corresponding serving cell of control information for the terminal (UL control information). 
         [0264]    Next, details of the processing in relay apparatuses and terminals according to the present embodiment will be described. 
         [0265]    The below explanation will be provided for a case where multihop communication in uplink is performed by three or more RNs. However, in  FIG. 17 , only two RN 1  and RN 2  from the three or more RNs are illustrated. Also, RN 1  is a downstream RN and RN 2  is an upstream RN between RN 1  and RN 2  illustrated in  FIG. 17 . Also, in  FIG. 17 , MS 0  (not illustrated) is connected to RN 1 , and MS 1  is connected to RN 2 . Also, MS 2  illustrated in  FIG. 17  is connected to RN 3  (not illustrated). 
         [0266]    Furthermore, in  FIG. 17 , transmission processing is represented by “TX,” and reception processing is represented by “RX.” 
         [0267]    In period pre-A′ illustrated in  FIG. 17 , MS 1  under the control of RN 2  transmits control information for MS 1 . MS 1  is notified of the control information for MS 1  by RN 2 , which is a serving cell. Also, RN 2  is notified of the control information for MS 1  by a downstream RN (that is, an RN closer to a base station). Then, in period pre-A′, RN 1  receives the control information for MS 1 . In other words, in period pre-A′, RN 1  receives the control information for MS 1 , which is a transmission source of an interference signal in period A′ (control information on an interference signal). Then, RN 1  obtains a channel estimation value between RN 1  and MS 1  (channel estimation value for an interference signal) using the control information for MS 1  received in period pre-A′. Also, in period pre-A′, RN 2  provides a guard time, and thus, does not receive the control information for MS 1 . 
         [0268]    Next, in period A′ illustrated in  FIG. 17 , RN 1  receives a relay signal from MS 0  under the control of RN 1 , and RN 2  receives a relay signal from MS 1  under the control of RN 2 . However, the signal received by RN 1  in period A′ contains the relay signal from MS 1  under the control of RN 2  (interference signal) in addition to the relay signal from MS 0  (desired signal). Likewise, the signal received by RN 2  in period A′ contains a relay signal from MS 2  under the control of RN 3  (interference signal) in addition to the relay signal from MS 1  (desired signal). 
         [0269]    Next, in period post-A′ illustrated in  FIG. 17 , MS 2  under the control of RN 3  (not illustrated) transmits control information for MS 2 . MS 2  is notified of the control information for MS 2  by RN 3  (not illustrated), which is a serving cell. Also, RN 3  (not illustrated) is notified of the control information for MS 2  by a downstream RN (that is, a RN closer to the base station). Then, in period post-A′, RN 2  receives the control information for MS 2 . In other words, in period post-A′, RN 2  can receive the control information for MS 2  (control information on an interference signal), which is a transmission source of an interference signal. Then, RN 2  obtains a channel estimation value between RN 2  and MS 2  (channel estimation value for an interference signal) using the control information for MS 2  received in period post-A′. Also, in period post-A′, RN 1  provides a guard time. 
         [0270]    In period B′ illustrated in  FIG. 14 , RN 1 , which is an odd-numbered RN, transmits a relay signal to the macrocell base station, which is a downstream apparatus. Also, RN 3  (not illustrated), which is an odd-numbered RN, transmits a relay signal to RN 2 , which is a downstream RN. Also, in period C′ illustrated in  FIG. 14 , RN 2 , which is an even-numbered RN, transmits a relay signal to RN 1 , which is a downstream RN. Consequently, as in embodiment 4, RN 1  extracts the interference signal in period A′ (signal transmitted from MS 1  under the control of RN 2 ) from the relay signal received in period C′. Likewise, RN 2  extracts the interference signal in period A′ (signal transmitted from MS 2  under the control of RN 3 ) from the relay signal received in period B′. Consequently, RN 1  and RN 2  each obtain a replica of the interference signal in period A′ using the control information on the interference signal obtained in period pre-A′ or period post-A′. 
         [0271]    Then, as in embodiment 4, RN 1  and RN 2  illustrated in  FIG. 17  each remove the interference signal from the signal received in period A′ using the replica of the interference signal obtained in period B′ or period C′, the channel estimation value for the interference signal obtained in period pre-A′ or period post-A′ and the known control information for the terminal under the control of the relay apparatus (control information on a desired signal), thereby obtaining a desired signal. 
         [0272]    As described above, in the present embodiment, the terminals each transmit control information for the respective terminals in either one of the guard time provided between period A′ and period B′ (guard time provided for switching between transmission/reception processing (period post-A′)) or the guard time between downlink and uplink (guard time provided for switching between downlink and uplink (period pre-A′)). Then, the relay apparatuses each receive control information transmitted from the terminal under the control of respective upstream RNs, that is, receive control information on an interference signal in the guard time between period A′ and period B′ or the guard time between the downlink and the uplink. 
         [0273]    Consequently, in the guard time between period A′ and period B′, the relay apparatuses not requiring switching between transmission/reception processing (here, even-numbered RNs) can receive the control information from the terminals under the control of the respective upstream RNs (here, the odd-numbered RNs) without interference. Likewise, in the guard time between downlink and uplink, the relay apparatuses requiring provision of the guard time between period A′ and period B′ (here, the odd-numbered RNs) can receive the control information from the respective upstream RNs (here, the even-numbered RNs) without interference. 
         [0274]    As described above, according to the present embodiment, even in a case where multihop communication is performed between a plurality of relay apparatuses in uplink using the same frequency, as in embodiment 4, interference to a signal from a terminal connected to a relay apparatus, by a signal from a terminal connected to another relay apparatus can be reduced. Furthermore, according the present embodiment, a relay apparatus utilizes a guard time for switching between transmission/reception processing in the relay apparatus or a guard time for switching between downlink and uplink, for communication of control information, enabling reliable obtainment of control information on an interference signal. Thus, in the present embodiment, in a relay apparatus, interference to a signal from a terminal connected to the relay apparatus by a signal from a terminal connected to another relay apparatus can reliably be reduced. 
       Embodiment 7 
       [0275]    The present embodiment is similar to embodiments 1 to 3 in that a terminal performs interference removal processing using control information for this terminal and control information for another terminal (control information on an interference signal). Meanwhile, the present embodiment is different from embodiment 2 and embodiment 3 in a method for providing notification of control information that a terminal uses for interference removal processing. 
         [0276]    A specific explanation of the present embodiment will be provided below. First, a relay apparatus according to the present embodiment will be described below. Relay apparatus  100  according to the present embodiment ( FIG. 2 ) has a configuration similar to that of embodiment 1, but different from that of embodiment 1 in operations of reception processing section  104 , transmission processing section  106  and timing control section  109 . 
         [0277]    In the present embodiment, a relay signal transmitted from a base station or an upstream RN to relay apparatus  100  contains, e.g., a known signal (also referred to as a reference signal or a pilot signal), a relay signal for a terminal connected to relay apparatus  100  (terminal under the control of relay apparatus  100 ) transmitted in period C (data signal and control information on the data signal), a relay signal for a terminal connected to a relay apparatus downstream of relay apparatus  100  (downstream RN) (data signal and control information on the data signal), and control information used when relaying relay data to a terminal connected to relay apparatus  100 , which is transmitted in period C. 
         [0278]    In relay apparatus  100  illustrated in  FIG. 2 , first, reception processing section  104  performs demodulation and decoding of control information for a relay signal between relay apparatuses contained in a relay signal input from first memory  103 . Here, it is assumed that a mapping position and an MCS (modulation and coding scheme) of the control information is information previously obtained by relay apparatus  100 , such as information set in advance. Furthermore, the control information contains a mapping position and an MCS of a relay signal between relay apparatuses (data directed to a terminal connected to relay apparatus  100  and/or data directed to a terminal connected to a downstream RN). Then, reception processing section  104  performs demodulation and decoding of the data signal contained in the relay signal input from first memory  103 , based on the mapping position and the MCS included in the control information. Then, reception processing section  104  outputs the decoded signal to second memory  105 . 
