Simulation of Two Bandwidth Efficient Modulation Efforts in Satellite Communications

Abstract

A bandpass limited satellite channel with uplink and downlink noise was simulated for several constant envelope modulation schemes. Minimum shift keying (MSK) significantly outperformed quadriphase shift keying (QPSK) in achieving bit error rates of 0.005 with less than 1 dB degradation for a channel bandwidth to data rate ratio B/R = 0.78, for example. Frequency division multiple access (FDMA) scenarios with unsynchronized satellite signals were also simulated. A processing satellite performed the functions of Doppler and symbol timing correction and demodulation of each uplink. Additional filtering mitigated intersymbol interference (ISI) deliberately introduced for spectral shaping by prolate spheroidal data windows. Even when the received power in each satellite signal was 10 dB above the desired signal, 16 kbps rate-1/2 coded QPSK satellite signals on odd 12.5 kHz centers could coexist with line of sight (LOS) signals on 25 kHz centers. These results are applicable to the ever growing problems deriving from increased spectral occupancy.