François Dolivo

A PRML system for digital magnetic recording

The realization of a digital recording system using partial-response class-IV signaling with maximum-likelihood sequence detection (MLSD) is described. To perform MLSD at the high data rates encountered in recording systems, a simple implementation of the Viterbi detector based on a difference-metric algorithm is developed. Decision-directed schemes for gain control and timing recovery, for tracking variations of the gain and timing phase during data readback, and for fast initial adjustment from a known preamble are presented. The dynamic behavior of the control algorithms was studied by computer simulations. Coding was used to facilitate timing recovery and gain control, to limit the path memory length of the Viterbi detector, and to allow fast and reliable startup of the receiver. The design and properties of rate 8/9 constrained codes are examined. The problem of equalization is addressed, and analog and combined analog/digital filter implementations are developed. A simple adaptive equalizer capable of compensating variations of the recording channel characteristics with track radius and/or head-to-medium distance is described. >

Preamble recognition and synchronization detection in partial-response systems

To achieve fast initial gain and timing-phase adjustment in receivers for communication or storage systems using partial-response signaling, a synchronization preamble preceding user data is transmitted. A method for recognizing that synchronization has been achieved and that the preamble is being received, and for detecting the end of preamble is presented. The method is based on a maximum-likelihood test. Its efficiency is demonstrating by computing the probability of not recognizing the preamble when it is actually received and the probability of falsely recognizing the preamble when in fact user data are received.<<ETX>>