Improved BER performance with rotated head array and 2D detector in two-dimensional magnetic recording

Two-dimensional magnetic recording (TDMR) is a promising candidate to further extend the areal density above 1 Tb/in2 density while using 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 inter-track interference (ITI), fewer grains per channel bit and corresponding lower signal-to-noise ratio (SNR). As a consequence, for the current shingled magnetic recording (SMR) system, a normally oriented head array (NHA) is usually implemented to detect a single track by using 2D 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 study, the RHA is investigated to simultaneously detect three tracks with 1D and joint pattern-dependent noise-predictive (PDNP) Bahl-Cocke-Jelinek-Raviv (BCJR) detectors. Simulation indicates that, for the perfect writing at the 6nm Voronoi grains, if the 1D PDNP BCJR detector is implemented, the RHA combined with a designed 2D equalizer producing multiple equalized waveforms can provide 16% density gains compared to the NHA with a 2D equalizer and 1D target at the target bit error rate (BER) of 10-2. If the joint PDNP BCJR detector is implemented, the RHA can provide 25% density gain compared to that for the NHA with the same detection algorithm at the target BER of 10-2. With respect to error correction, a longer codeword length of binary low density parity check (LDPC) code can be used for decoding of the multi-track detection compared to that for the single track detection, which provides extra SNR gain.