Abstract:
A broadcast method in a mobile communication system is disclosed. When the same information is broadcast to a plurality of cells, broadcast is carried out in a radio base station device.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from Japanese patent application No. 2007-030569 filed on Feb. 9, 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 more particularly, to a method of broadcasting in a radio base station. 
         [0004]    2. Description of the Related Art 
         [0005]    In mobile communication systems, such as for example mobile telephone systems, control signals and data signals on common channels are conventionally transmitted in units called cells. However, a service that broadcasts the same data signal to multiple cells, such as MBMS (Multimedia Broadcast Multicast Service), needs to transmit the same data signal to the respective cells. As a radio base station typically handles a number of cells and a radio control device thus transmits the same signal to the respective cells, traffic on a transmission line between the radio base station and the radio control device may increase unnecessarily. 
         [0006]      FIG. 1  shows as an example a mobile communication system which broadcasts the same data to three cells. In this system, the same data is transmitted from radio control device  5  to three cells  8   a ,  8   b  and  8   c  via radio base station device  6  which manages those cells. As shown in  FIG. 2 , radio control device  5  includes radio control processor  51  and wired data transmitter  52 , and radio base station device  6  includes wired data receiver  61  and radio data transmitters  62   a ,  62   b  and  62   c . In this system, radio control device  5  is required to transmit three pieces of the same data onto inter-device transmission channel  7 , which produces unnecessary traffic. 
         [0007]    With the recent growth in the number of users and/or a diversity of services in mobile communication systems, an increasing amount of data has been transmitted over the networks of such systems. In addition, it is desired to minimize the amount of traffic on a transmission channel between network devices because high-rate data cannot be transmitted due to physical restrictions of the channel or because the data rate has to be kept low in terms of cost. While broadcast services such as MBMS are under consideration, there is no mechanism for realizing broadcast at a radio base station under the present standards. Traffic between a radio base station and a radio control device can thus increase unnecessarily. 
         [0008]    JP2004-15609A discloses that a base station adds, to data, multicast identification data for specifying that the data is transmitted to all of multiple subscriber stations, and multicasts the data to each of the subscriber stations by utilizing the capability of radio communication to simultaneously transmit to multiple recipients. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to provide a broadcast method, a mobile communication system, a radio control device, and a radio base station device for eliminating an unnecessary increase in traffic over a network when the same information is broadcast to a number of cells in a mobile communication system. 
         [0010]    According to the invention, the radio base station device performs a broadcast when the same information is to be broadcast to a number of cells. 
         [0011]    By broadcasting a data signal in the radio base station device, it is possible to eliminate unnecessary traffic increase on an inter-device transmission channel between the radio control device and the radio base station device. 
         [0012]    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 
         [0013]      FIG. 1  is a view showing the configuration of a related system; 
           [0014]      FIG. 2  is a block diagram of a radio control device and a radio base station device of  FIG. 1 ; 
           [0015]      FIG. 3  is a view showing a system configuration according to a first exemplary embodiment of the invention; 
           [0016]      FIG. 4  is a block diagram of a radio control device and a radio base station device of  FIG. 3 ; 
           [0017]      FIG. 5  is a sequence chart illustrating the operation of the first exemplary embodiment; 
           [0018]      FIG. 6  shows a system configuration according to a second exemplary embodiment of the invention; 
           [0019]      FIG. 7  is a block diagram of the radio control device and the radio base station device of  FIG. 4 ; and 
           [0020]      FIG. 8  is a sequence chart illustrating the operation of the second exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Exemplary Embodiment 
       [0021]    Referring to  FIG. 3 , a mobile communication system according to a first exemplary embodiment of the invention comprises radio control device  1 , radio base station device  2 , inter-device transmission channel  3 , and cells  4   a ,  4   b , and  4   c.    
