Patent ID: 7292857

Claim:
A mobile station for communicating with a plurality of base stations, comprising: a first antenna; a field strength detecting circuit that uses the first antenna to perform a wave strength detecting operation which detects a wave strength received from the base stations and outputs a received wave strength; and a base station switching control circuit that is provided with i) a first field strength threshold level which specifies a minimum wave strength to perform stable communication with a connected based station, and ii) a second field strength threshold level which specifies a minimum wave strength to continue communication with the connected base station for comparing with the received wave strength, and classifies the received wave strength into three classified strength levels of i) a first level which is higher than the first field strength threshold level, ii) a second level which is lower than the first field strength threshold level and higher than the second field strength threshold level, and iii) a third level which is lower than the second field strength threshold level, wherein, when the classified strength level is the first level, the base switching control circuit continues communication without performing a first operation of searching candidate base stations for switching over to a target base station, when the classified strength level has become the second level, the base station switching control circuit i) starts to perform the first operation for preparing for a second operation of switching over communication to the target one of the candidate base stations and ii) instructs the field strength detecting circuit to increase a frequency of the wave strength detecting operation, and the second operation is performed when the classified strength level has become the third level.