Abstract:
By reducing the overlap between HARQ subpackets transmitted by means of a transmitting MS and a cooperative MS, the disclosed method is capable of increasing gains in HARQ IR signal synthesis. The method transmits a hybrid automatic repeat request (HARQ) in a cooperative communication system formed so as to comprise a transmitting mobile station (MS) and a cooperative MS, and involves creating individual HARQ subpackets transmitted by means of the transmitting MS and the cooperative MS such that said subpackets are arranged in mutually opposite directions in a circular buffer.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to the field of a hybrid automatic repeat request when performing a client collaboration. 
       BACKGROUND ART  
       [0002]    The IEEE (Institute of Electrical and Electronics Engineers) 802.16 working group is creating an 802.16m radio interface specification that satisfies requirements of an IMT (International Mobile Telecommunications)-advanced next-generation mobile phone system. Based on the IEEE 802.16m draft standard, the WiMAX (Worldwide Interoperability for Microwave Access) forum is working out the WiMAX release 2.0 MSP (Mobile System Profile; mobile communication system profile) (see NPL 1). The IEEE 802.16m standard and WiMAX release 2.0 MSP are expected to be completed by early 2011. 
         [0003]    The IEEE802.16 working group has also started envisioning and designing a future 802.16/WiMAX network which excels 802.16m/WiMAX2.0. There is common recognition among the 802.16/WiMAX community that the future 802.16/WiMAX will support an explosive increase of mobile communication data traffic spurred by apparatuses with greater screens, multimedia applications and an increasing number of connected users and apparatuses. The future 802.16/WiMAX network will also efficiently cooperate with other wireless techniques such as 802.11/Wi-Fi (“Wireless Fidelity). 
         [0004]    The future 802.16/WiMAX network will be drastically improved regarding various performance index values such as throughput and SE (Spectral Efficiency) compared to the 802.16m network. For example, when coverage in a metropolitan area is assumed, the future 802.16/WiMAX network is aiming at SE at a cell edge twice that of the 802.16m/WiMAX2.0 network on both UL (uplink) and DL (downlink) (see NPL 2). It should be noted that the 802.16m/WiMAX2.0 network has SE at a cell edge of at least 0.06 bps/Hz/sec of DL in a 4x2 antenna configuration and SE at a cell edge of at least 0.03 bps/Hz/see of UL in a 2x4 antenna configuration. 
         [0005]    For example, collaboration techniques such as CliCo (Client Collaboration) has assured a drastic improvement in SE at a cell edge and energy efficiency of an entire network of a radio communication system. CliCo is a technique for clients to jointly transmit/receive data in radio communication (see NPL 3). CliCo uses client clustering and peer-to-peer communication to transmit/receive information through a plurality of paths between a BS and a client. As a result, it is possible to improve SE at a cell edge without any increase in infrastructure costs. Furthermore, CliCo can extend the service life of a battery of a client having a poor channel. 
         [0006]      FIG. 1  shows a diagram illustrating typical radio communication system  100  that performs CliCo. Radio communication system  100  includes BS (base station)  102  and a plurality of MSs (mobile stations), for example MS  104  and MS  106 . 
         [0007]      FIG. 2  is a block diagram illustrating typical BS  102 . BS  102  is equipped with only WiMAX and is constructed of WiMAX PHY block  130  and WiMAX MAC block  120 . WiMAX MAC block  120  performs a WiMAX OFDMA (Orthogonal Frequency Division Multiple Access)-based media access control protocol. WiMAX PHY block  130  performs the WiMAX OFDMA-based physical layer protocol under the control of WiMAX MAC block  120 . 
         [0008]    Referring to  FIG. 2 , WiMAX MAC block  120  is further constructed of control section  122 , scheduler  124 , message creation section  126  and message processing section  128 . 
         [0009]    Control section  122  controls a general MAC protocol operation. Scheduler  124  schedules allocation of resources to each MS under the control of control section  122 . Upon receiving resource allocation scheduling information from scheduler  124 , message creation section  126  creates a data packet and DL control signaling. Message processing section  128  analyzes the data packet and UL control signaling received from the plurality of MSs under the control of control section  122  and reports the analysis result to control section  122 . 
         [0010]    It should be noted that the data packet and DL control signaling created by message creation section  126  are transmitted to the plurality of MSs by BS  102  via OFDMA transmitter  136  in WiMAX PHY block  130 . The data packet and UL control signaling analyzed by message processing section  128  is received by BS  102  via OFDMA receiver  138  in WiMAX PHY block  130 . 
         [0011]    Referring to  FIG. 2 , message creation section  126  includes HFBCH (HARQ Feedback Channel) creation section  132  and resource allocation creation section  134 . Here, HARQ represents a hybrid automatic repeat request. HFBCH creation section  132  creates a HARQ feedback channel for UL data transmission that carries HARQ feedback information (e.g., ACK/NACK) for UL data transmission. Resource allocation creation section  134  creates resource allocation control signalling for UL/DL data transmission that carries resource allocation information for each of the plurality of MSs. 
         [0012]    Referring to  FIG. 2 , channel coder  502  exists in OFDMA transmitter  136 . Channel coder  502  converts a data burst obtained from message creation section  126  to a baseband modulated signal.  FIG. 3  shows a block diagram illustrating typical channel coder  502 . Channel coder  502  is constructed of FEC encoder  304 , circular buffer  308 , HARQ subpacket generator (bit selection and repetition block)  306 , modulator  310  and subpacket generation control section  312 . 
         [0013]    Referring to  FIG. 3 , FEC encoder  304  converts a data burst to coded bits using a predetermined coding scheme such as CTC (Convolutional Turbo Coding). The coded bits made up of information bits and parity bits are normally stored in circular buffer  308 . The information bits are arranged from the leading part of circular buffer  308 , followed by the parity bits. The size of circular buffer  308  for the data burst can be expressed as follows, 
         [0000]    
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     N 
                     CB 
                   
