Abstract
The increased track density in bit patterned media recording (BPMR) causes increased inter-track interference (ITI), which degrades the bit error rate (BER) performance. In order to mitigate the effect of the ITI, signals from multiple tracks can be equalized by a 2D equalizer with 1D target. Usually, the 2D fixed equalizer coefficients are obtained by using a pseudo-random bit sequence (PRBS) for training. In this study, a 2D variable equalizer is proposed, where various sets of 2D equalizer coefficients are predetermined and stored for different ITI patterns besides the usual PRBS training. For data detection, as the ITI patterns are unknown in the first global iteration, the main and adjacent tracks are equalized with the conventional 2D fixed equalizer, detected with Bahl-Cocke-Jelinek-Raviv (BCJR) detector and decoded with low-density parity-check (LDPC) decoder. Then using the estimated bit information from main and adjacent tracks, the ITI pattern for each island of the main track can be estimated and the corresponding 2D variable equalizers are used to better equalize the bits on the main track. This process is executed iteratively by feeding back the main track information. Simulation results indicate that for both single-track and two-track detection, the proposed 2D variable equalizer can achieve better BER and frame error rate (FER) compared to that with the 2D fixed equalizer.
Highlights
Bit patterned media recording (BPMR)[1] is a promising candidate to further increase the user density above 1 Tb/in[2]
As the inter-track interference (ITI) pattern is unknown in the first global iteration, the signals from the main track and the adjacent tracks are first equalized with a conventional 2D fixed equalizer, detected with BCJR detector and decoded with low-density paritycheck (LDPC) decoder
It is found that the mean squared error (MSE) of equalization for the variable equalizer coefficients trained with different ITI patterns is over 50% smaller than that trained with pseudo-random bit sequence (PRBS)
Summary
Bit patterned media recording (BPMR)[1] is a promising candidate to further increase the user density above 1 Tb/in[2]. Using the estimated bit information from those tracks, we can estimate the ITI patterns and use the corresponding 2D equalizers with different coefficients to better equalize the signals from the main track This process is executed iteratively by feeding back the main track information. We propose and investigate the use of different 2D equalizer coefficients for different estimated ITI patterns during the iterative detection. For continuous media the ITI contributions can take on many more values because the locations of the above-bit and the below-bit are unknown and can vary significantly Because of this limited set of ITI values in BPMR, it is feasible to use our proposed 2D variable equalizer because the 2D equalizer coefficients will be nearly same for the same ITI patterns at different locations.
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