A Comparison of Two Types of Symbol Synchronizers for Which Self-Noise Is Absent

For most symbol synchronizers operating on a PAM waveform corrupted by noise, the timing error consists of a noisedependent term and a data-dependent term. When the signal-to-noise ratio (SNR) is high, the data-dependent term, which is often called self-noise, dominates, and the timing error variance becomes independent of SNR. In this paper we present two types of symbol synchronizers for which self-noise is absent: the modified maximum-likelihood (MML) synchronizer and the minimum mean-square error (MMSE) synchronizer. As a consequence of the absence of self-noise, their timing error variances at high SNR are inversely proportional to the SNR. The performances of these synchronizers are evaluated and compared with the Cramér-Rao bound.