                   = 
                   
                     
                       N 
                       DB 
                     
                     
                       M 
                       cr 
                     
                   
                 
               
               
                 
                   [ 
                   1 
                   ] 
                 
               
             
           
         
       
     
         [0000]    Here, N DB  is a size of the data burst, M er  is a mother coding rate of FEC encoder  304  such as M er =⅓. 
         [0014]    Referring to  FIG. 3 , HARQ subpacket generator  306  punctures (or repeats) the coded bits in circular buffer  308  to thereby create a HARQ subpacket. 
         [0015]      FIG. 4  illustrates a HARQ subpacket generation method at M er 32 ⅓. 
         [0016]    To create a HARQ subpacket to be transmitted at i-th transmission, HARQ subpacket generator  306  needs to know the starting position (that is, P i ) in circular buffer  308  and the size (that is, N i ) of the HARQ subpacket transmitted at the i-th transmission. The starting position and size are supplied by subpacket generation control section  312 . 
         [0017]    The starting position of the HARQ subpacket transmitted at the i-th transmission is normally determined by an SPID (subpacket identifier) of a HARQ transmitted at the i-th transmission. Subpacket generation control section  312  determines the size of the HARQ subpacket according to MCS information and resource allocation information and indicates the size to HARQ subpacket generator  306 . The MCS information and the resource allocation information are described in the resource allocation control signalling created by resource allocation creation section  134 . 
         [0018]    Referring to  FIG. 3 , modulator  310  converts the HARQ subpacket to a baseband modulated signal. 
         [0019]    Referring to  FIG. 2 , channel decoder  504  exists in OFDMA receiver  138 . Channel decoder  504  demodulates/decodes a baseband modulated signal received using HARQ soft combining such as HARQ IR (Incremental Redundancy). 
         [0020]      FIG. 5  shows a block diagram illustrating typical MS  104 . MS  104  is provided with WiMAX and Wi-Fi, and is constructed of WiMAX PHY block  142 , Wi-Fi PHY block  144 , WiMAX MAC block  146 , Wi-Fi MAC block  148  and GLL (general link layer) block  150 . WiMAX MAC block  146  executes a WiMAX OFDMA-based media access control protocol. WiMAX PHY block  142  executes a WiMAX OFDMA-based physical layer protocol under the control of WiMAX MAC block  146 . Wi-Fi MAC block  148  executes a Wi-Fi CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)-based media access control protocol. Wi-Fi PHY block  144  executes a Wi-Fi OFDM (Orthogonal Frequency Division Multiplexing)/DSSS (Direct Sequence Spread Spectrum)-based physical layer protocol, under the control of Wi-Fi MAC block  148 . GLL block  150  has a function of managing coordinated operation between heterogeneous WiMAX and Wi-Fi links. 
         [0021]    Referring to  FIG. 5 , WiMAX MAC block  146  is further constructed of control section  154 , message creation section  152  and message processing section  156 . Control section  154  controls a general MAC protocol operation. Message creation section  152  creates UL control signaling and a data packet under the control of control section  154 . Message processing section  156  analyzes a data packet and DL control signaling received from BS  102  under the control of control section  154  and reports the analysis result to control section  154 . 
         [0022]    It should be noted that the data packet and UL control signalling created by message creation section  152  is transmitted to BS  102  by MS  104  via OFDMA transmitter  162  in WiMAX PHY block  142 . The data packet and DL control signaling to be analyzed by message processing section  156  is received by MS  104  via OFDMA receiver  164  in WiMAX PHY block  142 . 
         [0023]    Referring to  FIG. 5 , resource analysis section  151  and HFBCH analysis section  153  exist in message processing section  156 . HFBCH analysis section  153  analyzes a received HFBCH in response to UL data transmission and decides whether the corresponding UL data transmission has been successful or not. Resource analysis section  151  analyzes the received resource allocation control signalling and extracts resource allocation information identified for MS  104 . In the case of UL data transmission, a data packet created by message creation section  152  under the control of control section  154  is then transmitted by MS  104  to BS  102  according to the extracted resource allocation information. 
         [0024]    Referring to  FIG. 5 , channel coder  402  exists in OFDMA transmitter  162  and channel decoder  404  exists in OFDMA receiver  164 . It should be noted that channel coder  402  in OFDMA transmitter  162  has a configuration and function similar to those of channel coder  502  in OFDMA transmitter  136 , and channel decoder  404  in OFDMA receiver  164  has a configuration and function similar to those of channel decoder  504  in OFDMA receiver  138 . 
         [0025]      FIG. 6  shows a block diagram illustrating typical MS  106 . MS  106  is also provided with both WiMAX and Wi-Fi, and has a configuration and function quite similar to those of MS  104 . Channel coder  602  in OFDMA transmitter  182  has a configuration and function similar to those of channel coder  402  in OFDMA transmitter  162 . As shown in  FIG. 5 , a main difference between MS  104  and MS  106  is that scheduler  158  exists in the “Wi-Fi MAC block of MS  104  and this scheduler is used for collaboration scheduling for CliCo. 
