Motorola Corporation

Dariusz Andrzej Blasiak

Daniel Richard Tayloe

Mark S Frank

Paul R Christian

Bradley B Bakke

John William Arens

Mark Steven Frank

In cellular communication systems, hand-offs are performed to maintain links as subscriber units (110) and beams move relative to each other. The hand-off determination procedure (500) is performed in overlap regions (240, 340). Candidate beams are identified and hand-off types are determined based on the satellite (120) associated with the candidate beam. Thresholds are established and changed to optimize a hand-off request determination procedure (500). Two hand-off types are considered. An inter-satellite hand-off is requested (514) when the current beam and the candidate beam are on different satellites (120). An intra-satellite hand-off is requested (510) when the current beam and the candidate beam are on the same satellite (120). Thresholds are dynamically changed and algorithms are used to minimize the number of inter-satellite hand-offs.

Method and apparatus for dynamically controlling hand-off thresholds in

A subscriber unit (26) communicates with a satellite communication system (10) that projects cells. The satellites (12) and cells move relative to the earth. During every other TDMA frame, a subscriber unit (26) measures the signal strength of all candidate hand-off beams. The signal strength of the current beam is compared to the signal strength of the candidate hand-off beams. When the signal strength of the current beam is not the strongest, a counter is incremented (108). A hand-off is requested to the beam with the greatest signal level when the counter exceeds a predetermined threshold. Accordingly, only after the current antenna beam has not been the strongest beam for a certain period of time, is a hand-off requested. A different counter threshold is used for candidate hand-off beams from other satellites (12).

Method and apparatus for optimal hand-offs in a satellite cellular

A decoding apparatus (200) decodes a coherent, differentially encoded multi-level phase shift keying (DEPSK) modulated signal. A coherent receiver (101) receives and, subsequently, outputs the coherent DEPSK modulated signal to a metric computer (201). The metric computer (201) generates a soft decision metric .LAMBDA.(s(n)) corresponding to the coherent DEPSK modulated signal which is outputted to a forward error correction (FEC) decoder (107). The FEC decoder (107) decodes the coherent DEPSK modulated signal in accordance with the soft derision metric .LAMBDA.(s(n)) corresponding to the coherent DEPSK modulated signal.

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Chicago, IL, United States of America

Dariusz Andrzej Blasiak