Joint gain and timing recovery with applications to magnetic tape storage

Abstract

We discuss a joint gain and timing recovery scheme that provides performance advantages in tape recording environments plagued by deep amplitude fades and timing error fluctuations. The idea is to find a particular combination of the gain and phase errors that best matches with a window of playback samples and use the resulting estimates to drive the automatic gain control (AGC) loop and the timing recovery loop. The gain and phase estimate pair is obtained and maintained separately for each survivor path in the Viterbi processor, and is used to compensate for the corresponding distortions in the Viterbi branch metric computation. The gain and phase error estimates are then taken out of the best survivor path possibly with some delay and are used to drive the respective loops. The BER performance and cycle slip probabilities are compared with those of a conventional AGC and timing recovery scheme.