Abstract

Constant-envelope Quadrature Pulse-Overlapping Modulated (QPOM) signals have good spectral properties suitable to applications using nonlinear or saturated power amplifiers. In this thesis we present a Maximum Likelihood Sequence Estimation (MLSE) receiver structure for QPOM signals and analyze its performance in both Additive White Gaussian Noise (AWGN) and fading channels. The quadrature pulse-overlapping modulator is first decomposed into a linear encoder followed by a memoryless modulator. The trellis diagram representing this inherent non-redundant 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. Performance of the introduced scheme in fast fading, shadowed mobile satellite channels is also studied. Results show that this scheme outperforms conventional QPSK techniques in fading channels. While maintaining a low constellation density of 4PSK, its performance is comparable to those of 4-state 8PSK Trellis Coded Modulation (TCM) schemes. The performance of QPOM signals over fading channels can be further improved using some extra redundancy. Based on the new representation of the QPOM scheme, an external convolutional code is combined with the QPOM memory and considered as one entity to be optimized. This optimization is achieved by maximizing the minimum length of the shortest error event path through the trellis diagram of the equivalent code as well as the product of the squared branch distances along that error event path. The obtained structure is then applied to M-ary QPOM signals. The constant envelope, compact spectrum, superior performance, and low complexity make the QPOM scheme a good choice for portable/mobile satellite communications to achieve the requirements of low cost, small size, and high power and bandwidth efficiencies