Method and apparatus for handoff between different cellular communications systems

摘要

A method and system for performing an intersystem handoff of communication with a mobile station between base stations of first and second cellular systems is disclosed herein. At the mobile station, a quantifiable parameter of a signal transmitted by a second base station of the second system is measured. When the measured value of the quantifiable parameter passes through a first predetermined level, the mobile station communicates a signal quality message via a first base station of the first system to a first mobile switching control station. A channel request message is then communicated from the first mobile switching control station to a second mobile switching control station within the second system. At the second base station, a quantifiable parameter of the signal received from the mobile station is also measured. The second base station establishes communication with the mobile station when the measured value of the quantifiable parameter passes through a predetermined level. Alternately, the signal strength of a first pilot signal transmitted by the first base station is measured at the mobile station. A handoff request message is then sent to the second base station when the measured signal strength of the first pilot signal becomes less than a second predetermined level, thereby mobile station communication to be established. The provision of a voice link between the mobile switching control stations allows for the forwarding of an existing connection between the first and second cellular systems, and enables the performance of soft intersystem handoffs.