Coded modulation for channels affected by noise, correlated Rice fading, and Doppler frequency shift

Discusses the relative performance of coherent (PSK), differential (DPSK), and double-differential PSK (DDPSK) over a channel in which, in addition to additive noise, a constant carrier phase offset, and a constant Doppler frequency shift, correlated Rice fading affects the transmission. The authors first compare the performance of these systems to assess the amount of degradation caused on each one of them by fading. They observe that DDPSK turns out to be less sensitive to the effects of correlated fading than the other two schemes, and that in these conditions interleaving may not be beneficial. Then they consider the introduction of a trellis-coded modulation (TCM) scheme. The system the authors advocate includes double-differential encoding, differential detection, an open-loop Doppler phase tracking circuit, and differential decoding in addition to an 8-state TCM scheme transparent to phase rotations. Its performance is assessed by simulation, and it is found that it can transmit one bit per waveform over the channel considered with an error performance comparable to that achieved by coherent binary PSK over the AWGN channel.