Abstract:
A base transceiver station of a soft handover destination node does not perform control by using Hybrid Automatic Repeat Request, and a base transceiver station of a soft handover origin node sends data to a mobile node according to control performed by using Hybrid Automatic Repeat Request when the soft handover occurs. A radio network controller sends data destined for the mobile node only to the base transceiver station of the soft handover origin node. When the data is transferred from the base transceiver station of the soft handover origin node, the radio network controller transfers the data to the base transceiver station of the soft handover destination node. When a request to resend the data is received from the base transceiver station of the soft handover destination node, the radio network controller transfers the resend request to the base transceiver station of the soft handover origin node.

Description:
[0001]    This application is based upon and claims the benefit of priority from Japanese patent application No. 2007-014988, filed on Jan. 25, 2007, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a mobile communication system and a soft handover method used for the same. 
         [0004]    2. Description of the Related Art 
         [0005]    The CDMA (Code Division Multiple Access) that has been mainly used as the third generation mobile communication system and the OFDMA (Orthogonal Frequency Division Multiple Access) that is a candidate for the next generation mobile communication system have features (soft handover) for providing stable services without breaking communication by causing a mobile terminal to simultaneously communicate with two or more Base Transceiver Stations (hereinafter referred to as BTS) when the mobile terminal moves from one cell to another. The CDMA and the OFDMA also have high communication performance by using Hybrid Automatic Repeat Request (hereinafter referred to as HARQ) technique. 
         [0006]    In the mobile communication system, high speed communication (such as the high quality streaming communication for moving pictures) is expected to be provided for a moving terminal and the HSDPA (High Speed Downlink Packet Access) technique is standardized in W-CDMA (Wideband-CDMA). 
         [0007]    Conventional soft handover and the HARQ performed in the CDMA mobile communication system will be described. They will be described below by taking a case where a Mobil Node (hereinafter referred to as an MN) communicates with a Correspondent Node (hereinafter referred to a CN) as an example. 
         [0008]      FIG. 1  is a block diagram showing the configuration of a conventional mobile communication system. 
         [0009]    As shown in  FIG. 1 , the mobile communication system includes higher level network  1  including a core network (hereinafter simply referred to as a higher level network), Radio Network Controller  2  (hereinafter referred to as an RNC), and a plurality of BTSes (only BTS  21  and BTS  22  are exemplified in  FIG. 1 ). 
         [0010]    RNC  2  is connected with higher level network  1 , while including a plurality of BTSes (BTS  21  and BTS  22 ) connected thereto. CN  3  can communicate with MN  61  when CN  3  connects with higher level network  1 . 
         [0011]    Each of BTS  21  and BTS  22  is capable of wirelessly communicating with a plurality of MNs (only MN  61  is shown in  FIG. 1 ) which are present in a cell managed by BTS  21  or BTS  22 . In the mobile communication system shown in  FIG. 1 , cell  31  and cell  32  are located side by side with cell  31  being managed by BTS  21  and cell  32  being managed by BTS  22 . 
         [0012]    MN  61  reports information on the received power level of each BTS to RNC  2  in a predetermined cycle. MN  61  determines whether received data is erroneous or not by using HARQ. When the received data has no error, MN  61  sends a response of ACK (ACKnowledgments) to a BTS that originates the wireless transmission. When the received data has an error, MN  61  sends a response of NACK (Negative ACKnowledgments) to a BTS that originates the wireless transmission. When MN  61  receives the same data from a plurality of BTSes, MN  61  Rake-combines the radio signals to perform HARQ by using the data reproduced from the Rake-combined signals. 
         [0013]    RNC  2  determines the BTS for managing a cell in which MN  61  is present, and relays the data exchanged between CN  3  and MN  61  through the determined BTS. RNC  2  also determines whether MN  61  needs soft handover based on information on a received power level of each BTS reported by MN  61 . 
         [0014]    BTS  121  and BTS  122  relay data exchanged between CN  3  and MN  61  through higher level network  1  and RNC  2 . Here, BTS  121  and BTS  122  send data to be sent to MN  61  with a redundant bit for detecting an error or a redundant bit for correcting an error added by using HARQ. When BTS  121  and BTS  122  receive a NACK response from MN  61 , BTS  121  and BTS  122  resend data to MN  61  by using HARQ. 
