Abstract:
In a mobile terminal communication method, when a zone in which a mobile terminal is positioned becomes in a congestion state, a calling channel having high emergency can be secured. A connection priority rank is given to each mobile terminal. When an area in which a calling mobile terminal is positioned is in the congestion state, the number of currently-used calling channels in the same connection priority rank as that of the mobile terminal is compared with the number of the calling channels set to the rank. Depending on its result, the call is disconnected or another mobile terminal in a low connection priority rank is handed off to another area.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a mobile communication system. More specifically, the present invention relates to a mobile communication system which limits use of a calling channel when congestion occurs. 
   2. Description of the Related Prior Art 
   Current mobile communication systems have mobile terminals, base stations communicating with the mobile terminals, a home memory managing position information of the mobile terminals, and an exchange station transmitting a call to a public telephone network. In general, due to a disaster or an accident, the number of calls may be temporarily increased abruptly from a certain area. In such case, congestion occurs in the mobile communication system to cause confusion in the network. Japanese Patent Application Laid-Open No. Hei 10-308978 discloses an example of a mobile communication system regulating a call in the above case. Referring to  FIG. 1 , the mobile communication system has a traffic controller  102  with a home memory  101 , a mobile communication exchanger  103 , base stations  104 , and a plurality of mobile terminals  105 . The base station  104  has a regulation part  117  regulating a call from the mobile terminal  105 . A traffic measurement part  115  of the mobile communication exchanger  103  measures the number of accesses to transmit it to the traffic controller  102 . The home memory  101  stores information of the mobile terminal. A congestion detection part  111  accesses the home memory  101  to detect congestion. A regulation decision part  113  decides the base station regulated based on the detected result. A regulation indication part  114  calculates a regulation amount to send it to the targeted mobile communication exchanger  103 . A regulation amount distribution part  116  distributes the regulation amount to the base station  104  at a predetermined rate. The regulation part  117  of the base station  104  regulates the call from the mobile terminal  105  at the notified rate. 
   In the mobile communication system, however, the regulation part  117  automatically disconnects the call at the predetermined rate. An emergency call may be disconnected. 
   SUMMARY OF THE INVENTION 
   In a first specific example of a mobile communication method of the present invention, a connection priority rank is set to each mobile terminal to be stored. When an area in which a calling mobile terminal is positioned is in a congestion state and the number of currently-used calling channels in the same connection priority rank as that of the mobile terminal is equal to or larger than the number of calling channels set to the rank, the call is disconnected. When the number of currently-used calling channels in the same connection priority rank as that of the mobile terminal is smaller than the number of calling channels set to the rank, the rank in which the number of currently-used calling channels is larger than the set number of calling channels of the respective connection priority ranks of the area is searched for, the mobile terminal in the rank is handed off to another area, and a calling channel is allocated to the calling mobile terminal. 
   In a second specific example of the mobile communication method of the present invention, a connection priority rank is set to each mobile terminal to be stored. When a calling mobile terminal belongs to the highest connection priority rank, a calling channel is allocated to establish a call. When a base station which has received a call is in a congestion state and the mobile terminal belongs to the lowest connection priority rank, the call is disconnected. Then, when a base station which is adjacent the base station and is not in the congestion state is searched for and there is no corresponding base station, the call is disconnected. When there is the corresponding base station, use of an available channel of the base station is permitted. When there is no available channel, a calling channel of the mobile terminal having the longest call in a zone of the base station is allocated to the call. 
   The above-mentioned mobile communication methods can reduce the number of cases of disconnecting a mobile terminal whose connection priority rank is high when congestion occurs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a block diagram showing an example of a mobile communication system; 
       FIG. 2  is a block diagram showing a specific example of a mobile communication system executing a mobile communication method of the present invention; 
       FIG. 3  shows an example of the structure of a zone of a base station; 
       FIG. 4  is a block diagram of a specific example of a base control station; 
       FIG. 5  shows a specific example of data of a home memory; 
       FIG. 6  shows a specific example of data of calling channels during calling stored in a storage part of the base control station; 
       FIG. 7  is a flowchart showing a specific example of operation at congestion; 
       FIG. 8  shows another specific example of data of the home memory; 
       FIG. 9  shows another specific example of data of calling channels during calling stored in the storage part of the base control station; and 
       FIG. 10  is a flowchart showing another specific example of operation at congestion. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 2 , a specific example of a mobile communication system has an exchanger  1  connected to a public telephone network, base control stations  2 - 1 ,  2 - 2  controlling a call, and base stations  3 - 1  to  3 - 8  receiving a call from mobile terminals in predetermined wireless zones  4 - 1  to  4 - 8 . In this example, the zones  4 - 1 ,  4 - 7  have fire stations  5 - 1 ,  5 - 2 , respectively. The zone  4 - 4  has a gas company  5 - 3 . The zone  4 - 8  has an electric power company  5 - 4 . The exchanger  1  is connected to a home memory  11  storing information such as connection priority ranks and the set number of calling channels of subscribers including the fire stations, gas company and electric power company. In a congestion state, the base control stations  2 - 1 ,  2 - 2  secure the set number of calling channels of the fire stations  5 - 1 ,  5 - 2 , the gas company  5 - 3 , and the electric power company  5 - 4  to control calling so as to connect these calls in a priority manner. 
