LDPC Coded DQPSK Modulation with Iterative Detection Method for Underwater Acoustic Communications

Aimed at the conventional serial communication system fails when the channel was frequency-selec- tive, long delay and multi-paths effect, resulting in inter-symbol-interference （ISI） , an iterative system for un- derwater acoustic communication （ UWAC ） was proposed, which employed iterative differential detection and spread spectrum technique. The proposed scheme adopts 7r/4-DQPSK soft demodulation to overcome the diffi- culty of phase ambiguity. For suppression of ISI in UWAC, joint demodulation and decoding iteration was used. The communication scheme has the characteristic of long communication range at low SNR, and the maximum range is up to 100 km. The theoretic analysis and simulation results show that the proposed scheme outperforms traditional serial one. When SNR is -6 dB, after four joint iterations, compared with serial scheme, BER can deereaa from 10-2 In 10-5.