ML-oriented NDA symbol synchronizers for time-varying nonselective fading channels

The tracking performances of two maximum-likelihood (ML) non-decision-aided (NDA) symbol synchronization algorithms, operating on a very noisy M-ary phase-shift-keying (M-PSK) signal transmitted over a time-varying nonselective Rician fading channel, are investigated. The first algorithm is non-channel-aided (NCA): timing is acquired independently of the channel gain estimation. The second algorithm is channel-aided (CA): it makes use of (an estimate of) the instantaneous channel gain; as the channel gain estimator requires timing information, use of the CA algorithm implies that the timing and the channel gain must be acquired jointly. Both algorithms are suitable for fully digital implementation, and have a similar complexity. For E_s/E₀ values of practical interest, the NCA algorithm performs better than the CA algorithm