Abstract:
In order to achieve a more efficient data transmission, an RN  200,  which is to relay communications between UE  300  and a DeNB  100,  notifies, in advance, the DeNB  100  of a timing at which RN  200  can transmit, to the DeNB  100,  upstream data received from the UE  300,  and thereafter the RN  200  transmits the upstream data to the DeNB  100.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a radio relay station, a radio base station, a communication system, and a communication method that perform communication. 
       BACKGROUND ART 
       [0002]    In recent years, in order to substantially widen a cover area of a radio base station or to maintain an electric field strength of received signals at a communication terminal, a technology in which a radio relay station connected to a radio base station is provided and the radio relay station is caused to relay communications between the radio base station and a communication terminal has been considered. 
         [0003]      FIG. 21  is a diagram illustrating one form of a common radio communication system provided with a relay apparatus. 
         [0004]    The radio communication system illustrated in  FIG. 21  is composed of DeNBs (Donor evolved Node Bs)  1000 - 1  and  1000 - 2  that are radio base stations, an RN (Relay Node)  2000  that is a radio relay station, and UEs (User Equipments)  3000 - 1  and  3000 - 2  that are communication terminals. 
         [0005]    The RN  2000  relays communication between the DeNB  1000 - 1  and the UE  3000 - 1 . 
         [0006]    Furthermore, the RN  2000  relays communication between the DeNB  1000 - 2  and the UE  3000 - 2 . 
         [0007]    Furthermore, a technology in which, when, in a radio relay station as described above, a downlink line control signal is sent from a radio base station to the radio relay station at a timing at which the radio relay station is sending a downlink line control signal to a communication terminal, the radio relay station allocates a resource region that can receive the downlink line control signal sent from the radio base station has been considered (refer to, e.g., PTL 1). 
       CITATION LIST 
     Patent Literature 
       [0008]    [PTL 1] International Publication No. WO 2012/147295 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    Hereinafter, processing in the radio communication system illustrated in  FIG. 21  will be described. 
         [0010]      FIG. 22  is a sequence chart for describing an example of uplink data transmission processing in the radio communication system illustrated in  FIG. 21 . 
         [0011]    Firstly, the UE  3000 - 1  sends, to the RN  2000 , an uplink scheduling request signal (SR_a) for sending uplink data to the DeNB  1000 - 1 . Then, the RN  2000  sends, as a response signal therefor, an uplink scheduling information signal (UL_Grant for SR_a) to the UE  3000 - 1 . Subsequently, the UE  3000 - 1  sends, to the RN  2000 , an uplink buffer status-reporting signal (BSR_a) indicating a storage status of a buffer that temporarily stores uplink data. Then, the RN  2000  sends a response signal (UL_Grant for BSR_a) therefor to the UE  3000 - 1 . When receiving the UL_Grant for BSR_a, the UE  3000 - 1  sends, to the RN  2000 , uplink data (UL_Data_a) that are to be sent to the DeNB  1000 - 1 . After receiving the UL_Data_a from the UE  3000 - 1 , the RN  2000  sends an SR_a to the DeNB  1000 - 1 . 
         [0012]    Furthermore, the UE  3000 - 2  sends, to the RN  2000 , an uplink scheduling request signal (SR_b) for sending uplink data to the DeNB  1000 - 2 . Then, the RN  2000  sends, as a response signal therefor, an uplink scheduling information signal (UL_Grant for SR_b) to the UE  3000 - 2 . Subsequently, the UE  3000 - 2  sends, to the RN  2000 , an uplink buffer status-reporting signal (BSR_b) that indicates a storage status of a buffer that temporarily stores uplink data. Then, the RN  2000  sends a response signal (UL_Grant for BSR_b) therefor to the UE  3000 - 2 . When receiving the UL_Grant for BSR_b, the UE  3000 - 2  sends, to the RN  2000 , uplink data (UL_Data_b) that are to be sent to the DeNB  1000 - 2 . After receiving the UL_Data_b from the UE  3000 - 2 , the RN  2000  sends an SR_b to the DeNB  1000 - 2 . 
         [0013]    After that, when, simultaneously with the DeNB  1000 - 1  sending the UL_Grant for SR_a to the RN  2000 , the DeNB  1000 - 2  sends the UL_Grant for SR_b to the RN  2000 , the RN  2000  can perform reception processing of only one of the uplink scheduling information signals. Furthermore, even when the RN  2000  attempts to simultaneously perform sending of the BSR_a to the DeNB  1000 - 1  and sending of the BSR_b to the DeNB  1000 - 2 , the RN  2000  can send the uplink buffer status-reporting signal for only one thereof. 
         [0014]    Furthermore, when the DeNB  1000 - 2  sends the UL_Grant for BSR_b to the RN  2000  simultaneously with the DeNB  1000 - 1  sending the UL_Grant for BSR_a to the RN  2000 , the RN  2000  can only perform reception processing of only one thereof. Furthermore, even when the RN  2000  attempts to simultaneously perform transmission of the UL_Data_a to the DeNB  1000 - 1  and transmission of the UL_Data_b to the DeNB  1000 - 2 , the RN  2000  can send only the uplink data to one thereof. 
         [0015]    Thus, in some cases, timings at which signals are sent to or received from a plurality of radio base stations are simultaneous. For example, when transmission/reception of such signals between the RN  2000  and the DeNB  1000 - 2  cannot be carried out, retransmission processing for these signals is performed with the DeNB  1000 - 2 , resulting in a problem of delayed uplink data transmission. 
         [0016]      FIG. 23  is a sequence chart for describing another example of the uplink data transmission processing in the radio communication system illustrated in  FIG. 21 . In  FIG. 23 , a procedure until the RN  2000  attempts to perform simultaneously sending of the UL_Data_a to the DeNB  1000 - 1  and sending of the UL_Data_b to the DeNB  1000 - 2  is substantially the same as a procedure in  FIG. 22 . In  FIG. 23 , a case where a packet is subsequently discarded will be described. 
         [0017]      FIG. 23  illustrates a case where, when timings at which signals are sent to or received from a plurality of radio base stations become simultaneous and, therefore, for example, the RN  2000  cannot perform transmission/reception of such signals to/from the DeNB  1000 - 2 , a packet (uplink data) related to delay is discarded. For example, when the RN  2000  cannot send uplink data to the DeNB  1000 - 2  and, therefore, an amount of time for which the uplink data are buffered within the RN  2000  runs out, the buffered uplink data are discarded. Then, transmission/reception of the signals are performed between the UE  3000 - 2  and the RN  2000  again, retransmission processing for these signals is performed between the RN  2000  and the DeNB  1000 - 2 , resulting in a problem of the uplink data transmission being delayed. 
         [0018]      FIG. 24  is a sequence chart for describing an example of downlink data transmission processing performed by the radio communication system illustrated in  FIG. 21 . 
         [0019]    When the DeNB  1000 - 2  sends downlink data (DL_Data_b) to the RN  2000  simultaneously with the DeNB  1000 - 1  sending downlink data (DL_Data_a) to the RN  2000 , the RN  2000  can perform reception processing for the downlink data from only one of the DeNB  1000 - 2  and the DeNB  1000 - 1 . For example, when the RN  2000  has performed only reception processing of the DL_Data_a sent from the DeNB  1000 - 1 , the RN  2000  sends the DL_Data_a to the UE  3000 - 1 . Then, as a response to receiving the downlink data, the UE  3000 - 1  sends an Ack(HARQ)_a to the RN  2000 . 
         [0020]    After receiving the Ack(HARQ)_a from the UE  3000 - 1 , the RN  2000  sends the Ack(HARQ)_a to the DeNB  1000 - 1 . On the other hand, since the RN  2000  has not received the downlink data from the DeNB  1000 - 2 , the RN  2000  sends, to the DeNB  1000 - 2 , a Nack(HARQ)_b that is a signal indicating that the RN  2000  has not received the downlink data from the DeNB  1000 - 2 . 
         [0021]    Then, the DeNB  1000 - 2  resends, to the RN  2000 , the downlink data (DL_Data_b) to be sent to the UE  3000 - 2 . When receiving the DL_Data_b from the DeNB  1000 - 2 , the RN  2000  sends the DL_Data_b to the UE  3000 - 2 . 
         [0022]    Thus, the downlink data transmission has a problem of being delayed by simultaneous transmission, as is the case with the uplink data transmission. 
         [0023]    Furthermore, the technology described in PTL 1 is merely a technology that carries out allocation of resource regions and, as is the case with the foregoing configuration, has a problem of being incapable of preventing data transmission delay caused by simultaneous sending to or simultaneous reception from a plurality of nodes. 
         [0024]    An object of the present invention is to provide a radio relay station, a radio base station, a communication system, and a communication method that solve the problems stated above. 
       Solution to Problem 
       [0025]    A radio relay station according to the present invention includes 
         [0026]    a transmission means for notifying a radio base station of a timing at which uplink data sent from a communication terminal are able to be sent to the radio base station and then sending the uplink data to the radio base station. 
         [0027]    Furthermore, a radio base station according to the present invention includes 
         [0028]    a transmission means for notifying a radio relay station that relays communication with a communication terminal of a timing at which downlink data are able to be sent to the radio relay station and then sending the downlink data to the radio relay station. 
         [0029]    Furthermore, a communication system according to the present invention is a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, wherein 
         [0030]    the radio relay station includes a transmission means for notifying the radio base station of a timing at which uplink data sent from the communication terminal are able to be sent to the radio base station and then sending the uplink data to the radio base station. 
         [0031]    Furthermore, a communication system according to the present invention is a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, wherein 
         [0032]    the radio base station includes a transmission means for notifying the radio relay station of a timing at which downlink data are able to be sent to the radio relay station and then sending the downlink data to the radio relay station. 
         [0033]    Furthermore, a communication method according to the present invention includes 
         [0034]    notifying a radio base station of a timing at which uplink data sent from a communication terminal are able to be sent to the radio base station and then sending the uplink data to the radio base station. 
         [0035]    Furthermore, a communication method according to the present invention includes 
         [0036]    notifying a radio relay station that relays communication with a communication terminal of a timing at which downlink data are able to be sent to the radio relay station and then sending the downlink data to the radio relay station. 
         [0037]    Furthermore, a communication method according to the present invention 
         [0038]    is a communication method in a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, and 
         [0039]    includes, by the radio relay station, notifying the radio base station of a timing at which uplink data sent from the communication terminal are able to be sent to the radio base station and then sending the uplink data to the radio base station. 
