Patent ID: 7224937

Claim:
A mobile station apparatus in a communication system, the communication system comprising a plurality of base stations for providing mobile communication service within a covered communication area, the mobile station apparatus comprising: a memory for recording a predetermined access control class, so as to determine, under a normal condition, which base stations in the communication area the mobile station apparatus is allowed to camp on for conducting the mobile communication service; a battery for providing electrical power to the mobile station apparatus; a power detector for detecting the current power of the battery, when the power detector detects that the power provided by the battery is lower than a predetermined low power watermark, the power detector issuing a trigger signal; and a control program, wherein when the control program receives the trigger signal issued by the power detector, the control program overwrites the predetermined access control class recorded in the memory, so as to allow the mobile station apparatus to conduct the mobile communication service through other base stations in the communication area.