Patent Publication Number: US-2015085744-A1

Title: Retransmission method, wireless communication apparatus, and relay station

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 12/709,147, filed Feb. 19, 2010, which is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-072180, filed on Mar. 24, 2009, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The embodiments discussed herein are related to a retransmission method, a wireless communication apparatus, and a relay station performing data communication. 
     BACKGROUND 
     To comply with the fourth-generation mobile phone standards (4G), frequency aggregation in which wide bandwidth is established by bundling bands is under investigation. For example, a method of establishing a downlink bandwidth having a total of 100 MHz by simultaneously using a 10 MHz-wide band at the center band of 800 MHz, a 30 MHz-wide band at a band of 2 GHz, and a 60 MHz-wide band at a band of 4 GHz is under investigation. 
     Because the propagation distance of radio waves decreases as frequency thereof increases, introduction of a relay station (RS) has been considered for use in 4G in which high frequency is also used. It is expected that use of RS will expand the area covered by a base transceiver station (BTS) at a low cost. 
     Moreover, a technique for adjusting transmission output of base station ACK/NAK messages in a wireless communication system has been disclosed (for example, Japanese Patent Application Publication No. 2007-502052). Furthermore, a technique for controlling a narrow band channel (for example, Japanese Laid-open Patent Publication No. H10-257097) in an indoor wireless communication system in which various kinds of communication demands such as sound and data are transmitted sharing an identical wide band channel has been disclosed. 
     Further, a technique has been disclosed for simply and effectively suppressing the influence of multipath involving the use of first interference-component estimating circuits respectively for each carrier frequency to estimate interference components from received signals of each carrier; removal of a noise component by an adder, based on a result of estimation; and correction of a transfer function by optimized filtering (see, for example, Japanese Laid-open Patent Publication No. H7-66739). 
     However, in the conventional techniques described above, the transmission of data is delayed when retransmission processing of data is performed. For example, if retransmission processing of data is performed and transmission of data is delayed in streaming of multimedia content, real time communication of multimedia content is not maintained. 
     SUMMARY 
     According to an aspect of an embodiment, a retransmission method in a mobile communication system includes performing a first transmission of data from a first wireless communication apparatus to a second wireless communication apparatus through at least one relay station by wireless relaying; and performing retransmission processing of retransmitting the data through fewer relay stations than the first transmission, or without using any relay station, where the second wireless communication apparatus receives data transmitted based on the retransmission processing. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a communication system according to a first embodiment. 
         FIG. 2  is a block diagram of a modification of the communication system depicted in  FIG. 1 . 
         FIG. 3  is a block diagram of a communication system according to a second embodiment. 
         FIG. 4  is a flowchart of one example of operation of a BTS depicted in  FIG. 3 . 
         FIG. 5  is a flowchart of an example of operations performed by an MS depicted in  FIG. 3 . 
         FIG. 6  is a diagram of an example of operation of the communication system depicted in  FIG. 3 . 
         FIG. 7  is a block diagram of a communication system according to a third embodiment. 
         FIG. 8  is a flowchart of one example of operation of an MS depicted in  FIG. 7 . 
         FIG. 9  is a diagram of an example of operation of the communication system depicted in  FIG. 7 . 
         FIG. 10  is a block diagram of a communication system according to a fourth embodiment. 
         FIG. 11  is a flowchart of one example of operation of each RS depicted in  FIG. 10 . 
         FIG. 12  is a diagram of an example of the operation of the communication system depicted in  FIG. 10 . 
         FIG. 13  is one example of operation by a communication system according to a fifth embodiment. 
         FIG. 14  is a block diagram of a communication system according to a sixth embodiment. 
         FIG. 15  is a block diagram of a communication system according to a seventh embodiment. 
         FIG. 16  is a block diagram of a communication system according to an eighth embodiment. 
         FIG. 17  is a flowchart of one example of operation of an MS depicted in  FIG. 16 . 
         FIG. 18  is a diagram of an example of operation of the communication system depicted in  FIG. 16 . 
         FIG. 19  is a block diagram of a communication system according to a ninth embodiment. 
         FIG. 20  is a flowchart of an example of operations performed by an MS depicted in  FIG. 19 . 
         FIG. 21  is a diagram of an example of operation of the communication system depicted in  FIG. 19 . 
         FIG. 22  is a block diagram of a communication system according to a tenth embodiment. 
         FIG. 23  is a flowchart of one example of operation of an RS depicted in  FIG. 22 . 
         FIG. 24  is a flowchart of one example of operation of a BTS depicted in  FIG. 22 . 
         FIG. 25  is a diagram of an example of operation of the communication system depicted in  FIG. 22 . 
         FIG. 26  is a block diagram of a communication system according to an eleventh embodiment. 
         FIG. 27  is a flowchart of an example of operations performed by an RS depicted in  FIG. 26 . 
         FIG. 28  is a diagram of an example of operation of the communication system depicted in  FIG. 26 . 
         FIG. 29  is a graph depicting throughput of data in the communication system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the present invention will be explained with reference to the accompanying drawings. 
       FIG. 1  is a block diagram of a communication system according to a first embodiment. As depicted in  FIG. 1 , a communication system  100  according to the first embodiment includes a wireless communication apparatus  110 , a relay station  120 , and a wireless communication apparatus  130 . The wireless communication apparatus  110  transmits data to the wireless communication apparatus  130  by wireless communication. 
     Moreover, the wireless communication apparatus  110  and the wireless communication apparatus  130  are able to use more than one route to communicate data with each other. For example, the wireless communication apparatus  110  and the wireless communication apparatus  130  may use a first route R1 in which data is communicated through the relay station  120 , and a second route R2 in which data is communicated without passing through the relay station  120 . 
     The wireless communication device  110  has a transmitting unit  111  and a retransmitting unit  112 . The transmitting unit  111  performs a first transmission of data to the wireless communication apparatus  130  by using wireless relaying through the relay station  120  (the first route R1). In this case, the transmitting unit  111  sends data addressed to the wireless communication apparatus  130 , to the relay station  120 . The first transmission is a transmission of the data to the wireless communication apparatus  130  performed for the first time, for example. 
     The retransmitting unit  112  performs retransmission processing of the data transmitted via the first transmission by the transmitting unit  111 . For example, the retransmitting unit  112  performs retransmission processing of the data when an error occurs in the first transmission by the transmitting unit  111 . The retransmitting unit  112  performs the retransmission processing of the data transmitted via the first transmission by the transmitting unit  111 , without passing through any relay station (e.g., the relay station  120 ) (the second route R2). 
     The retransmission processing is, for example, a retransmission of data so that the wireless communication apparatus  130  is able to properly receive the data in which an error has occurred during the first transmission thereof. For example, in the retransmission processing, the data transmitted via the first transmission is retransmitted. The retransmission processing may be performed on a part (for example, a part corresponding to the error) of the data transmitted via the first transmission, or data including the data that has been transmitted via the first transmission. 
     The relay station  120  wirelessly relays the first transmission of data from the wireless communication apparatus  110  to the wireless communication apparatus  130 . For example, the relay station  120  has a relay unit  121 . The relay unit  121  receives data transmitted from the wireless communication apparatus  110 . The relay unit  121  then transmits the received data to the wireless communication apparatus  130 . The relay unit  121  does not relay retransmission of data from the wireless communication apparatus  110  to the wireless communication apparatus  130 . 
     The wireless communication apparatus  130  has a receiving unit  131 . The receiving unit  131  receives the data transmitted through the relay station  120  from the wireless communication apparatus  110 . The receiving unit  131  also receives data that is retransmitted from the wireless communication apparatus  110  and does not pass through the relay station  120 . 
       FIG. 2  is a block diagram of a modification of the communication system depicted in  FIG. 1 . Like reference characters refer to like parts in  FIGS. 1 and 2 , and explanation therefor is omitted. As depicted in  FIG. 2 , the wireless communication apparatus  110  and the wireless communication apparatus  130  use the first route R1 in which data is communicated through the relay station  120  and a relay station  210 , and the second route R2 in which data is communicated without passing through the relay station  120  but passes through the relay station  210 . 
     The transmitting unit  111  performs the first transmission of data to the wireless communication apparatus  130  by using wireless relaying through the relay station  120  and the relay station  210  (the first route R1). For example, the transmitting unit  111  sends data addressed to the wireless communication apparatus  130 , to the relay station  120 . 
     The retransmitting unit  112  performs retransmission processing of the data transmitted via the first transmission by the transmitting unit  111 , through fewer relay stations than the number of relay stations that have wirelessly relayed the data in the first transmission. In the example depicted in  FIG. 2 , because two relay stations (the relay station  120  and the relay station  210 ) are used to relay the data in the first transmission, the retransmitting unit  112  performs the retransmission processing of the data by using wireless relaying by the relay station  210  (the second route R2). 
     The relay unit  121  of the relay station  120  receives data transmitted from the wireless communication apparatus  110 , and transmits the received data to the relay station  210 . The relay unit  121  does not relay retransmission of data from the wireless communication apparatus  110  to the wireless communication apparatus  130 . 
     The relay station  210  wirelessly relays the first transmission of data from the wireless communication apparatus  110  to the wireless communication apparatus  130 . For example, the relay station  210  has a relay unit  211 . The relay unit  211  receives data transmitted from the relay station  120 , and transmits the received data to the wireless communication apparatus  130 . The relay unit  211  relays retransmission of data from the wireless communication apparatus  110  to the wireless communication apparatus  130 . For example, the relay unit  211  receives data transmitted from the wireless communication apparatus  110 , and transmits the received data to the wireless communication apparatus  130 . 
