Patent Publication Number: US-2011051648-A1

Title: Radio communication system, data distribution method, base station, base station control device, and program

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present invention is the National Phase of PCT/JP2009/050569, filed Jan. 16, 2009, which is based upon and claims the benefit of the priority of Japanese patent application No. 2008-007036 (filed on Jan. 16, 2008), the disclosure of which is incorporated herein in its entirety by reference thereto. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a radio communication system, a data distribution method, a base station, a base station control device, and a program, and more particularly to a radio communication system, a data distribution method, a base station, a base station control device, and a program for distributing broadcast data or multicast data. 
     BACKGROUND 
     In 3GPP (3rd Generation Partnership Project), the specifications for MBMS (Multimedia. Broadcast Multicast Service) are defined as the broadcast function and the multicast function for use in the W-CDMA system. 
     Patent Document 1 discloses a mobile communication system that has a buffer in which broadcast data, transmitted from other nodes, is temporarily stored for retransmission. When a data frame retransmission request signal is received from a mobile station, the radio base station described in the document encodes the data frames stored in the buffer and transmits the encoded data using the transmission power calculated by a predetermined expression. 
     Patent Document 2 discloses an information distribution system that comprises distribution destination cells, a distribution terminal used for specifying a distribution time, and a distribution management server that starts the information distribution procedure for a subscriber&#39;s device according to a specification received from the distribution terminal.
     [Patent Document 1] Japanese Patent Kokai Publication No. JP-P2006-135400A   [Patent Document 2] Japanese Patent Kokai Publication No. JP-P2007-128151A   [Non-Patent Document 1] 3GPP TS 23.246 V8.1.0 (Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description (Release 8))   

     SUMMARY 
     All the disclosed contents of Patent Documents 1 and 2 and Non-Patent Document 1 given above are hereby incorporated by reference thereto. The following analysis is given in the light of the present invention. 
     In the radio communication system disclosed in Patent Document 1 and so on, broadcast data is transmitted as follows. When broadcast data is transmitted from a broadcast station  240  that is the distribution source in the sequence diagram shown in  FIG. 6 , the broadcast station  240  establishes a session with a base station control device (radio control station)  220  (s 300 , s 301 ). Next the base station control device (radio control station)  220  establishes a session with a radio base station  210  (s 302 , s 304 ). And, after the radio base station  210  transmits a broadcast start notification to a mobile station  200  (s 305 ), the broadcast station  240  transmits broadcast data to the mobile station  200  (see 8.3 MBMS Session Start Procedure in Non-Patent Document 1). 
     After the transmission is ended, the broadcast station  240  first stops the session with the base station control device (radio control station)  220  (s 307 , s 308 ). Next, the base station control device (radio control station)  220  stops the session with the radio base station  210  (s 309 , s 310 ). After that, the radio base station  210  transmits a broadcast end notification to the mobile station  200  (s 311 ) (see 8.5 MBMS Session Stop Procedure in non-Patent Document 1). 
     However, the problem with the data distribution method in Non-Patent Document 1 described above is that, when the same broadcast data is transmitted repeatedly, the operations s 300 -s 311  described above must be performed repeatedly and that this repeated operation increases the processing load of the broadcast station  240  and wastefully increases the traffic between the broadcast station  240  and the radio base station  210 . 
     Meanwhile, the radio base station described in Patent Document 1 increases the transfer efficiency of broadcast data at retransmission time, but the document does not mention an increase in the processing efficiency when the same broadcast data is transmitted from the distribution source such as the broadcast station  240 . 
     Patent Document 2 discloses a configuration in which a distribution management server is provided in the gateway between a radio base station and a subscriber&#39;s station, but this configuration does not reduce the waste involved in repeatedly transmitting broadcast data between the broadcast station and the radio base station. In addition, the distribution service described in the document is carried out independently of the session start/end processing that is performed between the broadcast station  240  and the radio base station  210  for efficiently using the radio resources. 
     In view of the foregoing, it is an object of the present invention to provide a radio communication system, a data distribution method, a base station, a base station control device, and a program for increasing the efficiency of the repeated transmission of broadcast data or multicast data transmitted from a distribution source. 
