  We propose a three-track detection system for two dimensional magnetic
recording (TDMR) in which a local area influence probabilistic (LAIP) detector
works with a trellis-based Bahl-Cocke-Jelinek-Raviv (BCJR) detector to remove
intersymbol interference (ISI) and intertrack interference (ITI) among coded
data bits as well as media noise due to magnetic grain-bit interactions. Two
minimum mean-squared error (MMSE) linear equalizers with different response
targets are employed before the LAIP and BCJR detectors. The LAIP detector
considers local grain-bit interactions and passes coded bit log-likelihood
ratios (LLRs) to the channel decoder, whose output LLRs serve as a priori
information to the BCJR detector, which is followed by a second channel
decoding pass. Simulation results under 1-shot decoding on a
grain-flipping-probability (GFP) media model show that the proposed LAIP/BCJR
detection system achieves density gains of 6.8% for center-track detection and
1.2% for three-track detection compared to a standard BCJR/1D-PDNP. The
proposed system's BCJR detector bit error rates (BERs) are lower than those of
a recently proposed two-track BCJR/2D-PDNP system by factors of (0.55, 0.08)
for tracks 1 and 2 respectively.
