HAND-OFF METHOD BETWEEN BSCS IN CDMA MOBILE COMMUNICATION SYSTEM

摘要

PURPOSE: A hand-off method between BSCs(Base Station Controllers) in a CDMA(Code Division Multiple Access) mobile communication system is provided to prevent the degradation of speech quality by transcoding only a call frame of a corresponding base station in each vocoder of two BSCs. CONSTITUTION: After a soft add between BSCs is performed, a vocoder of a BSC-X compares a state of a Q-CELP(Qualcomm-Code Excited Linear Prediction) frame with a state of a Q-CELP frame of a base station-B transmitted through an MSC, selects a good Q-CELP frame, and transcodes the selected Q-CELP frame to a PCM(Pulse Code Modulation)(S1). If a mobile termination gets out of the region of the BSC-X, the mobile terminal requests the BSC-X through a pilot strength measurement message that a pilot of a base station-A is excepted from an active set(S2). The BSC-X receives the pilot strength measurement message, instructs a vocoder not to select the Q-CELP frame transmitted from a BSC-Y, and instructs a vocoder of the BSC-Y to convert a bypass mode into a transcoding mode(S3). After the switching in an MSC connects to a PSTN(Public Switched Telephone Network), the vocoder of the BSC-X is converted from the transcoding mode to the bypass mode for releasing the vocoder of the BSC-X(S4). The MSC converts a path from the BSC-X connected to the PSTN through a switching block into a path from the BSC-Y, and only the BSC-Y transmits a voice from the base station-B for smoothly performing a hand-off of the mobile terminal which is progressed from the BSC-X to the BSC-Y(S5).