TIMING JITTER EFFECTS ON DIGITAL SUBSCRIBER LOOP ECHO CANCELLERS:CONSIDERATIONS FOR SOUARING LOOP TIMING RECOVERY

摘要

The performance of an adaptive echo canceller at the loop-timed subscriber end of a diqital subscriber loop has been shown to be sensitive to jitter arising from the timing recovery subsystem.We evaluate this degradation for the common timing recovery subsystem consisting of a prefilter,squarer,and a second-order phase-locked loop.The evaluation shows the influence of equalization,prefilter shade and phase-locked loop parameters.A narrow-band accurately-tuned prefilter,line equalizer,and a narrow-band phase-locked loop are found to be necessary for adequate performance in a 144 kbps bipolar-coded digital subscriber loop system employing echo cancellation.