     Next, one example of hardware configuration of the wireless communication apparatus  110  depicted in  FIG. 1  and  FIG. 2  will be explained. The transmitting unit  111  and the retransmitting unit  112  of the wireless communication apparatus  110  are implemented by, for example, an information processing means such as a central processing unit (CPU) and a communication interface. A data processing unit (not depicted) of the wireless communication apparatus  110  outputs data to be sent to the wireless communication apparatus  130 . 
     The data output from the data processing unit is written to a memory (not depicted) of the wireless communication apparatus  110 . The transmitting unit  111  reads the data written to the memory, and performs the first transmission of the read data. The retransmitting unit  112  reads from the memory, the data transmitted via the first transmission by the transmitting unit  111 , and performs retransmission processing for the read data. 
     The relay unit  121  of the relay station  120  and the relay unit  211  of the relay station  210  are implemented by, for example, an information processing means such as CPU and a communication interface. The relay unit  121  reproduces the data received from the wireless communication apparatus  110  in a digital signal, and transmits the reproduced data to the wireless communication apparatus  130 . 
     Alternatively, the relay unit  121  may be implemented by, for example, an analog amplifier circuit or a waveform shaping circuit, and a communication interface. The relay unit  121  performs analog processing such as amplification and waveform shaping on data received from the wireless communication apparatus  110 . The relay unit  121  transmits to the wireless communication apparatus  130 , the data subjected to the analog processing. 
     Next, one example of hardware configuration of the wireless communication apparatus  130  depicted in  FIG. 1  and  FIG. 2  will be explained. The receiving unit  131  of the wireless communication apparatus  130  is implemented by, for example, an information processing means such as CPU and a communication interface. The receiving unit  131  writes the received data to a memory (not depicted) of the wireless communication apparatus  130 . The written data is read by, for example, an information processing unit (not depicted) of the wireless communication apparatus  130  to be processed. 
     As described, according to the communication system  100  of the first embodiment, retransmission processing of data is performed through less relay stations than the relay stations used in wireless relaying in the first transmission, or without passing through any relay station. This speeds up retransmission processing of data, and can reduce delay in data transmission when retransmission processing occurs. 
       FIG. 3  is a block diagram of a communication system according to a second embodiment. As depicted in  FIG. 3 , a communication system  300  according to the second embodiment includes a base station (BTS)  310  (first wireless communication apparatus), a relay station (RS)  320 , and a mobile station (MS)  330  (second wireless communication apparatus). 
     The BTS  310  transmits data to the MS  330  by wireless communication. The BTS  310  and the MS  330  may use plural routes to communication data with each other. For example, the BTS  310  and the MS  330  may use the first route R1 in which data is communicated through the RS  320 , and the second route R2 in which data is communicated without passing through the RS  320 . 
     The BTS  310  has a transmitting unit  311 , a receiving unit  312 , and a retransmission control unit  313 . The transmitting unit  311  performs the first transmission of data to the MS  330  by the first route R1. For example, the transmitting unit  311 , when the first transmission of data to the MS  330  is performed, sends data addressed to the MS  330 , to the RS  320 . Furthermore, the transmitting unit  311  stores the data transmitted via the first transmission to a memory not depicted. 
     Additionally, when a retransmission request is output from the retransmission control unit  313 , the transmitting unit  311  retransmits, without passing through any relay station, the data transmitted via the first transmission (for example, the RS  320 ) (the second route R2). For example, the transmitting unit  311  reads the data written to the memory, and directly transmits the read data to the MS  330 . Moreover, the transmitting unit  311  performs the first transmission of new data when a transmission request is output from the retransmission control unit  313 . 
     The receiving unit  312  receives a reply signal that is sent from the MS  330  and wirelessly relayed by the RS  320 . The reply signal is, for example, either acknowledgement (Ack) indicating that data transmitted from the BTS  310  is properly received by the MS  330 , or negative acknowledgement (Nack) indicating that the data is not properly received. The receiving unit  312  outputs the received reply signal (Ack or Nack) to the retransmission control unit  313 . 
     The retransmission control unit  313  controls transmission and retransmission of data by the transmitting unit  311  according to the reply signal output from the receiving unit  312 . For example, when Ack is output from the receiving unit  312 , the retransmission control unit  313  outputs to the transmitting unit  311 , a transmission request indicating that next data should be transmitted. When Nack is output from the receiving unit  312 , the retransmission control unit  313  outputs to the transmitting unit  311 , a retransmission request indicating that the transmitted data should be retransmitted. 
     The RS  320  wirelessly relays to the MS  330 , the first transmission of data from the BTS  310 . The RS  320  does not relay retransmission of data from the BTS  310  to the MS  330 . Furthermore, the RS  320  wirelessly relays a reply signal from the MS  330  to the BTS  310 . 
     The MS  330  includes a receiving unit  331 , a signal processing unit  332 , and a transmitting unit  333 . The receiving unit  331  receives data transmitted from the BTS  310  through the RS  320  as the first transmission. Moreover, the receiving unit  331  receives data retransmitted from the BTS  310  without passing through the RS  320 . The receiving unit  331  demodulates the received data. The receiving unit  331  outputs the demodulated data to the signal processing unit  332 . 
     The signal processing unit  332  performs signal processing on data output from the receiving unit  331 . For example, the signal processing unit  332  performs decoding processing. Further, the signal processing unit  332  detects an error in the data subjected to the decoding processing. The signal processing unit  332  then informs a result of error detection to the transmitting unit  333 . 
     The transmitting unit  333  transmits a reply signal to the BTS  310  according to the result of error detection of the data informed by the signal processing unit  332 . For example, when the signal processing unit  332  reports that “there is no error”, the transmitting unit  333  transmits Ack to the BTS  310 . When the signal processing unit  332  reports that “there is an error”, the transmitting unit  333  transmits Nack to the BTS  310 . 
     The transmitting unit  333  transmits a reply signal to the BTS  310 , by using wireless relaying by the RS  320  (the first route R1). For example, the transmitting unit  333  transmits to the RS  320 , a reply signal addressed to the BTS  310 . 
     Next, one example of hardware configuration of the BTS  310  depicted in  FIG. 3  will be explained. The transmitting unit  311  of the BTS  310  is implemented by, for example, an information processing means such as CPU, and a communication interface. A data processing unit (not depicted) of the BTS  310  outputs data to be transmitted to the MS  330 . 
     The data output from the data processing unit is written to a memory (not depicted) of the BTS  310 . The transmitting unit  311  reads the data written to the memory, and performs the first transmission of the read data. The transmitting unit  311  reads the data transmitted via the first transmission from the memory, and performs retransmission processing for the read data. 
     The receiving unit  312  of the BTS  310  is implemented by, for example, an information processing means such as CPU and a communication interface. The receiving unit  312  writes the received reply signal to a memory of the BTS  310 . The retransmission control unit  313  of the BTS  310  is implemented by, for example, an information processing means such as CPU. The retransmission control unit  313  controls transmission and retransmission of data by the transmitting unit  311  according to the reply signal written to the memory. 
     Next, one example of hardware configuration of the MS  330  depicted in  FIG. 3  will be explained. The transmitting unit  333  of the MS  330  is implemented by, for example, an information processing means such as CPU and a communication interface. The receiving unit  331  of the MS  330  is implemented by, for example, an information processing means such as CPU, and a communication interface. The receiving unit  331  writes the received data to a memory (not depicted) of the MS  330 . The signal processing unit  332  of the MS  330  is implemented by, for example, an information processing means such as CPU. The signal processing unit  332  reads the data written to the memory by the receiving unit  331 , and detects an error of the read data. 
     The signal processing unit  332  writes a result of error detection to the memory. The transmitting unit  333  reads the result of error detection written to the memory by the signal processing unit  332 , and transmits to the RS  320 , a reply signal according to the read result of error detection. 
       FIG. 4  is a flowchart of one example of operation of the BTS depicted in  FIG. 3 . The BTS  310  (START) uses the first route R1 to perform the first transmission of data to the MS  330  via the transmitting unit  311  (step S 401 ). Next, whether the receiving unit  312  has received a reply signal for the data transmitted at step S 401  is determined (step S 402 ), and waiting occurs until a reply signal is received (step S 402 : NO). 
     When a reply signal is received (step S 402 : YES), whether the received reply signal is Ack is determined (step S 403 ). If the reply signal is not Ack (step S 403 : NO), the data is retransmitted by the transmitting unit  311  using the second route R2 (step S 404 ), and the process returns to step S 402  to be continued. 
     If the reply signal is Ack (step S 403 : YES), a series of processing is ended (END). The data transmitted at step S 404  is, for example, the data transmitted at step S 401 . By repeating the above processing, for example, a series of data is sequentially transmitted to the MS  330 . 
     Because the data is retransmitted using the second route R2 that does not pass through the RS  320  at step S 404 , the time from the retransmission of the data until the reception of the reply signal at S 402  is shortened. 
       FIG. 5  is a flowchart of an example of operations performed by the MS depicted in  FIG. 3 . The MS  330  (START) determines whether the receiving unit  331  has received data transmitted from the BTS  310  (step S 501 ), and waiting occurs until data is received (step S 501 : NO). When the data has been received (step S 501 : YES), the signal processing unit  332  performs the decoding processing on the received data (step S 502 ). 
