Performance of LDPC Coded MC-MFSK in Shallow Water Acoustic Channel

In shallow water channels, incoherent MFSK demonstrates significant performance advantages over coherent modulation due to its anti-multipath properties. However, there is limited research on MFSK coding in shallow water multipath environments, with few studies conducted in real-world scenarios. Therefore, this paper proposes a communication system scheme that integrates low code rate LDPC coding with multicarrier MFSK (MC-MFSK). Addressing the mismatch of the existing LDPC standard code rate with the hydroacoustic harsh environment, a rapid method for generating low code rate LDPC codes through base matrix expansion is proposed. Additionally, the article derives an expression for the initialization logarithmic likelihood ratio for MFSK over AWGN channels. Simulation results demonstrate that the performance of the low-bitrate LDPC code surpasses that of convolutional codes and Hadamard-Convolution joint codes. The reliability of the proposed communication scheme is further verified through a shallow sea experiment conducted in Wuyuan Bay, Xiamen, China.