Iterative symbol-level detection and decoding for nonbinary LDPC coded 2D intersymbol interference channels

In this paper, we propose an iterative symbol-level detection and decoding scheme for nonbinary low-density parity-check (LDPC) coded generalized two-dimensional (2D) intersymbol interference (ISI) channels. The proposed 2D channel detector consists of two constituent detectors that work iteratively to mitigate downtrack and crosstrack interference. The downtrack detector is based on the nonbinary BCJR algorithm; while the crosstrack detector performs the sum-product algorithm (SPA) over a cycle-free symbol-level factor graph of the crosstrack channel, which can be directly concatenated to the nonbinary LDPC code graph without resorting to bit/symbol log-likelihood ratio (LLR) conversions. Simulation results show that the proposed symbol-level receiver outperforms bit-level schemes and also enables nonbinary LDPC codes to achieve a noticeable performance gain over binary codes when transmitted over severely ISI-distorted 2D channels.