Unbalanced Track Pitch Combined with 2D Modulation Code in TDMR Systems.

Abstract

Two-dimensional magnetic recording (TDMR) [1, 2] is a promising high density storage technology, which is expected to increase an areal density (AD) up to 10 terabit per square inch (Tbpsi). This technology is required write narrow-read wide technique that opposite to write wide-read narrow of one-dimensional (1D) read channel. The narrow track writing operated by shingled writing can greatly improve track per inch (TPI) gain. However, the side reading effect of reader is an unwanted situation because the intertrack interference (ITI) from sidetracks, which degrades the overall system bit error rate (BER) performance. Therefore, we introduce the methods to overcome this severe ITI effect. For instance, the two-dimensional (2D) modulation code that designed based on cross-track data dependent readback. The data pattern such as [1 −1 1]T and [−1 1 −1]T are forbidden to record onto medium. The rate-5/6 2D modulation code will map the 5 user bits into a 6-bits codeword, which are not contained any forbidden patterns. Furthermore, since the recoded bit is protected from severe ITI effect using modulation code, the middle track can provide a very high reliability. Therefore, we present ITI subtraction to improve upper and lower track performance using data from middle track. Moreover, we also propose an unbalanced track pitch technique, which the middle track can be narrower than upper and lower tracks. The utilization from the high reliability of middle track can improve BER performances both of upper and lower tracks. The reason because the ITI effect that interfere from their sidetracks is reduced by using the properly wider track pitch.