         [0015]    Conventional soft handover will be described in the above mentioned configuration by taking a case where MN  61  moves from cell  31  to cell  32  by using  FIG. 2 . When MN  61  moves from cell  32  to cell  31 , the operations performed by BTS  21  and BTS  22  are basically the same as those described above except that those performed by BTS  21  and BTS  22  are switched. 
         [0016]    MN  61  communicates with CN  3  via BTS  21 , RNC  2  and higher level network  1  in cell  31  that originates the soft handover (step  301 ). Here, RNC  2  sends data, which is received from CN  3  and destined for MN  61 , to BTS  21  (step  302 ). BTS  21  converts data, which is received from RNC  2  and destined for MN  61 , into radio signals and sends them to MN  61  (step  303 ). [Situation A]. 
         [0017]    When MN  61  moves near to the boundary of cell  32  (step  304 ), the soft handover from cell  31  to cell  32  is performed according to the procedure described below. 
         [0018]    As mentioned above, MN  61  reports information on the received power level of the radio signals sent from BTS  21  and BTS  22  to RNC  2  in a predetermined cycle. RNC  2  determines whether MN  61  needs the soft handover from BTS  21  to BTS  22  based on the information on the received power level for each BTS reported by MN  61 . If the soft handover is performed (step  305 ) and RNC  2  receives data destined for MN  61  from CN  3  (step  306 ), RNC  2  sends the data to BTS  21  and BTS  22  (step  307 ). 
         [0019]    BTS  21  and BTS  22  convert data, which is received from RNC  2  and destined for MN  61 , into radio signals and send the signals to MN  61  (steps  308  and  309 ). Here, the same data is sent from BTS  21  and BTS  22  to MN  61 . 
         [0020]    MN  61  Rake-combines the radio signals received from BTS  21  and BTS  22  (step  310 ). This situation is the soft handover to MN  61  (step  311 ). [Situation B]. 
         [0021]    When RNC  2  determines that the soft handover to MN  61  can finish based on the information on the received power level of BTS  21  and BTS  22  reported by MN  61  (step  312 ), RNC  2  sends the data that is received from CN  3  and that is destined for MN  61  only to BTS  22  (steps  313 ,  314 ). 
         [0022]    When BTS  22  receives data destined for MN  61  from RNC  2 , BTS  22  converts the data into radio signals and sends the signals to MN  61  (step  315 ). Here, MN  61  receives data only from BTS  22  (step  316 ). Then, the soft handover finishes. [Situation C]. 
         [0023]    Now, a conventional HARQ will be described with reference to  FIG. 3 . 
         [0024]      FIG. 3  is a sequence diagram showing the procedure of the conventional HARQ. 
         [0025]    MN  61  is in cell  31  and communicates with CN  3  via BTS  21 , RNC  2  and higher level network  1  (step  321 ). Here, RNC  2  sends data that is received from CN  3  and destined for MN  61  to BTS  21  (step  322 ). BTS  21  converts data that is received from RNC  2  and destined for MN  61  into radio signals and sends the signals to MN  61  (step  323 ). 
         [0026]    As mentioned above, MN  61  and BTS  21  are performing the HARQ process: MN  61  determines whether the received data is erroneous. When the received data has no error, MN  61  sends a response of ACK to BTS  21 . When the received data has an error, MN  61  sends a response of NACK to BTS  21  (step  324 ). 
         [0027]    When BTS  21  receives the response of NACK from MN  61 , BTS  21  resends the data to MN  61  (step  325 ). 
         [0028]    Now, operations that may cause a problem in a case where the soft handover is performed while HARQ is being used will be described with reference to  FIG. 4 , assuming that the abovementioned processing has been performed. The operation will be described by taking a case where MN  61  moves from cell  31  to cell  32  as an example. When MN  61  moves from cell  31  to cell  32 , the operations performed by BTS  21  and BTS  22  are basically the same as those described above except that those performed by BTS  21  and BTS  22  are switched. 
