1. Field of the Invention
The present invention relates to a multiplexed radio system with a plurality of base stations having overlapping coverage areas, and particularly to the dynamic apportionment of channels in a multiplexed radio system.
2. Description of the Related Art
In many communication applications, a user with a mobile terminal communicates via a relatively short range radio link with a base station, which may pass his communication to other proximate mobile terminals via the short range link, or which may pass his communication to other base stations or to networks such as the PSTN.
In many such applications a user may roam throughout an area larger than the reliable coverage area of a single base station, yet the user may wish to maintain his communication capability as he roams. Typically, multiple base stations with overlapping coverage areas are provided for such applications.
Since a great many communication services are in place or contemplated, space in the radio spectrum is quite scarce. Thus, while it might be desirable for each base station to have frequencies allocated for its own exclusive use, multiple base stations must operate within lower spectrum bandwidth than ideal, and in many instances must share frequencies. Yet, this must be accomplished while minimizing interference between communication channels, i.e., timeslots in a time-multiplexed system, such as a UMTS/TDD radio system.
Typically, each base station has a number of slots on which it is capable of communicating with mobile stations. In typical conventional systems, when a mobile station wishes to initiate communication the associated base station makes path-loss and interference measurements on each of the slots that it is not presently using, in order to find a slot not being seriously interfered with by another base station or a mobile station.
An existing example of a radio communication system with dynamic channel apportionment is the DECT (Digital European Cordless Telephone) system in which the mobile terminal chooses the slot to be used for communication, without any consideration of the type or quality class (QoS class) of service. There is a need for faster and more reliable operation with more optimal radio resource usage, especially when the requirements of the traffic become more diverse with data and multi-media transmissions.