     Next, the signal processing unit  332  determines whether there is an error in the data subjected to the decoding processing (step S 503 ). If there is an error (step S 503 : YES), the transmitting unit  333  transmits Nack to the BTS  310  using the first route R1 (step S 504 ), and the processing returns to step S 501  to be continued. 
     If there is no error in the data subjected to the decoding processing (step S 503 : NO), the transmitting unit  333  transmits Ack to the BTS  310  using the first route R1 (step S 505 ), and a series of processing is ended (END). By repeating the above processing, for example, a series of data is received from the BTS  310 . 
       FIG. 6  is a diagram of an example of operation of the communication system depicted in  FIG. 3 . As depicted in  FIG. 6 , the BTS  310  and the MS  330  may use two routes of different frequencies to communicate data with each other. One of the two routes is the first route R1 using, for example, a 5 GHz band, and the other of the two routes is the second route R2 using, for example, a 800 MHz band. 
     The frequency of the first route R1 is high and the propagation distance is short, and therefore, the first route R1 passes through the RS  320  (see  FIG. 3 ). The frequency of second route R2 is low and the propagation distance long, and therefore, the second route R2 does not pass through the RS  320 . In a sequence diagram  610  (with RS) and a sequence diagram  620  (without RS), the time axis is common. The sequence diagram  610  depicts transmission and reception of a signal in the first route R1. The sequence diagram  620  depicts transmission and reception of a signal in the second route R2. 
     In the first route R1, the BTS  310  transmits data to the RS  320  as the first transmission ( 611 ). Next, in the first route R1, the RS  320  transmits the data received from the BTS  310  to the MS  330  ( 612 ). In this example, it is assumed that an error occurs between the BTS  310  and the RS  320  or between the RS  320  and the MS  330 , and as a result, there is an error in the data received by the MS  330 . 
     Subsequently, in the first route R1, the MS  330  transmits Nack to the RS  320  ( 613 ). The RS  320  then transmits Nack received from the MS  330  to the BTS  310  ( 614 ). Next, in the second route R2, the BTS  310  retransmits the data to MS  330  ( 621 ). Thus, the retransmission processing is performed at high speed. 
     Reference numerals  615  and  616  indicate the flow of data when retransmission of data from the BTS  310  to the MS  330  is performed using the first route R1. When the first route R1 is used for retransmission of data as indicated by reference numerals  615  and  616 , it takes time to send data from the BTS  310  to the RS  320  ( 615 ), and time ( 630 ) to send the data from the RS  320  to the MS  330  ( 616 ). 
     On the other hand, by using the second route R2 for retransmission of data ( 621 ), the time indicated by reference numeral  630  is saved because data is retransmitted directly from the BTS  310  to the MS  330 . Thus, the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing is performed is reduced. 
     As described, according to the communication system  300  of the second embodiment, by performing the retransmission processing using the second route R2 that is faster than the first route R1 by which the first transmission is performed, the retransmission processing is speeded up and delay in data transmission when the retransmission processing is performed is reduced. As depicted in  FIG. 3 , for example, by setting the first route R1 as a route passing through the RS  320  and the second route R2 as a route not passing through any RS, the second route R2 is a faster route than the first route R1. 
     Although in this example, a configuration in which the first wireless communication apparatus transmitting data is applied to BTS and the second wireless communication apparatus receiving data is applied to MS has been explained, configuration may be such that the first wireless communication apparatus is applied to MS and the second wireless communication apparatus is applied to BTS. 
     Moreover, configuration may be such that the first wireless communication apparatus is applied to RS and the second wireless communication apparatus is applied to MS, or that the first wireless communication apparatus is applied to BTS and the second wireless communication apparatus is applied to RS. Furthermore, the first wireless communication apparatus, the relay station, and the second wireless communication apparatus are applicable to wireless communication apparatuses other than BTS, RS, and MS, respectively. 
     In addition, the MS  330  transmits a retransmission request signal (Nack) of data including an error to the BTS  310  using the first route R1 when there is an error in the data transmitted via the first transmission by the BTS  310 . The BTS  310  performs the retransmission processing when the request signal is transmitted by the MS  330 . Thus, the BTS  310  performs the retransmission processing of data when an error occurs in data transmitted via the first transmission. 
       FIG. 7  is a block diagram of a communication system according to a third embodiment. Like reference characters refer to like parts in  FIG. 3 , and explanation therefor is omitted. In the communication system  300  according to the third embodiment, the transmitting unit  333  of the MS  330  transmits a reply signal to the BTS  310  without passing through the RS  320  (the second route R2). 
     For example, the transmitting unit  333  of the MS  330  transmits a reply signal to be sent to the BTS  310  directly to the BTS  310 . In this case, the receiving unit  312  of the BTS  310  directly receives the reply signal transmitted by the MS  330 . An example of operation of the BTS  310  depicted in  FIG. 7  is identical to that depicted in  FIG. 4 , and thus, explanation therefor is omitted. 
       FIG. 8  is a flowchart of one example of operation of the MS depicted in  FIG. 7 . Because processing at steps S 801  to S 803  is identical to that at steps S 501  to S 503  depicted in  FIG. 5 , explanation therefor is omitted. At step S 803 , if there is an error (step S 803 : YES), the transmitting unit  333  transmits Nack to the BTS  310  using the second route R2 (step S 804 ), and the process returns to step S 801  to be continued. 
     If there is no error in the data subjected to the decoding processing (step S 803 : NO), the transmitting unit  333  transmits Ack to the BTS  310  using the second route R2 (step S 805 ), and a series of processing is ended (END). By repeating the above processing, for example, a series of data is received from the BTS  310 . 
     Moreover, because Nack is transmitted using the second route R2 that does not pass through the RS  320  at step S 804 , the time from transmission of Nack to re-reception of data at step S 801  is shortened. Furthermore, because Ack is transmitted using the second route R2 that does not pass through the RS  320  at step S 805 , the time from transmission of Ack until reception of next data at step S 801  is shortened. 
     Although in this example, a case where the second route R2 is used when the MS  330  transmits Ack and when the MS  330  transmits Nack has been explained, configuration may be such that the second route R2 is used when the MS  330  transmits Nack and the first route R1 is used when the MS  330  transmits Ack. In this case as well, the time from transmission of Nack until re-reception of data at step S 801  is shortened. 
       FIG. 9  is a diagram of an example of operation of the communication system depicted in  FIG. 7 . As depicted in  FIG. 9 , the BTS  310  and the MS  330  may use two routes of different frequencies to communicate data with each other. One of the two routes is the first route R1 using, for example, a 5 GHz band, and the other of the two routes is the second route R2 using, for example, a 800 MHz band. 
     The frequency of the first route R1 is high and the propagation distance is short, and therefore, the first route R1 passes through the RS  320  (see  FIG. 7 ). The frequency of second route R2 is low and the propagation distance long, and therefore, the second route R2 does not pass through the RS  320 . In a sequence diagram  910  (with RS) and a sequence diagram  920  (without RS), the time axis is common. The sequence diagram  910  depicts transmission and reception of a signal in the first route R1. The sequence diagram  920  depicts transmission and reception of a signal in the second route R2. 
     In the first route R1, the BTS  310  transmits data to the RS  320  ( 911 ). Next, in the first route R1, the RS  320  transmits the data received from the BTS  310  to the MS  330  by wireless transmission ( 912 ). In this example, it is assumed that the data received by the MS  330  has an error. Subsequently, in the second route R2, the MS  330  transmits Nack to the BTS  310  ( 921 ). The BTS  310  then retransmits the data to MS  330  ( 922 ). 
     Reference numerals  913  to  916  indicate the flow of data when transmission of Nack by the MS  330  and retransmission of data by the BTS  310  are performed using the first route R1. When the first route R1 is used for the transmission of Nack as indicated by reference numerals  913  and  914 , it takes time ( 931 ) to send Nack from the MS  330  to the RS  320  ( 913 ), and time ( 932 ) to send Nack from the RS  320  to the BTS  310  ( 914 ). 
     On the other hand, by using the second route R2 for the transmission of Nack ( 921 ), the time, as indicated by reference numeral  931 , is saved because Nack is transmitted directly from the MS  330  to the BTS  310 . Hence, the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing is performed is reduced. 
     Moreover, when the first route R1 is used for retransmission of data as indicated by reference numerals  915  and  916 , it takes time to send the data from the BTS  310  to the RS  320  ( 915 ) and time ( 932 ) to send the data from the RS  320  to the MS  330  ( 916 ). 
     On the other hand, by using the second route R2 for retransmission of the data ( 922 ), the time indicated by reference numeral  932  is saved because the data is retransmitted directly from the BTS  310  to the MS  330 . Thus, the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing is performed is reduced. 
     Thus, according to the communication system  300  of the third embodiment, when there is an error in the data transmitted via the first transmission by the BTS  310 , a retransmission request signal (Nack) for the data that includes the error is transmitted to the BTS  310  using the second route R2. The BTS  310  performs the retransmission processing when the request signal is transmitted by the MS  330 . 
     Thus, the time taken for transmission of a retransmission request signal (Nack) from the MS  330  to the BTS  330  is shortened. Therefore, according to the communication system  300  of the third embodiment, an effect similar to that of the communication system  300  of the second embodiment is achieved, and delay in data transmission when the retransmission processing occurs is further reduced. 
