Underwater Decode-Interleave-Forward Cooperative Strategy for Underwater Acoustic Communication

To overcome the problem caused by the large propagation delays of underwater acoustic channel, an asynchronous underwater decode-interleave-forward (UDIF) cooperative strategy is considered for the underwater acoustic cooperative communication system. The UDIF strategy is designed to realize the cooperative transmission and to decrease the end-to-end delay. Aiming at the strategy, a joint multi-branch combining and turbo equalization detector is proposed. To compensate the channel effects and achieve the diversity gain, the turbo equalization, multiuser detection, and combining technique are jointly realized. In the implementation of the detector, the detector is iteratively adapted by switching soft information according to log-likelihood ratio estimates with the turbo processing stage. Moreover, at each iteration, the combining coefficients for the received signals from the source and relay nodes are updated based on the steady-state mean square error, and thus, the proposed detector can effectively combine the received signals without the assumption that full and perfect channel state information of all the links at the receiver is known. The simulation results validate the feasibility and show the advantages of the proposed detector against existing counterparts.