         [0279]    Transmission processing section  106  performs coding and modulation of the signal input from second memory  105  (relay signal to a terminal connected to relay apparatus  100  (relay data to a terminal connected to relay apparatus  100 ), the control information for the relay signal for the terminal connected to relay apparatus  100  (control information for the terminal, that is, control information for transmission of the relay data to the terminal), the relay signal for the terminal connected to the downstream RN (relay data to the terminal connected to the downstream RN), or the control information for the relay signal for the terminal connected to the downstream RN (control information for the RN, that is, control information for transmission of the relay data between relay apparatuses)). Then, transmission processing section  106  outputs the modulated signal to first memory  103 . 
         [0280]    Timing control section  109  instructs first memory  103  and second memory  105  about timings for inputting/outputting a relay signal, based on setting information input from odd/even number switching section  108 . 
         [0281]    For example, if the setting information input from odd/even number switching section  108  indicates “odd number” (if relay apparatus  100  is an odd-numbered RN), in period A, timing control section  109  instructs (gives a read instruction to) first memory  103  to output control information on relay data to the terminal under the control of relay apparatus  100  transmitted in period C, control information on relay data to the downstream RN and the relay data to the downstream RN (data signal) to RF transmitting section  107 . 
         [0282]    Also, in period B, timing control section  109  instructs (gives a write instruction to) first memory  103  to store a relay signal input from RF receiving section  102  (relay signal for the terminal connected to relay apparatus  100 , a relay signal for the terminal connected to the downstream RN and control information on these relay signals). Also, in period B, when the relay signal is stored in first memory  103 , timing control section  109  instructs (gives a read instruction to) first memory  103  to output the stored relay signal to reception processing section  104 , and instructs (gives a write instruction to) second memory  105  to store the signal input from reception processing section  104  (decoded signal). Also, in period B, when the decoded signal is stored in second memory  105 , timing control section  109  instructs (gives a read instruction to) second memory  105  to output the relay signal (relay signal for the terminal connected to relay apparatus  100  and/or the relay signal for the terminal connected to the downstream RN, and the control information on these relay signals) to transmission processing section  106 , and instructs (gives a write instruction to) first memory  103  to store the relay signal input from transmission processing section  106  (relay signal for the terminal connected to relay apparatus  100  and/or the relay signal for the terminal connected to the downstream RN, and the control information on these relay signals). 
         [0283]    Meanwhile, if the setting information input from odd/even number switching section  108  indicates “even number” (if relay apparatus  100  is an even-numbered RN), timing control section  109  performs, in period B, processing similar to the processing performed in period A when the setting information indicates “odd number” and performs, in period A, processing similar to the processing performed in period B when the setting information indicates “odd number.” In other words, the processing in period A and the processing in period B in timing control section  109  are interchanged between an odd-numbered RN and an even-numbered RN. 
         [0284]    Also, regardless of the setting information input from odd/even number switching section  108 , in period C, timing control section  109  instructs (gives a read instruction to) first memory  103  to output the relay signal for the terminal connected to relay apparatus  100  to RF transmitting section  107 . 
         [0285]    Next, a terminal according to the present embodiment will be described. Terminal  200  ( FIG. 3 ) according to the present embodiment has a configuration similar to that of embodiment 1, but is different in operations of reception processing section  207  (receiving section  208  and interference removal section  209 ) and timing control section  214 . 
         [0286]    In the present embodiment, a relay signal transmitted from relay apparatus  100  connected to terminal  200  contains a relay signal (data signal) for terminal  200  and a known signal. 
         [0287]    In terminal  200  illustrated in  FIG. 3 , receiving section  208  of reception processing section  207  performs demodulation and decoding of a relay signal input from first memory  203 . More specifically, when terminal  200  is connectable to two adjacent relay apparatuses (RNs), receiving section  208  performs the following processing. In period A or period B (period for communication between relay apparatuses), receiving section  208  receives a relay signal transmitted from the upstream RN to the downstream RN in the two relay apparatuses to which terminal  200  is connectable (known signal, control information for relay data to terminal  200  to be transmitted in period C (control information for terminal  200 ), relay data to another terminal under the control of the downstream RN (relay data to the downstream RN), and control information for relay data to the other terminal under the control of the downstream RN (control information for the downstream RN)). Furthermore, in period A or period B (period for communication between relay apparatuses), receiving section  208  receives a relay signal transmitted by the downstream RN in the two relay apparatuses to which terminal  200  is connectable (control information for relay data to the other terminal (interference station for terminal  200 ) to be transmitted in period C). Then, receiving section  208  demodulates and decodes the received relay signal. 
         [0288]    In other words, in period A or period B, receiving section  208  receives the relay data to the other terminal and the control information for the other terminal (that is, a signal that may provide interference to terminal  200  in period C (interference signal) and control information), and control information for the relay data to terminal  200  (that is, control information for the signal to be transmitted to terminal  200  in period C). Then, receiving section  208  outputs the relay data to the other terminal (interference signal) and control information for the other terminal, and the control information for terminal  200 , which were received in period A or period B, to second memory  210 . 
         [0289]    Also, receiving section  208  calculates a channel estimation value between the relay apparatus to which terminal  200  is connected (upstream RN) and terminal  200  using the known signal contained in the relay signal from the upstream RN to the downstream RN in period A or period B (period for communication between relay apparatuses), and outputs the channel estimation value to second memory  210 . Likewise, receiving section  208  calculates a channel estimation value between the downstream RN and terminal  200  using the known signal contained in the relay signal from the downstream RN in period A or period B (period for communication between relay apparatuses), and outputs the channel estimation value to second memory  210  as a channel estimation value of an interference signal. 
         [0290]    Interference removal section  209  of reception processing section  207  removes the relay data to the other terminal transmitted from the downstream RN in period C from the relay signal received in period C, using the relay data to the other terminal (interference signal), the control information for the other terminal, the channel estimation value of the interference signal and the control information for terminal  200 , which were received in period A or period B and stored in second memory  210 . Then, receiving section  208  performs demodulation and decoding of the signal from which the interference signal has been removed in interference removal section  209  in the relay signal received in period C of a DL subframe (period for communication between relay apparatuses and terminals), thereby obtaining relay data to terminal  200  (desired signal) transmitted from the upstream RN (serving cell for terminal  200 ). 
         [0291]    As in timing control section  109  ( FIG. 2 ), timing control section  214  instructs first memory  203  and second memory  210  about timings for inputting/outputting relay signals, based on setting information input from odd/even number switching section  213 . 
         [0292]    For example, if the setting information input from odd/even number switching section  213  indicates “odd number” (if the serving cell is an odd-numbered RN), in period A, timing control section  214  instructs (gives a write instruction to) first memory  203  to store the known signal, the relay signal for the downstream RN, the control information for the downstream RN and the control information for terminal  200 , which are input from RF receiving section  202 . Also, in period A, when the relay signal for the downstream RN and the control information for terminal  200  are stored in first memory  203 , timing control section  214  instructs (gives a read instruction to) first memory  203  to output the known signal, the relay signal for the downstream RN, the control information for the downstream RN and the control information for terminal  200  to reception processing section  207 , and instructs (gives a write instruction to) second memory  210  to store the interference signal (relay signal for the other terminal) and control information for terminal  200 , and the channel estimation value between the serving cell and the terminal  200 , which are input from reception processing section  207 . 
         [0293]    Also, in period B, timing control section  214  instructs (gives a write instruction to) first memory  203  to store the relay signal (known signal and the control information for the other terminal) transmitted from the downstream RN among the two relay apparatuses to which terminal  200  is connectable, the signal being input from RF receiving section  202 . Also, in period B, when the relay signal from the downstream RN is stored in first memory  203 , timing control section  214  instructs (gives a read instruction to) first memory  203  to output the stored relay signal from the downstream RN to reception processing section  207 , and instructs (gives a write instruction to) second memory  210  to store the channel estimation value between the downstream RN and terminal  200  input from reception processing section  207 . 