       FIG. 10  is a block diagram of a communication system according to a fourth embodiment. Like reference characters refer to like parts in  FIG. 3 , and explanation therefor is omitted. For example, the BTS  310  and the MS  330  may use the first route R1 (the number of wireless relays: 2) in which data is communicated through the RS  320  and an RS  1011 , and the second route R2 (the number of wireless relays: 1) in which data is communicated through an RS  1012 . 
     The RS  320  wirelessly relays to the RS  1011 , data that is addressed to the MS  330  and that is transmitted from the BTS  310 . The RS  1011  wirelessly relays to the MS  330 , the data that is addressed to the MS  330  and that is transmitted from the RS  320 . The RS  1012  wirelessly relays to the MS  330 , the data that is addressed to the MS  330  and that is transmitted from the BTS  310 . 
     The RS  320 , the RS  1011 , and the RS  1012  respectively report the number of wireless relays performed therefrom to the MS  330 , to the upstream communication apparatus. For example, the RS  320  notifies the BTS  310  of the number of wireless relays from the RS  320  to the MS  330 . The RS  1011  notifies the RS  320  of the number of wireless relays from the MS  330  to the RS  1011 . The RS  1012  notifies the BTS  310  of the number of wireless relays from the MS  320  to the RS  1012 . The notification of the number of wireless relays is performed by using a control channel of a mobile communication network. 
     The receiving unit  312  of the BTS  310  receives the number of wireless relays reported by the RS  320  as the number of wireless relays of the first route R1. Moreover, the receiving unit  312  receives the number of wireless relays reported by the RS  1012  as the number of wireless relays of the second route R2. The receiving unit  312  outputs to the retransmission control unit  313 , the number of wireless relays in the first route R1 and the number of wireless relays in the second route R2. 
     The retransmission control unit  313  compares the number of wireless relays in the first route R1 and the number of wireless relays in the second route R2 output from the receiving unit  312 . The retransmission control unit  313  reports to the transmitting unit  311 , the route having less number of wireless relays from among the first route R1 and the second route R2, as the route to be used for retransmission. The transmitting unit  311 , using the route reported by the retransmission control unit  313 , performs the retransmission processing for data that is transmitted by the transmitting unit  311  by the first transmission. 
     The reporting of the number of wireless relays by each of the RS  320  to the upstream communication apparatus, the RS  1011 , and the RS  1012  is performed, for example, at the time when data from the BTS  310  is wirelessly relayed to the MS  330 . To acquire the number of wireless relays for the first route R1 and the second route R2 in this case, for example, the transmitting unit  311  performs the first transmission of the data to the MS  330  using the first route R1 and the second route R2 in the initial operation. 
     For example, the transmitting unit  311  performs a first transmission of first data to the MS  330  using the first route R1. Further, the transmitting unit  311  performs a first transmission of second data (data following the first data) to the MS  330  using the second route R2. Thus, the BTS  310  is able to acquire the number of wireless relays in the first route R1 and in the second route R2, respectively and selects the route having fewer wireless relays for future retransmission processing. 
       FIG. 11  is a flowchart of one example of operation of each RS depicted in  FIG. 10 . First (START), whether data that is transmitted from the BTS  310  and that is addressed to the MS  330  has been received is determined (step S 1101 ), and waiting occurs until such data is received (step S 1101 : NO). When such data has been received (step S 1101 : YES), whether the destination to which the RS transmits is the MS  330  for the received data is determined (step S 1102 ). 
     If the destination is the MS  330  (step S 1102 : YES), the data received at step S 1101  is wirelessly relayed to the MS  330  (step S 1103 ). Subsequently, the number of wireless relays “1” is reported to the transmission origin of the data received at step S 1101  (step S 1104 ), and a series of processing is ended. 
     If the destination is not the MS  330  (step S 1102 : NO), the data received at step S 1101  is wirelessly relayed to the downstream apparatus (step S 1105 ). Next, whether the number of wireless relays has been reported by the downstream apparatus at step S 1105  is determined (step S 1106 ), and waiting occurs until the number of wireless relays is reported (step S 1106 : NO). 
     When the number of wireless relays is reported (step S 1106 : YES), the reported number of wireless relays “N” is incremented (step S 1107 ). Subsequently, the number of wireless relays “N+1” obtained by the increment at step S 1107  is reported to the transmission origin of the data received at step S 1101  (step S 1108 ), and a series of processing is ended. 
     By repeating the above processing by the RS  320 , the RS  1011 , and the RS  1012  depicted in  FIG. 10 , respectively, data from the BTS  310  to the MS  330  is wirelessly relayed. In addition, by the above processing, the number of wireless relays in the first route R1 and in the second route R2 is reported to the BTS  310 . 
       FIG. 12  is a diagram of an example of the operation of the communication system depicted in  FIG. 10 . Here, the reporting of the number of wireless relays in the first route R1 (via the RS  320  and the RS  1011 ) depicted in  FIG. 10  is explained. The BTS  310  first transmits data to the RS  320 . The RS  320  then wirelessly relays the data transmitted from the BTS  310  to the RS  1011 . 
     Next, the RS  1011  wirelessly relays the data transmitted from the RS  320  to the MS  330 . Moreover, the RS  1011  reports the number of wireless relays “1” to the transmission origin of the data, the RS  320 , because the destination of the received data for the RS  1011  is the MS  330 . The RS  320  increments the number of wireless relays “1” reported by the RS  1011 , and reports to the BTS  310 , the number of wireless relays “2” obtained by the increment. Thus, the BTS  310  obtains the number of wireless relays “2” in the first route R1. 
     Here, the reporting of the number of wireless relays in the second route R2 (via the RS  1012 ) depicted in  FIG. 10  is explained. The BTS  310  transmits data to the RS  1012 . Next, the RS  1012  wirelessly relays to the MS  330 , the data transmitted from the BTS  310 . Moreover, the RS  1012  reports the number of wireless relays “1” to the transmission origin of the data, the BTS  310 , because the destination to which the RS  1012  transmits is the MS  330 , the destination of the received data. 
     Thus, the BTS  310  obtains the number of wireless relays “1” in the second route R2. Accordingly, the BTS  310  obtains the respective numbers of wireless relays in the first route R1 and in the second route R2. In this case, the BTS  310 , using the second route R2 which has fewer wireless relays than the first route R1, performs the retransmission processing of data transmitted via the first transmission. 
     As described, according to the communication system  300  of the fourth embodiment, by performing the retransmission processing using the second route R2 which is faster than the first route R1 which is used for the first transmission, the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing occurs is reduced. For example, as depicted in  FIG. 10 , by setting a route passing through multiple RS such as the first route R1, and a route passing through fewer RSs than in the first route R1, such as the second route R2, the second route R2 is faster than the first route R1. 
     In addition, the RS  320 , the RS  1011 , and the RS  1012  respectively reports the number of wireless relays therefrom to the MS  330 , to the relay station or the BTS  310  positioned upstream therefrom, and the BTS  310  performs the retransmission processing of data using the route having fewer reported wireless relays. Thus, the BTS  310  is able to select a route having less RSs than the first route R1 which is used for the first transmission, as the second route R2 to be used for the retransmission processing. 
     Therefore, an effect similar to the communication system  300  according to the second embodiment is achieved, and the retransmission processing is performed at high speed even when all routes in the system pass through relay stations such as RS, or when there is a route that does not pass through any relay station in the system, but the route is not usable because sufficient communication quality is not guaranteed thereby. 
       FIG. 13  is one example of operation of a communication system according to a fifth embodiment. As depicted in  FIG. 13 , the BTS  310  and the MS  330  perform frequency aggregation in which multiple routes at different frequencies are used at the same time, to communicate data with each other. In this case, the configuration of the communication system  300  is similar to that depicted in  FIG. 3 , and therefore, the illustration thereof is omitted. 
     As depicted in  FIG. 13 , the BTS  310  performs the first transmission of data to the MS  330  using, at the same time, the first route R1 that passes through the RS  320  and the second route that does not pass through any RS. For example, the transmitting unit  311  of the BTS  310  allocates each data to be transmitted as the first transmission to the first route R1 and the second route R2. Hereinafter, a link of data allocated to the first route R1 by the transmitting unit  311  is referred to as a first link, and a link of data allocated to the second route R2 is referred to as a second link. 
     In a sequence diagram  1310  (with RS) and a sequence diagram  1320  (without RS), the time axis is common. The sequence diagram  1310  depicts transmission and reception of a signal in the first route R1. The sequence diagram  1320  depicts transmission and reception of a signal in the second route R2. In the sequence diagram  1310  and the sequence diagram  1320 , a solid lined arrow depicts the flow of data of the first link, and an arrow having an alternating long and short dashed lined tail depicts the flow of data of the second link. 
     As depicted in the sequence diagrams  1310  and  1320 , the BTS  310  transmits data of the first link using the first route R1, and data of the second link using the second route R2. Furthermore, the BTS  310 , using the first route R1 by interrupting the first transmission of the data of the second link using the second route R2, performs the retransmission processing for the data of the first link for which the first transmission has been performed. 
     First, the BTS  310  transmits data to the RS  320  by the first route R1 ( 1311 ). The RS  320  then transmits the data received from the BTS  310  to the MS  330  ( 1312 ). Here, it is assumed that there is an error in the data received by the MS  330 , next, the MS  330  transmits Nack to the RS  320  ( 1313 ). 