         [0029]    MN  61  communicates with CN  3  via BTS  21 , RNC  2  and higher level network  1  in cell  31  that originates the soft handover (step  341 ). Here, RNC  2  sends data, which is received from CN  3  and destined for MN  61 , to BTS  21  (step  342 ). BTS  21  converts data, which is received from RNC  2  and destined for MN  61 , into radio signals and sends the signals to MN  61  (step  343 ). [Situation A]. 
         [0030]    MN  61  determines whether the received data is erroneous by using HARQ. When the received data has no error, MN  61  sends a response of ACK to BTS  21 . When the received data has an error, MN  61  sends a response of NACK to BTS  21  (step  344 ). When BTS  21  receives the NACK response from MN  61 , BTS  21  resends data to MN  61  (step  345 ). 
         [0031]    When MN  61  moves near to the boundary of cell  32  (step  346 ), the soft handover from cell  31  to cell  32  is performed according to the procedure described below. 
         [0032]    As mentioned above, MN  61  reports information on the received power level of the radio signals sent from BTS  21  and BTS  22  to RNC  2  in a predetermined cycle. RNC  2  determines whether MN  61  needs the soft handover from BTS  21  to BTS  22  based on the information on the received power level for each BTS reported by MN  61 . If the soft handover is performed (step  347 ) and RNC  2  receives data destined for MN  61  from CN  3  (step  348 ), RNC  2  sends the data to BTS  21  and BTS  22  (step  349 ). 
         [0033]    BTS  21  and BTS  22  convert data, which is received from RNC  2  and destined for MN  61 , into radio signals and send the signals to MN  61  (steps  350  and  351 ). Here, the same data is sent from BTS  21  and BTS  22  to MN  61 . 
         [0034]    MN  61  Rake-combines the radio signals received from BTS  21  and BTS  22  (step  352 ). 
         [0035]    MN  61  determines whether the data reproduced from the Rake-combined signals is erroneous. When the received data has no error, MN  61  sends a response of ACK to BTS  21 . When the received data has an error, MN  61  sends a response of NACK to BTS  21  (step  353 ). When MN  61  determines whether the data is erroneous based on Rake-combined signals, the same response (a response of ACK or a response of NACK) is sent to BTS  21  and BTS  22 . 
         [0036]    When BTS  21  and BTS  22  receive the NACK response from MN  61 , they resend data to MN  61  (step  354  and  355 ). [Situation B]. 
         [0037]    When RNC  2  determines that the soft handover to MN  61  can finish based on the information on the received power level of BTS  21  and BTS  22  reported by MN  61  (step  357 ), RNC  2  sends the data that is received from CN  3  and destined for MN  61  only to BTS  22  (steps  358 ,  359 ). 
         [0038]    When BTS  22  receives data destined for MN  61  from RNC  2 , BTS  22  converts the data into radio signals and sends the signals to MN  61  (step  360 ). Here, MN  61  receives data only from BTS  22 . Then, the soft handover finishes. 
         [0039]    MN  61  determines whether the received data is erroneous. When the received data has no error, MN  61  sends a response of ACK to BTS  22 . When the received data has an error, MN  61  sends a response of NACK to BTS  22  (step  361 ). 
         [0040]    When BTS  22  receives the NACK response from MN  61 , BTS  22  resends data to MN  61  (step  362 ). [Situation C]. 
         [0041]    Soft handover is also described in International Unexamined Patent Application Publication No. WO2004/030396 pamphlet and the like in detail. HARQ is also described in Japanese Patent Laid-Open No. 2006-295912 and the like in detail. 
         [0042]    Now, it is assumed that an ACK response is sent from MN  61  to BTS  21  and BTS  22  in the processing performed at steps  354  and  355  in the abovementioned conventional mobile communication system. Here, MN  61  is near the boundary of the cell. Thus, BTS  21  may successfully receive the ACK response and BTS  22  may not successfully receive the ACK response, for example. Then, the ACK response is resent by BTS  22  via HARQ. This situation results from the fact that HARQ is independently performed at each BTS. 
