Doppler shift robust receiver for digital parallel signaling in fading channels

This paper proposes a new scheme suited to parallel (simultaneous) transmission of phase-modulated waveforms in fading multipath channels. The waveforms are quasi-orthogonal in the symbol interval and have good correlation characteristics making detection quite insensitive to large delay spreads. Besides, the spectral efficiency of the modulation increases with the number of simultaneous signals. A pilot signal is jointly transmitted conveying information about the carrier phase and the symbol timing. Coherent detection is accomplished by a bank of correlators driven by a stochastic nonlinear filter that estimates the phase of the pilot carrier and derives the symbol epochs from those estimates. Simulations show that the proposed open-loop digital receiver is robust to fast fading and large phase drifts caused by Doppler effect and/or oscillators instabilities.