Mobile communications system and mobile station therefor

DETAILED DESCRIPTION Taking the above into consideration, an object of the present invention is to provide a mobile communications system which effectively suppresses the control message traffic when updating location registers and paging a specific mobile station.
To accomplish the above object, according to the present invention, there is provided a mobile communications system where base stations provide radio links for mobile stations in each cell and a mobile switching center controls connections between the mobile stations by switching circuits.
In this system, each mobile station comprises the following element: (1a) a notification message receiver which receives a notification message from the nearest base station; (1b) a base station ID extractor which extracts a base station ID from the received notification message to identify which base station is sending the notification message; (1c) a location change counting unit which detects a change in the mobile location by comparing two consecutive instances of the base station ID extracted by the base station ID extractor, and counts the detected location changes separately for each pair of base station IDs involved in each change; (1d) a personal location area (PLA) setting unit which defines personal location areas by grouping associated cells into one area, based on the location change count values obtained by the location change counting unit; (1e) a PLA memory which stores records of the personal location areas defined by the PLA setting unit, each of the records containing the base station IDs indicating which cells constitute each personal location area; (1f) a location change detector which tests whether the personal location area registered at present is valid, each time the base station ID extracting unit extracts a base station ID that is different from before; and (1g) a location registration unit which is activated when the location change detector has detected that the registered personal location area is no longer valid