         [0294]    Meanwhile, if the setting information input from odd/even number switching section  213  indicates “even number” (if the serving cell is an even-numbered RN), timing control section  214  performs, in period B, processing similar to the processing performed in period A when the setting information indicates “odd number” and performs, in period A, processing similar to the processing in period B when the setting information indicates “odd number.” In other words, the processing in period A and the processing in period B in timing control section  214  are interchanged between terminal  200  connected to an odd-numbered RN and terminal  200  connected to an even-numbered RN. 
         [0295]    Also, regardless of the setting information input from odd/even number switching section  213 , in period C, timing control section  214  instructs (gives a write instruction to) first memory  203  to store a signal from each RN, which is input from RF receiving section  202 . Also, in period C, when the signal from each RN is stored in first memory  203 , timing control section  214  instructs (gives a read instruction to) first memory  203  to output the stored signal from each RN to reception processing section  207 , and instructs (gives a read instruction to) second memory  210  to output the interference signal, the control information on the interference signal, the control information for terminal  200 , the channel estimation value between the serving cell and terminal  200  and the channel estimation value between the downstream RN and terminal  200 , which were received in period A and period B, to reception processing section  207 . Also, timing control section  214  instructs (gives a write instruction to) second memory  210  to store the signal input from reception processing section  207  (signal after interference removal). 
         [0296]    Next, details of the processing in relay apparatus  100  and terminal  200  according to the present embodiment will be described. 
         [0297]    The below explanation will be provided for a case where multihop communication is performed using three or more RNs. However, in  FIG. 18 , among the three or more RNs, only three RN 1 , RN 2  and RN 3  are illustrated. Also, RN 1  is an upstream RN and RN 2  is a downstream RN between RN 1  and RN 2  illustrated in  FIG. 18 . Also, RN 2  is an upstream RN and RN 3  is a downstream RN between RN 2  and RN 3  illustrated in  FIG. 18 . Also, in  FIG. 18 , MS 1  is connected to RN 1  and MS 2  is connected to RN 2 . Also, RN 1 , RN 2  and RN 3  illustrated in  FIG. 18  each include the configuration of relay apparatus  100  illustrated in  FIG. 2 , and MS 1  and MS 2  each include the configuration of terminal  200  illustrated in  FIG. 3 . 
         [0298]    Also, in  FIG. 18 , transmission processing is represented by “TX,” and reception processing is represented by “RX.” 
         [0299]    Also, in  FIG. 18 , control information for relay data transmission between relay apparatuses (control information for a downstream RN) is represented by “CONTROL INFORMATION for RN” and relay data between relay apparatuses (relay data to a downstream RN) is represented by “DATA to RN.” Likewise, in  FIG. 18 , control information for relay data transmission for a terminal (control information for a tell final) is represented by “CONTROL INFORMATION for MS” and relay data to a terminal is represented by “DATA to MS.” In other words, as indicated by the dotted arrows in  FIG. 18 , “CONTROL INFORMATION for MS” is control information (e.g., a mapping position and an MCS) used for relaying “DATA to MS,” and “CONTROL INFORMATION for RN” is control information (e.g., a mapping position and an MCS) used for relaying “DATA to RN.” 
         [0300]    Here, an explanation will be provided focusing on control information notification processing in RN 2  (even-numbered RN) and MS 2  connected to RN 2  (MS 2  under the control of RN 2 ), which are illustrated in  FIG. 18 . 
         [0301]    In period A in the DL subframe illustrated in  FIG. 18 , RN 2  receives a known signal, control information for relay data transmission between relay apparatuses (CONTROL INFORMATION for RN) and relay data between relay apparatuses (DATA to RN) from RN 1 , which is an upstream RN of RN 2 . Meanwhile, in period A, MS 2  receives a known signal and control information for relay data transmission for a terminal under the control of RN 3  (CONTROL INFORMATION for MS), which are transmitted to a downstream RN for RN 3 , from RN 3 . Then, MS 2  obtains a channel estimation value between RN 3  and MS 2  (channel estimation value of an interference signal in period C), using the known signal from RN 3 . Also, in period A, MS 2  obtains control information for a terminal (not illustrated) under the control of RN 3  (control information on an interference signal), which is transmitted from RN 3 . 
         [0302]    Next, in period B of the DL subframe illustrated in  FIG. 18 , RN 2  transmits a known signal, control information for a terminal under the control of RN 2  (MS 2 ) (CONTROL INFORMATION for MS), control information for relay data transmission between relay apparatuses (control information for RN), and relay data between relay apparatuses (DATA to RN). Meanwhile, in period B, MS 2  receives the control information for relay data transmission for the terminal under the control of RN 2  (CONTROL INFORMATION for MS), which is transmitted from RN 2  to MS 2 . Also, MS 2  receives the known signal, the control information for relay data transmission between relay apparatuses (CONTROL INFORMATION for RN) and the relay data between relay apparatuses (DATA to RN), which are transmitted from RN 2  to RN 3 . Then, in period B, MS 2  obtains an interference signal for MS 2  in period C using the relay data to the terminal under the control of RN 3  and the control information, which are transmitted from RN 2 . Also, in period B, MS 2  obtains a channel estimation value between RN 2  and MS 2  (channel estimation value for a desired signal) using the known signal transmitted from RN 2 . Also, in period B, MS 2  obtains the control information for MS 2  (control information on a desired signal) transmitted from RN 2 . 
         [0303]    Next, in period C in the DL subframe illustrated in  FIG. 18 , RN 2  transmits the relay data to the terminal under the control of RN 2  (MS 2 ) (DATA to MS) to MS 2 . Meanwhile, in period C, MS 2  receives the relay data to the terminal under the control of RN 2  (MS 2 ) from RN 2  (DATA to MS). Then, MS 2  removes the interference signal from the signal received in period C (relay data from RN 2  (desired signal) and the relay data from RN 3  (interference signal)) using the interference signal, the control information on the interference signal, the control information for MS 2 , the channel estimation value between RN 2  and MS 2  and the channel estimation value between RN 3  and MS 2 , which are obtained in period A and period B, thereby obtaining the desired signal. 
         [0304]    As described above, in period C, relay apparatus  100  transmits control information for relay data transmitted to terminal  200  (e.g., a mapping position and an MCS of relay data to terminal  200 ) during the time of communication between relay apparatuses (period A or period B). For example, in  FIG. 18 , in period A, odd-numbered RNs (RN 1  and RN 3 ) transmit control information for relay data to be transmitted to terminals under the control of the relay apparatuses in period C (DATA to MS) (CONTROL INFORMATION for MS). Also, in  FIG. 18 , in period B, an even-numbered RN (RN 2 ) transmit control information for relay data to be transmitted to the terminal under the control of the relay apparatus in period C (DATA to MS) (CONTROL INFORMATION for MS). 
         [0305]    Then, terminal  200  receives the control information for terminal  200  transmitted in period A or period B by relay apparatus  100  to which terminal  200  is connected, and control information for a terminal under the control of a downstream RN (control information on an interference signal), which is transmitted in period B or period A (in other words, a period different from that of relay apparatus  100 ) by the downstream RN for relay apparatus  100  to which terminal  200  is connected. Consequently, in period A or period B, terminal  200  can receive the control information for terminal  200  (control information on a desired signal) and the control information for a terminal under the control of the downstream RN (control information on the interference signal) from two adjacent relay apparatuses to which terminal  200  is connectable (RN 2  and RN 3  for MS 2  illustrated in  FIG. 18 ) without interference, enabling interference removal (interference cancelling) with good precision. 
         [0306]    As described above, according to the present embodiment, as in embodiment 1, even in a case where multihop communication is performed between a plurality of relay apparatuses using the same frequency, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reduced. Furthermore, according to the present embodiment, a terminal uses periods for communication between relay apparatuses (period A and period B) for communication of control information for terminals, making it possible to reliably obtain control information on a desired signal (relay data to the terminal) and control information on an interference signal (relay data to another terminal). Thus, in the present embodiment, as in embodiment 2 and embodiment 3, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can reliably be reduced. 
