Joint equalization and decoding scheme for underwater acoustic communications using spinal code

InterSymbol Interference (ISI) cancellation over UnderWater Acoustic (UWA) channel can be performed efficiently using iterative joint equalization and decoding scheme which is also called Turbo equalization. However, the limitation of interleaver length would lead a performance loss of Turbo equalization, thus limit the performance of Turbo equalization using short block length. What's more, the iterative structure of Turbo equalization needs a high Signal-Noise-Ratio (SNR) threshold, which may also yield dramatic performance loss. We propose a joint equalization and decoding scheme to overcome these problems. Firstly, it uses a noniterative maximum likelihood joint equalization and decoding scheme to avoid the high SNR threshold. Secondly, the Spinal code with powerful ability of message-mixing is used to improve the performance under short block length. Thirdly, a linear time complexity joint equalization and decoding fast algorithm achieved. This benefit from the property of Spinal code, which increases the Hamming distance between similar source sequences. In the experiment over Fuxian Lake, the bit error rate of proposed scheme is lower than the Turbo equalization by two orders of magnitude, achieving the 3.34 kbps communication similarly. The results of time-varying UWA channel simulations and lake experiment show that, the proposed scheme outperforms Turboequalization with the same code block length. To achieve the same bit error rate,the minimum SNR needed by proposed scheme is lower than Turbo equalization.