Symbol-rate timing recovery comprising the optimum signal-to-noise ratio in a digital subscriber loop

Abstract

The paper investigates a symbol-rate timing recovery algorithm that is based on the correlation between an error from the decision feedback equalizer and the arriving signal samples. The mean-square error due to uncancelled precursor intersymbol interference is applied as a criterion to choose optimal timing instants. Various signal and error combinations may be used to approximate its minimum as a function of the steady-state location of the sampling instants. The timing function is selected on the premise that the estimated correlation function passes through zero only once, at the desired sampling phase. We propose a semianalytical framework for analyzing the relationship among the timing estimate variance, the acceptable noise level, and the dead-zone thresholds. It allows us to achieve a compromise between, on the one hand, the ability to track and compensate for frequency drift and for changes in the transmission media, and on the other hand, immunity against unnecessary phase corrections. The performance of the postulated timing function is examined by means of simulations.