         [0026]    Referring to  FIG. 1 , BS  102  communicates with MS  104  via WiMAX links  108   a  and  108   b,  and communicates with MS  106  via WiMAX links  110   a  and  110   b.  MS  104  communicates with MS  106  peer-to-peer Wi-Fi links  112   a  and  112   b.  Alternatively, MS  104  may also communicate with MS  104  using other wireless techniques such as WiMAX, Bluetooth or 60 GHz mmW (millimeter wave). 
         [0027]    It should be, noted that CliCo can be realized on both DL and UL of radio communication system  100 . In the present invention, the operation of CliCo on an UL (uplink) in radio communication system  100  is taken as an example. 
         [0028]    Referring to  FIG. 1 , when signal quality of WiMAX link  108   a  between BS  102  and MS  104  degrades, MS  104  can start an. UL (uplink) CliCo procedure such as neighbor discovery, cooperator selection/allocation. When signal quality of WiMAX link  110   a  between BS  102  and. MS  106  is good, MS  104  can select MS  106  as a cooperator. In the context of CliCo, MS  104  is called originating MS and MS  106  is called cooperating MS. 
         [0029]    CliCo may occur in various situations. For example, if originating MS  104  is assumed to be located at the back of a cafeteria, signal quality of the WiMAX link to originating MS  104  may be quite low. On the other hand, if cooperating MS  106  is assumed to be located much closer to the window or entrance of the cafeteria than originating MS  104 , cooperating MS  106  can thereby have much higher signal quality of WiMAX link than originating MS  104 . 
         [0030]      FIG. 7  shows a diagram illustrating typical frame configuration  200  applicable to a radio communication system that performs the CliCo shown in  FIG. 1 . Referring to  FIG. 7 , each of frame  202  and frame 212 is made up of eight subframes. Five of the eight subframes are DL subframes and the rest are UL subframes 
         [0031]    As far as CliCo of the UL (uplink) is concerned, BS  102  can transmit MAP  220  to a plurality of mobile stations connected to BS  102  including originating MS  104  and cooperating MS  106  involved in CliCo in first DL subframe  204  of frame  202 . MAP  220  is made up of a plurality of MAP IEs (information elements). Some of the MAP IEs can carry HARQ feedback information for UL data transmission and some other MAP IEs can carry resource allocation information for DL/UL data transmission. One MAP IE in MAP  220  that carries HARQ feedback information forms an HBFCH for UL data transmission. 
         [0032]    During period  208  between first DL subframe  204  and first UL subframe  206  of frame  202 , originating MS  104  and cooperating MS  106  need to decode MAP  220  to obtain resource allocation information including their respective items of HFBCH index information. Furthermore, originating MS  104  needs to transmit UL data burst  250  to cooperating MS  106  via peer-to-peer Wi-Fi link  112   a.    
         [0033]    If originating MS  104  has successfully decoded MAP  220  transmitted by BS  102  via WiMAX link  108   b,  originating MS  104  transmits a HARQ subpacket of UL data burst  250  to BS  102  via WiMAX link  108   a  according to the received resource allocation information in first UL subframe  206  of frame  202 . On the other band, if cooperating MS  106  has successfully decoded MAP  220  transmitted by BS  102  via WiMAX link  110   b  and has also successfully received UL data burst  250  transmitted from originating MS  104  via peer-to-peer Wi-Fi link  112   a,  cooperating MS  106  simultaneously transmits the HARQ subpacket of same UL data burst  250  to BS  102  via WiMAX link  110   a  according to the received resource allocation information in first UL subframe  206  of frame  202 . As a result, BS  102  can perform HARQ soft combining of combining two HARQ subpackets of UL data burst  250  received from WiMAX link  108   a  and WiMAX link  110   a  to improve quality of the received signal. 
         [0034]    In second DL subframe  214  of frame  212 , BS  102  can transmit MAP  240  to a plurality of mobile stations connected to BS  102  including originating MS  104  and cooperating MS  106  involved in CliCo. As described above, HFBCHs which form a part of MAP  240  can carry HARQ feedback information for UL data burst  250  transmitted by originating MS  104  and cooperating MS  106  in first UL subframe  206  of frame  202 . 
         [0035]    During period  218  between second DL subframe  214  and first UL subframe  216  of frame  212 , in order to obtain the respective items of HARQ feedback information for UL data burst  250 , originating MS  104  and cooperating MS  106  need to decode their respective HFBCHs in MAP  240  according to HFBCH index information obtained by decoding MAP  220  during period  208 . 
         [0036]    When the HARQ feedback information indicates in first UL subframe  206  of frame  202  that BS  102  has not correctly decoded UL data burst  250  transmitted by originating MS  104  and cooperating MS  106 , originating MS  104  and cooperating MS  106  need to retransmit UL data burst  250  in first UL subframe  216  of frame  212 . 
         [0037]    According to the IEEE 802.16m draft standard, the specified HARQ transmission mechanism does not deal with UL (uplink) CliCo (see NPL 1). However, the same mechanism is applicable to UL (uplink) CliCo in a direct way. 
         [0038]    According to the IEEE 802.16m draft standard, on an UL, a “synchronous HARQ operating mode” in which HARQ timing is performed at a constant interval is used and a “non-adaptive HARQ operating mode” in which the resource size or the like is not changed is used (see NPL 1). 
         [0039]    In the synchronous HARQ operating mode, both originating MS  104  and cooperating MS  106  can use the same HARQ subpacket transmission rule as shown in Table 1. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 SPID 
               
