Study of Fractionally Spaced Equalizers for Bit-Patterned Media Recording

Bit-patterned media recording (BPMR) is a promising technology to enhance the areal density (AD) of hard disk drives beyond the limit imposed by the current perpendicular recording technology. Practically, a T-spaced equalizer is employed in a conventional (symbol-rate) BPMR system to shape the overall channel response to a target response before performing the data-detection process, where T is a bit period. Because the BPMR channel response has a large excess bandwidth, we propose to use a fractionally spaced equalizer (FSE) in the oversampled BPMR system so as to improve the system performance. A design of the FSE and its corresponding 1-D and 2-D targets is given. Thus, we compare the performance of the oversampled BPMR system with the symbol-rate one. Results indicate that the oversampled system performs better than the symbol-rate one in terms of bit-error rate (BER). Specifically, at BER = 10^-4 and no media noise, the oversampled system can provide ~1 dB gain at the ADs of 2 and 2.5 Tb/in² over the symbol-rate system. In addition, we found that the oversampled system is more robust to media noise than the symbol-rate one.