State reduction in Viterbi detector using preliminary decisions

This paper presents a technique to reduce the number of states in the trellis of a conventional partial response Viterbi detector (PR-VD) using preliminary decisions. The preliminary decisions are obtained from a lower order PR-VD which are used to shorten the tail of the higher order partial response. Since it does not use decision feedback to shorten the tail of the higher order PR, it does not suffer from error propagation. Theoretical analysis is carried out to show the influence of error events in the preliminary and reduced state Viterbi detectors on the system performance, and to provide possible ways to effectively implement the scheme. Simulation results are provided to bring out certain key features of the approach.