     Subsequently, the RS  320  transmits the Nack received from the MS  330  to the BTS  310  ( 1314 ). The BTS  310  interrupts the transmission of data of the second link that is simultaneously being executed in the second route R2 to perform the retransmission processing of the data of the first link for which the Nack has been received ( 1321 ). Here, it is assumed that there is no error in the data retransmitted by the BTS  310  and re-received by the MS  330 . 
     Next, the MS  330  transmits, to the RS  320 , Ack for the data received from the BTS  310  ( 1315 ). The RS  320  then transmits the Ack received from the MS  330  to the BTS  310  ( 1316 ). Subsequently, the BTS  310  transmits new data to the RS  320  ( 1317 ). The RS  320  transmits the data received from the BTS  310  to the MS  330  ( 1318 ). Here, it is assumed that there is no error in the data received by the MS  330 . 
     Next, the MS  330  transmits, to the RS  320 , Ack for the data received from the RS  320  ( 1319 ). The operations depicted by reference numerals  1320  to  1322  are similar to those depicted by reference numerals  1316  to  1318 , and therefore, the explanation therefor is omitted. By using the second route R2 for retransmission of data ( 1321 ), the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing occurs is reduced. 
     As described, according to the communication system  300  of the fifth embodiment, the retransmission of data of the first link for which the first transmission has been performed using the first route R1 is performed by interrupting the first transmission of the second link using the second route R2. Thus, the retransmission processing is performed using the second route R2 which is faster than the first route R1 which is used for the first transmission. Therefore, even in a communication system in which the first transmission is performed using multiple routes at the same time (frequency aggregation, etc.), the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing occurs is reduced. 
       FIG. 14  is a block diagram of a communication system according to a sixth embodiment. In the sixth embodiment, the explanation of points similar to the second embodiment is omitted. In the communication system  300  according to the sixth embodiment, the BTS  310  may be configured to transmit data to the MS  330  and to transmit data to an MS  1401  besides the MS  330 . 
     In this case, the BTS  310  uses the first route R1 when the first transmission is performed and uses the second route R2 when the retransmission processing is performed also for data to be transmitted to the MS  1401 . In a sequence diagram  1410  (with RS) and a sequence diagram  1420  (with RS), and a sequence diagram  1430  (without RS), the time axis is common. 
     In the sequence diagram  1410  and the sequence diagram  1420 , a solid lined arrow depicts the flow of a signal between the BTS  310  and the MS  330 , and an arrow having an alternating long and short dashed lined tail depicts the flow of a signal between the BTS  310  and the MS  1401 . The sequence diagram  1410  indicates transmission and reception of a signal between the BTS  310  and the MS  330  in the first route R1. 
     The sequence diagram  1420  indicates transmission and reception of a signal between the BTS  310  and the MS  1401  in the first route R1. The sequence diagram  1430  indicates transmission and reception of a signal between the BTS  310  and the MS  330 , and between the BTS  310  and the MS  1401  in the second route R2. 
     First, the BTS  310  transmits to the RS  320  by the first route R1, data addressed to the MS  1401  ( 1421 ). The RS  320  then transmits to the MS  1401 , the data received from the BTS  310  ( 1422 ). Here, it is assumed that there is an error in the data received by the MS  1401 . 
     Next, in the second route R2, the MS  1401  transmits Nack to the BTS  310  ( 1431 ). Subsequently, in the second route R2, the BTS  310  retransmits data to the MS  1401  ( 1432 ). Next, in the first route R1, the BTS  310  transmits data addressed to the MS  330  to the RS  320  ( 1411 ). The RS  320  then wirelessly relays the data received from the BTS  310  to the MS  330  ( 1412 ). 
     Here, it is assumed that there is an error in the data received by the MS  330 . In the second route R2, the MS  330  transmits Nack to the BTS  310  ( 1433 ). Subsequently, in the second route R2, the BTS  310  retransmits data to the MS  330  ( 1434 ). Here, it is assumed that there is no error in the data received by the MS  330 . 
     Further, at this time, in the first route R1, the BTS  310  transmits data addressed to MS  1401  to the RS  320  ( 1423 ). Next, the RS  320  wirelessly relays the data received from the BTS  310  to the MS  1401  ( 1424 ). Here, it is assumed that there is no error in the data received by the MS  1401 . In the second route R2, the MS  1401  then transmits Ack to the BTS  310  ( 1435 ). 
     Further, at this time, in the first route R1, the BTS  310  transmits data addressed to the RS  320  ( 1413 ). The RS  320  then wirelessly relays the data received from the BTS  310  to the MS  330  ( 1414 ). Assuming that there is no error in the data received by the MS  330 , the MS  330  then transmits, in the second route R2, Ack to the BTS  310  ( 1436 ). 
     Thereafter, the BTS  310  performs the first transmission to the MS  330  and to the MS  1401  using the first route R1 and the retransmission processing to the MS  330  and to the MS  1401  using the second route R2, similarly. Therefore, the communication source of the second route R2 is shared by the retransmission processing between the BTS  310  and the MS  330  and the retransmission processing between the BTS  310  and the MS  1401 . 
     As described, according to the communication system  300  of the sixth embodiment, an effect similar to that of the communication system  300  of the second embodiment is achieved, and the BTS  310  performs the retransmission processing to each MS using the second route R2 in data communication with multiple MSs. Thus, the retransmission processing in communication with each MS is performed at high speed, and delay in data transmission when the retransmission processing occurs is reduced. 
       FIG. 15  is a block diagram of a communication system according to a seventh embodiment. Like reference characters refer to like parts in  FIG. 1 , and explanation therefor is omitted. As depicted in  FIG. 15 , the wireless communication apparatus  110  and the wireless communication apparatus  130  may be configured such that the first route R1 in which data is communicated through the relay station  120  and the second route R2 in which data is communicated through the relay station  210  are used. 
     The retransmitting unit  112  performs the retransmission processing using the route whose total relay time at a relay station present in the relay route at retransmission of data is shorter than the total relay time at a relay station present in the relay route (the first route R1) at the first transmission of the data by the transmitting unit  111 . For example, in the example depicted in  FIG. 15 , suppose that the relay time of data at the relay station  120  included in the first route R1 is longer than the total relay time of data at the relay station  210  included in the second route R2. 
     In this case, the retransmitting unit  112 , using the second route R2, performs the retransmission processing of data transmitted via the first transmission by the transmitting unit  111 . The relay station  120  wirelessly relays, to the wireless communication apparatus  130 , the data transmitted from the wireless communication apparatus  110  addressing to the wireless communication apparatus  130 . 
     As described, according to the communication system  100  of the seventh embodiment, the retransmission processing is performed using the route whose total relay time for the respective relay stations in the relay route at retransmission of data is shorter than the total relay time for the respective relay stations in the relay route (the first route R1) for the first transmission of the data. Thus, the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing occurs is reduced. 
       FIG. 16  is a block diagram of a communication system according to an eighth embodiment. Like reference characters refer to like parts in  FIG. 3 , and explanation therefor is omitted. In the eighth embodiment, for example, the BTS  310  and the MS  330  may be configured such that the first route R1 in which data is communicated through the RS  320  and the second route R2 in which data is communicated through an RS  1620  are used. 
     The BTS  310  includes a measuring unit  1611  in addition to the components depicted in  FIG. 3 . The measuring unit  1611  measures the response time from the first transmission by the transmitting unit  311  until the reception of a reply signal in response to the first transmission from the MS  330 , for the first route R1 and the second route R2. The measuring unit  1611  outputs the measured response time for each route to the retransmission control unit  313 . 
     The retransmission control unit  313  compares the respective times measured in the first route R1 and the second route R2 and output from the measuring unit  1611 . The retransmission control unit  313  reports, to the transmitting unit  311 , the route whose measured time is shorter among the first route R1 and the second route R2 as the route to be used for retransmission. The transmitting unit  311 , using the route reported by the retransmission control unit  313 , performs the retransmission processing for the data transmitted via the first transmission. 
     Next, the method of measuring response time by the measuring unit  1611  is explained. For example, the transmitting unit  311  outputs a measurement start signal to the measuring unit  1611  when the first transmission is performed. Moreover, the receiving unit  312  outputs a measurement end signal to the measuring unit  1611  when a reply signal from the MS  330  is received. The measuring unit  1611  measures time from the measuring start signal is output from the transmitting unit  311  until the measurement end signal is output from the receiving unit  312 , as the response time. 
     Furthermore, to measure the response time of the first route R1 and the second route R2 by the measuring unit  1611 , for example, the transmitting unit  311  of the BTS  310  performs the first transmission of data to the MS  330  using the first route R1 and the second route R2 at the initial operation. For example, the transmitting unit  311  performs the first transmission of first data to the MS  330  using the first route R1. 
     Further, the transmitting unit  311  performs the first transmission of second data (data following the first data) to the MS  320  using the second route R2. Thus, the measuring unit  1611  obtains the response time for both the first route R1 and the second route R2. Therefore, the BTS  310  selects the route having the shorter response time when retransmission of data is performed after that. 
     Next, one example of hardware configuration of the measuring unit  1611  of the BTS  310  depicted in  FIG. 16  will be explained. The measuring unit  1611  may be implemented by, for example, a communication processing means such as a CPU. The measuring unit  1611  writes the measured response time to a memory (not depicted) of the BTS  310 . The retransmission control unit  313  of the BTS  310  reads the response time written to the memory by the measuring unit  1611 , and performs retransmission control based on the read response time. 
