Group communication system having group number specified by mobile unit to permit intergroup calls

A control station in a group communication system, comprising:

• means for receiving a location registration signal including a group communication number from a mobile station among a plurality of mobile stations when power of the mobile station is turned on or when the mobile station in communication over a plurality of zones enters a group-communication objective wireless zone due to hand-over, the group communication number being an identification number for a group communication made up of a group of mobile stations from among said plurality of mobile stations;
• means for examining presence or absence of a group communication call of the mobile station based on the group communication number received from the mobile station and a group number controlling register that identifies which group communication calls are active;
• and
• means for notifying the mobile station with information indicating the presence of the group communication call based on the examination and information enabling the mobile station to participate in the group communication.

A method for supporting communication in a group communication system comprising one or more control stations, one or more base stations connected to the control station via a wire line or a wireless line, and a plurality of mobile stations connected to the base stations via wireless lines, the method comprising:

• receiving a location registration signal including a group communication number from a mobile station, the group communication number being an identification number for a group communication made up of a group of mobile stations from among said plurality of mobile stations;
• determining whether a group communication call corresponding to the received group communication number is active based on a group number controlling register that identifies which group communication calls are active;
• and
• notifying the mobile station that the group communication call corresponding to the received group communication number is active based upon the determination.