             
          
           
               
                   
                 Initial 
                 Second 
                 Third 
                 Fourth 
                 Fifth 
                   
               
               
                   
                 trans- 
                 trans- 
                 trans- 
                 trans- 
                 trans- 
               
               
                   
                 mission 
                 mission 
                 mission 
                 mission 
                 mission 
                 . . . 
               
               
                   
                   
               
             
          
           
               
                 Originating MS 
                 0 
                 1 
                 2 
                 3 
                 0 
                 . . . 
               
               
                 Cooperating MS 
                 0 
                 1 
                 2 
                 3 
                 0 
                 . . . 
               
               
                   
               
             
          
         
       
     
         [0040]    According to the subpacket transmission rule shown in Table 1, each of originating MS  104  and cooperating MS  106  transmits a subpacket having SPID=0 at initial transmission and transmits one of subpackets having SPID=0, 1, 2, 3 in cyclic order of retransmission. 
         [0041]    According to the IEEE 802.16m draft standard, the resource allocation information is transmitted by BS  102  only at the initial transmission using MAP IEs addressed to originating MS  104  and cooperating MS  106 , and this information is also used for retransmission by originating MS  104  and cooperating MS  106  (see NPL 1). That is, this means that the size of the HARQ subpacket is the same for both originating MS  104  and cooperating MS  106  whether in HARQ transmission or in HARQ retransmission. 
         [0042]    According to the IEEE 802.16m draft standard, for both originating MS  104  and cooperating MS  106 , the starting position of the HARQ subpacket transmitted at i-th transmission is determined as follows (see NPL). 
         [0000]        P   i   [SPID ( i )· N ]mod  N   CB    (Equation 2)
 
         [0043]    Here, N is a size of a HARQ subpacket (N=N OM  for originating MS  104 , N=N CM  for cooperating MS  106 ), N=N RE ′ N SN ′ N mod , where N RE  is the number of data tones (data units) allocated for transmission of a data burst and N SM  is an STC (space-time coding) rate and N mod  is a modulation order. The values of N RE , N SM  and N mod  can be obtained from the resource allocation information. N CB  is a circular buffer size for a data burst defined in equation 1. SPID(i) is an SPIN of a HARQ subpacket transmitted at i-th transmission. 
         [0044]      FIG. 8  illustrates typical HARQ subpacket transmission performed by both originating MS  104  and cooperating MS  106  according to the subpacket transmission rule shown in Table 1 and the rule for determining the starting positions of HARQ subpackets defined in equation 2. In  FIG. 8 , suppose coding rate M cr =⅓ and N OM =N CM =⅜·N CB  of the FEC encoder. 
         [0045]    Referring to  FIG. 8 , in originating MS  104 , the starting positions of the HARQ subpackets in four transmissions including the initial transmission are calculated as follows. 
         [0000]      P 1 =0 
         [0000]        P   2 =⅜· N   CB  
 
         [0000]        P   3 =¾ ·N   CB (= 6/8 ·N   CB )
 
         [0000]        P   4 =⅛ ·N   CB  
 
         [0046]    In cooperating MS  106 , the starting positions of the HARQ subpackets in four transmissions including the initial transmission are calculated as follows. 
         [0000]      P 1 =0 
         [0000]        P   2 =¼ ·N   CB  
 
         [0000]        P   3 =½ ·N   CB )
 
         [0000]        P   4 =¾ ·N   CB  
 
         [0047]    It is easily understandable from  FIG. 8  that individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  are created so as to be in the same direction in the circular buffer. Furthermore, the individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  apparently overlap with each other even in initial transmission. 
       CITATION LIST  
     Non-Patent Literature 
     NPL 1  
       [0000]    
       
         IEEE P802.16tn/D6, DRAFT Amendment to IEEE Standard for local and metropolitan area networks—Part 16: Air Interface for Broadband Wireless Access Systems—Advanced Air Interface 
       
     
       NPL 2  
       [0000]    
       
         IEEE C802.16-10/0016r1, Future 802.16 Networks: Challenges and Possibilities 
       
     
       NPL 3 
       [0000]    
       
         IEEE C802.16-10/0005r1, Client Collaboration in. Future Wireless Broadband Networks 
       