   Referring to  FIG. 3 , the zone of the base station in the system in the specific example has six areas called a sector. The base station  3 - 1  has six antennas having directivity. The six antennas can independently communicate with the mobile terminals in sectors  4 - 1 - 11  to  4 - 1 - 16 . 
   Referring to  FIG. 4 , the base control station  2 - 1  has a base station interface  21 , an exchanger interface  22 , a display part  23 , a storage part  24 , and a message generation part  25 . The display part  23  displays the usage state of the calling channel in real time. The sector in the congestion state can be displayed in red color. The storage part  24  stores the usage state of the calling channel of the base station controlled by the base control station  2 - 1 . When congestion occurs in a certain sector of the zone of the base station, the message generation part  25  generates a predetermined voice message and character message under the control of a control part  26  to send the message to the caller of the sector using a control channel. The control part  26  performs control of connection and disconnection about a call inputted/outputted to/from the base control station  2 - 1 . 
   Referring to  FIG. 5 , the home memory  11  includes data about connection priority ranks and the number of calling channels set to mobile terminals (subscribers). High connection priority ranks are set to the fire stations, gas company, and electric power company performing high priority communication based on an agreement. In this example, the highest connection priority rank is set to the fire stations, the next rank is set to the gas company, and the rank after next is set to the electric power company. General subscribers are set to the lowest priority rank. The data such as the telephone numbers and inherent numbers of the mobile terminals, areas in which the mobile terminals are currently positioned, and conditions deciding congestion are stored. In this example, when the currently-usable calling channels are all in use in each of the sectors of the respective base stations controlled by the base control station  2 - 1 , the sector is decided to be in the congestion state. When a calling channel cannot be used due to interference of an illegal electric wave, the calling channel is decided to be in use. 
   Referring to  FIG. 6 , the storage part  24  in the base control station  2 - 1  stores that the fire station  5 - 1  whose connection priority rank is highest (1) is using a calling channel number  3 - 1 - 1  in the sector  4 - 1 - 11  of the zone  4 - 1  of the base station  3 - 1 . The storage part  24  also stores that of whether the respective sectors are in the congestion state or not. The contents of the storage part  24  can be displayed on the display part  23 . The display part  23  can display the sector in the congestion state, for example, in red color. The control part  26  performs control of a call depending on the stored contents of the storage part  24 . 
   Referring to  FIG. 7 , a flowchart showing a specific example of operation of transmission regulation at congestion is shown, In this example, the total number of calling channels at normal in one sector is larger than the total number of calling channels set to organizations, companies, and general subscribers in the sector. When the total calling channels at normal are all in use, or other calling channels except for the calling channels unusable due to an illegal electric wave are all in use, the sector is decided to be in the congestion state. In this example, the sector is decided to be in the state shown in  FIGS. 5 ,  6 . 
   The control part  26  of the base control station detects a call via the base station interface part  21  (S 11 ). The control part  26  stores information of the caller shown in  FIG. 6  to the storage part  24  based on received information (S 12 ). At this time, the connection priority rank of the caller is detected to be stored. The control part  26  checks whether a sector in which the caller is positioned is in the congestion state or not (S 13 ). When the sector is not in the congestion state (No of S 13 ), the control part  26  allocates a calling channel to the base station controlling the sector to establish a calling path (S 23 ). When the sector is in the congestion state (Yes of S 13 ), the control part  26  calculates the currently-used calling channels in the connection priority rank of the caller based on the information of the storage part  24  (S 14 ). The number of calling channels set in the connection priority rank of the caller is checked based on the information of the home memory  11  (S 15 ). When the number of currently-used calling channels is equal to or larger than the set number of call channels (Yes of S 15 ), the control part  26  starts the message generation part  25  to generate a message of the congestion state, and sends it to the caller via the control channel (S 22 ) to disconnect the call (S 24 ). When the number of currently-used calling channels is smaller than the set number of calling channels (No of S 15 ), the control part  26  calculates the number of currently-used calling channels for each connection priority rank in the same sector based on the information of the storage part  24  (S 16 ). The lowest connection priority rank is selected (S 17 ). When deciding, in the connection priority rank, that the calling channels in number equal to or larger than the set number of calling channels are currently used (Yes of S 18 ), one mobile terminal in the connection priority rank is selected (S 20 ). When the number of currently-used calling channels is smaller than the set number of calling channels (No of S 18 ), the next higher connection priority rank is selected (S 19 ) to perform the S 18 . When the mobile terminal can be handed off to an adjacent sector (Yes of S 21 ), the control part  26  allocates a calling channel to the caller to establish a calling path (S 23 ). When the selected mobile terminal cannot be handed off to the adjacent sector (No of S 21 ), the control part  26  starts the message generation part  25  to generate a message of the congestion state, and sends it to the selected mobile terminal via the control channel (S 22 ) to disconnect the call of the mobile terminal (S 24 ). 
