Method and apparatus for coordinating independent communications systems

Abstract

A method and apparatus for coordinating the transfer of communications control from one independent radio communications system to another is disclosed. A remote unit which communicates data messages is associated with a home system which has a plurality of fixed sites and overlapping radio coverage areas. As the remote unit travels away from its home system, communications may be maintained by providing radio coverage from an independent roam system. The last message received by the home and roam systems from the remote unit has the associated radio signal strength and time of reception stored at each system. When a current message is transmitted by the remote unit and both the home and the roam system receive the message, the roam system time stamps the message and calculates the signal strength associated with the current message. If the amount of time elapsed between the last and the current message exceeds a predetermined amount of time or if the signal strength exceeds a predetermined threshold, the roam system requests transfer of control of the processing of the current message from the home system. When the home system receives this request, it calculates the difference in signal strength between the signal strength of the current message as received by the roam system and the signal strength of the current message as received by the home system. If the difference exceeds a predetermined amount, the request of the roam system to further process the message is granted.