         [0043]    Accordingly, the processing performed by BTS  21  and the processing performed by BTS  22  do not match. That causes a problem in that soft handover cannot be performed on MN  61   
       SUMMARY OF THE INVENTION 
       [0044]    The present invention intends to provide a mobile communication system that enables soft handover even on a Mobil Node (MN) that moves while HARQ is being used, and the soft handover method used in the system. 
         [0045]    In order to achieve the abovementioned object, the mobile communication system according to the present invention is a mobile communication system for performing soft handover that is intended to prevent communication from being broken when a mobile node (MN) moves from one cell to another, comprising: 
         [0046]    a plurality of base transceiver stations (BTSes) each of which sends data to the MN according to control that is performed by using the Hybrid Automatic Repeat Request (HARQ) at an origin node of the soft handover instead of according to control that is performed by using the HARQ when the BTS is a destination node of the soft handover when the soft handover occurs; and 
         [0047]    a radio network controller (RNC) that sends the data only to the BTS that serves the soft handover origin node; and when the data is transferred from the BTS that serves the soft handover origin node, the RNC transfers the data to the BTS that serves the soft handover destination node; and when a request to resend the data is received from the BTS that serves the soft handover destination node, the RNC transfers the resend request to the BTS that serves the soft handover origin node when soft handover is performed. 
         [0048]    The soft handover method according to the present invention is a soft handover method performed in a mobile communication system that is intended to prevent communication from being broken when a mobile node (MN) moves from one cell to another, comprising: 
         [0049]    sending data to the MN according to control performed by using Hybrid Automatic Repeat Request at an origin node of soft handover instead of according to control performed by using the Hybrid Automatic Repeat Request when a base transceiver station (BTS) is a destination node of soft handover when the soft handover occurs; and 
         [0050]    a radio network controller (RNC) sending the data only to the BTS that serves the soft handover origin node; and when the data is transferred from the BTS that serves the soft handover origin node, the RNC transfers the data to the BTS that serves the soft handover destination node; and when a request to resend the data is received from the BTS that serves the soft handover destination node, the RNC transfers the resend request to the BTS that serves the soft handover origin node. 
         [0051]    The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings, which illustrate examples of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]      FIG. 1  is a block diagram showing the configuration of a conventional mobile communication system; 
           [0053]      FIG. 2  is a sequence diagram showing the procedure of conventional soft handover; 
           [0054]      FIG. 3  is a sequence diagram showing the procedure of conventional HARQ; 
           [0055]      FIG. 4  is a sequence diagram showing a conventional procedure in a case where soft handover is performed while HARQ is being used; 
           [0056]      FIG. 5  is a block diagram showing the configuration of the mobile communication system of the present invention; and 
           [0057]      FIG. 6  is a sequence diagram showing the procedure of the soft handover method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0058]    Now, the present invention will be described with reference to the drawings. 
         [0059]      FIG. 5  is a block diagram showing the configuration of the mobile communication system of the present invention. 
         [0060]    As shown in  FIG. 5 , the mobile communication system includes higher level network  101  including a core network, RNC  102  and a plurality of BTSes (only BTS  121  and BTS  122  are shown in  FIG. 5 ). Higher level network  101  including the core network is known to those skilled in the art and not directly related to the present invention. Thus, that is omitted in the detailed description. 
         [0061]    RNC  102  is connected to higher level network  101 , while including a plurality of BTSes (BTS  121  and BTS  122 ) connected thereto. CN  103  can communicate with MN  161  when it connects with higher level network  101 . 
         [0062]    Each of BTS  121  and BTS  122  is capable of wirelessly communicating with a plurality of MNs (only MN  161  is shown in  FIG. 5 ) which are present in a cell managed by BTS  121  and BTS  122 , respectively. In the mobile communication system shown in  FIG. 5 , cell  131  and cell  132  are located side by side with cell  131  being managed by BTS  121  and cell  132  being managed by BTS  122 . 
         [0063]    MN  161  reports information on a received power level of each BTS to RNC  2  in a predetermined cycle. MN  161  determines whether received data is erroneous by using HARQ. When the received data has no error, MN  161  sends a response of ACK to a transmission origin BTS. When the received data has an error, MN  161  sends a response of NACK to a transmission origin BTS. When MN  161  receives the same data from a plurality of BTSes, it Rake-combines the radio signals to perform the HARQ by using the data reproduced from the Rake-combined signals. 