         [0040]    Furthermore, a communication method according to the present invention 
         [0041]    is a communication method in a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, and 
         [0042]    includes, by the radio base station, performing processing of notifying the radio relay station of a timing at which downlink data are able to be sent to the radio relay station and then sending the downlink data to the radio relay station. 
       Advantageous Effects of Invention 
       [0043]    As described above, in the present invention, data transmission can be made more efficient. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0044]      FIG. 1  is a diagram illustrating a first example embodiment of the communication system of the present invention. 
           [0045]      FIG. 2  is a diagram illustrating an example of an internal structure of an RN illustrated in  FIG. 1 . 
           [0046]      FIG. 3  is a flowchart for describing an example of a communication method in the communication system illustrated in  FIG. 1 . 
           [0047]      FIG. 4  is a diagram illustrating a second example embodiment of the communication system of the present invention. 
           [0048]      FIG. 5  is a diagram illustrating an example of an internal structure of a DeNB illustrated in  FIG. 4 . 
           [0049]      FIG. 6  is a flowchart for describing an example of a communication method in the communication system illustrated in  FIG. 4 . 
           [0050]      FIG. 7  is a diagram illustrating a third example embodiment of the communication system of present invention. 
           [0051]      FIG. 8  is a diagram illustrating an example of an internal structure of an RN illustrated in  FIG. 7 . 
           [0052]      FIG. 9  is a diagram illustrating an example of an internal structure of a DeNB illustrated in  FIG. 7 . 
           [0053]      FIG. 10  is a flowchart for describing an example of transmission processing of a UL SR/UL BSR in the RN illustrated in  FIG. 7 , in a communication method in the communication system illustrated in  FIG. 7 . 
           [0054]      FIG. 11  is a flowchart for describing an example of transmission processing of a UL Grant in a DeNB illustrated in  FIG. 7 , in the communication method in the communication system illustrated in  FIG. 7 . 
           [0055]      FIG. 12  is a flowchart for describing an example of transmission processing of a UL Data in the RN illustrated in  FIG. 7 , in the communication method in the communication system illustrated in  FIG. 7 . 
           [0056]      FIG. 13  is a sequence chart for describing an example of flow of data in the communication system illustrated in  FIG. 7 . 
           [0057]      FIG. 14  is a diagram illustrating a fourth example embodiment of the communication system of the present invention. 
           [0058]      FIG. 15  is a diagram illustrating an example of an internal structure of an RN illustrated in  FIG. 14 . 
           [0059]      FIG. 16  is a diagram illustrating an example of an internal structure of a DeNB illustrated in  FIG. 14 . 
           [0060]      FIG. 17  is a flowchart for describing an example of transmission processing of DL SR/DL BSR in the DeNB illustrated in  FIG. 14 , in the communication method in the communication system illustrated in  FIG. 14 . 
           [0061]      FIG. 18  is a flowchart for describing an example of transmission processing of a DL Grant in the RN illustrated in  FIG. 14 , in the communication method in the communication system illustrated in  FIG. 14 . 
           [0062]      FIG. 19  is a flowchart for describing an example of transmission processing of a DL Data in the DeNB illustrated in  FIG. 14 , in the communication method in the communication system illustrated in  FIG. 14 . 
           [0063]      FIG. 20  is a sequence chart for describing an example of flow of data in the communication system illustrated in  FIG. 14 . 
           [0064]      FIG. 21  is a diagram illustrating a form of a general radio communication system provided with a relay apparatus. 
           [0065]      FIG. 22  is a sequence chart for describing an example of uplink data transmission processing in the radio communication system illustrated in  FIG. 21 . 
           [0066]      FIG. 23  is a sequence chart for describing another example of the uplink data transmission processing in the radio communication system illustrated in  FIG. 21 . 
           [0067]    FIG. 24  is a sequence chart for describing an example of downlink data transmission processing in the radio communication system illustrated in  FIG. 21 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0068]    Hereinafter, example embodiments of the present invention will be described with reference to the drawings. 
       First Example Embodiment 
       [0069]      FIG. 1  is a diagram illustrating a first example embodiment of the communication system of the present invention. A communication system in this example embodiment, as illustrated in  FIG. 1 , includes a DeNB  100 , an RN  200 , and a UE  300 . The DeNB  100  is a radio base station that communicates with the UE  300  via the RN  200 . The RN  200  is a radio relay station that relays communication between the DeNB  100  and the UE  300 . The UE  300  is a communication terminal that communicates with the DeNB  100  via the RN  200 . 
         [0070]      FIG. 2  is a diagram illustrating an example of an internal structure of the RN  200  illustrated in  FIG. 1 . The RN  200  illustrated in  FIG. 1  includes a transmission unit  201  as illustrated in  FIG. 2 . Note that  FIG. 2  illustrates only structural elements concerning this example embodiment, of structural elements that the RN  200  illustrated in  FIG. 1  includes. 
         [0071]    The transmission unit  201  sends to the DeNB  100  uplink data sent from the UE  300 . At this time, the transmission unit  201  notifies the DeNB  100  of the timing at which the uplink data sent from the UE  300  can be sent to the DeNB  100  and then sends the uplink data to the DeNB  100 . Note that in each block diagram in the present application, an arrow provided for a block indicates only a propagating direction of a signal that corresponds to a description and does not limit the propagating directions of other signals. 
         [0072]    Hereinafter, a communication method in the communication system illustrated in  FIG. 1  will be described.  FIG. 3  is a flowchart for describing an example of the communication method in the communication system illustrated in  FIG. 1 . First, when the RN  200  receives uplink data sent from the UE  300  (step S 1 ), the transmission unit  201  notifies the DeNB  100  of timing at which the transmission unit  201  can send the uplink data (step S 2 ). After that, at that timing, the transmission unit  201  sends the uplink data to the DeNB  100  (step S 3 ). In this manner, the radio relay station notifies the radio base station of the timing at which the radio relay station can send the uplink data, and then sends the uplink data to the radio base station at the timing. Therefore, the communication system of the first example embodiment can prevent failure in sending the uplink data and therefore can make the data transmission more efficient. 
       Second Example Embodiment 
       [0073]      FIG. 4  is a diagram illustrating a second example embodiment of the communication system of the present invention. The communication system in this example embodiment includes a DeNB  101 , an RN  202 , and a UE  300  as illustrated in  FIG. 4 . The DeNB  101  is a radio base station that communicates with the UE  300  via the RN  202 . The RN  202  is a radio relay station that relays communication between the DeNB  101  and the UE  300 . The UE  300  is a communication terminal that communicates with the DeNB  101  via the RN  202 . 
         [0074]      FIG. 5  is a diagram illustrating an example of an internal structure of the DeNB  101  illustrated in  FIG. 4 . The DeNB  101  illustrated in  FIG. 4  includes a transmission unit  102  as illustrated in  FIG. 5 . Note that  FIG. 5  illustrates only structural elements concerning this example embodiment, of the structural elements that the DeNB  101  illustrated in  FIG. 4  includes. The transmission unit  102  notifies the RN  202  of the timing at which downlink data can be sent to the RN  202  and then sends the downlink data to the RN  202 . 
         [0075]    Hereinafter, a communication method in the communication system illustrated in  FIG. 4  will be described.  FIG. 6  is a flowchart for describing an example of the communication method in the communication system illustrated in  FIG. 4 . First, when the DeNB  101  receives downlink data sent from a higher-order apparatus (e.g., a SGW (Serving Gateway)) of the DeNB  101  (step S 11 ), the transmission unit  102  notifies the RN  202  of the timing at which downlink data can be sent (step S 12 ). After that, the transmission unit  102 , at that timing, sends the downlink data to the RN  202  (step S 13 ). 
         [0076]    Thus, the radio base station notifies the radio relay station of the timing at which the station can send downlink data, and then, at that timing, sends the downlink data to the radio relay station. Therefore, the communication system of the second example embodiment can prevent failure in sending downlink data and therefore can make data transmission more efficient. 
       Third Example Embodiment 
       [0077]      FIG. 7  is a diagram illustrating a third example embodiment of the communication system of the present invention. The communication system in this example embodiment, as illustrated in  FIG. 7 , includes DeNBs  103 - 1  and  103 - 2 , the RN  203 , and UEs  300 - 1  and  300 - 2 . The DeNB  103 - 1  is a radio base station that communicates with the UE  300 - 1  via the RN  203 . The DeNB  103 - 2  is a radio base station that communicates with the UE  300 - 2  via the RN  203 . The RN  203  is a radio relay station that relays communication between the DeNB  103 - 1  and the UE  300 - 1  and communication between the DeNB  103 - 2  and the UE  300 - 2 . Furthermore, the RN  203  sends uplink signals to the DeNBs  103 - 1  and  103 - 2  by using a communication method of SC-FDMA or TD-SCDMA. The SC-FDMA is an abbreviation of “Single Carrier-Frequency Division Multiple Access” and TD-SCDMA is an abbreviation of “Time Division-Synchronous Code Division Multiple Access”. The UE  300 - 1  is a communication terminal that communicates with the DeNB  103 - 1  via the RN  203 . The UE  300 - 2  is a communication terminal that communicates with the DeNB  103 - 2  via the RN  203 . 
         [0078]      FIG. 8  is a diagram illustrating an example of an internal structure of the RN  203  illustrated in  FIG. 7 . 
         [0079]    The RN  203  illustrated in  FIG. 7  includes a transmission unit  204  and a UL Data receiving unit  211 , as illustrated in  FIG. 8 . Furthermore, the transmission unit  204  includes a UL Grant receiving unit  210 , a UL Grant information accumulating unit  212 , a UL SR/BSR information accumulating unit  213 , a UL transmission establishment timing extracting unit  214 , a UL transmission/reception candidate timing extracting unit  215 , a UL opposing node determination unit  216 , a UL opposing node flag providing unit  217 , a UL transmission/reception feasible timing candidate providing unit  218 , a UL SR/BSR determination unit  219 , a UL BSR generating unit  220 , a UL BSR transmission unit  221 , a UL SR generating unit  222 , a UL SR transmission unit  223 , a UL Data transmission feasibility determination unit  224 , an SR/BSR retransmission processing unit  225 , and a UL Data transmission unit  226 . Note that  FIG. 8  illustrates only structural elements concerning this example embodiment, of the structural elements that the RN  203  illustrated in  FIG. 7  includes. 
         [0080]    The UL Data receiving unit  211  receives uplink data sent from the UEs  300 - 1  and  300 - 2  and outputs the received uplink data to the UL opposing node determination unit  216 . 
