A high capacity third‐generation mobile satellite system design

Abstract

Abstract. This paper describes a CDWCDMA 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 intrabeadasynchronous CDM inter-beam approach, while the return link uses a quasi-synchronous CDMA intra-beadasynchronous 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 d4-QPSK or precompensated frequency modulation (PFMJ). PFM4 is intended for use with a saturated amplifier in low-cosdpower-efficient. e.g. hand-held, terminals, and can be demodulated using a d4-QPSK receiver. All forward and return link transmissions are coded using a rate constraint length 9, convolutional code. The paper summarizes several key tradeoffs and the resulting system design.

Interference evaluations and simulations for multisatellite multibeam systems

“…Hence, it seems reasonable to use orthogonal polarizations to reduce the interference level rather than for further stressing the frequency reuse. In fact, results reported in Reference [23] show that the isolation ranges from 3 to 5 dB for low elevation angles and for 50% of the time. Thus, to get a conservative evaluation of the interference, polarization orthogonality can be ignored, i.e.…”

“…Methods (E)-(H) are addressed in Reference [23] in case of FDMA access but most of them are suitable for CDMA too. Power control ðEÞ implemented to compensate satellite gain variations within a beam, for both the wanted signal and for the interfering signal, may reduce interference.…”

Analytical computation of the correlation of spreading sequences for nonlinear OQPSK‐type modulations

“…These modulations can be denoted as OQPSK‐type (offset quadrature phase‐shift keying) modulations because they can be decomposed as a sum of OQPSK components . OQPSK‐type modulations also include other ‘non‐continuous phase modulation’ schemes with almost constant envelope and good tradeoffs between spectral and power efficiencies . OQPSK‐type schemes are particularly important in the context of nonlinear amplification because an OQPSK‐type signal retains its OQPSK‐type structure when submitted to bandpass memoryless nonlinear devices, the usual model for power amplifiers , which simplifies the performance evaluation and receiver design .…”