Mutual Soft-Information Improvement Techniques for Lower Layer Performance Improvement in Double-Layered Magnetic Recording Systems

Double-layer magnetic recording (DLMR) development aims to increase areal density (AD) by stacking multiple recording layers on the same platter. This has the potential to revolutionize magnetic recording. On the other hand, bit-patterned magnetic recording (BPMR) uses nanoscale bit islands to enhance storage density, reduce transition noise, and maintain thermal stability. This study focuses on combining BPMR and DLMR to further increase AD. Unfortunately, this approach encounters difficulties in separating data from different layers within a single readback signal, which results in poor performance. Retrieving data from the lower layer is additionally complicated by its distance from the reader, leading to degraded bit-error-rate (BER) performance. To address this, we have developed mutual soft-information improvement techniques (MIITs) such as the maximum soft-information (MSI) and sum soft-information (SSI) schemes. These techniques enhance the soft-information output obtained from a soft-output Viterbi algorithm (SOVA) detector. Additionally, we propose three iterative systems that exchange soft information between SOVA and low-density parity-check (LDPC) codes. Our demonstrations show improved BER performance for both upper and lower layers, compared to conventional systems with single-layer media at the same AD of $4~\text {Tb/in}^{2}$ .