     Thus, there is much to be desired in the art. 
     According to a first aspect of the present invention, there is provided a radio communication system comprising a distribution device, which distributes broadcast data or multicast data, and a radio base station. The radio base station comprises a saving (storing) unit that saves (stores) the broadcast data or multicast data received from the distribution device; and a distribution unit that repeatedly distributes the saved broadcast data or multicast data to a mobile station at a predetermined distribution timing. 
     According to a second aspect of the present invention, there is provided a method for distributing broadcast data or multicast data for use in a radio communication system. The method comprises: performed by a radio base station or a base station control device in the radio communication system, for receiving broadcast data or multicast data from a distribution source and saving the received data; and, performed by the radio base station or base station control device that has saved the broadcast data or multicast data, repeatedly distributing the broadcast data or multicast data to a mobile station at a predetermined timing. 
     According to a third aspect of the present invention, there is provided a radio base station or a base station control device comprising a saving unit that saves broadcast data or multicast data received from a distribution source; and a distribution unit that repeatedly distributes the saved broadcast data or multicast data to a lower-level node at a predetermined distribution timing. 
     According to a fourth aspect of the present invention, there is provided a computer readable program causing a computer system, which acts as a radio base station or a base station control device, to perform processing that receives broadcast data or multicast data from a distribution source, and saves the received data; and processing that repeatedly distributes the saved broadcast data or multicast data to a lower-level node at a predetermined timing. 
     The meritorious effects of the present invention are summarized as follows. The present invention reduces both processing load of the distribution source (distribution device) and traffic between the distribution source (distribution device) and a radio base station (or between the distribution source (distribution device) and a base station control device) when broadcast data or multicast data is transmitted repeatedly at a predetermined distribution timing. The reason is that the system is configured in such a way that repeatedly-transmitted broadcast data or multicast data is saved in at least one of the radio base station and the base station control device for repeated distribution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically showing a radio communication system of the present invention. 
         FIG. 2  is a block diagram showing the configuration of a radio communication system in a first exemplary embodiment of the present invention. 
         FIG. 3  is a sequence diagram showing the operation of a mobile station, a radio base station, and a broadcast station in the first exemplary embodiment of the present invention. 
         FIG. 4  is a block diagram showing the configuration of a radio communication system in a second exemplary embodiment of the present invention. 
         FIG. 5  is a sequence diagram showing the operation of a mobile station, a radio base station, a base station control device, and a broadcast station in the second exemplary embodiment of the present invention. 
         FIG. 6  is a sequence showing the broadcast communication in the radio communication system described in Patent Document 1 and so on. 
     
    
    
     EXPLANATIONS OF SYMBOLS 
     
         
           10 , 100 , 200  Mobile station 
           11 , 110 , 210  Radio base station 
           12 , 112 , 222  Control unit 
           14 , 114 , 224  Accumulation unit 
           20  Distribution device 
           111  IF unit (interface unit) 
           113 , 211  Radio unit 
           120 , 230  Switch 
           130 , 240  Broadcast station 
           140 , 250  Core network 
           150  terminal 
           220  Base station control device (radio control station) 
           221  First IF unit (interface unit) 
           223  Second. IF unit (interface unit) 
       
    
     PREFERRED MODES 
     Next, preferred modes for carrying out the present invention will be described more in detail below with reference to the drawings. 
     OVERVIEW OF THE INVENTION 
     First, the following describes an overview of the present invention with reference to  FIG. 1 .  FIG. 1  is a diagram schematically showing the radio communication system of the present invention. Referring to  FIG. 1 , a radio base station  11  is shown that is connected to a distribution device  20 , such as a broadcast station (Broadcast Multicast Service Center), for transmission of broadcast data or multicast data, received from the distribution device  20 , to a mobile station  10 . 
     The radio base station  11  comprises an accumulation unit  14  that functions as a saving unit that saves broadcast data or multicast data received from the distribution device  20  and a control unit  12  that functions as a distribution unit that repeatedly distributes the saved broadcast data or multicast data to the mobile station  10  at a predetermined distribution timing. 