       FIG. 17  is a flowchart of one example of operation of the MS depicted in  FIG. 16 . The BTS  310  (START) uses the first route R1 to perform the first transmission of data to the MS  330  via the transmitting unit  311  (step S 1701 ). Next, the measuring unit  1611  starts time measurement (step S 1702 ). 
     Next, whether the receiving unit  312  has received a reply signal for the data transmitted at step S 1701  is determined (step S 1703 ), and waiting occurs until a reply signal is received (step S 1703 : NO). When a reply signal is received (step S 1703 : YES), the measuring unit  1611  measures, as the response time, the time that has elapsed since the start of the time measurement at step S 1702  (step S 1704 ). 
     Subsequently, whether the reply signal received at step S 1703  is Ack is determined (step S 1705 ). If the reply signal is not Ack (step S 1705 : NO), the route whose response time measured at step S 1704  is shortest is selected (step S 1706 ). 
     Next, the transmitting unit  311  retransmits data using the route selected at step S 1706  (step S 1707 ), and the process returns to step S 1702  to be continued. When the reply signal is Ack (step S 1705 : YES), a series of processing is ended (END). The data transmitted at step S 1707  is, for example, the data transmitted at step S 1701 . 
     By repeating the above processing, for example, a series of data is transmitted to the MS  330 . Moreover, because data is retransmitted using the second route R2 in which the RS  320  is not passed through at step S 1704 , the time from the retransmission of data to the reception of a reply signal at step S 1703  is shortened. 
     Moreover, by measuring the time from step S 1701  to step S 1704  by the measuring unit  1611 , the response time for a route used for the first transmission is measured. Thus, the total relay time in the respective relay stations included in the first route R1 and the total relay time in respective relay stations included in the second route R2 are measured. 
       FIG. 18  is a diagram of an example of operation of the communication system depicted in  FIG. 16 . A sequence diagram  1800  depicts transmission and reception of a signal in the first route R1. First, the BTS  310  transmits data to the RS  320  ( 1811 ). The RS  320  then wirelessly relays to the MS  330 , the data transmitted from the BTS  310  ( 1812 ). 
     Next, the MS  330  transmits a reply signal to the RS  320  ( 1813 ). The RS  320  then transmits the reply signal received from the MS  330  to the BTS  310  ( 1814 ). The measuring unit  1611  of the BTS  310  measures the time  1820  from the transmission of data from the BTS  310  to the MS  330  ( 1811 ) until the reception of the reply signal from the MS  330  by the BTS  310  ( 1814 ). 
     As described, according to the communication system  300  of the eighth embodiment, by performing the retransmission processing using the second route R2 which is faster than the first route R1 which is used for the first transmission, the retransmission processing is performed at high speed, and delay in data transmission when the retransmission processing occurs is reduced. For example, as depicted in  FIG. 16 , by measuring the response time of each route, and by setting the route whose measured time is shortest as the second route R2, the second route R2 is the faster route than the first route R1. 
     Furthermore, the time  1820  from the transmission of data to the MS  330  by the BTS  310  ( 1811 ) until the reception of a reply signal from the MS  330  by the BTS  310  ( 1814 ) is measured. Thus, the response time for each route is measured. Therefore, the BTS  310  is able to select, as the second route R2 to be used for the retransmission processing, a route having a shorter response time than the first route R1 which is used for the first transmission. 
     Therefore, an effect similar to that of the communication system  300  according to the second embodiment is achieved, and the retransmission processing is performed at high speed even when a route that does not pass through any relay station such as RS is not present in the system, or when a route that does not through any relay station is present, but is not usable because sufficient communication quality is not guaranteed thereby. 
       FIG. 19  is a block diagram of a communication system according to a ninth embodiment. Like reference characters refer to like parts in  FIG. 3 , and explanation therefor is omitted. In the communication system  300  according to the ninth embodiment, the retransmission control is performed independently between the BTS  310  and the RS  320 , and between the RS  320  and the MS  330 . 
     The transmitting unit  311  performs the first transmission of data to the MS using, at the same time, the first route R1 that passes through the RS  320  and the second route R2 that does not pass through any RS. For example, the transmitting unit  311  allocates data to be transmitted as the first transmission to the first route R1 and the second route R2. Hereinafter, a link of data allocated to the first route R1 by the transmitting unit  311  is referred to as the first link, and a link of data allocated to the second route R2 is referred to as the second link. 
     The transmitting unit  311  transmits data to the RS  320  when data of the first link is transmitted. The transmitting unit  311  transmits data directly to the MS  330  when data of the second link is transmitted. Furthermore, the transmitting unit  311  retransmits, without passing through any relay station (for example, the RS  320 ) (the second route R2), the data that is transmitted via the first transmission when a retransmission request is output from the retransmission control unit  313 . Further, the transmitting unit  311  performs the first transmission of new data when a transmission request is output from the retransmission control unit  313 . 
     The RS  320  has a function of performing retransmission control between the RS  320  and the MS  330 . For example, the RS  320  includes a receiving unit  1911 , a signal processing unit  1912 , a transmitting unit  1913 , a transmitting unit  1921 , a receiving unit  1922 , and a retransmission control unit  1923 . The receiving unit  1911  receives data transmitted from the BTS  310  as the first transmission. The receiving unit  1911  performs decoding processing on the received data, and outputs the data subjected to the decoding processing to the signal processing unit  1912 . 
     The signal processing unit  1912  performs signal processing on the data output from the receiving unit  1911 . For example, the signal processing unit  1912  performs decoding processing of the data output from the receiving unit  1911 . Moreover, the signal processing unit  1912  detects an error in the data subjected to the decoding processing, and reports the result of detection to the transmitting unit  1913 . The signal processing unit  1912  stores the data subjected to the signal processing to a buffer (not depicted) of the RS  320  when there is no error in the data. 
     The transmitting unit  1913  transmits a reply signal to the BTS  310  according to the result of detection reported by the signal processing unit  1912 . For example, the transmitting unit  1913  transmits Ack to the BTS  310  when it is reported that “there is no error” by the signal processing unit  1912 . The transmitting unit  1913  transmits Nack to the BTS  310  when it is reported that “there is an error” by the signal processing unit  1912 . 
     The transmitting unit  1921  reads the data stored to a transmission buffer of the RS  320  by the signal processing unit  1912 . The transmitting unit  1921  then transmits the read data to the MS  330  as the first transmission. Furthermore, the transmitting unit  1921  stores the data transmitted via the first transmission to a memory not depicted. 
     The transmitting unit  1921  retransmits the data transmitted via the first transmission when a retransmission request is output from the retransmission control unit  1923 . For example, the transmitting unit  1921  reads the data stored to the memory, and transmits the read data to the MS  330 . Further, the transmitting unit  1921  performs the first transmission of next data output from the signal processing unit  1912  when a transmission request is output from the retransmission control unit  1923 . 
     The receiving unit  1922  receives a reply signal transmitted by the MS  330 . The reply signal is for example, either Ack indicating that the data transmitted from the RS  320  is properly received by the MS  330 , or Nack indicating that the data is not properly received. The receiving unit  1922  outputs the received reply signal to the retransmission control unit  1923 . 
     The retransmission control unit  1923  controls retransmission of data by the transmitting unit  1921 . For example, when Ack is output from the receiving unit  1922 , the retransmission control unit  1923  deletes data corresponding to Ack from the transmission buffer, and outputs a transmission request for next data to the transmitting unit  1921 . On the other hand, when Nack is output from the receiving unit  1922 , the retransmission control unit  1923  outputs a retransmission request for the transmitted data to the transmitting unit  1921 . 
     The signal processing unit  332  of the MS  330  reports the result of data error detection to the transmitting unit  333 , and further reports which among the first route R1 and the second route R2 is used to transmit the data, to the transmitting unit  333 . 
     The transmitting unit  333  of the MS  330  transmits Ack to the RS  320  when the result of detection is received from the signal processing unit  332  for the data transmitted by the first route R1 regardless of the result of detection indicating “there is an error” or “there is no error”. The transmitting unit  333  of the MS  330 , using the second route R2, transmits Ack to the BTS  310  when the result of detection is “there is no error” and using the second route R2, transmits Nack when the result of detecting is “there is an error”. 
     Furthermore, when the result of detection for the data transmitted using the second route R2 is received from the signal processing unit  332 , the transmitting unit  333  transmits a reply signal to the BTS  310  according to the result of detection using the second route R2. For example, when it is reported that “there is no error” from the signal processing unit  332 , the transmitting unit  333  transmits Ack to the BTS  310 . When it is reported that “there is an error” from the signal processing unit  332 , the transmitting unit  333  transmits Nack to the BTS  310 . 
     Next, one example of hardware configuration of the RS  320  depicted in  FIG. 19  will be explained. The receiving unit  1911 , the transmitting unit  1913 , the transmitting unit  1921 , and the receiving unit  1922  of the RS  320  are implemented by, for example, an information processing means such as a CPU and a communication interface. The signal processing unit  1912  and the retransmission control unit  1923  of the RS  320  are implemented by, for example, an information processing means such as a CPU and a communication interface. 
     The receiving unit  1911  writes received data to a memory of the RS  320 . The signal processing unit  1912  reads the data written to the memory by the receiving unit  1911 , and performs signal processing of the read data. The signal processing unit  1912  writes the result of error detection and the data to a memory of the RS  320 . The transmitting unit  1913  transmits a reply signal according to the result of detection written to the memory of the RS  320  by the signal processing unit  1912 . 
