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

IEEE Transactions on Magnetics has published an article written by Anawin Khametong, College of Advanced Manufacturing Innovation, King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok -, Thailand, Simon John Greaves, Research Institute of Electrical Communication (RIEC), Tohoku University, Sendai, Japan, and Chanon Warisarn, College of Advanced Manufacturing Innovation, King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok, Thailand.

Abstract: “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 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 Terabits per square inch.“