         [0081]    The UL Grant receiving unit  210  receives response signals (UL Grant), such as uplink scheduling information, that are sent from the DeNBs  103 - 1  and  103 - 2 , and outputs the signals to the UL Grant information accumulating unit  212 . 
         [0082]    The UL Grant information accumulating unit  212  accumulates the UL Grant that have been output from the UL Grant receiving unit  210 . 
         [0083]    The UL SR/BSR information accumulating unit  213  accumulates reception timing information regarding UL Grant and send timing information regarding an uplink buffer status report (UL Buffer Status Report, referred to hereinafter as UL BSR) signal contained in an uplink scheduling request (UL Scheduling Request, referred to hereinafter as UL SR) signal that has already been sent from the UL SR transmission unit  223 . Furthermore, the UL SR/BSR information accumulating unit  213  accumulates the reception timing information regarding UL Grant and the send timing information regarding uplink data (UL Data) contained in the UL BSR that has already been sent from the UL BSR transmission unit  221 . 
         [0084]    The UL transmission establishment timing extracting unit  214  extracts a send feasible timing candidate for UL BSR that is to be contained in UL SR, based on the UL Grant accumulated in the UL Grant information accumulating unit  212 . Furthermore, the UL transmission establishment timing extracting unit  214  extracts a send feasible timing candidate for UL Data that is to be contained in UL BSR, based on the UL Grant accumulated in the UL Grant information accumulating unit  212 . 
         [0085]    The UL transmission/reception candidate timing extracting unit  215  refers to the reception timing for UL Grant and the transmission timing candidate for sending UL BSR contained in the UL SR accumulated in the UL SR/BSR information accumulating unit  213 . Furthermore, the UL transmission/reception candidate timing extracting unit  215  refers to the reception timing for the UL Grant and the send timing candidate for sending UL Data contained in the UL BSR accumulated in the UL SR/BSR information accumulating unit  213 . Then, the UL transmission/reception candidate timing extracting unit  215  extracts, from these timings referred to, a send timing candidate for next UL BSR/UL Data that can be sent by the UL SR/BSR and a reception timing candidate for receiving a UL Grant for sending the UL BSR/UL Data. 
         [0086]    The UL opposing node determination unit  216  determines an opposing node. Concretely, the UL opposing node determination unit  216  determines whether the opposing node is the DeNB  103 - 1  or  103 - 2  or a higher-order apparatus such as a SGW. In this example embodiment, because the transmission unit  204  is packaged in the RN  203 , the UL opposing node determination unit  216  determines that the opposing node is the DeNB  103 - 1  or  103 - 2 . On the other hand, in the case where the transmission unit  204  is packaged in the DeNB  103 - 1  or the DeNB  103 - 2 , the UL opposing node determination unit  216  determines that the opposing node is an SGW that is a higher-order apparatus above the DeNBs  103 - 1  and the DeNB  103 - 2 . 
         [0087]    The UL opposing node flag providing unit  217  provides a flag according to a result of determination by the UL opposing node determination unit  216 . 
         [0088]    The UL transmission/reception feasible timing candidate providing unit  218 , based on information extracted by the UL transmission establishment timing extracting unit  214  and the UL transmission/reception candidate timing extracting unit  215 , provides a send feasible timing candidate for a UL BSR contained in the UL SR and a reception feasible timing candidate for the UL Grant. Furthermore, the UL transmission/reception feasible timing candidate providing unit  218 , based on information extracted by the UL transmission establishment timing extracting unit  214  and the UL transmission/reception candidate timing extracting unit  215 , provides a send feasible timing candidate for UL Data that is to be contained in the UL BSR and a reception feasible timing candidate for the UL Grant. 
         [0089]    Based on the UL Grant, the UL SR/BSR determination unit  219  determines which one of the UL SR and the UL BSR is the signal that is to be sent next. 
         [0090]    When the UL SR/BSR determination unit  219  has determined that the signal to be sent next is a UL BSR, the UL BSR generating unit  220  generates a UL BSR in which the timing information is contained. 
         [0091]    The UL BSR transmission unit  221  is an uplink buffer status-reporting signal transmission unit that sends the UL BSR generated by the UL BSR generating unit  220  to the DeNBs  103 - 1  and  103 - 2 . In other words, the UL BSR transmission unit  221 , when sending the UL BSR to the DeNBs  103 - 1  and  103 - 2 , sends the UL BSR in which information indicating the timing at which a UL Grant for the UL BSR can be received and information indicating a timing at which the UL Data can be sent to the DeNBs  103 - 1  and  103 - 2  are contained. 
         [0092]    The UL SR generating unit  222  generates a UL SR in which the timing information is contained, when the UL SR/BSR determination unit  219  has determined that the signal to be sent next is a UL SR. 
         [0093]    The UL SR transmission unit  223  is an uplink scheduling request signal transmission unit that sends the UL SR generated by the UL SR generating unit  222  to the DeNBs  103 - 1  and  103 - 2 . In other words, the UL SR transmission unit  223 , when sending the UL SR to the DeNBs  103 - 1  and  103 - 2 , sends a UL SR in which information indicating the timing at which the UL Grant for the UL SR can be received and information indicating the timing at which the UL BSR can be sent to the DeNBs  103 - 1  and  103 - 2  are contained. 
         [0094]    The UL Data transmission feasibility determination unit  224  determines whether the sending of the UL Data is feasible, based on the UL Grant accumulated in the UL Grant information accumulating unit  212 . Concretely, the UL Data transmission feasibility determination unit  224  determines whether the sending of the UL Data is feasible, based on the send timing notified by the UL Grant accumulated by the UL Grant information accumulating unit  212 . 
         [0095]    The SR/BSR retransmission processing unit  225  performs retransmission processing for the UL SR and the UL BSR when the UL Data transmission feasibility determination unit  224  has determined that the UL Data cannot be sent. 
         [0096]    The UL Data transmission unit  226  sends the UL Data to the DeNBs  103 - 1  and  103 - 2  when the UL Data transmission feasibility determination unit  224  has determined that the UL Data can be sent. 
         [0097]      FIG. 9  is a diagram illustrating an example of an internal structure of the DeNB  103 - 1  illustrated in  FIG. 7 . The DeNB  103 - 1  illustrated in  FIG. 7  includes, as illustrated in  FIG. 9 , a UL SR/BSR receiving unit  110 , a UL SR/BSR information accumulating unit  111 , a UL transmission/reception candidate timing extracting unit  112 , a UL Grant information accumulating unit  113 , a UL transmission/reception establishment timing extracting unit  114 , a UL opposing node determination unit  115 , a UL Grant establishment timing providing unit  116 , a UL Grant generation unit  117 , and a UL Grant transmission unit  118 . Note that  FIG. 9  illustrates only structure elements concerning this example embodiment, of the structure elements that the DeNB  103 - 1  illustrated in  FIG. 7  includes. Furthermore, the DeNB  103 - 2  illustrated in  FIG. 7  also includes the structure elements illustrated in  FIG. 9 . 
         [0098]    The UL SR/BSR receiving unit  110  receives the UL SR and the UL BSR sent from the RN  203  and outputs the UL SR and the UL BSR to the UL opposing node determination unit  115 . 
         [0099]    The UL SR/BSR information accumulating unit  111  accumulates a send feasible timing candidate for the UL BSR and reception feasible timing candidate information regarding the UL Grant that are contained in the UL SR that the UL SR/BSR receiving unit  110  has output. Furthermore, the UL SR/BSR information accumulating unit  111  accumulates a send feasible timing candidate for the UL Data and reception feasible timing candidate information regarding the UL Grant that are contained in the UL BSR that the UL SR/BSR receiving unit  110  has output. 
         [0100]    The UL transmission/reception candidate timing extracting unit  112  extracts the send feasible timing candidate for the UL BSR and the reception feasible timing candidate information regarding the UL Grant that are accumulated in the UL SR/BSR information accumulating unit  111 . Furthermore, the UL transmission/reception candidate timing extracting unit  112  extracts the send feasible timing candidate for the UL Data and the reception feasible timing candidate information regarding the UL Grant that are accumulated in the UL SR/BSR information accumulating unit  111 . 
         [0101]    The UL Grant information accumulating unit  113  accumulates the send timing of the UL BSR/UL Data and the reception timing information regarding the UL Grant that have already been sent from the UL Grant transmission unit  118 . 
         [0102]    The UL transmission/reception establishment timing extracting unit  114  extracts the send timing of the UL BSR/UL Data and the reception timing information regarding the UL Grant that are accumulated in the UL Grant information accumulating unit  113 . 
         [0103]    The UL opposing node determination unit  115  performs determination regarding an opposing node. Concretely, the UL opposing node determination unit  115  determines whether the opposing node connected to a lower order is the UE  300 - 1 ,  300 - 2  or the RN  203 . In this example embodiment, because the structure elements illustrated in  FIG. 9  are packaged in the DeNB  103 - 1 , the UL opposing node determination unit  115  determines that the opposing node is the RN  203 . On the other hand, in the case where the structure elements illustrated in  FIG. 9  are packaged in the RN  203 , the UL opposing node determination unit  115  determines that the opposing node is the UE  300 - 1  or  300 - 2 . 
         [0104]    It is assumed here that the UL opposing node determination unit  115  has determined that the opposing node is the UE  300 - 1  or  300 - 2 . In this case, the UL Grant establishment timing providing unit  116  provides timings other than the timings extracted by the UL transmission/reception establishment timing extracting unit  114  as a reception timing of the UL Grant and a send timing of the UL BSR/UL Data. 
         [0105]    Furthermore, it is assumed that the UL opposing node determination unit  115  has determined that the opposing node is the RN  203 . In this case, the UL Grant establishment timing providing unit  116  provides the timings extracted by the UL transmission/reception establishment timing extracting unit  114  and the UL transmission/reception candidate timing extracting unit  112  as a reception timing of the UL Grant and a send timing of the UL BSR/UL Data. 
         [0106]    The UL Grant generation unit  117 , based on the information provided by the UL Grant establishment timing providing unit  116 , generates a UL Grant and outputs the UL Grant to the UL Grant transmission unit  118 . 
         [0107]    The UL Grant transmission unit  118  sends to the RN  203  the UL Grant that the UL Grant generation unit  117  has output. 
         [0108]    Hereinafter, a communication method in the communication system illustrated in  FIG. 7  will be described. Here, the communication method will be described with reference to an example case where communication between the DeNB  103 - 1  and the UE  300 - 1  is relayed by the RN  203 . 
         [0109]    First, the transmission processing of the UL SR/UL BSR in the RN  203  illustrated in  FIG. 7  will be described. 
