Direct-adaption based bidirectional turbo equalization for multiple-input multiple-output underwater acoustic communications

A direct-adaption based bidirectional turbo equalizer (DA-BTEQ) is proposed for multiple-input multiple output (MIMO) underwater acoustic (UWA) communications. Abandoning the traditional channel estimation process, the proposed DA-BTEQ works in a direct-adaption mode and is implemented with bidirectional soft-decision feedback equalizer (SDFE) to suppress error propagation. The diversity gain is exploited by combining the outputs of the bidirectional SDFE with an equal-gain combining scheme. The comparison between the DA-BTEQ and channel-estimation based bidirectional turbo equalizer (CE-BTEQ) is conducted through simulations. The superiority of the proposed method over the conventional method is also verified in terms of bit error rate (BER) performance and extrinsic information transfer (EXIT) charts.