     The transmitting unit  1921  reads the data written to the memory of the RS  320  by the signal processing unit  1912 , and transmits the read data. The receiving unit  1922  writes a received reply signal to the memory of the RS  320 . The retransmission control unit  1923  of the RS  320  performs retransmission control according to the reply signal written to the memory by the receiving unit  1922 . 
       FIG. 20  is a flowchart of an example of operations performed by the MS depicted in  FIG. 19 . The MS  330  (START) determines whether the receiving unit  331  has received data transmitted through the first route R1 or the second route R2 (step S 2001 ), and waiting occurs until data is received (step S 2001 : NO). When data is received (step S 2001 : YES), whether the received data is received from the first route R1 is determined (step S 2002 ). 
     If the data is received from the first route R1 (step S 2002 : YES), decoding processing of the data received at step S 2001  is performed by the signal processing unit  332  (step S 2003 ). Subsequently, Ack is transmitted to the RS  320  using the first route R1 (step S 2004 ), and the processing proceeds to step S 2007  to be continued. 
     If the data is not received from the first route R1 (step S 2002 : NO), whether the data received at step S 2001  is received from the second route R2 is determined (step S 2005 ). If the data is not received from the second route R2 (step S 2005 : NO), the processing returns to step S 2001  to be continued. 
     If the data is received from the second route R2 (step S 2005 : YES), decoding processing of the data received at step S 2001  is performed by the signal processing unit  332  (step S 2006 ). Next, the signal processing unit  332  determines whether there is an error in the data subjected to the decoding processing (step S 2007 ). 
     If there is an error (step S 2007 : YES), using the second route R2, Nack is transmitted to the BTS  310  (step S 2008 ), a series of processing is ended (END), and the process returns to step S 2001  to be continued. If there is no error in the data subjected to the decoding processing (step S 2007 : NO), using the second route R2, Ack is transmitted to the BTS  310  (step S 2009 ), and a series of processing is ended (END). By repeating the above processing, for example, a series of data is received from the BTS  310 . 
     By repeating the above processing, the MS  330  transmits Ack to the RS  320  regardless of the presence or absence of an error in data when the data is received from the first route R1, and transmits a reply signal according to the presence or absence of an error in the data to the BTS  310 . Thus, the RS  320  does not perform retransmission control to the MS  330  even if an error is detected in the data at MS  330 , and transmission between the RS  320  and the MS  330  is not interrupted by retransmission control. 
       FIG. 21  is a diagram of an example of operation of the communication system depicted in  FIG. 19 . In  FIG. 21 , a sequence diagram  2110  depicts transmission and reception of a signal in the first route R1. A sequence diagram  2120  depicts transmission and reception of a signal in the second route R2. In the sequence diagram  2110  and the sequence diagram  2120 , blocks with numerals indicate data. 
     As depicted in the sequence diagram  2110 , the BTS  310  performs the first transmission of data “1” to data “5” by the first route R1. As depicted in the sequence diagram  2120 , The BTS  310  performs the first transmission of data “10” to data “13” by the second route R2. “A” indicates Ack, and “N” indicates Nack. 
     For example, Ack indicated by a numeral  2111  is a reply signal to data “1” transmitted by the RS  320  to the BTS  310 . Ack indicated by a numeral  2112  is a reply signal to data “1” transmitted by the MS  330  to the RS  320 . Ack indicated by a numeral  2121  is a reply signal to data “11” transmitted by the MS  330  to the BTS  310 . 
     Here, it is assumed that the MS  330  detects an error of received data “2”. In this case, the MS  330  transmits Ack to the RS  320  ( 2113 ). Moreover, the MS  330  transmits Nack to the BTS  310  ( 2132 ). Thus, the BTS  310  transmits retransmission data “2R” of data “2” to the MS  330  using the second route R2. 
     Ack indicated by a numeral  2133  is a reply signal to data “3” transmitted by the MS  330  to the BTS  310 . Ack indicated by a numeral  2134  is a reply signal to data “4” transmitted by the MS  330  to the BTS  310 . Ack indicated by a numeral  2122  is a reply signal to retransmission data “2R” transmitted by the MS  330  to the BTS  310 . 
     As described, according to the communication system  300  of the ninth embodiment, an effect similar to that of the communication system  300  according to the second embodiment is achieved, and the RS  320  has a function of performing retransmission control between the RS  320  and the MS  330 . Furthermore, the MS  330  transmits a retransmission request signal for data that has an error to the BTS  310  when there is an error in the data transmitted via the first transmission, and transmits Ack to the RS  320  regardless of presence of an error in the data. 
     Thus, the RS  320  does not perform retransmission control to the MS  330  even if an error is detected in data at MS  330 , and transmission between the RS  320  and the MS  330  is not interrupted by retransmission control. Therefore, even if the transmission speed between the RS  320  and the MS  330  is slower than the transmission speed between the BTS  310  and the RS  320 , reduction in throughput because of transmission between the RS  320  and the MS  330  being bottlenecked or buffer overflow at the RS  320  is prevented. 
       FIG. 22  is a block diagram of a communication system according to a tenth embodiment. Like reference characters refer to like parts in  FIG. 19 , and explanation therefor is omitted. The transmitting unit  311  of the BTS  310  performs, simultaneously, the first transmission of data to the MS  330  using the first route R1 which passes through the RS  320  and the second route R2 which does not pass any RS. 
     Furthermore, the transmitting unit  333  of the MS  330  transmits a reply signal to the RS  320  according to the result of detection reported by the signal processing unit  332 . For example, the transmitting unit  333  transmits Ack to the RS  320  when it is reported that “there is no error” from the signal processing unit  332 , and transmits Nack to the RS  320  when it is reported that “there is an error” from the signal processing unit  332 . 
     When the reply signal is received from the MS  330 , the receiving unit  1922  of the RS  320  outputs the received reply signal to the transmitting unit  1913 . The transmitting unit  1913  transmits to the BTS  310 , the reply signal output from the receiving unit  1922 . When the reply signal is received from the MS  330 , the receiving unit  1922  transmits Ack to the retransmission control unit  1923  regardless of the contents of the reply signal. 
     When Nack for the first link is output from the receiving unit  312 , the retransmission control unit  313  of the BTS  310  outputs to the transmitting unit  311 , a retransmission request for the first link. When Nack for the second link is output from the receiving unit  311 , the retransmission control unit  313  outputs to the transmitting unit  311 , a retransmission request for the second link. 
     When the retransmission request for the first link is output from the retransmission control unit  313 , the transmitting unit  311  retransmits, without passing through any relay stations, the data of the first link that has been transmitted via the first transmission (the second route R2). Moreover, when the retransmission request for the second link is output from the retransmission control unit  313 , the transmitting unit  311  retransmits, without passing through any relay stations, the data of the second link that has been transmitted via the first transmission (the second route R2). 
       FIG. 23  is a flowchart of one example of operation of the RS depicted in  FIG. 22 . The RS  320  (START) performs the first transmission of data received from the BTS  310  via the transmitting unit  1921  (step S 2301 ). Next, whether the receiving unit  1922  has received a reply signal for the data transmitted at step S 2301  is determined (step S 2302 ), and waiting occurs until a reply signal is received (step S 2302 : NO). 
     When a reply signal is received (step S 2302 : YES), the transmitting unit  1913  wirelessly relays the received reply signal to the BTS  310  (step S 2303 ), and a series of processing is ended (END). By repeating the above processing, the RS  320  wirelessly relays a reply signal from the MS  330  to the BTS  310  regardless of the contents of the reply signal. Thus, it can be arranged such that the RS  320  does not perform retransmission control to the MS  330  even when an error is detected in data at the MS  330 . 
       FIG. 24  is a flowchart of one example of operation of the BTS depicted in  FIG. 22 . The BTS  310  (START) uses the first route R1 to perform the first transmission of data to the MS  330  via the transmitting unit  311  (step S 2401 ). Next, whether the receiving unit  312  has received a reply signal for the first link and the second link is determined (step S 2402 ), and waiting occurs until a reply signal is received (step S 2402 : NO). 
     When respective reply signals are received (step S 2402 : YES), whether the reply signal for the first link among the received reply signals is Ack is determined by the retransmission control unit  313  (step S 2403 ). If the reply signal of the first link is Ack (step S 2403 : YES), the processing proceeds to step S 2405  to be continued. 
     If the reply signal of the first link is not Ack (step S 2403 : NO), the transmitting unit  311  retransmits, using the second route R2, the data of the first link that has been transmitted via the first route R1 (step S 2404 ). Next, whether the reply signal of the second link among the reply signals received at step S 2402  is Ack is determined by the retransmission control unit  313  (step S 2405 ). 
     If the reply signal of the second link is Ack (step S 2405 : YES), a series of processing is ended (END). If the reply signal of the second link is not Ack (step S 2405 : NO), the data of the second link that has been transmitted by the first route R1 is retransmitted using the second route R2, (step S 2406 ), and the processing returns to step S 2402  to be continued. 
     By repeating the above processing, when Nack of the first link is received, the BTS  310  performs retransmission control of the first link using the second route R2 by interrupting transmission of data of the second link. Thus, the retransmission control of the first link is performed using the second route R2 even if the RS  320  does not perform retransmission control. 
       FIG. 25  is a diagram of an example of operation of the communication system depicted in  FIG. 22 . Like reference characters refer to like parts in  FIG. 21 , and explanation therefor is omitted. Ack indicated by reference numeral  2511  is Ack ( 2112 ) that is transmitted from the MS  330  to the RS  320  and that is further wirelessly relayed by the RS  320  to the BTS  310 . 