       Embodiment 8 
       [0307]    In the present embodiment, as in embodiment 7, a terminal receives control information for terminals in periods for communication between relay apparatuses. Furthermore, the present embodiment will be described for a case where a control header provided in control information for a terminal contains notification information indicating existence or non-existence of relay data (relay signal) to each terminal. 
         [0308]    A specific explanation of the present embodiment will be provided below. 
         [0309]    Relay apparatus  100  ( FIG. 2 ) according to the present embodiment has a configuration similar to that of embodiment 7 and performs an operation similar to that of embodiment 7. In other words, as in embodiment 7, in period A or period B, relay apparatus  100  transmits a known signal, control information for a terminal under the control of relay apparatus  100 , relay data to a terminal connected to a relay apparatus positioned downstream of relay apparatus  100  (downstream RN) (relay data to a downstream RN) and control information for the terminal connected to the downstream RN. Also, as in embodiment 7, in period C, relay apparatus  100  transmits relay data (data signal) to the terminal under the control of relay apparatus  100 . 
         [0310]    Here, each piece of control information is provided with a control header. The control header contains a length (data amount) of the control information, information for a terminal to recognize a time resource or a frequency resource assigned to the control information (that is, information for recognizing a start position of data following the control information) or information for a terminal to recognize a modulation method for control information such as MCS, and a channel coding rate. 
         [0311]    However, in relay apparatus  100  according to the present embodiment, a control header provided in control information for a terminal under the control of relay apparatus  100  further contains notification information indicating existence or non-existence of a relay signal (relay data and control information) to the terminal. 
         [0312]    Also, as in embodiment 3, relay apparatus  100  transmits a known signal in a guard time (between period B and period C) provided for switching between transmission/reception processing in an adjacent RN. 
         [0313]      FIG. 19  is a block diagram illustrating a configuration of a terminal according to the present embodiment. In terminal  700  illustrated in  FIG. 19 , components that are the same as those of embodiment 7 ( FIG. 3 ) are provided with reference numerals that are the same as those of embodiment 7 and explanation of the components will be omitted. 
         [0314]    In terminal  700  illustrated in  FIG. 19 , receiving section  208  of reception processing section  207  performs demodulation and decoding of a relay signal input from first memory  203 . More specifically, if terminal  200  is connectable to two adjacent relay apparatuses (RNs), receiving section  208  performs the following processing. In period A or period B (period for communication between relay apparatuses), receiving section  208  receives a relay signal (a known signal, control information for relay data to terminal  200 , which is to be transmitted in period C, and a control header for the control information (hereinafter represented by CH), control information for a downstream RN and a control header for the control information (hereinafter indicated by CH) and relay data to another terminal under the control of the downstream RN), which is transmitted from the upstream RN to the downstream RN among the two relay apparatuses to which terminal  200  is connectable. 
         [0315]    However, receiving section  208  performs demodulation and decoding of control header CH′ for control information for the relay data to terminal  200  to be transmitted in period C, and outputs the decoded control header CH′ to relay signal existence/non-existence detection section  701 . 
         [0316]    Next, if information indicating that there is a relay signal (relay data and control information) for terminal  700  is input from relay signal existence/non-existence detection section  701  (which will described later), receiving section  208  performs demodulation and decoding of the control information for the relay data to terminal  700  to be transmitted in period C, the control information for the downstream RN and control header C 11  for the control information, and the relay data to the downstream RN. Furthermore, in period A or period B (period for communication between relay apparatuses), receiving section  208  receives a relay signal transmitted by the downstream RN in the two relay apparatuses to which terminal  700  is connectable (a known signal, control information for the relay data to another terminal (interference station for terminal  700 ) to be transmitted in period C and control header CH′ for the control information). Then, receiving section  208  performs demodulation and decoding of the received relay signal. 
         [0317]    Also, if information indicating that there is a relay signal (relay data and control information) for terminal  700  is input from relay signal existence/non-existence detection section  701 , in a guard time provided for switching between transmission/reception processing in one RN among two adjacent RNs (between period B and period C), receiving section  208  receives a known signal transmitted from the other RN. Then, receiving section  208  calculates a channel estimation value between the RN that has transmitted the known signal and terminal  700 , and outputs the channel estimation value to second memory  210 . Likewise, receiving section  208  calculates a channel estimation value between each RN and terminal  700  using the known signal from each RN, which is transmitted in periods A to C, and outputs the channel estimation value to second memory  210 . 
         [0318]    Meanwhile, if information indicating that there is no relay signal (relay data and control information) for terminal  700  is input from relay signal existence/non-existence detection section  701 , receiving section  208  stops reception processing in a DL subframe in which no relay signal for terminal  700  exists. 
         [0319]    Relay signal existence/non-existence detection section  701  determines whether or not a relay signal (relay data and control information) for terminal  700  exists (detects existence or non-existence of a relay signal) using notification information included in control header CH′ input from receiving section  208 . In other words, relay signal existence/non-existence detection section  701  detects notification information indicating existence or non-existence of a relay signal for terminal  700 , which is contained in control header CH′ provided in the control information for terminal  700 , to determine whether or not a relay signal for terminal  700  is transmitted from relay apparatus  100  (the upstream RN to which terminal  700  is connected). Then, relay signal existence/non-existence detection section  701  outputs information indicating existence or non-existence of a relay signal (“relay signal exists” or “no relay signal exists”) to receiving section  208  and timing control section  214 . 
         [0320]    If information indicating that a relay signal for terminal  700  exists is input from relay signal existence/non-existence detection section  701 , as in embodiment 7, timing control section  214  instructs first memory  203  and second memory  210  about timings for inputting/outputting a relay signal, based on the setting information input from odd/even number switching section  213 . Meanwhile, if information indicating that no relay signal for terminal  700  exists is input from relay signal existence/non-existence detection section  701 , timing control section  214  instructs first memory  203  and second memory  210  to stop reception processing in a DL subframe in which no relay signal for terminal  700  exists. 
         [0321]    Next, details of the processing in relay apparatus  100  and terminal  700  according to the present embodiment will be described. 
         [0322]    The below explanation will be provided for a case where multihop communication is performed by three or more RNs as in embodiment 7 ( FIG. 18 ). However, in  FIG. 20  and  FIG. 21 , only three relay apparatuses RN 1 , RN 2  and RN 3  among the three or more RNs are illustrated. Also, RN  1  is an upstream RN and RN 2  is a downstream RN between RN 1  and RN 2  illustrated in  FIG. 20  and  FIG. 21 . Also, between RN 2  and RN 3  illustrated in  FIG. 20  and  FIG. 21 , RN 2  is an upstream RN and RN 3  is a downstream RN. Also, in  FIG. 20  and  FIG. 21 , MS 1  is connected to RN 1 , and MS 2  is connected to RN 2 . Also, RN 1 , RN 2  and RN 3  illustrated in  FIG. 20  and  FIG. 21  each include the configuration of relay apparatus  100  illustrated in  FIG. 2 , and MS 1  and MS 2  each include the configuration of terminal  700  illustrated in  FIG. 19 . 
         [0323]    Also, in  FIG. 20  and  FIG. 21 , transmission processing is represented by “TX,” and reception processing is represented by “RX.” 
         [0324]    Also, in  FIG. 20  and  FIG. 21 , control information for relay data transmission between relay apparatuses (control information for a downstream RN) is represented by “CONTROL INFORMATION for RN,” and a control header for control information for relay data transmission between relay apparatuses is represented by “CH,” and relay data between relay apparatuses (relay data to a downstream RN) is represented by “DATA to RN.” Also, in  FIG. 20  and  FIG. 21 , control information for transmission of relay data to a terminal (control information for a terminal) is represented by “CONTROL INFORMATION for MS” and a control header for control information for transmission of relay data to a terminal is represented by “CH′,” and relay data to a terminal is represented by “DATA to MS.” 
