Investigation of Synchronization Parameters in a Digital Subscriber Loop Transmission System

The degree of echo reduction achieved in a digital subscriber loop (DSL) transceiver employing adaptive echo cancellation has previously been shown to be very sensitive to timing jitter. This paper reports the experimental study, by computer simulation, of a 144 kbit/s DSL timing recovery system incorporating a prefilter, nonlinearity, and second-order phase-locked loop. The simulations were carried out for a wide variety of line lengths, bridged-tap conditions, loop and filter parameters, and choice of nonlinearity. The results showed that a properly designed timing recovery system with a 20 khzwide prefilter allows satisfactory echo reduction performance, even for long loops with bridged taps. For shorter loops the achievable echo reduction is less, but is still sufficient to yield satisfactory performance.