Many promising recording technologies have been introduced for hard disk drives to increase an areal density (AD), this paper considers the bit-patterned magnetic recording (BPMR) technology because it can achieve AD beyond 4 Tb/in² 1. To increase an AD in BPMR, which unavoidably leads to a problem of two-dimensional (2D) interference. To combat this difficulty, several techniques have been proposed based on modulation codes 2 and iterative processing 3. Additionally, the BPMR system performance can be further enhanced by the proper island placement 4.
In this paper, we propose to optimize the bit-length (T_x) and track pitch (T_z) of BPMR under a single reader/two-track reading (SRTR) technique, which leads to getting greatly improved BER performance. Here, we arrange the island in a staggered pattern. The single reader was then employed to read both desired data tracks simultaneously. The signal waveforms from the upper and lower tracks, and the readback signal, that correspond to the data bits stored in the staggered medium through our proposed system are illustrated in Fig. 1. Here, we then investigate five cases under an iterative partial response maximum likelihood (PRML) system as follows: Case 1: T_x = 13.0 nm and T_z = 16.2 nm, Case 2: T_x = 14.0 nm and T_z = 15.0 nm, Case 3: T_x = 14.5 nm and T_z = 14.5 nm, Case 4: T_x = 15.0 nm and T_z = 14.0 nm, and Case 5: T_x = 16.2 nm and T_z = 13.0 nm, to obtain AD of 3 Tb/in². Its data samples that were obtained from the over-sampling technique will then be processed through iterative PRML detection.
Simulation results indicate that a system that has a larger bit-length distance, T_x, (Case 5) can provide the highest system performance when compared to other cases as shown in Fig. 2. In addition, the proposed system that encountered media noise still provides the highest system performance. It means that choosing proper T_x and T_z spacing can increase the efficiency of the staggered SRTR BPMR system.
References
1 M. Mehrmohammadi et al., IOPscience, pp. 1-8 (2010)
2 C. Warisarn, A. Arrayangkool, and P. Kovintavewat, IEICE Trans. Electronics, vol. E98-C, pp. 528-533 (2015)
3 M. Tuchler, R. Koetter, and A. C. Singer, IEEE Trans. Commun., vol. 50, pp. 754-767 (2002)
4 S. Jeong, J. Kim, and J. Lee, Trans. Magn. vol. 54, pp. 1-4 (2018)

Fig. 1. Position of a single reader between two desired tracks over the staggered island pattern and its readback signal.

Fig. 2. BER performances of different cases of SRTR BPMR system (a) without and (b) with 5% media noises.