         [0325]    Here, the explanation will be provided focusing on control information notification processing in RN 1  (odd-numbered RN) and MS 1  connected to RN 1  (MS 1  under the control of RN 1 ), which are illustrated in  FIG. 20  and  FIG. 21 . 
         [0326]    First, an explanation will be provided for a case where relay data to MS 1  (DATA to MS) is transmitted from RN 1  to MS 1  in a DL subframe as illustrated in  FIG. 20 . 
         [0327]    In other words, in period A of the DL subframe illustrated in  FIG. 20 , RN 1  transmits a known signal, control information for transmission of relay data to a terminal under the control of RN 1  (MS 1 ) (CONTROL INFORMATION for MS) and control header CH′ for the control information, control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN). At this time, control header CH′ contains notification information indicating that a relay signal for the terminal under the control of RN 1  (MS 1 ) (DATA to MS) is contained (assigned data exists). 
         [0328]    Also, in period B, RN 1  receives, from an upstream apparatus, a known signal, control header CH′ for control information for transmission of relay data to a terminal under the control of the upstream apparatus, control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN). Also, in period C, RN 1  transmits the relay data to the terminal under the control of RN 1  (MS 1 ) (DATA to MS) to MS 1 . 
         [0329]    Meanwhile, in period A of the DL subframe illustrated in  FIG. 20 , first, MS 1  (receiving section  208 ) receives control header CH′ for control information for transmission of relay data to the terminal under the control of RN 1  (MS 1 ), and performs demodulation and decoding of control header CH′. Then, MS 1  (relay signal existence/non-existence detection section  701 ) determines that relay data to MS 1  (DATA to MS) is transmitted from RN 1 , using notification information contained in control header CH′. 
         [0330]    Therefore, as in embodiment 7, in period A, MS 1  further receives control information for transmission of relay data to a terminal under the control of RN 2  (MS 2 ) (CONTROL INFORMATION for MS), a known signal, control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN), which are transmitted from RN 1  to RN 2 . Also, in period B, MS 1  receives a known signal, and control information for transmission of relay data to the terminal under the control of RN 2  (MS 2 ) (CONTROL INFORMATION for MS) and control header CH′ for the control information, which are transmitted from RN 2  to RN 3 . Also, in period C, MS 1  receives relay data to the terminal under the control of RN 1  (MS 1 ) (DATA to MS) from RN 1 . Then, as in embodiment 7, MS 1  removes an interference signal from the signal received in period C (relay data from RN 1  (desired signal) and relay data from RN 2  (interference signal)), using the interference signal, the control information on the interference signal, the control information for MS 1 , a channel estimation value between RN 1  and MS 1  and a channel estimation value between RN 2  and MS 1 , which are obtained in period A and period B, thereby obtaining a desired signal. 
         [0331]    Next, the explanation will be provided for a case where no relay data to MS 1  (DATA to MS) is transmitted from RN 1  to MS 1  in a DL subframe as illustrated in  FIG. 21 . 
         [0332]    In other words, in period A in the DL subframe illustrated in  FIG. 21 , RN 1  transmits a known signal, control header CH′ for control information for transmission of relay data to the terminal under the control of RN 1  (MS 1 ) (CONTROL INFORMATION for MS), control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN). In other words, in the DL subframe illustrated in  FIG. 21 , RN 1  does not transmit control information for transmission of relay data to MS 1  (CONTROL INFORMATION for MS) and relay data to MS 1  (DATA to MS). Control header CH′ transmitted in period A contains notification information indicating that no relay data to the terminal under the control of RN 1  (MS 1 ) (DATA to MS) is contained (NO ASSIGNED DATA EXISTS). 
         [0333]    Meanwhile, in period A in the DL subframe illustrated in  FIG. 21 , as in  FIG. 20 , MS 1  (receiving section  208 ) first receives control header CH′ for control information for transmission of relay data to the terminal under the control of RN 1  (MS 1 ), and performs demodulation and decoding of control header CH′. Then, MS 1  (relay signal existence/non-existence detection section  701 ) determines that no relay data to MS 1  (DATA to MS) is transmitted from RN 1 , using the notification information contained in control header CH′. Therefore, MS 1  stops reception processing (demodulation and decoding) of a part following control header CH′ in the DL subframe illustrated in  FIG. 21 . 
         [0334]    As described above, if terminal  700  determines that a relay signal for terminal  700  (relay data and control information) is transmitted from relay apparatus  100  (upstream RN) to which terminal  700  is connected ( FIG. 20 ), using notification information contained in control header CH′, terminal  700  performs reception processing of control information for terminal  700  transmitted from an upstream RN and control information for another terminal apparatus transmitted from a downstream RN in period A or period B as in embodiment 7. Then, terminal  700  performs interference removal processing in period C as in embodiment 7. 
         [0335]    In other words, if a relay signal for terminal  700  exists in period C, terminal  700  receives control information for terminal  700  and control information for a terminal under the control of a downstream RN from two adjacent relay apparatuses to which terminal  700  is connectable (RN 1  and RN 2  for MS 1  illustrated in  FIG. 20 ) in period A or period B without interference as in embodiment 7, and thus, can perform interference removal (interference cancellation) with good precision. 
         [0336]    Meanwhile, if terminal  700  determines that no relay signal for terminal  700  is transmitted from relay apparatus  100  (upstream RN) to which terminal  700  is connected ( FIG. 21 ), using notification information contained in control header CH′, terminal  700  stops reception processing for the control information for terminal  700  transmitted from the upstream RN and the control information for the other terminal apparatus transmitted from the downstream RN in period A or period B. 
         [0337]    In other words, terminal  700  activates relay signal reception processing in period A and period B only if a relay signal for terminal  700  is received in period C (that is, if interference removal processing is needed). In other words, if no relay data to terminal  700  exists in period C, terminal  700  stops the relay signal reception processing in period A or period B, enabling suppression of wasteful processing such as reception processing for an interference signal and control information on the interference signal and estimation processing for a channel to an interference station. 
         [0338]    As described above, according to the present embodiment, even in a case where multihop communication is performed between a plurality of relay apparatuses using the same frequency, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reduced as in embodiment 1. Furthermore, according to the present embodiment, a terminal uses periods for communication between relay apparatuses (period A and period B) for transmission of control information for terminals, making it possible to reliably obtain control information on a desired signal (relay data to this terminal) and control information on an interference signal (relay data to another terminal). Thus, in the present embodiment, as in embodiment 7, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reliably reduced. Furthermore, according to the present embodiment, in a certain subframe, if no relay data to a terminal exists (if interference removal processing is not needed), the terminal stops processing for reception of relay signals from each relay apparatus, enabling suppression of wasteful processing for interference removal processing. 
       Embodiment 9 
       [0339]    Embodiment 8 has been described for a case where notification information indicating existence or non-existence of a relay signal for a terminal is contained in a control header provided in control information for the terminal. Meanwhile, the present embodiment will be described for a case where a relay apparatus transmits information indicating existence or non-existence of a relay signal (relay data and control information) for a terminal in a certain subframe, in a subframe immediately before the subframe (previous subframe). 
         [0340]    The present embodiment will be specifically described below. 
         [0341]      FIG. 22  illustrates relay apparatus  800  according to the present embodiment. In relay apparatus  800  illustrated in  FIG. 22 , components that are the same as those of relay apparatus  100  ( FIG. 2 ) in embodiment 8 are provided with reference numerals that are the same as those of relay apparatus  100 , and explanation of the components will be omitted. Relay apparatus  800  illustrated in  FIG. 22  is different from relay apparatus  100  in addition of next subframe transmission information generation section  801 , and operations of reception processing section  104  and timing control section  109 . 
