Defect Detection and Burst Erasure Correction for TDMR

Abstract

Media defects are common in magnetic recording, resulting in the bursts of erasures. The use of error correcting codes can be aided by a defect detector for indicating the location of erasures. In this paper, we propose a model to study 2-D media defects that can occur in 2-D magnetic recording (TDMR). We also propose a novel defect identification and detection algorithm to identify the location of defects by the magnitude thresholding of the readback samples and identifying defective data patterns at the output of a 2-D signal detector. The defect detector identifies a 2-D edge-connected region of defects for burst erasure correction. Using simulations, we show that the defect detector can be designed to identify the location of 2-D defects with >90% accuracy for deep defects. The effect of the defect detector in TDMR is studied over a Voronoi-based media model where low density parity check (LDPC) codes are used for error correction. The defect detector is observed to achieve >2 dB gain in signal-to-noise ratio (SNR) for a $38\times 38$ burst erasure. We also study simple interleaving schemes for LDPC codes that give a further gain of >0.3 dB in SNR and can correct $76\times 76$ and larger burst erasures.