A high capacity third-generation mobile satellite system design

This paper describes a CDM/CDMA based approach for a 3-rd generation multi-beam satellite mobile and personal communications system using Highly Elliptical Orbit (HEO) satellites. The forward link uses a synchronous CDM intra-beam/asynchronous CDM inter-beam approach, while the return link uses a quasi-synchronous CDMA intra-beam/asynchronous CDMA inter-beam approach. Using probabilistic analysis, these approaches are shown to provide higher forward and return link capacities than equivalently synchronized FDM/FDMA approaches. Forward link transmissions are modulated using QPSK. Return link transmissions are modulated using either ϕ/4-QPSK or precompensated frequency modulation (PFM4). PFM4 is intended for use with a saturated amplifier in low-cost/power-efficient, e.g. hand-held, terminals, and can be demodulated using a ϕ/4-QPSK receiver. All forward and return link transmissions are coded using a rate 1/2, constraint length 9, convolutional code. The paper summarizes several key tradeoffs and the resulting system design.