Combined partial response decision feedback equalization and coding for the Lorentzian channel

This paper considers a combined coding and equalization technique applied to the magnetic recording channel. The optimization of the coded-equalization scheme for this channel requires balancing the coding rate with its associated distance gain and equalization loss. A major concern in a coded-equalization scheme using decision feedback equalization (DFE) is error propagation. A new indicator to measure the effect of error propagation when using soft decision decoding is proposed. For medium to high normalized recording densities (S>1.5), it is shown that error propagation significantly degrades the theoretical performance of a detection scheme which combines a partial response DFE and simple trellis codes. In fact, this combined system performs worse than the uncoded one. The addition of delayed decision feedback sequence estimation (DDFSE) to limit the effect of error propagation is then investigated. With a moderate decoding complexity, positive coding gains have been achieved at such densities when choosing the partial response polynomial according to the derived indicator.