     
       SUMMARY OF INVENTION  
     Technical Problem 
       [0051]    According to the IEEE 802.16m draft standard, as shown in  FIG. 8 , HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  apparently overlap with each other even at initial transmission (see NPL 1). Thus, no signal combining gain by HARQ IR may be obtained even at initial transmission. Especially, when the propagation path characteristics in WiMAX link  108   a  and WiMAX link  110   a  in  FIG. 1  arc similar, it is difficult to obtain a combining gain. 
         [0052]    Furthermore, as shown in  FIG. 8 , there may also be a case where the size of a HARQ subpacket transmitted by originating MS  104  is different from the size of a HARQ subpacket transmitted by cooperating MS  106 , and in this case, at initial transmission in particular, a HARQ subpacket transmitted by cooperating MS  106  becomes part of a HARQ subpacket transmitted by originating MS  104  and it becomes noticeable that no signal combining gain by HARQ IR can be obtained. 
       Solution to Problem 
       [0053]    According to an aspect of the present invention, a method for transmitting a hybrid automatic repeat request (HARQ) in a cooperative communication system including an originating mobile station (MS) and a cooperating MS, includes creating individual HARQ subpackets transmitted by the originating MS and the cooperating MS so as to be in mutually opposite directions in a circular buffer. 
         [0054]    According to another aspect of the present invention, the above method further includes setting a starting position in the circular buffer of a first HARQ subpacket transmitted by the originating MS at a leading end of the circular buffer and setting a termination position in the circular buffer of the first HARQ subpacket transmitted by the cooperating MS at a rear end of the circular buffer. 
         [0055]    According to a further aspect of the present invention, the above method further includes setting the starting position in the circular buffer of the first HARQ subpacket transmitted by the originating MS at a certain position within a range of information bits in the circular buffer and setting the termination position in the circular buffer of the first HARQ subpacket transmitted by the cooperating MS at a certain position in the range of information bits in the circular buffer. 
         [0056]    According to a still further aspect of the present invention, an offset (difference) of the starting position in the circular buffer of the first HARQ subpacket transmitted by the originating MS, relative to the position of the last information bit in the circular buffer is either predetermined or settable. 
         [0057]    According to a still further aspect of the present invention, an offset (difference) of the termination position in the circular buffer of the first HARQ subpacket transmitted by the cooperating MS, relative to the leading end of the circular buffer is either predetermined or settable. 
         [0058]    According to a still further aspect of the present invention, a method for transmitting a hybrid automatic repeat request (HARQ) in a cooperative communication system including an originating mobile station (MS) and a cooperating MS, includes setting starting positions of individual HARQ subpackets transmitted by the originating MS according to the size of the HARQ subpackets transmitted by the cooperating MS and setting starting positions of the individual HARQ subpackets transmitted by the cooperating MS according to the size of the HARQ subpackets transmitted by the originating MS. 
         [0059]    According to a still further aspect of the present invention, the above method further includes setting the starting position of an i-th HARQ subpacket of the cooperating MS at a termination position of the i-th HARQ subpacket of the originating MS and setting the starting position of an (i+1)-th HARQ subpacket of the originating MS at a termination position of the i-th HARQ subpacket of the cooperating MS. 
         [0060]    The above and other features and advantages of the present invention will be better understood by referring to the detailed description of the invention which will be described below with the accompanying drawings and the accompanying scope of patent claims. 
       Advantageous Effects of Invention 
       [0061]    The present invention allows a signal combining gain of HARQ IR to be improved by reducing overlapping between individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106 . 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0062]      FIG. 1  is a diagram illustrating a typical radio communication system that performs CliCo (client collaboration); 
           [0063]      FIG. 2  is a block diagram illustrating a typical BS (base station); 
           [0064]      FIG. 3  is a block diagram illustrating a typical channel coder; 
           [0065]      FIG. 4  is a diagram illustrating a method for generating a typical HARQ subpacket; 
           [0066]      FIG. 5  is a block diagram illustrating a typical originating MS (mobile station); 
           [0067]      FIG. 6  is a block diagram illustrating a typical cooperating MS; 
           [0068]      FIG. 7  is a diagram illustrating a typical frame configuration; 
           [0069]      FIG. 8  is a diagram illustrating transmission of a typical HARQ subpacket transmitted four times including the initial transmission according to a conventional technique when the sizes of HARQ subpackets transmitted by an originating MS and a cooperating MS are different; 
           [0070]      FIG. 9  is a diagram illustrating transmission of a typical HARQ subpacket transmitted four times including the initial transmission according to a first embodiment of the present invention; 
           [0071]      FIG. 10  is a diagram illustrating transmission of a typical HARQ subpacket transmitted four times including the initial transmission with parameter a set as a first value according to a second embodiment of the present invention; 
           [0072]      FIG. 11  is a diagram illustrating transmission of a typical HARQ subpacket transmitted four times including the initial transmission with parameter a set as a second value according to the second embodiment of the present invention; and 
           [0073]      FIG. 12  is a diagram illustrating transmission of a typical HARQ subpacket transmitted four times including the initial transmission according to a third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0074]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Detailed descriptions of known functions and configurations used for the specification of the present application are omitted for clarity and simplicity. 
       First Embodiment  
       [0075]    In a method for transmitting a HARQ subpacket when performing UL (uplink) CliCo according to a first embodiment of the present invention, individual HARQ subpackets transmitted by originating MS  104  in  FIG. 5  and cooperating MS  106  in  FIG. 6  are created so as to be in mutually opposite directions in a circular buffer as shown in  FIG. 9 . 
         [0076]    Examples of the method for reversing the reading direction of the circular buffer include “changing an equation of determining a HARQ subpacket starting position” or “changing a HARQ subpacket transmission rule and an equation of determining a HARQ subpacket starting position.” 
         [0077]    In the method for only “changing an equation of determining a HARQ subpacket starting position,” originating MS  104  and cooperating MS  106  use the same HARQ subpacket transmission rule (e.g., the rule as shown in Table 1), but they use different equations to determine a HARQ subpacket starting position. 
         [0078]    For example, based on the HARQ subpacket transmission rule shown in Table 1, a SPIT is reported by resource allocation creation section  134  and is inputted to subpacket generation control section  312 . Based on the information of subpacket generation control section  312 , HARQ subpacket generator  306  of originating MS  104  can determine the starting position of a HARQ subpacket transmitted at i-th transmission as follows. 
         [0000]      (Equation 3) 
         [0000]        P   i   =[SPID ( i )· N   OM ]mod  N   CB    (3)
 
         [0079]    Here, N OM  is a size of a HARQ subpacket in originating MS  104 . N CB  is a size of a data packet circular buffer defined in equation 1. SPID(i) is an SPID of a HARQ subpacket transmitted at i-th transmission in originating MS  104 . 
         [0080]    HARQ subpacket generator  306  of cooperating MS  106  can determine the starting position of a HARQ subpacket transmitted at i-th transmission as follows. 
         [0000]      (Equation 4) 
         [0000]        P   i   =[N   CB −( SPID ( i )+1)· N   CM ]mod  N   CB    [4]
 
         [0081]    Here, N CM  is a size of a HARQ subpacket in cooperating MS  106 . NCB is a size of a data packet circular buffer defined in equation 1. SPID(i) is an SPID of a HARQ subpacket transmitted at i-th transmission in cooperating MS  106 . 
         [0082]    According to the method for “changing a HARQ subpacket transmission rule and an equation of determining a HARQ subpacket starting position,” originating MS  104  and cooperating MS  106  use different HARQ subpacket transmission rules and use different rules for determining a HARQ subpacket starting position. Table 2 shows a typical subpacket transmission rule in originating MS  104  and cooperating MS  106 . 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 SPID 
               
             
          
           
               
                   
                 Initial 
                 Second 
                 Third 
                 Fourth 
                 Fifth 
                   
               
               
                   
                 trans- 
                 trans- 
                 trans- 
                 trans- 
                 trans- 
               
               
                   
                 mission 
                 mission 
                 mission 
                 mission 
                 mission 
                 . . . 
               
               
                   
                   
               
             
          
           
               
                 Originating MS 
                 0 
                 1 
                 2 
                 3 
                 0 
                 . . . 
               
               
                 Cooperating MS 
                 3 
                 2 
                 1 
                 0 
                 3 
                 . . . 
               