         [0064]    Each of RNC  102 , BTS  121 , BTS  122  and MN  161  is composed of a LSI (Large Scale Integration) including a logical circuit, for example, or a semiconductor integrated circuit including a CPU, a DSP (Digital Signal Processor) or the like which implements various functions to be described below. When each of RNC  102 , BTS  121 , BTS  122  and MN  161  has a CPU or a DSP, the CPU or the DSP implements the functions described below by executing processing according to programs recorded in a recording medium (not shown). 
         [0065]    The mobile communication system of the present invention has relay functional part  110  in RNC  102 , transfer functional part  111  in BTS  121 , and transfer functional part  112  in BTS  122 . 
         [0066]    In the mobile communication system of the present invention, the BTS of the soft handover destination node sends data to MN  161  according to control that is performed by using the HARQ at an origin node of the soft handover when said soft handover occurs. Specifically, the BTS of the soft handover origin node adds redundancy bits to be used in performing HARQ as well as information about the required time schedule for sending the data destined for MN  161  to the data and transfers the data to the BTS of the soft handover destination node via RNC  102 . The data will be referred to as transfer data below. When the BTS receives a NACK response from MN  161 , it adds redundancy bits to be used in performing HARQ as well as information about the required time schedule for sending the data to be resent to MN  161  to the data and transfers the data to the BTS of the soft handover destination node via RNC  102 . If an ACK/NACK response cannot be received by the BTS of the soft handover destination node, the BTS of the soft handover destination node sends a resend request to the BTS of the soft handover origin node. Then, the BTS of the soft handover origin node adds redundancy bits to be used in performing HARQ as well as information about the required time schedule for sending the data to be resent to MN  161  to the data and transfers the data to the BTS of the soft handover destination node via RNC  102 . 
         [0067]    The data destined to MN  161  is simultaneously sent from the BTS of the soft handover destination node and from the BTS of the soft handover origin node at the designated sending time, and the data to be resent to MN  161  is simultaneously sent from the BTS of the soft handover destination node and from the BTS of the soft handover origin node at the designated resending time. 
         [0068]    RNC  102  determines the BTS for managing a cell in which MN  161  is present, and relays the data exchanged between CN  103  and MN  161  through the determined BTS. RNC  102  also determines whether MN  161  needs soft handover or not based on information on the received power level of each BTS reported from MN  161 . When soft handover is to be performed, RNC  102  sets a flag that is given to data to be sent to MN  161  indicating that it is under soft handover and sends the data only to the BTS of the soft handover origin node. When relay functional part  110  receives the transferred data from the BTS of the soft handover origin node, it transfers (relays) the data to the BTS of the soft handover destination node. 
         [0069]    Each of BTS  121  and BTS  122  relays data exchanged between CN  103  and MN  161  via higher level network  101  and RNC  102  as in the conventional manner. Here, each of BTS  121  and BTS  122  sends data to be sent to MN  161  with redundancy bits for detecting an error or with redundancy bits for correcting an error by using HARQ. When each of BTS  121  and BTS  122  receives a NACK response from MN  161 , it resends data to MN  161  by using HARQ. 
         [0070]    When each of BTS  121  and BTS  122  included in the mobile communication system of the present invention is the soft handover origin node, each of them checks whether the flagged data received from RNC  102 , that indicates that it is undergoing soft handover, has been set or not. When the flag is set, each of BTS  121  and BTS  122  encapsulates data destined to MN  161  with information about the required time schedule for sending the data and transfers the encapsulated data (transfer data) to RNC  102  at transfer functional parts  111  and  112  respectively. The data destined for MN  161  is sent to MN  161  at the sending time. When a NACK response is received from MN  161 , each of BTS  121  and BTS  122  encapsulates the data to be resent to MN  161  with information about the required time schedule for resending the data at transfer functional parts  111  and  112  respectively and transfers the encapsulated data (transfer data) to RNC  102  as resend processing. The data to be resent to MN  161  is sent to MN  161  at the resending time. When each of BTS  121  and BTS  122  receives a resend request from a BTS of another soft handover destination node via RNC  102 , each of them encapsulates the data to be resent to MN  161  with information about the required time schedule for resending the data and transfer the encapsulated data to RNC  102  at transfer functional parts  111  and  112  respectively. The data to be resent to MN  161  is sent to MN  161  at the resending time schedule. Only if a NACK response is received from MN  161  and the data has been transferred to RNC  102  and then if a request to resend the data is received from the BTS of the other soft handover destination node, will the resend request be ignored. 
