M-DPSK receiver for Doppler-shift mobile communications

Differential detection of phase-shift keying signals entails the ability to establish a phase reference based on previous symbol(s). In communications strongly affected by the Doppler effect, like those involving non-geostationary satellites, the carrier phase drift within the symbol interval may be significant; thus, a better strategy than averaging the phase over previous symbols is to continuously estimate it along the corresponding interval. We propose a receiver for M-DPSK signals in channels affected by fast fading and Doppler frequency shift. A bank of stochastic nonlinear filters estimates the carrier phase drift and the fading vector, which are modeled as stochastic processes within the symbol interval; a key algorithm driven by the filters' outputs estimates the carrier offset frequency, which is considered a constant parameter in each estimation interval (corresponding to at least two-symbol intervals). Simulations with 4-DPSK show that the receiver performs much better than conventional differential phase detectors; it exhibits short convergence times, being able to cope with large Doppler frequency shifts.