         [0110]      FIG. 10  is a flowchart for describing an example of the transmission processing of the UL SR/UL BSR in the RN  203  illustrated in  FIG. 7 , in the communication method in the communication system illustrated in  FIG. 7 . 
         [0111]    First, after the RN  203  starts sending the UL SR or the UL BSR (step S 21 ), the UL opposing node determination unit  216  determines whether the opposing node is the DeNB  103 - 1  or a higher-order apparatus, such as SGW (step S 22 ). When the UL opposing node determination unit  216  determines that the opposing node is the DeNB  103 - 1 , the UL opposing node flag providing unit  217  provides a DeNB flag (step S 23 ). 
         [0112]    Then, the UL transmission establishment timing extracting unit  214  determines whether the UL Grant receiving unit  210  has received the UL Grant, that is, whether the UL Grant information accumulating unit  212  has accumulated UL Grant (step S 24 ). When the UL Grant information accumulating unit  212  has accumulated the UL Grant, the UL transmission establishment timing extracting unit  214  removes the send timing of the Uplink that has already been allocated by the accumulated UL Grant (step S 25 ). 
         [0113]    On the other hand, when in the step S 24 , the UL Grant information accumulating unit  212  has not accumulated the UL Grant, the processing in step S 25  is not performed. 
         [0114]    Subsequently, the UL SR/BSR information accumulating unit  213  determines whether the UL SR transmission unit  223  has already sent the UL SR or whether the UL BSR transmission unit  221  has already sent the UL BSR (step S 26 ). This determination utilizes the determination carried out by the UL SR/BSR information accumulating unit  213  as to whether the UL SR/BSR information accumulating unit  213  has accumulated the send timing information on the UL BSR and the reception timing information on the UL Grant, or, the send timing information on the UL Data and the reception timing information on the UL Grant. 
         [0115]    For example, when the UL SR/BSR information accumulating unit  213  has accumulated the send timing information on the UL BSR and the reception timing information on the UL Grant, the UL SR/BSR information accumulating unit  213  determines that the UL SR transmission unit  223  has already sent the UL SR. Furthermore, for example, when the UL SR/BSR information accumulating unit  213  has accumulated the send timing information on the UL Data and the reception timing information on the UL Grant, the UL SR/BSR information accumulating unit  213  determines that the UL BSR transmission unit  221  has already sent the UL BSR. 
         [0116]    When the UL SR/BSR information accumulating unit  213  has determined that the UL SR transmission unit  223  has already sent the UL SR, the UL transmission/reception candidate timing extracting unit  215 , using the UL SR, removes the UL Grant reception feasible timing and the Uplink send feasible timing that have been already notified. Furthermore, when the UL SR/BSR information accumulating unit  213  has determined that the UL BSR transmission unit  221  has already sent the UL BSR, the UL transmission/reception candidate timing extracting unit  215 , using the UL BSR, removes the UL Grant reception feasible timing and the Uplink send feasible timing that have been already notified (step S 27 ). 
         [0117]    On the other hand, when, in step S 26 , the UL SR/BSR information accumulating unit  213  has determined that the UL SR transmission unit  223  has not already sent the UL SR or the UL BSR transmission unit  221  has not already sent the UL BSR, the processing in step S 27  is not performed. 
         [0118]    Subsequently, when the signal to be sent is the UL SR, the UL transmission/reception feasible timing candidate providing unit  218 , based on a result of the foregoing timing removal, provides a reception feasible timing candidate for the UL Grant and a send feasible timing candidate for the UL BSR that are to be contained in the UL SR. Then, the UL SR in which the provided timing information is contained is generated by the UL SR generating unit  222  and is sent to the DeNB  103 - 1  by the UL SR transmission unit  223 . Furthermore, when the signal to be sent is the UL BSR, the UL transmission/reception feasible timing candidate providing unit  218 , based on a result of the foregoing timing removal, provides a send feasible timing candidate for the UL Data and a reception feasible timing candidate for the UL Grant. Then, the UL BSR in which the provided timing information is contained is generated by the UL BSR generating unit  220  and sent to the DeNB  103 - 1  by the UL BSR transmission unit  221  (step S 28 ). 
         [0119]    On the other hand, in the case where the transmission unit  204  is packaged in the DeNB  103 - 1 , the UL opposing node determination unit  216  determines in step S 22  that the opposing node is an SGW, so that the UL opposing node flag providing unit  217  provides an SGW flag (step S 29 ). Then, the DeNB  103 - 1  sends the UL Data to the SGW (step S 30 ). 
         [0120]    Next, the transmission processing of the UL Grant in the DeNB  103 - 1  illustrated in  FIG. 7  will be described. 
         [0121]      FIG. 11  is a flowchart for describing an example of the transmission processing of the UL Grant in the DeNB  103 - 1  illustrated in  FIG. 7 , in the communication method in the communication system illustrated in  FIG. 7 . 
         [0122]    First, when the UL SR/BSR receiving unit  110  receives the UL SR or the UL BSR (step S 41 ), it is determined whether the UL Grant transmission unit  118  has sent another UL Grant (step S 42 ). For example, it may be determined whether the UL Grant transmission unit  118  has sent another UL Grant, based on whether the UL Grant information accumulating unit  113  has accumulated the reception timing information on the UL Grant already sent from the UL Grant transmission unit  118 . Concretely, when the UL Grant information accumulating unit  113  has accumulated the reception timing information on the UL Grant already sent from the UL Grant transmission unit  118 , it may be determined that the UL Grant transmission unit  118  has sent another UL Grant. 
         [0123]    When it is determined that the UL Grant transmission unit  118  has sent another UL Grant, the UL transmission/reception establishment timing extracting unit  114  removes the send timing of the Uplink and the reception timing of the UL Grant already allocated in the UL Grant accumulated in the UL Grant information accumulating unit  113  (step S 43 ). 
         [0124]    On the other hand, when, in step S 42 , the UL Grant information accumulating unit  113  has not accumulated the UL Grant, the processing in step S 43  is not performed. 
         [0125]    Subsequently, the UL SR/BSR information accumulating unit  111  determines whether the UL SR/UL BSR received by the UL SR/BSR receiving unit  110  contains the UL Grant reception feasible timing and the Uplink send feasible timing (step S 44 ). When the UL SR/UL BSR received by the UL SR/BSR receiving unit  110  contains the UL Grant reception feasible timing and the Uplink send feasible timing, the UL SR/BSR information accumulating unit  111  accumulates these timings. Then, the UL transmission/reception candidate timing extracting unit  112  extracts the UL Grant reception feasible timing and the Uplink send feasible timing accumulated in the UL SR/BSR information accumulating unit  111  (step S 45 ). 
         [0126]    Subsequently, the UL Grant establishment timing providing unit  116  determines whether the UL Grant can be sent at the timings extracted by the UL transmission/reception establishment timing extracting unit  114  and the UL transmission/reception candidate timing extracting unit  112  (step S 46 ). When the UL Grant establishment timing providing unit  116  has determined that the UL Grant can be sent at the extracted timings, the UL Grant establishment timing providing unit  116  provides the timings as the reception timing of the UL Grant and the send timing of the UL BSR/UL Data. Then, the UL Grant generation unit  117  generates the UL Grant, based on information provided by the UL Grant establishment timing providing unit  116 . Subsequently, the UL Grant transmission unit  118  sends the UL Grant generated by the UL Grant generation unit  117  to the RN  203  (step S 47 ). 
         [0127]    On the other hand, when, in step S 44 , the UL SR/UL BSR received by the UL SR/BSR receiving unit  110  does not contain the UL Grant reception feasible timing and the Uplink send feasible timing, the UL Grant generation unit  117  generates a UL Grant. Subsequently, the UL Grant transmission unit  118  sends the UL Grant generated by the UL Grant generation unit  117  to the RN  203  (step S 48 ). 
         [0128]    Furthermore, it is assumed that, in step S 46 , the UL Grant establishment timing providing unit  116  determines that the UL Grant cannot be sent at the extracted timings. In this case, the UL Grant establishment timing providing unit  116  provides timings other than the aforementioned timings as a reception timing of the UL Grant and a send timing of the UL BSR/UL Data. Then, the UL Grant generation unit  117  generates a UL Grant based on information provided by the UL Grant establishment timing providing unit  116 . Subsequently, the UL Grant transmission unit  118  sends the UL Grant generated by the UL Grant generation unit  117  to the RN  203  (step S 49 ). 
         [0129]    Next, transmission processing of the UL Data in the RN  203  illustrated in  FIG. 7  will be described. 
         [0130]      FIG. 12  is a flowchart for describing an example of the transmission processing of the UL Data in the RN  203  illustrated in  FIG. 7 , in the communication method in the communication system illustrated in  FIG. 7 . 
         [0131]    First, when the UL Grant receiving unit  210  receives a UL Grant sent from the DeNB  103 - 1  (step S 51 ), the UL Grant information accumulating unit  212  accumulates timing information contained in the received UL Grant. Subsequently, the UL Data transmission feasibility determination unit  224  determines whether the UL Data can be sent, based on the timing information accumulated in the UL Grant information accumulating unit  212  (step S 52 ). For example, the UL Data transmission feasibility determination unit  224  determines that the UL Data cannot be sent, when the timing information accumulated in the UL Grant information accumulating unit  212  is used for sending to another DeNB. When the UL Data transmission feasibility determination unit  224  has determined that the UL Data can be sent at the timing received by the UL Grant receiving unit  210 , the UL Data transmission unit  226  sends the UL Data to the DeNB  103 - 1  at that timing (step S 53 ). 
         [0132]    On the other hand, when, in step S 52 , the UL Data transmission feasibility determination unit  224  determines that the UL Data cannot be sent at the timing received by the UL Grant receiving unit  210 , the SR/BSR retransmission processing unit  225  performs the retransmission processing of the UL SR/BSR (step S 54 ). 
         [0133]    Hereinafter, flow of data among the UEs  300 - 1  and  300 - 2 , the RN  203 , and the DeNBs  103 - 1  and  103 - 2  based on the foregoing processing will be described.  FIG. 13  is a sequence chart for describing an example of the flow of data in the communication system illustrated in  FIG. 7 . 
         [0134]    First, the UE  300 - 1  sends to the RN  203  an uplink scheduling request signal (UL SR_a) for sending to the DeNB  103 - 1  UL Data that are uplink data (step S 61 ). Then, the RN  203  sends the response signal (UL Grant for SR_a) to the UE  300 - 1  (step S 62 ). Subsequently, the UE  300 - 1  sends to the RN  203  an uplink buffer status-reporting signal (UL BSR_a) that indicates the storage status of a buffer that temporarily stores the UL Data (step S 63 ). Then, the RN  203  sends the response signal (UL Grant for BSR_a) to the UE  300 - 1  (step S 64 ). The UE  300 - 1 , receiving the UL Grant for BSR_a, sends to the RN  203  the uplink data (UL Data_a) that is to be sent to the DeNB  103 - 1  (step S 65 ). 
