Multitrack Detection With Two-Dimensional Hybrid Equalizer for High-Density Bit-Patterned Media Recording

Abstract

Bit-patterned media recording (BPMR) is one of the most promising candidates to further increase recording density beyond 1 Tb/in2. For high-density BPMR systems, severe intertrack interference (ITI) and media noise caused by decreased track pitch bring severe deterioration to the readback signals. To mitigate the impact of ITI and media noise on bit error rate (BER) performance, we developed a multitrack detection scheme with a two-dimensional (2-D) hybrid equalizer, which utilizes 2-D distinct equalizer coefficients corresponding to the different estimated ITI patterns. By analyzing the probability density distribution of the log likelihood ratio (LLR) output by the decoder, a LLR threshold is implemented to evaluate the reliability of estimated ITI patterns. Then, the 2-D variable equalizer trained with different ITI patterns is implemented for the reliably estimated ITI patterns; otherwise a 2-D fixed equalizer trained with a pseudorandom bit sequence is utilized. Hence, compared to the conventional 2-D fixed equalizer, the 2-D hybrid equalizer decreases the mean squared error of equalization with reduced error propagation risk. The simulation results indicate that the 2-D hybrid equalizer provides increased signal-to-noise ratio gains compared to the 2-D fixed equalizer when the media noise and track misregistration become more severe.