RA coding joint adaptive equalization for underwater acoustic communications

Underwater acoustic (UWA) communication channels that vary from stationary with sparse arrivals to rapidly varying and fully reverberant present fading, multipath and refractive properties, greatly impede UWA data transmissions. In order to solve this problem, a receiver with the iterative soft-input/soft-output equalization and decoding that employs Repeat-Accumulate (RA) coding joint adaptive decision feedback equalizer (DFE) is proposed. By using computer simulations, a 5-path UWA channel model is built to establish the UWA communication system model with the proposed receiver structure. The error correction capability of RA codes is discussed and how the parameter affects on the performance of the adaptive DFE with LMS algorithm is analyzed. Simulation results show that the UWA communication system with the proposed channel coding scheme can get about 6 dB coding gain comparing with that without channel coding, and the DFE with proper parameters can overcome the effects of the ISI and channel fading, lower the overall bit error ratio (BER). Furthermore, due to the receiver structure which performs in RA decoder with 10 iterations and in adaptive DFE with proper parameters, the reliability of the system can get significant improvement, demonstrating that the iterative soft-input/soft-output equalization and decoding which employs RA coding combined with the adaptive DFE, with algorithmic simplicity, will have good prospect in UWA communications.