The performance of two symbol timing recovery algorithms for PSK demodulators

A statistical analysis of a decision-directed symbol timing algorithm for phase shift keyed modems is presented. The timing detector uses only one sample per symbol period and is suitable for high speed modems which employ discrete-time synchronization methods. Expressions for the timing detector’s mean value and variance, as a function of timing offset, are derived and compared to simulation results. The analysis includes the effects of decision errors which occur at low signal-to-noise ratios and eventually limit the useful operating range of the decisiondirected methods. A modification is described so that the need for prior phase recovery is avoided. These algorithms are compared to a popular two-sample-per-symbol nondecision-directed timing detector. A method of examining the relative performance of the various algorithms is presented and results are given for a range of signal-to-noise ratios and channel bandwidths.