         [0135]    The RN  203 , after receiving the UL Data_a from the UE  300 - 1 , sends the UL SR_a to the DeNB  103 - 1  (step S 66 ). At this time, the RN  203  sends the UL SR_a in which a timing at which a UL Grant for SR_a that is a response signal to the UL SR_a can be received and a timing at which a UL BSR_a can be sent are contained. 
         [0136]    Furthermore, the UE  300 - 2  sends to the RN  203  an uplink scheduling request signal (UL SR_b) for sending to the DeNB  103 - 2  UL Data that are uplink data (step S 67 ). Then, the RN  203  sends a response signal (UL Grant for SR_b) to the UE  300 - 2  (step S 68 ). Subsequently, the UE  300 - 2  sends to the RN  203  an uplink buffer status-reporting signal (UL BSR_b) that indicates the storage status of a buffer that temporarily stores the UL Data (step S 69 ). Then, the RN  203  sends a response signal (UL Grant for BSR_b) to the UE  300 - 2  (step S 70 ). Receiving the UL Grant for BSR_b, the UE  300 - 2  sends to the RN  203  uplink data (UL Data_b) that are to be sent to the DeNB  103 - 2  (step S 71 ). 
         [0137]    The RN  203 , after receiving the UL Data_b from the UE  300 - 2 , sends the UL SR_b to the DeNB  103 - 2  (step S 72 ). At this time, the RN  203  sends the UL SR_b in which a timing at which a UL Grant for SR_b that is a response signal to the UL SR_b can be received and a timing at which a UL BSR_b can be sent are contained. 
         [0138]    Note that the timing at which the UL Grant for SR_a can be received and which is sent in step S 66  and the timing at which the UL Grant for SR_b can be received and which is sent in step S 72  are timings such that the reception processing of one of the signals does not affect the reception processing of the other signal. This is just as stated above. 
         [0139]    Furthermore, the timing at which the UL BSR_a can be sent and which is contained in the UL SR_a in step S 66  and the timing at which the UL BSR_b can be sent and which is contained in the UL SR_b in step S 72  are timings such that the transmission processing of one of the two signals does not affect the transmission processing of the other signal. This is also just as stated above. 
         [0140]    Then, the DeNB  103 - 1  sends the UL Grant for SR_a to the RN  203 , based on the timing at which UL Grant for SR_a can be received and which is contained in the UL SR_a sent from the RN  203  (step S 73 ). Furthermore, the DeNB  103 - 2  sends the UL Grant for SR_b to the RN  203 , based on the timing at which the UL Grant for SR_b can be received and which is contained in the UL SR_b sent from the RN  203  (step S 74 ). 
         [0141]    Subsequently, the RN  203  sends the UL BSR_a to the DeNB  103 - 1  at the timing notified to the DeNB  103 - 1  in step S 66  (step S 75 ). At this time, the RN  203  sends the UL BSR_a in which a timing at which the UL Grant for BSR_a, which is a response signal to the UL BSR_a, can be received and a timing at which the UL Data_a can be sent are contained. Furthermore, the RN  203  sends the UL BSR_b to the DeNB  103 - 2  at the timing notified to the DeNB  103 - 2  in step S 72  (step S 76 ). At this time, the RN  203  sends the UL BSR_b in which a timing at which the UL Grant for BSR_b, which is a response signal to the UL BSR_b, can be received and a timing at which the UL Data_b can be sent are contained. 
         [0142]    Note that the timing at which the UL Grant for BSR_a can be received and which is contained in the UL BSR_a in step S 75  and the timing at which the UL Grant for BSR_b can be received and which is contained in the UL BSR_b in step S 76  are timings such that the reception processing of one of the two signals does not affect the reception processing of the other signal. This is just as stated above. Furthermore, the timing at which the UL Data_a can be sent and which is contained in the UL BSR_a in step S 75  and the timing at which the UL Data_b can be sent and which is contained in the UL BSR_b in step S 76  are timings such that the transmission processing of one of the two signals does not affect the transmission processing of the other signal. This is also just as stated above. 
         [0143]    Then, the DeNB  103 - 1  sends the UL Grant for BSR_a to the RN  203 , based on the timing at which the UL Grant for BSR_a can be received and which is contained in the UL BSR_a sent from the RN  203  (step S 77 ). Furthermore, the DeNB  103 - 2  sends the UL Grant for BSR_b to the RN  203 , based on the timing at which the UL Grant for BSR_b can be received and which is contained in the UL BSR_b sent from the RN  203  (step S 78 ). 
         [0144]    Subsequently, the RN  203  sends the UL Data_a to the DeNB  103 - 1  at the timing notified to the DeNB  103 - 1  in step S 75  (step S 79 ). Furthermore, the RN  203  sends the UL Data_b to the DeNB  103 - 2  at the timing notified to the DeNB  103 - 2  in step S 76  (step S 80 ). 
         [0145]    Thus, the RN  203  notifies the DeNBs  103 - 1  and  103 - 2  of the timing at which the RN  203  can receive the response signal and the timing at which the RN  203  can send uplink data and then, at these timings, sends the request signal and the uplink data to the DeNBs  103 - 1  and  103 - 2 . Therefore, the communication system of the third example embodiment can prevent failure in the reception processing of the response signal and failure in the transmission processing of uplink data and therefore can made data transmission more efficient. 
       Fourth Example Embodiment 
       [0146]      FIG. 14  is a diagram illustrating a fourth example embodiment of the communication system of the present invention. 
         [0147]    The communication system in this example embodiment includes DeNBs  104 - 1  and  104 - 2 , an RN  205 , and UEs  300 - 1  and  300 - 2  as illustrated in  FIG. 14 . 
         [0148]    The DeNB  104 - 1  is a radio base station that communicates with the UE  300 - 1  via the RN  205 . The DeNB  104 - 2  is a radio base station that communicates with the UE  300 - 2  via the RN  205 . The DeNBs  104 - 1  and  104 - 2  send downlink signals to the RN  205 , using an orthogonal frequency-division multiplexing access method. 
         [0149]    The RN  205  is a radio relay station that relays communication between the DeNB  104 - 1  and the UE  300 - 1  and communication between the DeNB  104 - 2  and the UE  300 - 2 . 
         [0150]    The UE  300 - 1  is a communication terminal that communicates with the DeNB  104 - 1  via the RN  205 . The UE  300 - 2  is a communication terminal that communicates with the DeNB  104 - 2  via the RN  205 . 
         [0151]      FIG. 15  is a diagram illustrating an example of an internal structure of the RN  205  illustrated in  FIG. 14 . 
         [0152]    The RN  205  illustrated in  FIG. 14  includes, as illustrated in  FIG. 15 , a DL SR/BSR receiving unit  231 , a DL SR/BSR information accumulating unit  232 , a DL transmission/reception candidate timing extracting unit  233 , a DL Grant information accumulating unit  234 , a DL transmission/reception establishment timing extracting unit  235 , a DL Grant establishment timing providing unit  236 , a DL Grant generation unit  237 , and a DL Grant transmission unit  238 . Note that  FIG. 15  illustrates only structure elements concerning this example embodiment, of the structure elements that the RN  205  illustrated in  FIG. 14  include. 
         [0153]    The DL SR/BSR receiving unit  231  receives a downlink buffer status report (DL Buffer Status Report, referred to hereinafter as DL BSR) and a downlink scheduling information (DL Scheduling Request, referred to hereinafter as DL SR) sent from the DeNBs  104 - 1  and  104 - 2 . The DL SR/BSR receiving unit  231  outputs the DL SR and the DL BSR received to the DL SR/BSR information accumulating unit  232 . 
         [0154]    The DL SR/BSR information accumulating unit  232  accumulates a send feasible timing candidate for the DL BSR and reception feasible timing candidate information on a DL Grant that is a response signal to the DL SR which are contained in the DL SR output by the DL SR/BSR receiving unit  231 . The DL SR/BSR information accumulating unit  232  accumulates a send feasible timing candidate for downlink data (DL Data) and reception feasible timing candidate information on the DL Grant that is a response signal to the DL BSR which are contained in the DL BSR output by the DL SR/BSR receiving unit  231 . 
         [0155]    The DL transmission/reception candidate timing extracting unit  233  extracts from the DL SR/BSR information accumulating unit  232  the send feasible timing candidate for the DL BSR and the reception feasible timing candidate information for the DL Grant that is a response signal to the DL SR. Furthermore, the DL transmission/reception candidate timing extracting unit  233  extracts from the DL SR/BSR information accumulating unit  232  the send feasible timing candidate for the DL Data and the reception feasible timing candidate information on the DL Grant that is a response signal to the DL BSR. 
         [0156]    The DL Grant information accumulating unit  234  accumulates the send timing of the DL BSR/DL Data and the reception timing information on the DL Grant that the DL Grant transmission unit  238  sends. 
         [0157]    The DL transmission/reception establishment timing extracting unit  235  extracts the send timing of the DL SR/BSR and the reception timing information on the DL Grant from the DL Grant information accumulating unit  234 . 
         [0158]    The DL Grant establishment timing providing unit  236  provides the reception timing of the DL Grant and the send timing of the DL BSR/DL Data, based on the timings extracted by the DL transmission/reception establishment timing extracting unit  235  and the DL transmission/reception candidate timing extracting unit  233 . 
         [0159]    The DL Grant generation unit  237  generates the DL Grant based on the timing provided by the DL Grant establishment timing providing unit  236 . 
         [0160]    The DL Grant transmission unit  238  sends the DL Grant generated by the DL Grant generation unit  237  to the DeNBs  104 - 1  and  104 - 2 . 
         [0161]      FIG. 16  is a diagram illustrating an example of an internal structure of the DeNB  104 - 1  illustrated in  FIG. 14 . 