               
                   
               
             
          
         
       
     
         [0083]    Based on the subpacket transmission rule shown in Table 2, a SPID is reported by resource allocation creation section  134  and is inputted to subpacket generation control section  312 . 
         [0084]    In originating MS  104 , the starting position of a HARQ subpacket transmitted at i-th transmission can be determined by equation 3. In cooperating MS  106 , the starting position of a HARQ subpacket transmitted at i-th transmission can be determined as follows. 
         [0000]      (Equation 5) 
         [0000]        P   i   =[N   CB −(4 −SPID ( i ))· N   CM ]mod  N   CB    [5]
 
         [0085]    Here, N CM  is a size of a HARQ subpacket in cooperating MS  106 . N CB  is a size of a data packet circular buffer defined in equation 1. SPID(i) is an SPID of a HARQ subpacket transmitted at i-th transmission in cooperating MS  106 . 
         [0086]    It should be noted that the subpacket transmission rule shown in Table I and the rules for determining a HARQ subpacket starting position defined in equation 3 and equation 4 are substantially equivalent to the subpacket transmission rule shown in Table 2 and the rules for determining a HARQ subpacket starting position defined in equation 3 and equation 5. 
         [0087]      FIG. 9  shows transmission of a typical HARQ subpacket for both originating MS  104  and cooperating MS  106  according to the subpacket transmission rule shown in Table 1 and the rules for determining a HARQ subpacket starting position defined in equation 3 and equation 4. In  FIG. 9 , suppose M cr =⅓, N OM =⅜·N CB  and N CM =¼·N CB . 
         [0088]    in originating MS  104 , the starting positions of HARQ subpackets in four transmissions including the initial transmission are calculated as follows. 
         [0000]      P 1 =0 
         [0000]        P   2 =⅜ ·N   CB  
 
         [0000]        P   3 =¾ ·N   CB (= 6/8 ·N   CB )
 
         [0000]        P   4 =⅛ ·N   CB  
 
         [0089]    In cooperating MS  106 , the starting positions of HARQ subpackets in four transmissions including the initial transmission are calculated as follows. 
         [0000]        P   1 =¾ ·N   CB  
 
         [0000]        P   2 =½ ·N   CB (= 2/4 ·N   CB )
 
         [0000]        P   3 =¼ ·N   CB  
 
         [0000]      P 4 =0 
         [0090]    It is easily understandable from  FIG. 9  that individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  are created so as to be in mutually opposite directions in the circular buffer. Furthermore, since there is no overlapping between the first HARQ subpackets transmitted by originating MS  104  and cooperating MS  106 , a signal combining gain of HARQ IR at initial transmission is maximized. 
         [0091]    According to the first embodiment of the present invention, the starting position in the circular buffer of the first HARQ subpacket transmitted by originating MS  104  is set at a leading end of the circular buffer and the termination position in the circular buffer of the first HARQ subpacket transmitted by cooperating MS  106  is set at a rear end of the circular buffer. The starting position in the circular buffer of the first HARQ subpacket transmitted by originating MS  104  and the termination position in the circular buffer of the first HARQ subpacket transmitted by cooperating MS  106  may be set to the opposite of the positions described above. 
         [0092]    According to the first embodiment of the present invention, overlapping between the individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  is minimized and the signal combining gain of HARQ IR is thereby maximized at initial transmission in particular. 
       Second Embodiment  
       [0093]    According to the first embodiment of the present invention shown in  FIG. 9 , the first subpacket transmitted by originating MS  104  needs to include all information bits, that is, N OM M cr ·N CB . This constraint reduces flexibility of resource allocation by BS  102 . 
         [0094]    In a method for transmitting a HARQ subpacket when performing UL (uplink) CliCo according to a second embodiment of the present invention, both originating MS  104  and cooperating MS  106  transmit some of information bits at initial transmission. To be more specific, the starting position of a first HARQ subpacket transmitted by originating MS  104  is set at a certain position within a range of information bits in a circular buffer, and the termination position of the first HARQ subpacket transmitted by cooperating MS  106  is also set at a certain position within a range of information bits in the circular buffer. 
         [0095]    As in the case of the first embodiment of the present invention, according to the second embodiment of the present invention, individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  arc created so as to be in mutually opposite directions in the circular buffer. 
         [0096]    According to the second embodiment of the present invention, there are various methods for designing rules for determining starting positions of HARQ subpackets. 
         [0097]    For example, while satisfying the HARQ subpacket transmission rule shown in Table 1, the starting position of a HARQ subpacket transmitted at i-th transmission in originating MS  104  can be determined as follows. 
         [0000]      (Equation 6) 
         [0000]        P   i   =[M   cr   ·N   CB +( SPID ( i )−α)· N   OM]mod    N   CB    [6]
 
         [0098]    Here, M cr  is a mother coding rate of FEC encoder  304 . N OM  is a size of a HARQ subpacket in originating MS  104 . α·N OM  shows an offset (difference) of the starting position of a first subpacket of originating MS  104 , relative to the position of the last information bit in the circular buffer. The value of α (0&lt;α&lt;1) may be either predetermined or settable. N CB  is a size of a data packet circular buffer defined in equation 1. SPID(i) is an SPID of a HARQ subpacket transmitted at i-th transmission in originating MS  104 . 
         [0099]    In cooperating MS  106 , the starting position of a HARQ subpacket transmitted at i-th transmission is determined as follows. 
         [0000]      (Equation 7) 
         [0000]        P   i   =[N   CR   −SPID ( i )· N   CM ]mod  N   CB    [7]
 
         [0100]    Here, N CM  is a size of a HARQ subpacket in cooperating MS  106 . N CB  is a size of the data packet circular buffer defined in equation 1. SPID(i) is an SPID of a HARQ subpacket transmitted at i-th transmission in cooperating MS  106 . 
         [0101]    According to the HARQ subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 6 and equation 7, a constraint on resource allocation is α·N OM +N CM ≧M er ·N CB . Since the constraint is relaxed compared to the first embodiment of the present invention, flexibility of resource allocation by BS  102  is increased. 
         [0102]    In order to minimize overlapping between the first HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  according to the HARQ subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 6 and equation, an optimal value of α is assumed to be determined as follows. 
         [0000]    
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     8 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   α 
                   = 
                   