         [0071]    When each of BTS  121  and BTS  122  is the soft handover destination node and data (transfer data) is transferred from a BTS of another soft handover origin node via RNC  102 , each of them deencapsulates the transferred data and sends the data to MN  161  at the designated sending time. When each of them sends the data transferred from the BTS of another soft handover origin node to MN  161  and then receives a NACK response from MN  161 , each of them sends a request to resend the data to the BTS of the data transfer destination node via RNC  102  at transfer functional parts  111  and  112  respectively. 
         [0072]    Now, the soft handover of the present invention will be described with reference to  FIG. 6 . 
         [0073]      FIG. 6  is a sequence diagram showing the procedure of the soft handover method of the present invention. 
         [0074]    The procedure will be described below by taking a case where MN  161  moves from cell  131  to cell  132  while HARQ is being used. [Situation A→Situation B→Situation C]. When MN  161  moves from cell  132  to cell  131 , the operations performed by BTS  121  and BTS  122  are basically the same as those described above except that those performed by BTS  121  and BTS  122  are switched. The radio signals are sent from BTS  121  and BTS  122  at a synchronized time. GPS (Global Positioning System) or the like may be used in synchronizing the sending time. GPS is well-known to those skilled in the art and not directly related to the present invention. Thus, that is omitted in the detailed description. 
         [0075]    MN  161  communicates with CN  103  via BTS  121 , RNC  102  and the higher level network  101  in cell  131  of the soft handover origin node (step  401 ). Here, RNC  102  sends the data destined for MN  161  and that is received from CN  103  to BTS  121  (step  402 ) where the data destined to MN  161  and that is received from RNC  102  is converted into radio signals and sent to MN  161  (step  403 ). 
         [0076]    MN  161  determines whether the received data is erroneous or not by using HARQ. When the received data has no error, MN  161  sends an ACK response to BTS  121 , and when the received data has an error, MN  161  sends a NACK response to BTS  121  (step  404 ). When BTS  121  receives a NACK response from MN  161 , it resends the data to MN  161  (step  405 ). [Situation A]. 
         [0077]    When MN  161  moves to the boundary of cell  132  (step  406 ), the soft handover from cell  131  to cell  132  is performed according to the procedure described below. 
         [0078]    As mentioned above, MN  161  reports information on the received power level of the radio signals sent from BTS  121  and BTS  122  to RNC  102  by predetermined cycle. RNC  102  determines whether MN  161  needs the soft handover from BTS  121  to BTS  122  or not based on the information on the received power level for each BTS reported by MN  161 . If the soft handover is performed (step  407 ) and if RNC  102  receives data destined for MN  161  from CN  103  (step  408 ), RNC  102  gives and sets a flag indicating that it is undergoing soft handover to the data and sends the data only to BTS  121  (step  409 ). 
         [0079]    BTS  121  checks the flag included in the data destined for MN  161  and that is received from RNC  102  indicating that it is undergoing the soft handover. When the flag is set, BTS  121  encapsulates data destined for MN  161  with information about the required time schedule for sending the data and transfers the encapsulated data to relay functional part  110  of RNC  102  at transfer functional part  111  (step  410 ). 
         [0080]    When relay functional part  110  of RNC  102  receives the transfer data from BTS  121 , it transfers the data to BTS  122  of the soft handover destination node (step  411 ). 
         [0081]    BTS  121  converts the data, which is received from RNC  2  at the time that it is sent, into radio signals and sends them to MN  161  (step  413 ). When BTS  122  receives the transfer data destined for MN  161  from relay functional part  110  of RNC  102  (step  412 ), it deencapsulates the data, converts the transferred data destined for MN  161  into radio signals, and sends the radio signals to MN  161  at the designated sending time (step  414 ). Here, the same data is sent from BTS  121  and BTS  122  to MN  161 , which is undergoing the soft handover. 
