Nonbinary LDPC Coding for Multicarrier Underwater Acoustic Communications

In this paper, we propose to use nonbinary low density parity check (LDPC) codes to address two main issues in underwater acoustic OFDM communication: i) plain OFDM has poor performance in the presence of channel fading, and ii) OFDM transmission has a high peak-to-average-power ratio (PAPR). We propose new methods to construct nonbinary irregular LDPC codes that achieve excellent performance, match well with the underlying modulation, and can be encoded in linear time and in parallel. Simulation and experimental results confirm the excellent performance of the proposed nonbinary LDPC codes. Based on the property that the generator matrix of LDPC codes has high density, we further show how to reduce the PAPR considerably with minimal overhead.