Mobile communication system for accomplishing handover with phase difference of frame sync signals corrected

A method of switching a communication channel when a mobile station (106, 107, 108) moves from one service area (109, 110, 111) to another service area is disclosed. The mobile station determines a difference between the transmission phase of a frame synchronizing signal received from a first base station (103, 104, 105) currently holding a communication channel with the mobile station and the transmission phase of a frame synchronizing signal received from a second base station expected to newly set up a communication channel with the mobile station. The mobile station sends phase difference information representative of the above difference to the first base station via the communication channel. The first base station having received the phase difference information transfers the information to the second base station, causing it to correct the phase of data thereof to be sent to the mobile station. This successfully implements soft handover while guaranteeing the phase synchronization of frames sent from the two base stations.