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

The authors investigate the tracking performance of two maximum-likelihood (ML) data-aided (DA) symbol synchronization algorithms, operating on a noisy M-ary phase shift keying (M-PSK) signal transmitted over a time-varying nonselective Rician fading channel. The first algorithm is nonchannel-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. Both algorithms need a preamble for the acquisition of either symbol synchronization (NCA algorithm) or both symbol synchronization and channel gain (CA algorithm); after the preamble, a decision-directed mode is entered. The algorithms are suitable for fully digital implementation, and have a similar complexity. For E_s/N₀ values of practical interest, it is shown that the CA algorithm performs better than the NCA algorithm, but the difference in performance decreases with increasing C/M ratio