     The control unit  12  repeatedly distributes the broadcast data or the multicast data, received from the distribution device  20 , according to the distribution timing information received in advance from the distribution device  20 . 
     In the radio communication system having the radio base station  11  described above, the broadcast data or the multicast data transmitted from the distribution device  20  is saved in the accumulation unit  14  for repeated distribution on an as-needed basis. That is, when the same broadcast data or multicast data is distributed repeatedly, this configuration eliminates the need for retransmission from the distribution device  20 , thus reducing both the load of the distribution device  20  and the traffic between the distribution device  20  and the radio base station  11 . 
     A modified configuration may also be employed in which the control unit  12  and the accumulation unit  14  described above are provided not in the radio base station  11  but in the base station control device. In this case, the same broadcast data or multicast data is distributed repeatedly to a mobile station via a radio base station managed by the base station control device. 
     First Exemplary Embodiment 
       FIG. 2  is a block diagram showing the configuration of a radio communication system in a first exemplary embodiment of the present invention. Referring to  FIG. 2 , the system comprises a broadcast station  130  that is a data distribution device (distribution source) provided on a core network  140 , a radio base station  110  that receives broadcast data or multicast data (hereinafter simply called broadcast data) from the broadcast station  130  via a switch  120 , and a mobile station  100  that receives broadcast data from the radio base station  110 . A user terminal  150  in  FIG. 2  is a general-user&#39;s personal computer that functions as a device (distribution source) that distributes broadcast data in the same manner as the broadcast station  130 . 
     The radio base station  110  comprises an IF unit (interface unit)  111 , a control unit  112 , a radio unit  113 , and an accumulation unit  114 . The following describes the units of the radio base station  110 . 
     The IF unit  111  provides the interface function for communicating with the core network  140  that includes the broadcast station  130 . More specifically, the IF unit  111  receives a session start (stop) request message, which will be described later, and broadcast data from the broadcast station  130  and returns a response message. 
     The control unit  112  has the function to extract distribution timing information, which specifies a broadcast data transmission time and period, from a message received from the broadcast station  130  and the function to instruct the accumulation unit  114  to save, transmit, or delete broadcast data based on the distribution timing information. 
     The distribution timing information is specified in the form of a distribution period such as “every hour starting at 0:00 am, January 1st”. The distribution timing may also be specified in the form of a distribution time-of-day such as “12:00 on every Sunday”. 
     The radio unit  113  transmits broadcast data, transmitted from the broadcast station  130 , to the mobile station  100  via a radio channel. 
     The accumulation unit  114  has the following functions that are executed according to an instruction from the control unit  112 : that is, the function to save broadcast data transmitted from the broadcast station  130 , the function to transmit saved broadcast data to the mobile station  100 , and the function to delete broadcast data. 
     Note that the functions of the control unit  112  described above may be implemented by the programs executed by a computer that acts as the radio base station  110 . 
     The broadcast station  130  has the function to notify the radio base station  110  about the start of broadcast data transmission and to transmit the transmission time and period information and the function to request to stop the transmission of broadcast data or to delete broadcast data. 
     The other components shown in  FIG. 2 , such as the mobile station  100 , switch  120 , and core network  140 , may employ the configuration well-known to those skilled in the art. 
     Next, the following describes the operation of the mobile station  100 , radio base station  110 , and broadcast station  130  with reference to the sequence flow shown in  FIG. 3 . 
     Referring to  FIG. 3 , the broadcast station  130  first transmits a session start request to the radio base station  110  (step s 100 ). In response to the session start request, the radio base station  110  transmits a session start response (step s 101 ). In response to the session start response, the broadcast station  130  starts the transmission of broadcast data (step s 102 ). 
     Assume that the session start request message transmitted in step s 100  described above includes the distribution timing information on the broadcast data. 
     The control unit  112  of the radio base station  110  stores therein the distribution timing information included in the session start request received in step s 100  described above and, at the same time, saves the received broadcast data, as well as its corresponding distribution timing information, in the accumulation unit  114  (step s 103 ). 
