Detection of amplitude-phase modulated signals over frequency nonselective Rayleigh fading channels with adaptive symbol-aided channel estimation

Narrowband terrestrial mobile communications can be modelled as signalling through frequency nonselective Rayleigh fading channels. Conventional differential detection of both M-ary differential phase shift keying (DPSK) and differential quadrature amplitude modulation (DQAM) signals results in an irreducible bit error floor. This error floor can be greatly reduced or even eliminated if coherent detection is employed through some means of channel estimation. In this paper, a maximum likelihood sequence estimation receiver for DPSK and DQAM is derived heuristically. Adaptive symbol-aided channel estimation that requires no a priori information about either the channel impulse response or the strength of the additive white Gaussian noise is used in reduced complexity receivers. An approximate method to evaluate the bit error performance is given for the simplest receiver, namely, the decision feedback receiver. Error performance is also evaluated by computer simulation for both the decision feedback receiver and the trellis search receivers using the Viterbi algorithm.