Nonbinary LDPC Codes for 4-kB Sectors

The performance of nonbinary LDPC codes on perpendicular magnetic recording channels (PMRCs) with 4-kB sectors is investigated. Each sector is encoded by either 4- or 0.5-kB-long codes. Both quasi-cyclic (QC) and nonquasi-cyclic (non-QC) nonbinary low-density parity-check (LDPC) codes are designed, and a set of simulations in a mixture of 10% additive white Gaussian noise (AWGN) and 90% position jitter noise power, with and without turbo equalization and with a rereading technique, is presented. The results show that sector-long codes perform better than 0.5-kB codes for all decoding schemes considered. In addition, the erasure correction capabilities of these nonbinary LDPC codes are calculated under both maximum-likelihood decoding and iterative decoding, and, as expected, longer codes can correct longer erasures. QC and non-QC nonbinary LDPC codes exhibit similar performance and have almost the same erasure correction capability under iterative decoding. Because of their efficient encoding, QC nonbinary LDPC codes are a good choice for perpendicular recording channels with 4-kB sectors, and offer a tradeoff between performance and code length.