An advanced M2DFE detector for high-density magnetic recording channels

In high-density magnetic recording, multilevel DFE (MDFE) detectors are gaining importance because of their structural simplicity over PRML detectors. The MDFE detectors are developed for run-length-limited (RLL)(1,k) coded channels. At user densities below 2.0, bit-error-rate (BER) performance of M2DFE (an advanced version of the MDFE) is close to the maximum likelihood bound (MLB) for a Lorentzian channel. At higher user densities (2.5 and above), the performance degradation is severe and the BERs are farther away from the MLB. In this paper, we first propose an advanced version of the M2DFE detector, called an M3DFE, which improves the performance at higher user densities significantly. To achieve the improvement, the detector exploits the error events that violate the RLL code constraint at the slicer output, noise correlation and uncanceled inter-symbol-interference (ISI) at the slicer input. Later, we compare the performances of MDFE, M2DFE and M2DFE detectors at user densities in the range of 2.5 to 3.5 for a Lorentzian channel using bit-by-bit simulations