         [0022]    As shown in  FIG. 4 , radio control device  1  includes radio control processor  11  and wired data transmitter  12 . Radio base station device  2  includes wired data receiver  21  and radio data transmitters  22   a ,  22   b , and  22   c.    
         [0023]    The operation of this exemplary embodiment will be described below with reference to the sequence chart of  FIG. 5 . 
         [0024]    Radio controller  11  in radio control device  1  sets a special number for broadcast in the cell number in a control signal for setting a common channel used for broadcast and sets the number in radio base station  2  (step  101 ). Upon receipt of a response from radio base station device  2  (step  102 ), wired data transmitter  12  transmits a common channel data signal to be broadcast to radio base station device  2  via inter-device transmission channel  3  (step  103 ). Here, rather than transmitting as many pieces of data as there are cells, a single item of the data is transmitted just as when it transmitted to a single cell. Upon receipt of the data signal, wired data receiver  21  in radio base station device  2  broadcasts the data to transmit the data to cells  4   a ,  4   b  and  4   c  from radio data transmitters  22   a ,  22   b  and  22   c  (step  104 ). 
         [0025]    In this manner, by performing the broadcast in radio base station device  2 , which has not been conventionally carried out, traffic on inter-device transmission channel  3  can be significantly reduced (to one third in this example). 
       Second Exemplary Embodiment 
       [0026]    The exemplary embodiment shown in  FIG. 3  can only broadcast data to all cells managed by radio base station device  2 . However, in a second exemplary embodiment shown in  FIGS. 6 to 8 , data is broadcasted to particular cells which are under the management of radio base station device  2 . Initially, radio control processor  11 ′ in radio control device  1  specifies multiple cell numbers in the cell number in a control signal for setting a common channel and sets the numbers in radio base station  2  (step  201 ). Upon receipt of a response from radio base station device  2  (step  202 ), wired data transmitter  12  transmits a common channel data signal to be broadcast to radio base station device  2  over inter-device transmission channel  3  (step  203 ). Wired data receiver  21  in radio base station device  2  broadcasts the data only to cells having the specified cell numbers (step  204 ). In this case, as shown in  FIG. 6 , the data is delivered only to cell  4   a  (number  1 ) and cell  4   b  (number  2 ), and not to cell  4   c  (number  3 ). Although this exemplary embodiment has a smaller effect in reducing traffic on the inter-device transmission channel as compared with the exemplary embodiment shown in  FIG. 3 , it is effective when there are users who do not receive broadcasting services in cell  4   c  (number  3 ), for example. 
         [0027]    A radio control device that is, together with a radio base station device, included in a mobile communication system, comprises: 
         [0028]    means for setting a special number for broadcast in the cell number in a control signal for setting a common channel used for broadcast to set the control signal in the radio base station device; and 
         [0029]    means for transmitting a common channel data signal to be broadcast to the radio base station device. 
         [0030]    A radio control device that is, together with a radio base station device, included in a mobile communication system, comprises: 
         [0031]    means for setting a plurality of cell numbers in the cell number in a control signal for setting a common channel used for broadcasting to set the control signal in the radio base station device; and 
         [0032]    means for transmitting a common channel data signal to be broadcast to the radio base station device; 
         [0033]    A radio base station device that is, together with a radio control device, included in a mobile communication system, comprises: 
         [0034]    means for receiving a control signal for setting a common channel used for broadcast having a cell number in which a special number is set; 
         [0035]    means for receiving, from the radio control device, a common channel data signal to be broadcast; and 
         [0036]    means for broadcasting the common channel data signals to each cell. 
         [0037]    A radio base station device that is, together with a radio control device, included in a mobile communication system, comprises: 
         [0038]    means for receiving a control signal for setting a common channel used for broadcast having a cell number in which a plurality cell numbers are set; 
         [0039]    means for receiving, from the radio control device, a common channel data signal to be broadcast; and 
         [0040]    means for broadcasting the common channel data signals to cells having the respective cell numbers set in the control signal. 
         [0041]    While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.