     The control unit  112  of the radio base station  110  notifies the mobile station  100  about the start of broadcast according to the stored distribution timing information (step s 104 ) and, after that, transmits the broadcast data (step s 105 ). 
     After the transmission of the broadcast data is completed, the control unit  112  of the radio base station  110  transmits the broadcast end notification (step s 106 ). 
     Even after that, the radio base station  110  repeatedly transmits the broadcast start request (step s 107 ), retransmits the broadcast data (step s 108 ), and transmits the broadcast end notification (step s 109 ) according to the stored distribution timing information. 
     After that, the broadcast station  130  transmits a session stop request to the radio base station  110  (step s 110 ). When the session stop request is received, the radio base station  110  transmits the session stop response to end the repeated distribution of the broadcast data described above (step s 111 ). After that, the radio base station  110  deletes the stored distribution timing information and the broadcast data (step s 112 ). 
     As described above, even when the broadcast data is repeatedly distributed, this exemplary embodiment allows the second and the following distribution of broadcast data to be performed without having to transmit broadcast data from the broadcast station  130 , thus reducing both the load of the broadcast station  130  and the traffic between the broadcast station  130  and the radio base station  110 . 
     Although the radio base station  110  deletes the broadcast data after receiving a session stop request from the broadcast station  130  in the exemplary embodiment described above, not only the distribution timing information on the broadcast data but also the expiration date of the broadcast data may be included in the message transmitted when the session start request is issued in step s 100 . In such a case, the radio base station  110  deletes the expired broadcast data from the accumulation unit  114 . Deleting data in this way makes the capacity of the accumulation unit  114  of the radio base station  110  available for better use. 
     Especially, in the exemplary embodiment above, the repeated distribution of broadcast data or multicast data to a mobile station before the session stop request is received from the broadcast station  130  prevents the broadcast station  130  from being overloaded. 
     Furthermore, the configuration of this exemplary embodiment, in which the distribution timing information is included in the session start request message received from the broadcast station  130 , allows the present invention to be implemented simply by adding the function to the radio base station  110 . 
     Although the distribution source of broadcast data is the broadcast station  130  in the exemplary embodiment described above, the user terminal  150  may also transmit broadcast data and its distribution timing information to the radio base station  110  to allow data, received from a general user, to be processed in the same manner. 
     Next, a second exemplary embodiment of the present invention will be described in which the above-described temporary saving destination (accumulation unit  114  in  FIG. 2 ) of broadcast data is provided in the base station control device. 
     Second Exemplary Embodiment 
     Referring to  FIG. 4 , a system in the second exemplary embodiment comprises a broadcast station  240  provided on a core network  250 , a base station control device (radio control station)  220  that receives broadcast data from the broadcast station  240  via a switch  230 , a radio base station  210 , and a mobile station  200  that receives broadcast data from the radio base station  210 . 
     The base station control device  220  comprises a first IF unit (interface unit)  221 , a control unit  222 , a second IF unit (interface unit)  223 , and an accumulation unit  224 . The following describes the units of the base station control device  220 . 
     The IF unit  221  provides the interface function to communicate with the core network  250  that includes the broadcast station  240 . More specifically, the IF unit  221  receives a session start(stop) request message and broadcast data, which will be described later, from the broadcast station  240  and returns a response message. 
     The control unit  222  has the function to extract distribution timing information, which specifies the broadcast data transmission time and period, from the message received from the broadcast station  240  and the function to instruct the accumulation unit  224  to save, transmit, or delete broadcast data based on the distribution timing information. 
     The IF unit  223  provides the interface function for communicating with the radio base station  210 . More specifically, the IF unit  223  transmits a session start(stop) request message and broadcast data, which will be described later, to the radio base station  210  and receives a response message. 
     The accumulation unit  224  has the following functions that are executed according to an instruction from the control unit  222 : that is, the function to save broadcast data transmitted from the broadcast station  240 , the function to transmit saved broadcast data to the mobile station  200  via the IF unit  223 , and the function to delete broadcast data. 
     Note that the functions of the control unit  222  described above may be implemented by the programs executed by a computer that acts as the base station control device  220 . 
