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A personal communication system with multiple hierarchical cellular overlays is considered. The system can include a terrestrial segment and a space segment. The terrestrial segment, consisting of microcells and macrocells, provides high channel capacity by covering service areas with microcells. Overlaying macrocells cover spots that are difficult in radio propagation for microcells and provide overflow groups of channels for clusters of microcells. At the highest hierarchical level, communications satellites comprise a space segment. The satellite beams overlay clusters of terrestrial macrocells and provide primary access for satellite-only subscribers. Call attempts from ceUular/satellite dual subscribers are first directed to the terrestrial cellular network, with satellites providing necessary overlay. At each level of the hierarchy, hand-off calls are given priority access to the channels.The mathematicd structure is that of a multi-layer hierarchical overflow system. An analytical model for teletraffic performance (including hand-off) is developed. Theoretical performance measures are calculated for users having different mobility characteristics. These show the carried trafRc, traffic distribution, blocking, and forced termination probabilities. by the larger cells, i.e. cells that are higher in system hierarchy. This traffic distribution is achieved without any other mechanism for mobility management, such as those based on speed measurements for initial cell assignment.

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