Two-Reader Detection Method for Staggered Dual-Layer Bit-Patterned Magnetic Recording Media

Abstract

Dual-layer recording doubles the effective areal density of bit-patterned magnetic media, but because both layers are sensed by a common reader, interlayer interference (ILI) is the dominant impairment. This paper presents a two-reader detection method for staggered, dual-layer bit-patterned magnetic recording at 4.0 Tb/in2, in which both layers are read in a single pass by oversampling the outputs of each reader at half the bit period. Detection proceeds in two stages. The log-likelihood ratios from a between-track reader and an on-track reader, with the latter equalized by a fractionally spaced equalizer (FSE), are first combined by a sum soft-information technique to recover the bottom layer. The enhanced soft information then reconstructs and cancels the ILI that corrupts the top layer, where a convolutional neural network (CNN) predicts the residual interference left by a fixed-weight reconstruction. The FSE lowers the bottom-layer bit-error rate (BER) by more than an order of magnitude, combining soft-information gains of about 2 dB SNR at the same BER, and the CNN cancellation adds a further 2 dB. Under 10% media noise, a fixed-weight canceller develops an error floor, whereas the CNN does not, without retraining. This gives the bottom layer larger islands than the top layer, lowering the overall BER from 7.5 × 10−7 to below 10−7 at 18 dB SNR.