Fast symbol timing recovery techniques for flexible PAM and QAM modems

A fast symbol timing recovery (STR) scheme suitable for flexible-symbol-rate, burst-mode M-ary PAM and QAM demodulators used in point-to-multipoint broadband access systems is proposed. The maximum-likelihood (ML) estimation principle is used to derive a feed-forward STR strategy to achieve fast and accurate derivation of the optimum timing instant with a very short training preamble for applications requiring short packet transmission. In addition, the signal sample at the optimum timing instant is reproduced by interpolation. Analysis to derive the ML-based timing estimation algorithm is presented. Analytical models are used to evaluate the performance of the timing estimation and interpolated signal sample in the additive white Gaussian noise (AWGN) environment. Simulation is also used to confirm the analytical results. Examples of sub-optimal interpolators are exploited and compared.