Nonbinary LDPC code for noncoherent underwater acoustic communication and its experiment results

Noncoherent underwater acoustic communication channel in adverse condition is modeled as phase-random Rayleigh fading channel. Concatenated code based on nonbinary LDPC code and constant weight code is proposed in noncoherent communication and iteratively decoded in probability domain. Without information of channel amplitude or phase, statistic parameters of signal and noise bins were estimated based on moment estimation method, posterior probabilities of constant weight code-words were further calculated, and nonbinary LDPC code was decoded with nonbinary sum-product algorithm. It is verified by simulation that the proposed concatenated code has a 3 dB SNR benefit than non-iterative concatenated code. Underwater communication experiments were carried out in both deep ocean (vertical communication, 5 km) and shallow lake (horizontal communication, near 3 km, delay spread larger than 50 ms), signal frequency band was 6∼10 kHz, and data transmission rate was 357 bps. It is shown that the proposed scheme can correctly transmit in both experiments with a signal noise ratio of 2 dB. The performance of proposed algorithm was verified by experiment.