     The radio base station  210  has a radio unit  211  that transmits broadcast data, transmitted from the broadcast station  240 , to the mobile station  200  via a radio channel. 
     The broadcast station  240  has the function to notify the radio base station  210  about the start of broadcast data transmission and to transmit the distribution timing information, which specifies the transmission time and period, and the function to request to stop the transmission of broadcast data or to delete broadcast data. 
     The other components shown in  FIG. 4 , such as the mobile station  200 , switch  230 , and core network  250 , may employ the configuration well-known to those skilled in the art. 
     Next, the following describes the operation of the mobile station  200 , radio base station  210 , base station control device  220 , and broadcast station  240  with reference to the sequence flow shown in  FIG. 5 . 
     Referring to  FIG. 5 , the broadcast station  240  first transmits a session start request to the base station control device  220  (step s 200 ). In response to the session start request, the base station control device  220  transmits a session start response (step s 201 ). In response to the session start response, the broadcast station  240  starts the transmission of broadcast data (step s 202 ). 
     Assume that the session start request message transmitted in step s 200  described above includes the distribution timing information on the broadcast data in the same manner as in the first exemplary embodiment. 
     The control unit  222  of the base station control device  220  stores therein the distribution timing information included in the session start request received in step s 200  described above and, at the same time, saves the received broadcast data, as well as its corresponding distribution timing information, in the accumulation unit  224  (step s 203 ). 
     The control unit  222  of the base station control device  220  transmits a session start request to the radio base station  210  according to the stored distribution timing information (step s 204 ). And, the radio base station  210  transmits a session start request (step s 205 ). 
     The radio base station  210  notifies the mobile station  200  about the start of broadcast (step s 206 ), and the base station control device  220  starts transmitting the broadcast data in response to the session start response from the radio base station  210  (step s 207 ). 
     After that, the base station control device  220  repeatedly performs the processing from the transmission of the session start request to the transmission of the broadcast end notification (steps s 204 -S 209  [sic. S 210 ]) according to the saved distribution timing information (see  FIG. 5 ). 
     And, the broadcast station  240  transmits a session stop request to the base station control device  220  (step s 211 ). When the session stop request is received, the base station control device  220  transmits the session stop response (step s 212 ). 
     After that, the base station control device  220  deletes the stored distribution timing information and the broadcast data (step s 213 ). 
     As described above, this exemplary embodiment allows the second and the following distribution of broadcast data to be performed without having to transmit broadcast data from the broadcast station  240  even when the broadcast data is repeatedly distributed, thus reducing both the load of the broadcast station  240  and the traffic between the broadcast station  240  and the base station control device  220 . In addition, this exemplary embodiment has the advantages over the first exemplary embodiment described above in that the control unit  112  and the accumulation unit  114  need not be provided in each radio base station. 
     Although the base station control device  220  deletes the broadcast data after receiving the session stop request from the broadcast station  240  in the exemplary embodiment described above, not only the distribution timing information on the broadcast data but also the expiration date of the broadcast data may be included in a message transmitted when the session start request is transmitted in step s 200 . In such a case, the base station control device  220  deletes the expired broadcast data from the accumulation unit  224 . 
     While the preferred exemplary embodiments of the present invention have been described, it is to be understood that the present invention is not limited to the exemplary embodiments above and that further modifications, changes, and adjustments may be added without departing from the basic technical concept of the present invention. 
     For example, though the distribution source of broadcast data is a broadcast station in the exemplary embodiments described above, the radio base station or the base station control device may accept broadcast data and the distribution timing information from a user terminal exemplified in  FIG. 2 . Such a configuration allows a user, other than a broadcast operator, to distribute user-created broadcast data to the area of a specific radio base station. The disclosure of the Patent Documents given above is incorporated by reference into this specification. The exemplary embodiments and the examples may be changed and adjusted in the scope of the entire disclosure (including claims) of the present invention and based on the basic technological concept. In the scope of the claims of the present invention, various disclosed elements may be combined and selected in a variety of ways. That is, it is apparent that the present invention includes various modifications and changes that may be made by those skilled in the art based on the entire disclosure including the claims and on the technical concept.