         [0342]    In relay apparatus  800  illustrated in  FIG. 22 , reception processing section  104  first performs demodulation and decoding of control information for a relay signal between relay apparatuses contained in a relay signal input from first memory  103 . Here, notification of a mapping position and an MCS (modulation and coding scheme), or the like of the control information are provided in a control header provided in the control information. Also, the control information contains a mapping position and an MCS of the relay signal between relay apparatuses (data directed to a terminal connected to relay apparatus  100  and/or data directed to a terminal connected to a downstream RN). Then, reception processing section  104  performs demodulation and decoding of a data signal contained in the relay signal input from first memory  103 , based on the mapping position and the MCS contained in the control information. Then, reception processing section  104  outputs the decoded signal to second memory  105 . 
         [0343]    Furthermore, reception processing section  104  detects whether or not a relay signal for a terminal under the control of relay apparatus  800 , which is to be transmitted in a subframe following the current subframe, is contained in the received relay signal. Then, if a relay signal to be transmitted in the following subframe is contained in the received relay signal, reception processing section  104  outputs information indicating which terminal under the control of relay apparatus  800  the relay signal is directed, to next subframe transmission information generation section  801 . 
         [0344]    Next subframe transmission information generation section  801  generates information, as next subframe transmission information, in which whether or not a relay signal to be transmitted in the following subframe exists is mapped for every terminal under the control of relay apparatus  800 , based on the information input from reception processing section  104 . Then, next subframe transmission information generation section  801  outputs the generated next subframe transmission information to second memory  105 . Consequently, the next subframe transmission information is stored (written) in second memory  105 . 
         [0345]    Timing control section  109  instructs first memory  103  and second memory  105  about timings for inputting/outputting relay signals, based on setting information input from odd/even number switching section  108 . 
         [0346]    For example, if the setting information input from odd/even number switching section  108  indicates “odd number” (if relay apparatus  800  is an odd-numbered RN), in period A, timing control section  109  instructs (gives a read instruction to) first memory  103  to output control information for relay data to a terminal under the control of relay apparatus  100 , which is to be transmitted in period C, and a control header for the control information, and control information for relay data to a downstream RN and a control header for the control information, and a relay signal for the downstream RN to RF transmitting section  107 . 
         [0347]    Also, in period B, timing control section  109  instructs (gives a write instruction to) first memory  103  to store a relay signal input from RF receiving section  102  (relay signal for a terminal connected to relay apparatus  100  and/or a relay signal for a terminal connected to the downstream RN, and control information for each relay signal). Also, in period B, when the relay signal is stored in first memory  103 , timing control section  109  instructs (gives a read instruction to) first memory  103  to output the stored relay signal to reception processing section  104 , and instructs (gives a write instruction to) second memory  105  to store the signal input from reception processing section  104  (decoded signal) and the next subframe transmission information input from next subframe transmission information generation section  801 . Also, in period B, when the decoded signal is stored in second memory  105 , timing control section  109  instructs (gives a read instruction to) second memory  105  to output the relay signal (the relay signal for the terminal connected to relay apparatus  100  and/or the relay signal for the terminal connected to the downstream RN, the control information for each relay signal, and the next subframe transmission information) to transmission processing section  106 . Also, in period B, timing control section  109  instructs (gives a write instruction to) first memory  103  to store the relay signal input from transmission processing section  106  (the relay signal for the terminal connected to relay apparatus  100  and/or the relay signal for the terminal connected to the downstream RN, the control information for each relay signal, and the next subframe transmission information). 
         [0348]    Meanwhile, if the setting information input from odd/even number switching section  108  indicates “even number” (if relay apparatus  100  is an even-numbered RN), timing control section  109  performs, in period B, processing similar to the processing performed in period A when the setting information indicates “odd number,” and performs, in period A, processing similar to the processing performed in period B when the setting information indicates “odd number.” In other words, the processing in period A and the processing in period B in timing control section  109  are interchanged between an odd-numbered RN and an even-numbered RN. 
         [0349]    Also, regardless of the setting information input from odd/even number switching section  108 , in period C, timing control section  109  instructs (gives a read instruction to) first memory  103  to output the relay signal for the terminal connected to relay apparatus  100  to RF transmitting section  107 . Also, regardless of the setting information input from odd/even number switching section  108 , at a timing subsequent to period C (for example, an tail end of a subframe), timing control section  109  instructs (gives a read instruction to) first memory  103  to output the next subframe transmission information to RF transmitting section  107 . 
         [0350]    Also, as in embodiment 8, relay apparatus  100  transmits a known signal in a guard time provided for switching between transmission/reception processing in an adjacent RN (between period B and period C). 
         [0351]    Next, a terminal according to the present embodiment will be described. Terminal  700  ( FIG. 19 ) according to the present embodiment has a configuration similar to that of embodiment 8 and is different from that of embodiment 8 only in operations of receiving section  208 , timing control section  214  and relay signal existence/non-existence detection section  701 . 
         [0352]    In terminal  700  according to the present embodiment, receiving section  208  of reception processing section  207  performs demodulation and decoding of a relay signal input from first memory  203 . More specifically, if terminal  700  is connectable to two adjacent relay apparatuses (RNs), receiving section  208  performs the following processing. Receiving section  208  first performs demodulation and decoding of next subframe transmission information received at a timing following period C of a previous subframe, and outputs the decoded next subframe transmission information to relay signal existence/non-existence detection section  701 . The next subframe transmission information received in the previous subframe indicates existence or non-existence of a relay signal for terminal  700  in the current subframe. 
         [0353]    Next, if information indicating that a relay signal for terminal  700  exists in the current sub frame is input from relay signal existence/non-existence detection section  701  (which will be described later), in period A or period B (period for communication between relay apparatuses), receiving section  208  receives a relay signal transmitted by an upstream RN among two relay apparatuses to which terminal  700  is connectable (a known signal, control information for relay data to terminal  200  to be transmitted in period C and a control header for the control information (hereinafter represented by CH′), control information for a downstream RN and a control header for the control information (hereinafter represented by CH), and relay data to the downstream RN), and performs demodulation and decoding of the received relay signal. Furthermore, in period A or period B (period for communication between relay apparatuses), receiving section  208  receives a relay signal transmitted by the downstream RN among the two relay apparatuses to which terminal  700  is connectable (a known signal, control information for relay data to another terminal (an interference station for terminal  700 ) to be transmitted in period C and control header CH′ for the control information), and performs demodulation and decoding of the received relay signal. 
         [0354]    Also, if information indicating that a relay signal for terminal  700  exists is input from relay signal existence/non-existence detection section  701 , in a guard time provided for switching between transmission/reception processing in one RN among the two adjacent RNs (between period B and period C), receiving section  208  receives a known signal transmitted from the other RN. Then, receiving section  208  calculates a channel estimation value between the RN that transmitted the known signal and terminal  700 , and outputs the channel estimation value to second memory  210 . Likewise, receiving section  208  calculates a channel estimation value between each RN and terminal  700  using the known signal from each RN transmitted in periods A to C, and outputs the channel estimation value to second memory  210 . 
         [0355]    Meanwhile, if information indicating that no relay signal for terminal  700  exists in the current subframe is input from relay signal existence/non-existence detection section  701 , receiving section  208  receives a relay signal (a known signal only) transmitted in period A from the upstream RN to the downstream RN among the two relay apparatuses to which terminal  700  is connectable, and maintains synchronization with upstream RN. Also, receiving section  208  receives next subframe transmission information at a timing subsequent to period C in the current subframe. In other words, if information indicating that no relay signal for terminal  700  exists in the current subframe is input from relay signal existence/non-existence detection section  701  (that is, a DL subframe in which no relay signal for terminal  700  exists), receiving section  208  stops processing for reception of all of relay signals except the known signal and the next subframe transmission information in period A. 
         [0356]    Relay signal existence/non-existence detection section  701  detects the next subframe transmission information (notification information) transmitted from the upstream RN in the previous subframe, which is input from receiving section  208 , to determine whether or not a relay signal for terminal  700  is transmitted from relay apparatus  800  (the upstream RN to which terminal  700  is connected) in the current subframe (detects existence or non-existence of a relay signal). Then, relay signal existence/non-existence detection section  701  outputs information indicating existence or non-existence of a relay signal (“signal exists” or “no signal exists”) to receiving section  208  and timing control section  214 . 