                     
                       
                         
                           M 
                           cr 
                         
                         · 
                         
                           N 
                           CB 
                         
                       
                       - 
                       
                         N 
                         CM 
                       
                     
                     
                       N 
                       OM 
                     
                   
                 
               
               
                 
                   [ 
                   8 
                   ] 
                 
               
             
           
         
       
     
         [0103]    That is, parameter α is assumed to be settable depending on M cr , N CB , N OM  and N CM . In this case, the value of α can be indicated among MAP IEs that carry resource allocation information for initial transmission. This produces additional signalling overhead compared to predetermined α. 
         [0104]      FIG. 10  and  FIG. 11  illustrate typical HARQ subpacket transmission by both originating MS  104  and cooperating MS  106  when two different values of α are set according to the subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 6 and equation 7. In  FIG. 10  and  FIG. 11 , suppose M cr =⅓, N OM =¼·N CB  and N CM =⅙·N CB . 
         [0105]    Referring to  FIG. 10  when α= 7/9 is set, the starting positions of HARQ subpackets in four transmissions including the initial transmission in originating MS  104  are calculated as follows. 
         [0000]        P   1 = 5/36 ·N   CB    
         [0000]        P   2 = 7/18 ·N   CB (= 14/36 ·N   CB ) 
         [0000]        P   3 = 23/36 ·N   CB    
         [0000]        P   4 = 8/9 ·N   CB (= 32/36 ·N   CB ) 
         [0106]    Referring to  FIG. 11  when α=⅔ is set, the starting positions of HARQ subpackets in four transmissions including the initial transmission in originating MS  104  are calculated as follows. 
         [0000]        P   1 =⅙ ·N   CB (= 2/12 ·N   CB )
 
         [0000]        P   2 = 5/12 ·N   CB    
         [0000]        P   3 =⅔ ·N   CB  (= 8/12 ·N   CB )
 
         [0000]        P   4 = 11/12 ·N   CB    
         [0107]    Referring to  FIG. 10  and  FIG. 11 , the starting positions of HARQ subpackets in four transmissions including the initial transmission in cooperating MS  106  are calculated as follows. 
         [0000]      P 1 =0 
         [0000]        P   2 =⅚· N   CB  
 
         [0000]        P   3 =⅔ ·N   CB (= 4/6 ·N   CB )
 
         [0000]        P   4 =½ ·N   CB (= 3/6 ·N   CB )
 
         [0108]    It is easily understandable from  FIG. 10  and  FIG. 11  that the first HARQ subpacket transmitted by originating MS  104  starts within a range of information bits in the circular buffer and the first. HARQ subpacket transmitted by cooperating MS  106  terminates within a range of information bits in the circular buffer. Furthermore in the case of α= 7/9, there is still slight overlapping between the first HARQ subpackets transmitted by originating MS  104  and cooperating MS  106 . However, in the case of α=⅔, there is no more overlapping between the first HARQ subpackets transmitted by originating MS  104  and cooperating MS  106 . It is also understandable that the four HARQ subpackets transmitted by originating MS  104  are created so as to be in different directions in the circular buffer from the four HARQ subpackets transmitted by cooperating MS  106 . 
         [0109]    It should be noted that according to the rules for determining the starting positions of HARQ subpackets defined in equation 6 and equation 7, the starting positions of HARQ subpackets transmitted by originating MS  104  depend on parameter α. As an alternative technique, it is also possible to design rules for determining the starting positions of HARQ subpackets so that the starting positions of HARQ subpackets transmitted by cooperating MS  106  depend on parameter α. 
         [0110]    For example, the starting position of a HARQ subpacket transmitted at i-th transmission in originating MS  104  can be determined as follows 
         [0000]      (Equation 9) 
         [0000]        P   i   =[M   cr   ·N   CB +( SPID ( i )−1)· N   OM ]mod  N   CB    [9]
 
         [0111]    Here, M cr  is a mother coding rate of FEC encoder  304 . N OM  is a size of a HARQ subpacket in originating MS  104 . N CB  is a size of the data packet circular buffer defined in equation 1. SPID(i) is an SPID of a HARQ subpacket transmitted at i-th transmission in originating MS  104 . 
         [0112]    Cooperating MS  106  can determine the starting position of the HARQ subpacket transmitted at i-th transmission as follows. 
         [0000]      (Equation 10) 
         [0000]        P   i   =[N   CB −( SPID ( i )+1−α) ·N   CM ]mod  N   CB    [10]
 
         [0113]    Here, N CM  is a size of a HARQ subpacket in cooperating MS  106 . N CB  is a size of the data packet circular buffer defined in equation 1. α·N CM indicates an offset (difference) of the termination position of the first subpacket of cooperating MS  106 , relative to the leading end of the circular buffer. The value of α (0&lt;α&lt;1) is either predetermined or settable. SPID(i) is an SPUD of the HARQ subpacket transmitted at i-th transmission in cooperating MS  106 . 
         [0114]    According to the HARQ subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 9 and equation 10, the constraint on resource allocation is N OM +α·M cr ·N CB . Thus, the constraint is also relaxed compared to the first embodiment of the present invention. 
         [0115]    According to the HARQ subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 9 and equation 10, an optimal value of a is assumed to be determined to minimize overlapping between the first HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  as follows. 
         [0000]    
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     11 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   α 
                   = 
                   
                     
                       
                         
                           M 
                           cr 
                         
                         · 
                         
                           N 
                           CB 
                         
                       
                       - 
                       
                         N 
                         OM 
                       
                     
                     
                       N 
                       CM 
                     
                   
                 
               
               
                 
                   [ 
                   11 
                   ] 
                 
               
             
           
         
       
     
