A robust detector based on a combination of PR1 and EEPR4 for perpendicular magnetic recording

This paper describes a robust detector for a perpendicular magnetic recording channel. In this channel, an abrupt level shift of the reproduced signal amplitude due to thermal asperity, and jitter-like noise due to the fluctuation of magnetization transition, tend to be dominant. Partial response class I (PR1) detector and partial response class 4 detector (EEPR4) are combined by using log-likelihood ratios in order to compensate for the susceptibility of the PR1 detector to low-frequency fluctuations. Moreover, a PR1 detector with a four-state trellis structure is adopted in order to reduce the effect of jitter-like noise with the pattern-dependent characteristics. The proposed PR1 detector can improve the signal-to-noise ratio (SNR) of a conventional PR I detector by approximately 2 dB at a bit-error rate 10(-4). The SNR is defined as the ratio of the signal to the jitter-like noise including 20% additive white Gaussian noise. Completely combined detectors (an withstand the DC level shift, whose amplitude is the same as the average amplitude of the reproduced signal.