         [0357]    If information indicating that a relay signal for terminal  700  exists in the current subframe is input from relay signal existence/non-existence detection section  701 , in the current subframe, timing control section  214  instructs first memory  203  and second memory  210  about timings for inputting/outputting relay signals, based on setting information input from odd/even number switching section  213 , as in embodiment 7. 
         [0358]    Meanwhile, if information indicating that no relay signal for terminal  700  exists in the current subframe is input from relay signal existence/non-existence detection section  701 , in the current subframe, timing control section  214  instructs first memory  203  and second memory  210  to receive the known signal in period A and the next subframe transmission information at the timing subsequent to period C only and stop reception processing at other timings. For example, timing control section  214  masks clocks for the respective component units so that the component units operate at a timing corresponding to the known signal in period A and the timing subsequent to period C only. 
         [0359]    Next, details of the processing in relay apparatus  800  ( FIG. 22 ) and terminal  700  ( FIG. 19 ) according to the present embodiment will be described. 
         [0360]    The below explanation will be provided for a case where multihop communication is performed using three or more RNs as in embodiment 8 ( FIG. 20  and  FIG. 21 ). However, in  FIG. 23  and  FIG. 24 , only three relay apparatuses RN 1 , RN 2  and RN 3  among the three or more RNs are illustrated. Also, RN 1  is an upstream RN and RN 2  is a downstream RN between RN 1  and RN 2  illustrated in  FIG. 23  and  FIG. 24 . Also, RN 2  is an upstream RN and RN 3  is a downstream RN between RN 2  and RN 3  illustrated in  FIG. 23  and  FIG. 24 . Also, in  FIG. 23  and  FIG. 24 , MS 1  is connected to RN 1  and MS 2  is connected to RN 2 . RN 1 , RN 2  and RN 3  illustrated in  FIG. 23  and  FIG. 24  each include the configuration of relay apparatus  800  illustrated in  FIG. 22 , and MS 1  and MS 2  each include the configuration of terminal  700  illustrated in  FIG. 19 . 
         [0361]    Also, in  FIG. 23  and  FIG. 24 , transmission processing is represented by “TX” and reception processing is represented by “RX.” 
         [0362]    Also, in  FIG. 23  and  FIG. 24 , as in embodiment 8 ( FIG. 20  and  FIG. 21 ), control information for transmission of relay data between relay apparatuses (control information for a downstream RN) is represented by “CONTROL INFORMATION for RN,” a control header for control information for transmission of relay data between relay apparatuses is represented by “CH,” and relay data between relay apparatuses (relay data to the downstream RN) is represented by “DATA to RN.” Also, in  FIG. 23  and  FIG. 24 , control information for transmission of relay data to a terminal (control information for a terminal) is represented by “CONTROL INFORMATION for MS,” a control header of control information for transmission of relay data to a terminal is represented by “CH,” and relay data to a terminal is represented by “DATA to MS.” Also, in  FIG. 23  and  FIG. 24 , next subframe transmission information is represented by “i.” However, in order to avoid interference between adjacent relay apparatuses, next subframe transmission information i is transmitted using, for example, resources (e.g., time, frequency or code) different from each other between relay transmissions. 
         [0363]    Here, the explanation will be provided focusing on control information notification processing in RN 1  (odd-numbered RN) and MS 1  connected to RN 1  (MS 1  under the control of RN 1 ) illustrated in  FIG. 23  and  FIG. 24 . 
         [0364]    First, as illustrated in  FIG. 23 , a case where relay data to MS 1  (DATA to MS) is transmitted from RN 1  to MS 1  in DL subframe (n) will be described. 
         [0365]    Here, at a timing subsequent to period C in DL subframe (n−1), which is a subframe before DL subframe (n) illustrated in  FIG. 23 , RN 1  transmits next subframe transmission information i. Next subframe transmission information i in DL subframe (n−1) indicates that a relay signal for MS 1  (DATA to MS) transmitted in DL subframe (n) exists (ASSIGNED DATA EXISTS). 
         [0366]    Also, in period A in DL subframe (n) illustrated in  FIG. 23 , RN 1  transmits a known signal, control information for transmission of relay data to a terminal (MS 1 ) under the control of RN 1  (CONTROL INFORMATION for MS) and control header CH′ for the control information, control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN) as in embodiment 8. Also, in period B in DL subframe (n), RN 1  receives, from an upstream apparatus, a known signal, control header CH′ for control information for transmission of relay data to a terminal under the control of the upstream apparatus, control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN). Also, in period C in DL subframe (n), RN 1  transmits relay data to the terminal under the control of RN 1  (MS 1 ) (DATA to MS) to MS 1 . 
         [0367]    Also, at a timing subsequent to period C in DL subframe (n) illustrated in  FIG. 23 , RN 1  transmits next subframe transmission information i indicating existence or non-existence of relay signal to the terminal under the control of RN 1  in the next DL subframe (n+1) (not illustrated). 
         [0368]    Meanwhile, at a timing subsequent to period C in DL subframe (n−1), MS 1  (receiving section  208 ) receives next subframe transmission information i. Then, MS 1  (relay signal existence/non-existence detection section  701 ) determines that relay data to MS 1  (DATA to MS) is transmitted from RN 1  in DL subframe (n), using next subframe transmission information i. 
         [0369]    Therefore, in period A in DL subframe (n), MS 1  receives the control information for transmission of relay data to the terminal under the control of RN 1  (MS 1 ) (CONTROL INFORMATION for MS) and control header CH′ for the control information, and the known signal, the control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and the relay data between relay apparatuses (DATA to RN), which are transmitted from RN 1  to RN 2 . Also, in period B in DL subframe (n), MS 1  receives a known signal, and control information for transmission of relay data to a terminal under the control of RN 2  (MS 2 ) (CONTROL INFORMATION for MS) and control header CH′ for the control information, which are transmitted from RN 2  to RN 3 . Also, in period C in DL subframe (n), MS 1  receives relay data to the terminal under the control of RN 1  (MS 1 ) (DATA to MS) from RN 1 . Then, as in embodiment 8, MS 1  removes an interference signal from the signal received in period C (the relay data from RN 1  (desired signal) and the relay data from RN 2  (interference signal)), using the interference signal, the control information on the interference signal, the control information for MS 1 , a channel estimation value between RN 1  and MS 1  and a channel estimation value between RN 2  and MS 1 , which are obtained in period A and period B, thereby obtaining the desired signal. 
         [0370]    Next, the explanation will be provided for a case where no relay data to MS 1  (DATA to MS) is transmitted from RN 1  to MS 1  in DL subframe (n) as illustrated in  FIG. 24 . 
         [0371]    In this case, at a timing subsequent to period C in DL subframe (n−1), which is a subframe before DL subframe (n) illustrated in  FIG. 24 , RN 1  transmits next subframe transmission information i. Next subframe transmission information i in DL subframe (n−1) indicates that no relay signal for MS 1  (DATA to MS) transmitted in DL subframe (n) exists (NO ASSIGNED DATA EXISTS). 
         [0372]    Also, in period A in DL subframe (n) illustrated in  FIG. 24 , RN 1  transmits a known signal, control header CH′ for control information for transmission of relay data to the terminal under the control of RN 1  (MS 1 ) (CONTROL INFORMATION for MS), control information for transmission of relay data between relay apparatuses (CONTROL INFORMATION for RN) and control header CH for the control information, and relay data between relay apparatuses (DATA to RN). In other words, in DL subframe (n) illustrated in  FIG. 24 , RN 1  does not transmit control information for transmission of relay data to MS 1  (CONTROL INFORMATION for MS) and relay data to MS 1  (DATA to MS). 
         [0373]    Also, at a timing subsequent to period C in DL subframe (n) illustrated in  FIG. 24 , RN 1  transmits next subframe transmission information i indicating existence or non-existence of a relay signal for a terminal under the control of RN 1  in the next DL subframe (n+1) (not illustrated). 