         [0162]    The DeNB  104 - 1  illustrated in  FIG. 14  includes a transmission unit  105  and a DL Data receiving unit  131  as illustrated in  FIG. 16 . Furthermore, the transmission unit  105  includes a DL Grant receiving unit  130 , a DL Grant information accumulating unit  132 , a DL SR/BSR information accumulating unit  133 , a DL transmission establishment timing extracting unit  134 , a DL transmission/reception candidate timing extracting unit  135 , a DL opposing node determination unit  136 , a DL opposing node flag providing unit  137 , a DL transmission/reception feasible timing candidate providing unit  138 , a DL SR/BSR determination unit  139 , a DL BSR generating unit  140 , a DL BSR transmission unit  141 , a DL SR generating unit  142 , a DL SR transmission unit  143 , a DL Data transmission feasibility determination unit  144 , an SR/BSR retransmission processing unit  145 , and a DL Data transmission unit  146 . Note that  FIG. 16  illustrates only structure elements concerning this example embodiment, of the structure element that the DeNB  104 - 1  illustrated in  FIG. 14  includes. Furthermore, the DeNB  104 - 2  illustrated in  FIG. 14  also include the structure elements illustrated in  FIG. 16 . 
         [0163]    The DL Data receiving unit  131  receives downlink data (DL Data) sent from a higher-order apparatus such as an SGW. The DL Data receiving unit  131  outputs the received DL Data to the DL opposing node determination unit  136 . 
         [0164]    The DL Grant receiving unit  130  receives the DL Grant sent from the RN  205 . The DL Grant receiving unit  130  outputs the received DL Grant to the DL Grant information accumulating unit  132 . 
         [0165]    The DL Grant information accumulating unit  132  accumulates the DL Grant output by the DL Grant receiving unit  130 . 
         [0166]    The DL SR/BSR information accumulating unit  133  accumulates send timing information on the DL BSR and reception timing information on the DL Grant that are contained in a DL SR already sent by the DL SR transmission unit  143 . Furthermore, the DL SR/BSR information accumulating unit  133  accumulates send timing information on the DL Data and reception timing information on the DL Grant that are contained in a DL BSR already sent from the DL BSR transmission unit  141 . 
         [0167]    The DL transmission establishment timing extracting unit  134  extracts a send timing candidate for the DL BSR that is to be contained in the DL SR, by using the DL Grant accumulated in the DL Grant information accumulating unit  132 . Furthermore, the DL transmission establishment timing extracting unit  134  extracts a send feasible timing candidate for the DL Data that are to be contained in the DL BSR, by using the DL Grant accumulated in the DL Grant information accumulating unit  132 . 
         [0168]    The DL transmission/reception candidate timing extracting unit  135  refers to the send timing candidate for the DL BSR and the reception timing for the DL Grant that are contained in the DL SR accumulated in the DL SR/BSR information accumulating unit  133 . Furthermore, the DL transmission/reception candidate timing extracting unit  135  refers to the send timing candidate for the DL Data and the reception timing of the DL Grant that are contained in the DL BSR accumulated in the DL SR/BSR information accumulating unit  133 . Then, the DL transmission/reception candidate timing extracting unit  135  extracts, from these timings referred to, the send timing candidates for the next DL BSR/DL Data that can be sent in the DL SR/BSR and the reception timing candidate for receiving the DL Grant for sending the DL BSR/DL Data. 
         [0169]    The DL opposing node determination unit  136  determines an opposing node. Concretely, the DL opposing node determination unit  136  determines whether the opposing node is the RN  205  or the UE  300 - 1  or  300 - 2 . In this example embodiment, because the transmission unit  105  is packaged in the DeNB  104 - 1 , the DL opposing node determination unit  136  determines that the opposing node is the RN  205 . On the other hand, in the case where the transmission unit  105  is packaged in the RN  205 , the DL opposing node determination unit  136  determines that the opposing node is the UE  300 - 1  or  300 - 2 . 
         [0170]    The DL opposing node flag providing unit  137  provides a flag according to a result of the determination performed by the DL opposing node determination unit  136 . 
         [0171]    The DL transmission/reception feasible timing candidate providing unit  138  provides a send feasible timing candidate for the DL BSR and a reception feasible timing candidate for the DL Grant that are to be contained in the DL SR. These are accomplished based on the information extracted by the DL transmission/reception candidate timing extracting unit  135  and the DL transmission establishment timing extracting unit  134 . 
         [0172]    Furthermore, the DL transmission/reception feasible timing candidate providing unit  138  provides a send feasible timing candidate for the DL Data and a reception feasible timing candidate for the DL Grant that are to be contained in the DL BSR. These are accomplished based on the information extracted by the DL transmission/reception candidate timing extracting unit  135  and the DL transmission establishment timing extracting unit  134 . 
         [0173]    The DL SR/BSR determination unit  139  determines which one of the DL SR and the DL BSR is the next signal to be sent based on the DL Grant. 
         [0174]    The DL BSR generating unit  140  generates the DL BSR in which the foregoing timing information is contained, when the DL SR/BSR determination unit  139  has determined that the next signal to be sent is the DL BSR. 
         [0175]    The DL BSR transmission unit  141  is a downlink buffer status-reporting signal transmission unit that sends the DL BSR generated by the DL BSR generating unit  140  to the RN  205 . In other words, the DL BSR transmission unit  141 , when sending the DL BSR to the RN  205 , sends the DL BSR in which information that indicates a timing at which the DL Grant for the DL BSR can be received and information that indicates a timing at which the DL Data can be sent to the RN  205  are contained. 
         [0176]    The DL SR generating unit  142 , when the DL SR/BSR determination unit  139  has determined that the next signal to be sent is the DL SR, generates the DL SR in which the foregoing timing information is contained. 
         [0177]    The DL SR transmission unit  143  is a downlink scheduling request signal transmission unit that sends the DL SR generated by the DL SR generating unit  142  to the RN  205 . In other words, the DL SR transmission unit  143 , when sending the DL SR to the RN  205 , sends the DL SR in which information that indicates a timing at which the DL Grant for the DL SR can be received and information that indicates a timing at which the DL BSR can be sent to the RN  205  are contained. 
         [0178]    The DL Data transmission feasibility determination unit  144  determines whether the sending of the DL Data is feasible, based on the DL Grant accumulated in the DL Grant information accumulating unit  132 . Concretely, the DL Data transmission feasibility determination unit  144  determines whether the sending of the DL Data is feasible based on the send timing notified in the DL Grant accumulated in the DL Grant information accumulating unit  132 . 
         [0179]    The SR/BSR retransmission processing unit  145  performs the retransmission processing of the DL SR and the DL BSR when the DL Data transmission feasibility determination unit  144  has determined that the DL Data cannot be sent. 
         [0180]    When the DL Data transmission feasibility determination unit  144  has determined that the DL Data can be sent, the DL Data transmission unit  146  sends the DL Data to the RN  205 . 
         [0181]    Hereinafter, a communication method in the communication system illustrated in  FIG. 14  will be described. Here, the communication method will be described with reference to an example case where the RN  205  relays communication between the DeNB  104 - 1  and the UE  300 - 1 . 
         [0182]    First, the transmission processing of the DL SR/DL BSR in the DeNB  104 - 1  illustrated in  FIG. 14  will be described. 
         [0183]      FIG. 17  is a flowchart for describing an example of the transmission processing of the DL SR/DL BSR in the DeNB  104 - 1  illustrated in  FIG. 14 , in the communication method in the communication system illustrated in  FIG. 14 . 
         [0184]    First, when the DeNB  104 - 1  starts sending a DL SR or a DL BSR (step S 91 ), the DL opposing node determination unit  136  determines which one of the RN  205  and the UE  300 - 1  is the opposing node (step S 92 ). When the DL opposing node determination unit  136  has determined that the opposing node is the RN  205 , the DL opposing node flag providing unit  137  provides an RN flag (step S 93 ). 
         [0185]    Then, it is determined whether the DL Grant receiving unit  130  has received the DL Grant, that is, whether the DL Grant information accumulating unit  132  has accumulated the DL Grant (step S 94 ). When the DL Grant information accumulating unit  132  has accumulated the DL Grant, the DL transmission establishment timing extracting unit  134  removes the send timing of the Downlink already allocated in the accumulated DL Grant (step S 95 ). 
         [0186]    On the other hand, when, in step S 94 , the DL Grant information accumulating unit  132  has not accumulated the DL Grant, the processing in step S 95  is not performed. 
         [0187]    Subsequently, the DL SR/BSR information accumulating unit  133  determines whether the DL SR transmission unit  143  has already sent the DL SR or whether the DL BSR transmission unit  141  has already sent the DL BSR (step S 96 ). This determination utilizes the determination carried out by the DL SR/BSR information accumulating unit  133  as to whether the DL SR/BSR information accumulating unit  133  has accumulated the send timing information on the DL BSR and the reception timing information on the DL Grant or the send timing information on the DL Data and the reception timing information on the DL Grant. 
         [0188]    For example, when the DL SR/BSR information accumulating unit  133  has accumulated the send timing information on the DL BSR and the reception timing information on the DL Grant, the DL SR/BSR information accumulating unit  133  determines that the DL SR transmission unit  143  has already sent the DL SR. 
         [0189]    Furthermore, for example, it is assumed that the DL SR/BSR information accumulating unit  133  has accumulated the send timing information on the DL Data and the reception timing information on the DL Grant. In this case, the DL SR/BSR information accumulating unit  133  determines that the DL BSR transmission unit  141  has already sent the DL BSR. 
         [0190]    Furthermore, it is assumed that the DL SR/BSR information accumulating unit  133  has determined that the DL SR transmission unit  143  has already sent the DL SR. In this case, the DL transmission/reception candidate timing extracting unit  135  removes the DL Grant reception feasible timing and the Downlink send feasible timing that have been already notified by using the DL SR. 
         [0191]    Furthermore, it is assumed that the DL SR/BSR information accumulating unit  133  has determined that the DL BSR transmission unit  141  has already sent the DL BSR. In this case, the DL transmission/reception candidate timing extracting unit  135  removes the DL Grant reception feasible timing and the Downlink send feasible timing that have been already notified by using the DL BSR (step S 97 ). 
         [0192]    On the other hand, when, in step S 96 , the DL SR/BSR information accumulating unit  133  determines that the DL SR transmission unit  143  has not already sent the DL SR or the DL BSR transmission unit  141  has not already sent the DL BSR, the processing in step S 97  is not performed. 
         [0193]    Subsequently, when the signal to be sent is the DL SR, the DL transmission/reception feasible timing candidate providing unit  138 , based on a result of the foregoing timing removal, provides a send feasible timing candidate for the DL BSR and a reception feasible timing candidate for the DL Grant that are to be contained in the DL SR. Then, the DL SR in which the provided timing information is contained is generated by the DL SR generating unit  142  and sent to the RN  205  by the DL SR transmission unit  143 . Furthermore, when the signal to be sent is the DL BSR, the DL transmission/reception feasible timing candidate providing unit  138 , based on a result of the foregoing timing removal, provides a send feasible timing candidate for the DL Data and a reception feasible timing candidate for the DL Grant. Then, the DL BSR in which the provided timing information is contained is generated by the DL BSR generating unit  140  and sent to the RN  205  by the DL BSR transmission unit  141  (step S 98 ). 
