Symbol timing recovery in digital subscribers loops in the presence of residual echo and crosstalk

A general analysis is presented for the jitter performance of a common symbol timing recovery (STR) system used in a digital subscriber loop (DSL) transceiver that uses adaptive echo cancellation for high-speed digital communications. Exact analytical expressions for the mean and variance of the timing wave and for the RMS phase jitter are derived as a function of the bandwidth of the postfilter for a given set of input parameters representing a particular digital subscriber loop and its noise environment, including such effects as residual echo and crosstalk. Numerical results show that the presence of these disturbing signals can substantially degrade the STR performance. The effect of the excess bandwidth factor of the prefilter on this degradation is investigated.>