Maximum likelihood sequence estimation of quadrature pulse-overlapping modulated signals for portable/mobile satellite communications

A maximum-likelihood sequence estimation (MLSE) receiver structure for constant-envelope quadrature pulse-overlapping modulated (QPOM) signals in fading channels is presented. QPOM is first decomposed into a liner encoder followed by a memoryless modulator. The trellis diagram representing this inherent nonredundant coding structure is then used to construct its MLSE receiver. The upper bounds on the average bit error probability in both AWGN and Rayleigh fading channels are derived. Computer simulations are also used to verify the analytical results. In fast-fading shadowed mobile satellite channels the scheme is shown to outperform conventional QPSK techniques. It maintains the low complexity of 4PSK, but its performance is comparable to that of four-state 8PSK TCM schemes. The constant envelope, compact spectrum, superior performance, and low complexity enable QPOM to meet the requirements of low cost, small size, and high power and bandwidth efficiencies for portable/mobile satellite systems