Novel Soft-Feedback Equalization Method for Multilevel Magnetic Recording

This paper investigates the use of multilevel modulation for magnetic recording using a novel soft-feedback equalization (SFE) approach. Different aspects of investigation are 1)multilevel recording, 2) SFE, and 3) application of turbo codes. The SFE scheme is a model in which the partial response (PR) equalizer and maximum a posteriori (MAP) decoder are replaced by a linear filter with an iterative MAP decoder. Error correction codes (ECCs) are applied to the multilevel recording system in order to achieve very low error rates. Implementation of the SFE scheme for multilevel recording shows a reduction in complexity in comparison to various PRML schemes. The simulation results show a clear performance gain of multi-level-coded against binary-coded recording systems. At higher signal-to-noise ratio (SNR), the coded multilevel SFE scheme overcomes the error floor effect produced in the coded multilevel PRML scheme, which is caused by minimum distance error events. Overall, this paper proposes the use of coded multilevel recording with SFE scheme at lower rates rather than coded binary recording at higher densities in order to achieve similar performance