Mobile radio transmission system

A mobile radio station for communication with a plurality of receiving and transmitting base stations situated at respective geographic locations, defining a plurality of respective service areas, comprising

• means for storing a mobile location record capable of storing at least n service area identities, where n >
• 1,
• means for determining if the number of service area identities currently stored in that mobile location record equals n,
• means for sensing when that mobile station is not within communication range of any base station serving a service area whose identity is currently stored in that mobile location record, and
• means responsive to said means for sensing, when that mobile station is not within such range, for attempting to communicate with another base station having another service area identity, which may be within range;
• and upon communicating with said another base station, for replacing a service area identity already stored in said mobile location record with said another service area identity if n service area identities were already stored in said mobile location record, and otherwise storing said another service area identity in said mobile location record.

A method of operating a mobile radio transmission system comprising a plurality of receiving and transmitting base stations situated at respective geographic locations, defining a plurality of respective service areas;

• a plurality of mobile stations, each including means for transmitting a registration identification and communicating by two-way radio with each base station when in communication range of that base station;
• and control means including a station location record corresponding to each mobile station, for storing a service area identity responsive to receipt at one base station of a registration identification transmitted by the corresponding mobile station, comprising the steps of:
• sensing when a given mobile station is within communication range of a first base station, and transmitting a registration identification to said first base station,
• storing a service area identity corresponding to said first base station in said given station,
• sensing when the given mobile station is no longer within range of said first base station, then attempting to receive signals from a second base station,
• responsive to receipt of signals from said second base station, transmitting a registration identification to said second base station if a service area identity corresponding to said second base station is not already stored in said given station, and if a registration identification is transmitted to said second base station, determining if the number of service area identities currently stored in the location record equals n, where n >
• 1;
• and if the number equals n, replacing a service area identity already stored in said mobile location record with a second service area identity corresponding to said second base station;
• and if the number is less than n, storing in said given station said second service area identity,
• storing in a control arrangement a station location record containing the most recent service area identities of the base stations to which said given mobile station has transmitted a registration identification, up to a maximum of n identities,
• directing any message to be transmitted to said given mobile station to be transmitted from on of the base stations whose service area identity is stored in the station location record, and
• if transmission from said one base station is not answered, then transmitting the message from another base station whose service area identity is stored in the station location record.