Improved BER Performance With Rotated Head Array and 2-D Detector in Two-Dimensional Magnetic Recording

Abstract

Two-dimensional magnetic recording is a promising candidate to further extend the areal density above 1 Tb/in2 density while using a conventional writer and media. During the writing process, a shingled writer is usually used to write narrow tracks by overlapping previous tracks, which brings severe intertrack interference (ITI), fewer grains per channel bit and corresponding lower signal-to-noise ratio (SNR). As a consequence, for the current shingled magnetic recording system, a normally oriented head array (NHA) is usually implemented to detect a single track by using 2-D signal processing to mitigate the ITI and media noise. Then, a rotated head array (RHA) has been found to effectively avoid the ITI and regain the lost down-track resolution using signal processing. Correspondingly, in this paper, the RHA is investigated to simultaneously detect three tracks with 1-D and joint pattern-dependent noise-predictive (PDNP) Bahl–Cocke–Jelinek–Raviv (BCJR) detectors. Simulation indicates that, for the perfect writing at the 6 nm Voronoi grains, if the 1-D PDNP BCJR detector is implemented, the RHA combined with a designed 2-D equalizer producing multiple equalized waveforms can provide 16% density gains compared with the NHA with a 2-D equalizer and 1-D target at the target bit error rate (BER) of $10 ^{\mathrm {-2}}$ . If the joint PDNP BCJR detector is implemented, the RHA can provide 25% density gain compared with that for the NHA with the same detection algorithm at the target BER of $10 ^{\mathrm {-2}}$ . With respect to error correction, a longer codeword length of binary low density parity check code can be used for decoding of the multi-track detection compared with that for the single-track detection, which provides an extra SNR gain.