       Third Embodiment  
       [0116]    According to the second embodiment of the present invention, a settable a can be used to minimize overlapping between the first subpackets transmitted by originating MS  104  and cooperating MS  106 . However, the settable a produces additional signalling overhead. 
         [0117]    In the method for transmitting HARQ subpackets when performing UL (uplink) CliCo according to the third embodiment of the present invention, the starting positions of individual HARQ subpackets of originating MS  104  are determined according to the sizes of HARQ subpackets of cooperating MS  106  and the starting positions of individual HARQ subpackets of cooperating MS  106  are determined according to the sizes of HARQ subpackets of originating MS  104 . 
         [0118]    According to the third embodiment of the present invention, the starting position of an i-th HARQ subpacket transmitted by cooperating MS  106  is set at a termination position of the i-th HARQ subpacket transmitted by originating MS  104  and the starting position of the(i+1)-th HARQ subpacket transmitted by originating MS  104  is set at a termination position of the i-th HARQ subpacket transmitted by cooperating MS  106 . 
         [0119]    According to the third embodiment of the present invention, as in the ease of the conventional technique, individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  are created so as to be in the same direction in the circular buffer. 
         [0120]    According to the third embodiment of the present invention, overlapping between individual HARQ subpackets transmitted by originating MS  104  and cooperating MS  106  is minimized, and therefore the signal combining gain of HARQ IR is maximized. 
         [0121]    According to the third embodiment of the present invention, there are various methods for designing rules for determining the starting positions of HARQ subpackets. 
         [0122]    For example, while satisfying the subpacket transmission rule shown in Table 1, the starting positions of a HARQ subpacket transmitted at i-th transmission in originating MS  104  can be determined as follows. 
         [0000]      (Equation 12) 
         [0000]        P   i   =[SPID ( i )·( N   OM   +N   CM )]mod  N   CB    [12]
 
         [0123]    Here, N OM  is a size of a HARQ subpacket in originating MS  104 . N CM  is a size of a HARQ subpacket in cooperating MS  106 . N CB  is a size of the data packet circular buffer defined in equation 1. SPID(i) is an SPID of a subpacket transmitted at i-th transmission in originating MS  104 . 
         [0124]    In cooperating MS  106 , the starting position of a HARQ subpacket transmitted at i-th transmission is determined as follows. 
         [0000]      (Equation 13) 
         [0000]        P   i   =[N   OM   +SPID ( i )·( N   OM   +N   CM )]mod  N   CB    [13]
 
         [0125]    Here, N OM  is a size of a HARQ subpacket in originating. MS  104 . N CM  is a size of a HARQ subpacket in cooperating MS  106 . N CB  is a size of the data packet circular buffer defined in equation 1. SPID(i) is an SPID of a subpacket transmitted at i-th transmission in cooperating MS  106 . 
         [0126]    According to the rules for determining the starting positions of HARQ subpackets defined in equation 12 and equation 13, the requirement is that originating MS  104  should know the sizes of HARQ subpackets of cooperating MS  106  beforehand and that cooperating MS  106  should know the sizes of HARQ subpackets of originating MS  104 . 
         [0127]    According to the HARQ subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 12 and equation 13, the constraint on resource allocation is N OM +N CM ≧M Cr ·N CB . In this way, the constraint is also relaxed compared to the first embodiment of the present invention. 
         [0128]      FIG. 12  illustrates typical HARQ subpacket transmission in both originating MS  104  and cooperating MS  106  according to the subpacket transmission rule shown in Table 1 and the rules for determining the starting positions of HARQ subpackets defined in equation 12 and equation 13. In  FIG. 12 , suppose M cr =⅓, N OM =¼·N CB , and N CM =⅙·N CB . 
         [0129]    Referring to  FIG. 12 , the starting positions of HARQ subpackets in four transmissions including the initial transmission in originating MS  104  are calculated as follows. 
         [0000]      P 1 =0 
         [0000]      P 2 = 5/12 ·N   CB    
         [0000]        P   3 =⅚ ·N   CB (= 10/12 ·N   CB )
 
         [0000]        P   4 =¼ ·N   CB (= 3/12 ·N   CB )
 
         [0130]    The starting positions of HARQ subpackets in four transmissions including the initial transmission in originating MS  106  are calculated as follows, 
         [0000]        P   1 =¼ ·N   CB (= 3/12 ·N   CB )
 
         [0000]        P   2 =⅔ ·N   CB (= 8/12· N   CB )
 
         [0000]        P   4 =½ ·N   CB (= 6/12 ·N   CB )
 
         [0131]    It is easily understandable from  FIG. 12  that there is no overlapping between individual HARQ subpackets of originating MS  104  and cooperating MS  106  at first two transmissions, and therefore the signal combining gain of HARQ IR at the first two transmissions is maximized. 
         [0132]    The disclosure of Japanese Patent Application No.2010-206768, filed on Sep. 15, 2010, including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY  
       [0133]    The present invention is useful for a radio communication apparatus or the like. 
       REFERENCE SIGNS LIST  
       [0000]    
       
           100  Radio communication system 
           102  BS (base station) 
           104 ,  106  MS (mobile station) 
           108 ,  110  WiMAX link 
           112  Wi-Fi link 
           120 ,  146  WiMAX MAC 
           122 ,  154  Control section 
           124 ,  158  Scheduler 
           126 ,  152  Message creation section 
           128 ,  156  Message processing section 
           130 ,  142  WiMAX PHY 
           132  HFBCH creation section 
           134  Resource allocation creation section 
           136 ,  162 ,  182  OFDMA transmitter 
           138 ,  164  OFDMA receiver 
           144  Wi-Fi PHY 
           148  Wi-Fi MAC 
           150  GLL 
           151  Resource analysis section 
           153  HFBCH analysis section 
           304  FEC encoder 
           306  HARQ subpacket generator 
           308  Circular buffer 
           310  Modulator 
           312  Subpacket generation control section 
           502 ,  402 ,  602  Channel coder 
           504 ,  404  Channel decoder