         [0194]    On the other hand, in the case where the transmission unit  105  is packaged in the RN  205 , the DL opposing node determination unit  136  determines in step S 92  that the opposing node is the UE  300 - 1 . Therefore, the DL opposing node flag providing unit  137  provides a UE flag (step S 99 ). Then, the RN  205  sends the DL Data to the UE  300 - 1  (step S 100 ). 
         [0195]    Next, transmission processing of the DL Grant in the RN  205  illustrated in  FIG. 14  will be described. 
         [0196]      FIG. 18  is a flowchart for describing an example of the transmission processing of the DL Grant in the RN  205  illustrated in  FIG. 14 , in the communication method in the communication system illustrated in  FIG. 14 . 
         [0197]    First, when the DL SR/BSR receiving unit  231  receives a DL SR or a DL BSR (step S 111 ), it is determined whether the DL Grant transmission unit  238  has sent another DL Grant (step S 112 ). For example, the DL Grant information accumulating unit  234  may determine whether the DL Grant transmission unit  238  has sent another DL Grant, based on whether the DL Grant information accumulating unit  234  has accumulated the reception timing information on the DL Grant already sent from the DL Grant transmission unit  238 . Concretely, the DL Grant information accumulating unit  234  may determine that the DL Grant transmission unit  238  has sent another DL Grant, when the DL Grant information accumulating unit  234  has accumulated the reception timing information on the DL Grant already sent from the DL Grant transmission unit  238 . 
         [0198]    It is assumed that, in step S 112 , it is determined that the DL Grant transmission unit  238  has sent another DL Grant. In this case, the DL transmission/reception establishment timing extracting unit  235  removes the reception timing for the DL Grant and the send timing for the Downlink that have been already allocated in the DL Grant accumulated in the DL Grant information accumulating unit  234  (step S 113 ). 
         [0199]    On the other hand, when, in step S 112 , the DL Grant information accumulating unit  234  has not accumulated the DL Grant, the processing in step S 113  is not performed. 
         [0200]    Subsequently, the DL SR/BSR information accumulating unit  232  determines whether the DL SR/DL BSR received by the DL SR/BSR receiving unit  231  contains the DL Grant reception feasible timing and the Downlink send feasible timing (step S 114 ). When the DL SR/DL BSR received by the DL SR/BSR receiving unit  231  contains the DL Grant reception feasible timing and the Downlink send feasible timing, the DL SR/BSR information accumulating unit  232  accumulates these timings. Then, the DL transmission/reception candidate timing extracting unit  233  extracts the DL Grant reception feasible timing and the Downlink send feasible timing accumulated in the DL SR/BSR information accumulating unit  232  (step S 115 ). 
         [0201]    Subsequently, the DL Grant establishment timing providing unit  236  determines whether the DL Grant can be sent at the timings extracted by the DL transmission/reception establishment timing extracting unit  235  and the DL transmission/reception candidate timing extracting unit  233  (step S 116 ). When the DL Grant establishment timing providing unit  236  determines that the DL Grant can be sent at the extracted timings, the DL Grant establishment timing providing unit  236  provides these timings as the reception timing for the DL Grant and the send timing for the DL BSR/DL Data. Then, the DL Grant generation unit  237  generates the DL Grant based on the information provided by the DL Grant establishment timing providing unit  236 . Subsequently, the DL Grant transmission unit  238  sends the DL Grant generated by the DL Grant generation unit  237  to the DeNB  104 - 1  (step S 117 ). 
         [0202]    On the other hand, it is assumed that, in step S 114 , the DL SR/DL BSR received by the DL SR/BSR receiving unit  231  does not contain the DL Grant reception feasible timing and the Downlink send feasible timing. In this case, the DL Grant generation unit  237  generates a DL Grant. Subsequently, the DL Grant transmission unit  238  sends the DL Grant generated by the DL Grant generation unit  237  to the DeNB  104 - 1  (step S 118 ). 
         [0203]    Furthermore, it is assumed that, in step S 116 , the DL Grant establishment timing providing unit  236  determines that the DL Grant cannot be sent at the extracted timings. In this case, the DL Grant establishment timing providing unit  236  provides timings other than these timings as a reception timing for the DL Grant and a send timing for the DL BSR/DL Data. Then, the DL Grant generation unit  237  generates a DL Grant based on the information provided by the DL Grant establishment timing providing unit  236 . Subsequently, the DL Grant transmission unit  238  sends the DL Grant generated by the DL Grant generation unit  237  to the DeNB  104 - 1  (step S 119 ). 
         [0204]    Next, transmission processing of the DL Data in the DeNB  104 - 1  illustrated in  FIG. 14  will be described. 
         [0205]      FIG. 19  is a flowchart for describing an example of the transmission processing of the DL Data in DeNB  104 - 1  illustrated in  FIG. 14 , in the communication method in the communication system illustrated in  FIG. 14 . 
         [0206]    First, when the DL Grant receiving unit  130  receives a DL Grant sent from the RN  205  (step S 121 ), the DL Grant information accumulating unit  132  accumulates the timing information contained in the received DL Grant. Subsequently, the DL Data transmission feasibility determination unit  144  determines whether the DL Data can be sent, based on the timing information accumulated by the DL Grant information accumulating unit  132  (step S 122 ). For example, the DL Data transmission feasibility determination unit  144  determines that the DL Data cannot be sent, when the timing information accumulated in the DL Grant information accumulating unit  132  is used for sending to another RN. When the DL Data transmission feasibility determination unit  144  determines that the DL Data can be sent at the timing received by the DL Grant receiving unit  130 , the DL Data transmission unit  146  sends the DL Data to the RN  205  at that timing (step S 123 ). 
         [0207]    On the other hand, when, in step S 122 , the DL Data transmission feasibility determination unit  144  determines that the DL Data cannot be sent at the timing received by the DL Grant receiving unit  130 , the SR/BSR retransmission processing unit  145  performs the retransmission processing of the DL SR/BSR (step S 124 ). 
         [0208]    Hereinafter, flow of data among the UEs  300 - 1  and  300 - 2 , the RN  205 , and the DeNBs  104 - 1  and  104 - 2  based on the foregoing processing will be described. 
         [0209]      FIG. 20  is a sequence chart for describing an example of the flow of data in the communication system illustrated in  FIG. 14 . 
         [0210]    First, the DeNB  104 - 1 , after receiving downlink data from a higher-order apparatus, such as an SGW, sends a DL SR_a to the RN  205  (step S 131 ). At this time, the DeNB  104 - 1  sends the DL SR_a in which a timing at which the DL Grant for SR_a that is a response signal to the DL SR_a can be received and a timing at which the DL BSR_a can be sent are contained. 
         [0211]    Furthermore, the DeNB  104 - 2 , after receiving downlink data from a higher-order apparatus, such as SGW, sends a DL SR_b to the RN  205  (step S 132 ). At this time, the DeNB  104 - 2  sends the DL SR_b in which a timing at which the DL Grant for SR_b that is a response signal to the DL SR_b can be received and a timing at which the DL BSR_b can be sent are contained. 
         [0212]    Then, the RN  205  sends the DL Grant for SR_a, which is a response signal to the DL SR_a, to the DeNB  104 - 1  at the reception feasible timing contained in the DL SR_a sent from the DeNB  104 - 1  (step S 133 ). Furthermore, the RN  205  sends the DL Grant for SR_b, which is a response signal to the DL SR_b, to the DeNB  104 - 2  at the reception feasible timing contained in the DL SR_b sent from the DeNB  104 - 2  (step S 134 ). 
         [0213]    Note that when the send timings for the DL Grant for SR_a and the DL Grant for SR_b are simultaneous, the DL Grants cannot be sent at the timings contained in the DL SR_a and the DL SR_b. In this case, the RN  205  may change the reception timings for the DL Grant for SR_a and the DL Grant for SR_b to timings other than the timings contained in the DL SR_a and the DL SR_b. In this case, the RN  205  may also change the send timings for the DL BSR_a and the DL BSR_b to different timings. Then, the RN  205  may generate the DL Grant for SR_a and the DL Grant for SR_b and sent them to the DeNB  104 - 1 , based on these changed timings. These operations correspond to the processing in step S 119  in  FIG. 18 . 
         [0214]    Subsequently, the DeNB  104 - 1  sends the DL BSR_a to the RN  205  at the send feasible timing for the DL BSR_a that is contained in the DL SR_a that the DeNB  104 - 1  has sent (step S 135 ). At this time, the DeNB  104 - 1  sends the DL BSR_a in which a reception feasible timing for a DL Grant for BSR_a that is a response signal to the DL BSR_a and a send feasible timing for the DL Data_a are contained. Furthermore, the DeNB  104 - 2  sends the DL BSR_b to the RN  205  at the send feasible timing for the DL BSR b that is contained in the DL SR b that the DeNB  104 - 2  has sent (step S 136 ). At this time, the DeNB  104 - 2  sends the DL BSR_b in which a reception feasible timing for the DL Grant for BSR_b that is a response signal to the DL BSR_b and a send feasible timing for the DL Data_b are contained. 
         [0215]    Then, the RN  205  sends the DL Grant for BSR_a, which is a response signal to the DL BSR_a, to the DeNB  104 - 1  at the reception feasible timing contained in the DL BSR_a sent from the DeNB  104 - 1  (step S 137 ). Furthermore, the RN  205  sends the DL Grant for BSR_b, which is a response signal to the DL BSR_b, to the DeNB  104 - 2  at the reception feasible timing contained in the DL BSR_b sent from the DeNB  104 - 2  (step S 138 ). 
         [0216]    After that, the DeNB  104 - 1  sends the DL Data_a to the RN  205  at the send feasible timing for the DL Data_a contained in the DL BSR_a that has been sent (step S 139 ). The RN  205 , after receiving the DL Data_a sent from the DeNB  104 - 1 , sends the DL Data_a to the UE  300 - 1  (step S 140 ). 
         [0217]    Furthermore, the DeNB  104 - 2  sends the DL Data_b to the RN  205  at the send feasible timing for the DL Data_b contained in the DL BSR_b that has been sent (step S 141 ). The RN  205 , after receiving the DL Data_b sent from the DeNB  104 - 2 , sends the DL Data_b to the UE  300 - 2  (step S 142 ). 
