M-DPSK detection, channel estimation and power control in LEO satellite communications

Differential detection of phase-shift keying signals entails the ability to establish a stable phase reference based on previous symbol(s). In low bit-rate communications strongly affected by Doppler effect, like those making use of non-geostationary satellites, significant carrier phase drifts may occur within the symbol interval; thus, large irreducible error floors result if the Doppler frequency shift (DFS) is not estimated and subtracted. We propose a state-space based receiver for M-DPSK signals in transmissions affected by fast fading and DFS, which evaluates the multiplicative distortion (amplitude and phase) of the baseband signal and uses those estimates to track the frequency offset. In addition, the proposed receiver can estimate the power of the line-of-sight component and the Rician fading parameter K which allow to monitor the transmission quality and control the transmitted power in adaptive systems. Simulations presented for 4-DPSK show that the performance of the new receiver is superior to that of conventional receivers in the presence of large DFS, exhibiting substantially lower error floors.