   As described above, in the mobile communication method of the specific example, when a call occurs in the sector in the congestion state, the base control station searches for the connection priority rank in which the channels in number equal to or larger than the set number of calling channels are used in the sector to hand off the caller (mobile terminal) in the rank to the calling channel of the adjacent sector. A call from the fire station in the sector in the congestion state can always secure the calling channel. 
   A second specific example of the mobile communication method will be described. The second specific example is also executed in the mobile communication system shown in  FIGS. 2 ,  4 .  FIG. 8  shows a specific example of data of the home memory of the second specific example. Data is basically the same as that shown in FIG.  5 . In this specific example, however, the zone of the base station is not divided for each sector. Also in this specific example, when other calling channels except for the number of calling channels of 5 set to the fire station in the highest connection priority rank in the zone of each of the base stations are all in calling, the zone is decided to be in the congestion state. 
   Referring to  FIG. 9 , a specific example of data stored in the storage part  24  of the base control station is described. The storage part  24  stores that the fire station whose connection priority rank is the highest in the zone  4 - 1  of the base station  3 - 1  is using the calling channel number  3 - 1 - 1 . The storage part  24  stores the remaining number of calling channels of the zones to decide congestion. 
   Referring to  FIG. 10 , a flowchart of operation of transmission regulation at congestion of the second specific example is shown. The control part  26  of the base control station detects a call via the base station interface part  21  (S 31 ). The control part  26  accesses the home memory  11  connected to the exchanger  1  to identify whether the connection priority rank of the call is the highest rank or not (S 32 ). When the connection priority rank of the call is the highest rank (Yes of S 32 ), the control part  26  refers to the data of the storage part  24  to decide whether the base station which has received the call is in the congestion state or not (S 33 ). When the base station is in the congestion state (Yes of S 33 ) and is not in the congestion state (No of S 33 ), connection is permitted (S 41 ). This is because the call has the highest connection priority rank. The S 33  can thus be omitted. When the control part  26  identifies that the connection priority rank of the call is not the highest rank (No of S 32 ), the control part  26  decides whether the base station which has received the call is in the congestion state or not (S 34 ). When the base station is not in the congestion state, the control part  26  permits use of an available calling channel to permit calling connection (S 41 ). When the base station is in the congestion state (Yes of S 34 ), the control part  26  decides whether the call is a call in the lowest connection priority rank or not (S 35 ). When the call is in the lowest connection priority rank (Yes of S 35 ), the control part  26  sends a message that the calling channel is in the congestion state to the caller via the control channel (S 43 ) to disconnect the call (S 44 ). When the call is not a call in the lowest rank (No of S 35 ), the control part  26  decides whether there is an adjacent base station which is not in the congestion state based on the data of the storage part  24  (S 36 ). When there is not the adjacent base station which is not in the congestion state (No of S 36 ), the call is processed as in the above-mentioned call in the lowest connection priority rank. When there is the adjacent base station which is not in the congestion state (Yes of S 36 ), the control part  26  decides based on the data of the storage part  24  whether there is an available calling channel in the adjacent base station (S 37 ). When there is the available calling channel in the adjacent base station (Yes of S 37 ), the control part  26  permits use of the available calling channel (S 38 ) to permit calling connection (S 41 ). When there is not the available calling channel in the adjacent base station (No of S 37 ), the control part  26  selects a calling channel having the longest call in the zone of the base station (S 39 ) to permit use of the calling channel to the caller (S 40 ). The caller of the calling channel is moved into the available calling channel of the same zone or that of the adjacent base station (S 42 ). 
   In the second specific example, the number of calling channels set to a subscriber having the highest connection priority rank (for example, the fire station) can always be secured. When the congestion state occurs at a disaster, the subscriber can make a call. The number of calling channels of a subscriber in the second priority connection rank can be secured likewise. 
   While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by the present invention is not limited to those specific embodiments. On the contrary, it is intended to include all alternatives, modifications, and equivalents as can be included within the spirit and scope of the following claims.