         [0218]    Thus, each of the DeNBs  104 - 1  and  104 - 2  notifies the RN  205  of a timing at which the DeNB can receive a response signal and a timing at which the DeNB can send downlink data and then, at these timings, sends the request signal and the downlink data to the RN  205 . Therefore, the communication system of the fourth example embodiment can be prevent failure in the reception processing of the response signal and failure in the transmission processing of the downlink data and therefore can make data transmission more efficient. 
         [0219]    Note that, as a modification, a system combining the third example embodiment and the fourth example embodiment is also permissible. 
         [0220]    Advantageous effects of the example embodiments will be stated below. 
         [0221]    A first advantageous effect is that because of having the functions of sending and receiving the DL SR, the DL BSR, and the DL Grant, the example embodiments can negotiate the timing to send DL Data not only with higher-order radio base station apparatuses but also with lower-order radio relay base station apparatuses. Furthermore, the DL SR and the DL BSR can be provided with a send feasible timing for the next Downlink communication (DL BSR and DL Data) and a reception timing for the DL Grant. 
         [0222]    A reason for that is that the negotiation for the timing to send DL Data between nodes makes it possible to prevent DL Data from being received at the same timing. 
         [0223]    A second advantageous effect is that the UL SR and the UL BSR are provided with a send feasible timing for the next Uplink communication (UL BSR and UL Data) and a reception timing for a UL Grant. 
         [0224]    A reason for that is that the negotiation for the timing to send UL Data between nodes makes it possible to prevent UL Data from being received at the same timing. 
         [0225]    A third advantageous effect is that, using the DL opposing node determination unit, it can be determined whether to perform a method of sending DL Data as in the related art or the sending of a DL SR or the like, according to an opposing node. 
         [0226]    A reason for that is that because while a radio relay base station apparatus has a plurality of higher-order radio base station apparatuses, communication with a radio communication terminal involves a DeNB or a higher-order RN that is uniquely determined, an unnecessary radio scheduling function can be excluded. 
         [0227]    A fourth advantageous effect is that, using the UL opposing node determination unit, it can be determined whether to perform a method of sending UL Data as in the related art or the sending of a UL SR or the like, according to an opposing node. 
         [0228]    A reason for that is that because while a radio relay base station apparatus has a plurality of higher-order radio base station apparatuses, communication with an SGW or the like involves a high-order node that is uniquely determined, an unnecessary radio scheduling function can be excluded. 
         [0229]    As an example of application of the present invention, the case of sharing a radio base station apparatus in an MVNO (Mobile Virtual Network Operator) system or the like among a plurality of operators and performing the RAN (Radio Access Network) sharing including RNs will lead a better radio resource. 
         [0230]    A part or the entirety of the foregoing example embodiments can be described as in the following supplementary notes but not limited to the following. 
         [0231]    (Supplementary Note 1) A radio relay station that includes a transmission unit that notifies a radio base station of a timing at which uplink data sent from a communication terminal are able to be sent to the radio base station and then sends the uplink data to the radio base station. 
         [0232]    (Supplementary Note 2) The radio relay station according to supplementary note 1, wherein the transmission unit includes 
         [0233]    an uplink scheduling request signal transmission unit that sends to the radio base station an uplink scheduling request signal for sending to the radio base station the uplink data sent from the communication terminal, after containing, in the uplink scheduling request signal, information that indicates a timing at which a response signal to the uplink scheduling request signal is able to be received and information that indicates a timing at which an uplink buffer status-reporting signal is able to be sent to the radio base station, and 
         [0234]    an uplink buffer status-reporting signal transmission unit that receives the response signal to the uplink scheduling request signal and then sends to the radio base station the uplink buffer status-reporting signal after containing, in the uplink buffer status-reporting signal, information that indicates a timing at which a response signal to the uplink buffer status-reporting signal is able to be received and information that indicates a timing at which the uplink data are able to be sent to the radio base station. 
         [0235]    (Supplementary Note 3) A radio base station that includes a transmission unit that notifies a radio relay station that relays communication with communication terminals of a timing at which downlink data are able to be sent to the radio relay station and then sends the downlink data to the radio relay station. 
         [0236]    (Supplementary Note 4) The radio base station according to supplementary note 3, wherein the transmission unit includes 
         [0237]    a downlink scheduling request signal transmission unit that sends to the radio relay station a downlink scheduling request signal for sending the downlink data to the radio relay station, after containing, in the downlink scheduling request signal, information that indicates a timing at which a response signal to the downlink scheduling request signal is able to be received and information that indicates a timing at which a downlink buffer status-reporting signal is able to be sent to the radio relay station, and 
         [0238]    a downlink buffer status-reporting signal transmission unit that receives the response signal to the downlink scheduling request signal and then sends the downlink buffer status-reporting signal to the radio relay station after containing, in the downlink buffer status-reporting signal, information that indicates a timing at which a response signal to the downlink buffer status-reporting signal is able to be received and information that indicates a timing at which the downlink data are able to be sent to the radio relay station. 
         [0239]    (Supplementary Note 5) In a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, 
         [0240]    a communication system in which the radio relay station includes a transmission unit that notifies the radio base station of a timing at which uplink data sent from the communication terminal are able to be sent to the radio base station and then sends the uplink data to the radio base station. 
         [0241]    (Supplementary Note 6) In a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, 
         [0242]    a communication system in which the radio base station includes a transmission unit that notifies the radio relay station of a timing at which downlink data are able to be sent to the radio relay station and then sends the downlink data to the radio relay station. 
         [0243]    (Supplementary Note 7) A communication method that performs processing of notifying a radio base station of a timing at which uplink data sent from a communication terminal are able to be sent to the radio base station and then sending the uplink data to the radio base station. 
         [0244]    (Supplementary Note 8) A communication method that performs processing of notifying a radio relay station that relays communication between communication terminals of a timing at which downlink data are able to be sent to the radio relay station and then sending the downlink data to the radio relay station. 
         [0245]    (Supplementary Note 9) In a communication method in a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, 
         [0246]    a communication method in which the radio relay station performs processing of notifying the radio base station of a timing at which uplink data sent from the communication terminal are able to be sent to the radio base station and then sending the uplink data to the radio base station. 
         [0247]    (Supplementary Note 10) In a communication method in a communication system that includes a radio base station and a radio relay station that relays communication between the radio base station and a communication terminal, 
         [0248]    a communication method in which the radio base station performs processing of notifying the radio relay station of a timing at which downlink data are able to be sent to the radio relay station and then sending the downlink data to the radio relay station. 
         [0249]    (Supplementary Note 11) The radio relay station according to supplementary note 2, which sends an uplink signal to the radio base station by using a communication method of a SC-FDMA (Single Carrier-Frequency Division Multiple Access) or a TD-SCDMA (Time Division-Synchronous Code Division Multiple Access). 
         [0250]    (Supplementary Note 12) The radio base station according to supplementary note 4, which sends downlink signal to the radio relay station by using an orthogonal frequency-division multiplexing access method. 
         [0251]    While the invention of the present application has been described above with reference to example embodiments, the invention of the present application is not limited to the foregoing example embodiments. The structure and details of the invention of the present application can be changed in various manner that can be understood within the scope of the invention of the present application by a person with ordinary skill in the art. 
         [0252]    This application claims the benefit of the priority based on Japanese Patent Application No. 2014-210873 filed on Oct. 15, 2014, the disclosure of which is incorporated herein in its entirety. 
       REFERENCE SIGNS LIST 
       [0253]      100 ,  101 ,  103 - 1 ,  103 - 2 ,  104 - 1 ,  104 - 2  DeNB 
         [0254]      102 ,  105 ,  201 ,  204  Transmission unit 
         [0255]      110  UL SR/BSR receiving unit 
         [0256]      111  UL SR/BSR information accumulating unit 
         [0257]      112  UL Transmission/reception candidate timing extracting unit 
         [0258]      113  UL Grant information accumulating unit 
         [0259]      114  UL Transmission/reception establishment timing extracting unit 
         [0260]      115  UL opposing node determination unit 
         [0261]      116  UL Grant establishment timing providing unit 
         [0262]      117  UL Grant generation unit 
         [0263]      118  UL Grant transmission unit 
         [0264]      130  DL Grant receiving unit 
         [0265]      131  DL Data receiving unit 
         [0266]      132  DL Grant information accumulating unit 
         [0267]      133  DL SR/BSR information accumulating unit 
         [0268]      134  DL Transmission establishment timing extracting unit 
         [0269]      135  DL Transmission/reception candidate timing extracting unit 
         [0270]      136  DL opposing node determination unit 
         [0271]      137  DL opposing node flag providing unit 
         [0272]      138  DL transmission/reception feasible timing candidate providing unit 
         [0273]      139  DL SR/BSR determination unit 
         [0274]      140  DL BSR generating unit 
         [0275]      141  DL BSR transmission unit 
         [0276]      142  DL SR generating unit 
         [0277]      143  DL SR transmission unit 
         [0278]      144  DL Data transmission feasibility determination unit 
         [0279]      145 ,  225  SR/BSR retransmission processing unit 
         [0280]      146  DL Data transmission unit 
         [0281]      200 ,  202 ,  203 ,  205  RN 
         [0282]      210  UL Grant receiving unit 
         [0283]      211  UL Data receiving unit 
         [0284]      212  UL Grant information accumulating unit 
         [0285]      213  UL SR/BSR information accumulating unit 
         [0286]      214  UL transmission establishment timing extracting unit 
         [0287]      215  UL transmission/reception candidate timing extracting unit 
         [0288]      216  UL opposing node determination unit 
         [0289]      217  UL opposing node flag providing unit 
         [0290]      218  UL transmission/reception feasible timing candidate providing unit 
         [0291]      219  UL SR/BSR determination unit 
         [0292]      220  UL BSR generating unit 
         [0293]      221  UL BSR transmission unit 
         [0294]      222  UL SR generating unit 
         [0295]      223  UL SR transmission unit 
         [0296]      224  UL Data transmission feasibility determination unit 
         [0297]      226  UL Data transmission unit 
         [0298]      231  DL SR/BSR receiving unit 
         [0299]      232  DL SR/BSR information accumulating unit 
         [0300]      233  DL transmission/reception candidate timing extracting unit 
         [0301]      234  DL Grant information accumulating unit 
         [0302]      235  DL transmission/reception establishment timing extracting unit 
         [0303]      236  DL Grant establishment timing providing unit 
         [0304]      237  DL Grant generation unit 
         [0305]      238  DL Grant transmission unit 
         [0306]      300 ,  300 - 1 ,  300 - 2  UE