A HIGH-CAPACITY 3RD-GENERATION MOBILE SATELLITE SYSTEM-DESIGN

This paper describes a CDM/CDMA based approach for a 3-rd generation m ulti-beam satellite mobile and personal communications system using Hi ghly Elliptical Orbit (HEO) satellites. The forward link uses a synchr onous CDM intrabeam/asynchronous CDM inter-beam approach, while the re turn link uses a quasi-synchronous CDMA intra-beam/asynchronous CDMA i nter-beam approach. Using probabilistic analysis, these approaches are shown to provide higher forward and return link capacities than equiv alently synchronized FDM/FDMA approaches. Forward link transmissions a re modulated using QPSK. Return link transmissions are modulated using either pi/4-QPSK or precompensated frequency modulation (PFM4). PFM4 is intended for use with a saturated amplifier in low-cost/power-effic ient, e.g. hand-held, terminals, and can be demodulated using a pi/4-Q PSK receiver. All forward and return link transmissions are coded usin g a rate 1/2, constraint length 9, convolutional code. The paper summa rizes several key tradeoffs and the resulting system design.