Abstract:

Long-range communications in shallow water faces great challenges of severe multipath interference, fading, and low SNR. The traditional second-order digital phase lock loop (DPLL) embedded decision feedback equalizer can only work at high SNR, serious error propagation may occur at low and moderate SNR. In order to improve reliability of long-range shallow water communications, a low complexity joint iterative equalization and decoding (LC-JIED) scheme is proposed for sparse underwater communication channel. The method compensates for Doppler shifts using an embedded second-order DPLL, and updates the equalizer coefficients by taking into account sparsity of the channel. System performance is greatly improved by iteratively exchanging soft information between the equalizer and decoder. Simulations based on real lake channel profiles show that
the proposed method is effective for sparse underwater channel. It can significantly improve reliability of longrange shallow water acoustic communications by exchanging soft information between equalizer and decoder at low to moderate SNR.

Key words: underwater communication, second-order digital phase lock loopjoint iterative equalization and decoding (JIED), MAP decoding