Group communication system

A group communication system, comprising:

• at least one controlling station;
• at least one base station connected to said at least one controlling station through one of a wired circuit and a radio circuit;
• and
• a plurality of mobile stations connected to said at least one base station,
• wherein one of said at least one controlling station and said at least one base station has means for managing group communication numbers of said mobile stations,
• wherein said mobile stations each have means for transmitting a mobile station identification number and a group communication number to said at least one base station when a radio zone of each of said mobile stations is handed over and thereby a location registration operation is performed,
• wherein one of said at least one controlling station and said at least one base station has zone area presence determining means for determining whether or not a particular mobile station is present in a radio zone to which the particular mobile station has been handed over when one of said at least one controlling station and said at least one base station receives the group communication number from the relevant mobile station, and
• wherein said at least one base station has means for releasing a communication channel when the relevant mobile station is not present in the radio zone as the determined result of said zone area presence determining means.