Soft-information flipping scheme based on a priori LLRs summation for ultra-high density magnetic recording

Abstract

Inter-track interference (ITI) is the main problem in high areal density (AD) of magnetic recording systems such as bit-patterned magnetic recording (BPMR) technology thus the ITI avoidance scheme is the way to improve the performance of the recording system. Two-dimensional (2D) modulation codes i.e., the rate-5/6 2D modulation code, was proposed to avoid the severe ITI effect which can successfully improve the system performance when it was considered without the codeword border effect. However, when we have to consider the codeword border effect, some upper and lower tracks cannot avoid ITI because both of them still be interfered from their sidetracks. To improve this weakness, a rate-5/6 2D modulation code was combined with the bit-flipping technique based on the normalization criteria of the two-dimensional soft-output Viterbi algorithm (2D-SOVA). Although, the bit-flipping technique can improve the performance of all tracks; however, the gain optimization is difficult to describe the relationship of the soft-information flipping technique. Therefore, this research proposes a novel of soft-information flipping scheme to describe the bit-flipping technique based on a priori log-likelihood ratios of the rate-5/6 encoding constraint in BPMR system. The simulation results clearly indicate that, at the same user density, the proposed system can provide bit-error-rate performance gain over the other recording systems in both of with and without position jitter noise.