     Here, it is assumed that the MS  330  detects an error of received data “2”. In this case, the MS  330  transmits Nack to the RS  320  ( 2512 ). The RS  320  transmits the Nack received from the MS  330  to the BTS  310  ( 2513 ). The BTS  310  transmits, using the second rout R2, retransmission data “R2” of data “2” to the MS  330  ( 2521 ). 
     As described, according to the communication system  300  of the tenth embodiment, an effect similar to that of the communication system  300  according to the second embodiment is achieved, and the RS  320  has a function of performing retransmission control between the RS  320  and the MS  330 . Furthermore, the MS  330  transmits a reply signal according to the result of data error detection to the BTS  310  through the RS  320 . The RS  320  wirelessly relays the reply signal from the MS  330  to the BTS  310 , and outputs Ack to the retransmission control unit  1923  of the RS  320 . 
     Thus, the RS  320  does not perform retransmission control to the MS  330  even if an error is detected in data at MS  330 , and transmission between the RS  320  and the MS  330  is not interrupted by retransmission control. Therefore, even if the transmission speed between the RS  320  and the MS  330  is slower than the transmission speed between the BTS  310  and the RS  320 , reduction in throughput because of transmission between the RS  320  and the MS  330  being bottlenecked or buffer overflow at the RS  320  is prevented. 
       FIG. 26  is a block diagram of a communication system according to an eleventh embodiment. Like reference characters refer to like parts in  FIG. 19 , and explanation therefor is omitted. In the communication system  300  according to the eleventh embodiment, the retransmission control is performed independently between the BTS  310  and the RS  320 , and between the RS  320  and the MS  330 . 
     The BTS  310  and the MS  330  are not limited a configuration that uses multiple routes to communicate data with each other, and may be configured to use a single route to communicate data with each other. For example, the BTS  310  and the MS  330  may communicate data using a route in which data is communicated through the RS  320 . 
     The transmitting unit  311  of the BTS  310  transmits data addressed to the MS  330  to the RS  320  when the first transmission of data to the MS  330  is performed. Moreover, the transmitting unit  311  stores the data transmitted via the first transmission to a memory not depicted. 
     The transmitting unit  311  retransmits the data transmitted via the first transmission when a retransmission request is output from the retransmission control unit  313 . For example, the transmitting unit  311  reads the data stored to the memory, and transmits the read data to the RS  320 . 
     When Ack is output from the receiving unit  1922 , the retransmission control unit  1923  of the RS  320  outputs to the transmitting unit  1921 , a transmission request for next data. On the other hand, when Nack is output from the receiving unit  1922 , the retransmission control unit  1923  outputs to the transmitting unit  1921 , a retransmission request for the transmitted data and further outputs to the transmitting unit  1913 , a Nack transmission request for transmission of Nack. The transmitting unit  1913  transmits Nack to the BTS  310 , when the Nack transmission request is output from the retransmission control unit  1923 . 
     Thus, when Nack is received from the MS  330 , the RS  320  performs retransmission control to the MS  330  and transmits Nack to the BTS  310 . The receiving unit  1911  discards the data that has been transmitted from the BTS  310  in response to the Nack transmitted from the transmitting unit  1913  based on the Nack transmission request. This prevents repetition of transmission of the same data to the MS  330 . 
       FIG. 27  is a flowchart of an example of operations performed by the RS depicted in  FIG. 26 . The RS  320  (START) determines whether the receiving unit  1911  has received data transmitted from the BTS  310  (step S 2701 ), and waiting occurs until data is received (step S 2701 : NO). When the data has been received (step S 2701 : YES), the signal processing unit  1912  performs the decoding processing on the received data (step S 2702 ). 
     Next, the signal processing unit  1912  determines whether there is an error in the data subjected to the decoding processing (step S 2703 ). If there is an error (step S 2703 : YES), the transmitting unit  1913  transmits Nack to the BTS  310  (step S 2704 ), and the processing returns to step S 2701  to be continued. 
     If there is no error (step S 2703 : NO), the receiving unit  1922  determines whether Nack from the MS  330  is received (step S 2705 ). If Nack from the MS  330  has been received (step S 2705 : YES), the retransmission processing according to the received Nack is performed by the retransmission control unit  1923  (step S 2706 ), and the processing proceeds to step S 2704  to be continued. 
     If Nack from the MS  330  is not received (step S 2705 : NO), the transmitting unit  1913  transmits Ack to the BTS  310  (step S 2707 ), and a series of processing is ended (END). By repeating the above processing, when Nack from the MS  330  is received, the RS  320  performs retransmission control according to the Nack and transmits the Nack to the BTS  310 . 
       FIG. 28  is a diagram of an example of operation of the communication system depicted in  FIG. 26 . In  FIG. 28 , a sequence diagram  2810  depicts transmission and reception of data between the BTS  310  and the MS  330 . A sequence diagram  2820  depicts transmission and reception of data between the RS  320  and the MS  330 . Blocks with numerals indicate data. Further, “A” indicates Ack, and “N” indicates Nack. 
     For example, Ack indicated by reference numeral  2811  is a reply signal to data “1” transmitted to the RS  320  by the BTS  310 . Ack indicated by reference numeral  2821  is a reply signal to data “1” transmitted by the RS  320  to the MS  330 . Ack indicated by reference numeral  2812  is a reply signal to data “2” transmitted by the BTS  310  to the RS  320 . 
     Here, it is assumed that the MS  330  detects an error in the received data “2”. In this case, the MS  330  transmits Nack to the RS  320  ( 2822 ). The RS  320  transmits to the MS  330 , retransmission data “2R” of data “2” corresponding to Nack and transmits Nack to the BTS  310  ( 2813 ). 
     Consequently, the BTS  310  transmits retransmission data “3R” of data “3” to the RS  320 . The RS  320  discards retransmission data “3R” received from the BTS  310 , and transmits to the MS  330 , data “3” that has previously been received from the BTS  310 . Thus, when the RS  320  performs retransmission control corresponding to Nack ( 2822 ) from the MS  330 , the BTS  310  is able to also perform retransmission control to the RS  320 . 
     As described, according to the communication system  300  of the eleventh embodiment, retransmission control is performed independently between the BTS  310  and the RS  320 , and between the RS  320  and the MS  330 . Furthermore, the RS  320  performs retransmission control to the MS  330  and requests retransmission (transmits Nack) to the BTS  310  when a retransmission request (Nack) is received from the MS  330 . Thus, configuration may be such that the BTS  310  also performs retransmission control when the RS  320  performs retransmission control corresponding to Nack from the MS  330 . 
     Therefore, even if retransmission control frequently occurs between the RS  320  and the MS  330 , transmission of data between the BTS  310  and the RS  320  may be delayed according to the retransmission. As a result, reduction in throughput because of transmission between the RS  320  and the MS  330  being bottlenecked or buffer overflow at the RS  320  is prevented. 
     A case where a function of switching amplify and forward (AF) relay in which data is amplified by analog processing to be relayed, and decode and forward (DF) relay in which data is reproduced by digital processing to be relayed is included in the respective embodiments described above is explained. 
     For example, suppose that the RS  320  has the above function. In this case, both the first route R1 and the second route R2 pass through the RS  320 . The RS  320  may be configured to wirelessly relay data by DF when the first route R1 is used and to wirelessly relay data by AF when the second route R2 is used. Thus, the second route R2 is a faster route than the first route R1. 
     In the fourth embodiment, the eighth embodiment, and the like in which the second route R2 passes through RS, if the RS in the second route R2 has a function of switching AF and DF, the RS in the second route R2 may be configured to wirelessly relay, by AF, data that is retransmitted by the BTS  310 . Thus, the second route R2 may be an even fast route. 
       FIG. 29  is a graph depicting throughput of data in the communication system. In  FIG. 29 , the horizontal axis indicates an error rate [%] between the RS  320  and the MS  330 , and the vertical axis indicates throughput [Mbps] of data from the BTS  310  to the MS  330 . A throughput characteristic  2910  and a throughput characteristic  2920  are throughput characteristics with respect to the error rate between the RS  320  and the MS  330 . 
     The throughput characteristic  2910  indicates a characteristic in throughput with respect to the error rate when data is transmitted from the BTS  310  to the MS  330  without passing through the RS  320 . The throughput characteristic  2920  indicates a characteristic in throughput with respect to the error rate when data is transmitted from the BTS  310  to the MS  330  passing through the RS  320 . 
     As indicated by the throughput characteristic  2910  and the throughput characteristic  2920 , when the error rate between the RS  320  and the MS  330  is higher than 10 [%], the throughput characteristic  2920  significantly decreases relative to the throughput characteristic  2910 . Therefore, for example, the communication system  300  described in the second to the sixth embodiments and the eighth to the tenth embodiments is effective particularly when the error rate between the RS  320  and the MS  330  is higher than 10 [%]. 
     As explained, according to the retransmission method, the wireless communication apparatus, and the relay station disclosed herein, in communication systems in which multiple wireless routes respectively passing through a different number of relay stations may be used, a wireless route that passes through fewer relay stations than the route used at the first transmission is used when the data is retransmitted. This enables reduction in the delay of data transmission when retransmission processing occurs. For the retransmission processing in the respective embodiments described above, for example, hybrid automatic repeat request (HARQ) may be used. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.