         [0374]    Meanwhile, at a timing subsequent to period C in DL subframe (n−1), MS 1  (receiving section  208 ) receives next subframe transmission information i. Then, MS 1  (relay signal existence/non-existence detection section  701 ) determines that no relay data to MS 1  (DATA to MS) is transmitted from RN 1  in DL subframe (n), using next subframe transmission information i. 
         [0375]    Therefore, in period A in DL subframe (n) illustrated in  FIG. 24 , MS 1  receives a known signal from RN 1  in order to maintain synchronization with RN 1 . Also, at a timing subsequent to period C in DL subframe (n) illustrated in  FIG. 24 , MS 1  receives next subframe transmission information i in order to determine existence or non-existence of a relay signal for MS 1  in next DL subframe (n+1). In other words, in DL subframe (n) illustrated in  FIG. 24 , MS 1  stops reception processing for interference removal processing. 
         [0376]    Here, embodiment 8 ( FIG. 21 ) and the present embodiment ( FIG. 24 ) will be compared with each other in terms of a DL subframe in which no relay signal for terminal  700  exists. In embodiment 8 ( FIG. 21 ), each terminal receives notification information indicating existence or non-existence of a relay signal for the terminal in a certain DL subframe, in the DL subframe (control header CH′). Accordingly, for example, in embodiment 8 ( FIG. 21 ), focusing on MS 2 , MS 2  can determine existence or non-existence of a relay signal for MS 2  only in period B. In other words, in embodiment 8 ( FIG. 21 ), MS 2  (terminal under the control of an even-numbered RN) needs to receive control information for possible interference in period A regardless of existence or non-existence of a relay signal for MS 2 . Meanwhile, in the present embodiment ( FIG. 24 ), terminal  700  receives notification information indicating existence or non-existence of a relay signal for terminal  700  (next subframe transmission information) in a certain DL subframe, in a DL subframe before the DL subframe (previous DL subframe). In other words, in the present embodiment ( FIG. 24 ), every terminal  700  (MS 1  and MS 2  in  FIG. 24 ) can determine existence or non-existence of a relay signal for terminal  700  at a start point of a DL subframe regardless of which RN the terminal is connected to. 
         [0377]    Consequently, terminal  700  need not receive information for interference removal (relay data that may cause interference and control information) at all in a DL subframe in which no relay signal for terminal  700  exists, enabling further suppression of wasteful processing compared to embodiment 8. 
         [0378]    Also, as in embodiment 7 and embodiment 8, in period A or period B, terminal  700  can receive control information for terminal  700  and control information for a terminal under the control of a downstream RN from two adjacent relay apparatuses to which terminal  700  is connectable (RN 1  and RN 2  for MS 1  illustrated in  FIG. 20 ) without interference, respectively, enabling interference removal (interference cancellation) to be performed with good precision. 
         [0379]    As described above, according to the present embodiment, even in a case where multihop communication is performed between a plurality of relay apparatuses using the same frequency, as in embodiment 1, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reduced. Furthermore, according to the present embodiment, a terminal uses periods for communication between relay apparatuses (period A and period B) for communication of control information for the terminal, making it possible to reliably obtain control information on a desired signal (relay data to this terminal) and control information on an interference signal (relay data to another terminal). Thus, in the present embodiment, as in embodiment 7 and embodiment 8, interference to a signal from a relay apparatus to which a terminal is connected, by a signal from another relay apparatus can be reliably reduced. Furthermore, according to the present embodiment, if no relay data to a terminal exists (if interference removal processing is not needed) in a certain subframe, the terminal stops reception processing for a relay signal from each relay apparatus from a start point of the subframe, enabling further suppression of wasteful processing for interference removal processing compared to embodiment 8. 
         [0380]    Embodiments of the present invention have been described above. 
         [0381]    Embodiments 1 to 3 have been described assuming a case where relay apparatuses and terminals complete reception processing and transmission processing for all signals by period C in each DL subframe. However, time required for transmission/reception processing differs depending on, e.g., the content of the processing or the processing capability in a relay apparatus and a terminal or the data amount in the relay signal. However, in the present invention, effects similar to those of the above-described embodiments can be provided even in a case where processing of data received by a relay apparatus in period A or period B in each DL subframe is not completed by period C subsequent to period A and period B and a signal received in a previous DL subframe is transmitted in period C. 
         [0382]    Also, in the present invention, for example, as illustrated in  FIG. 25 , processing for selecting a connection-destination relay apparatus (RN) (serving cell) in a terminal (for example, the processing illustrated in  FIG. 4 ) may be performed in a period for connection-destination RN selection processing (“RN selection” illustrated in  FIG. 25 ), which is periodically provided between a DL subframe (“DL” illustrated in  FIG. 25 ) and an UL subframe (“UL” illustrated in  FIG. 25 ). Alternatively, processing for selecting a connection-destination RN in a terminal may be performed concurrently with communication between RNs and communication between RNs and terminals in downlink and uplink. In this case, in processing for selecting a connection-destination RN in a terminal, which is illustrated in  FIG. 4  (step  1  to step  4 ), step  1  and step  2  are performed in period A and period B in the DL subframe illustrated in  FIG. 5 . In other words, a known signal contained in a relay signal communicated between RNs (an upstream RN and a downstream RN) is used in step  1  and step  2  illustrated in  FIG. 4 . Also, in the processing for selecting a connection-destination RN in a terminal, which is illustrated in  FIG. 4 , step  3  is performed in period A′ in the UL subframe illustrated in  FIG. 14 . Also, in the processing for selecting a connection-destination RN in a terminal, which is illustrated in  FIG. 4 , step  4  is performed in period A or period B following the DL subframe in which step  1  and step  2  have been performed. 
         [0383]    Furthermore, although the above embodiments have been described taking a case where the present invention includes hardware as an example, the present invention can be provided by software. 
         [0384]    Also, the respective functional blocks used for the illustration of the above embodiments are typically provided as LSIs, which are integrated circuits. These may be formed into individual chips, or a part or all of these may be formed into one chip. Although LSIs are mentioned here, the LSIs may also be referred to as ICs, system LSIs, super LSIs or ultra LSIs according to the differences in integration density. 
         [0385]    Also, a technique of providing an integrated circuit is not limited to LSI and may be provided by a dedicated circuit or a general-purpose processor. An FPGA (field programmable gate array) that enables programming after manufacture of an LSI, or a reconfigurable processor enabling reconfiguration of connection and/or setting of circuit cells inside an LST may be used. 
         [0386]    Furthermore, it should be understood that if an integrated circuit technique replacing LSI emerges as a result of advancement in semiconductor technology or another technology derived from the semiconductor technology, integration of functional blocks may be performed using such technique. For example, biotechnology may be employed. 
         [0387]    The entire disclosure of the specification, drawings and abstract included in each of Japanese Patent Application No. 2010-019058 filed on Jan. 29, 2010 and Japanese Patent Application No. 2010-100870 filed on Apr. 26, 2010 are incorporated in the present application by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0388]    The present invention is applicable to, e.g., mobile communication systems. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100 ,  300 ,  500 ,  800  Relay apparatus 
           200 ,  400 ,  600 ,  700  Terminal 
           101 ,  201  Antenna 
           102 ,  202  RF receiving section 
           103 ,  203  First memory 
           104 ,  207  Reception processing section 
           105 ,  210  Second memory 
           106 ,  211 ,  302  Transmission processing section 
           107 ,  212  RF transmitting section 
           108 ,  213  Odd/even number switching section 
           109 ,  214 ,  303 ,  402 ,  501 ,  601  Timing control section 
           204  Known signal detection section 
           205  Signal strength measuring section 
           206  Selection section 
           208 ,  602  Receiving section 
           209 ,  603  Interference removal section 
           301  Scheduling section 
           401  Pointer generation section 
           701  Relay signal existence/non-existence detection section 
           801  Next subframe transmission information generation section