Patent ID: 7742761

Claim:
A mobile communication system comprising a plurality of base stations, each of which performs wireless communication with mobile stations located within a cell formed thereby, and a base station controller connected to the plurality of base stations, wherein each of said base stations includes: a system parameter storage for storing a base station identifier and a border flag indicative of whether the base station is a border cell base station forming a border cell located on a boundary portion of a service area or a normal cell base station forming a normal cell located on the inward side than the border cell; and a distance calculation unit for calculating a distance to each of the mobile stations connected via wireless channels and notifying said base station controller of distance information of each of the mobile stations in conjunction with the base station identifier and the border flag as handoff information, and said base station controller includes: a handoff information management table for storing the base station identifier, the border flag, and the mobile station distance information notified from each of the base stations in association with each of mobile station identifiers; and an out-of-range detection unit for updating said handoff information management table each time new handoff information is received from each of said base stations and detecting any of the mobile stations moving out of the service area into an out-of-communication region, wherein said out-of-range detection unit performs out-of-range detection by selectively monitoring any of the mobile stations that is currently communicative only with one or more of said border cell base stations discriminated by a state of the border flag as a detection target and comparing the distance information of the mobile station indicated by said handoff information management table with a specified threshold value; wherein said out-of-range detection unit performs the out-of-range detection of each of the mobile stations by using a threshold value common to the plurality of base stations; and wherein said out-of-range detection unit performs the out-of-range detection of each of the mobile stations by selecting the distance information with a minimum value from among the distance information on the same mobile station measured at the plurality of border cell base stations and compares the selected minimum distance information with said threshold value.