         [0082]    MN  161  Rake-combines the radio signals received from BTS  121  and BTS  122  (step  415 ). 
         [0083]    MN  161  determines whether the data reproduced from the Rake-combined signals is erroneous or not. When the received data has no error, MN  161  sends an ACK response to BTS  121  and BTS  122 . When the received data has an error, MN  161  sends an NACK response to BTS  121  and BTS  122  (step  416 ). 
         [0084]    When BTS  121  of the soft handover origin node receives an NACK response from MN  161 , it encapsulates the data destined for MN  161  with information about the required time schedule for resending the data and transfers the data to relay functional part  110  of RNC  102  at transfer functional part  111  (step  417 ). When BTS  122  of the soft handover destination node receives the NACK response from MN  161 , it issues a resend request to BTS  121  (data transfer origin) via relay functional part  110  of RNC  102  at transfer functional part  112  (step  418 ). 
         [0085]    If BTS  121  receives a resend request from relay functional part  110  of RNC  102  though it has received an ACK response from MN  161  during processing at step  417 , it encapsulates the data destined for MN  161  with information about the required time schedule for resending the data and transfers the data to relay functional part  110  of RNC  102  at transfer functional part  111  (step  419 ). 
         [0086]    If BTS  121  received the NACK response from MN  161  during processing at step  417  and has transferred the data to RNC  102  and then if BTS  121  receives a transfer request, it does not resend the data to RNC  102 . 
         [0087]    Relay functional part  110  of RNC  102  that received the data that was resent from BTS  121  transfers the data to BTS  122  of the soft handover destination node (step  420 ). BTS  121  resends the data to MN  161  at the resending time schedule (step  422 ). 
         [0088]    When BTS  122  receives the data to be resent and that is destined for MN  161  from relay functional part  1110  of RNC  102  (step  421 ), it deencapsulates the data and resends it for MN  161  at the designated resending time (step  423 ). Here, the same data is sent from BTS  121  and BTS  122  to MN  161 , which is undergoing the soft handover. [Situation B]. 
         [0089]    When RNC  102  determines that soft handover to MN  161  is able to be finished based on information on the received power level of BTS  121  and BTS  122  that is reported from MN  161  (step  424 ), it sends data destined to MN  161  that is received from CN  103  only to BTS  122  (steps  425  and  426 ). Here, RNC  102  does not set the flag, that has been given to data that is to be relayed, indicating that it is undergoing the soft handover. 
         [0090]    When BTS  122  receives the data destined for MN  161  from RNC  102 , it converts the data into radio signals and sends the radio signals to MN  161  (step  427 ). Here, MN  161  has received data only from BTS  122 . The soft handover finishes. 
         [0091]    MN  161  determines whether the data received from BTS  122  is erroneous or not. When the received data has no error, MN  161  sends an ACK response to BTS  122 , and when the received data has an error, MN  161  sends an NACK response to BTS  122  (step  428 ). 
         [0092]    When BTS  122  receives the NACK response from MN  161 , it resends the data to MN  161  (step  429 ). [Situation C]. 
         [0093]    As mentioned above, according to the present invention, the BTS of the soft handover destination node sends data to MN  161  according to control that is performed by using the HARQ at an origin node of the soft handover when said soft handover occurs. That prevents a situation in which, when each BTS controls the node by using HARQ independently, the processes which the BTSes perform with not match each other. 
         [0094]    Thus, when MN  161  moves from a cell to another cell, while HARQ is being used, the soft handover is available for MN  161 . Since soft handover is available, in the mobile communication system using the CDMA, MN  161  can receive radio waves from BTSes  121  and  122  and Rake-combine the radio waves even when received power levels from BTSes  121  and  122  are low as in a situation in which MN  161  is near the boundary of a cell. That improves communication quality. 
         [0095]    In the mobile communication system using OFDMA, the guard interval can be minimized. That improves communication efficiency. The transmission power from BTSes  121  and  122  to MN  161  can also be reduced so that radio resources may be effectively used. 
         [0096]    While this invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those ordinarily skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.