THE PERFORMANCE OF 2 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 on ly one sample per symbol period and is suitable for high speed modems which employ discrete-time synchronization methods. Expressions for th e timing detector's mean value and variance, as a function of timing o ffset, are derived and compared to simulation results. The analysis in cludes the effects of decision errors which occur at low signal-to-noi se ratios and eventually limit the useful operating range of the decis ion-directed methods. A modification is described so that the need for prior phase recovery is avoided. These algorithms are compared to a p opular two-sample-per-symbol nondecision-directed timing detector. A m ethod of examining the relative performance of the various algorithms is presented and results are given for a range of signal-to-noise rati os and channel bandwidths.