An Algorithm of Soft Iterative Channel Estimation for Turbo Equalization of Underwater Acoustic Communication

Turbo equalization is the effective method to overcome multipath fading and eliminate Inter-Symbol Interference (ISI) for underwater acoustic coherent communications. In practice, turbo equalization estimates information of time-varying and multi-path channel. In order to improve the performance of channel and phase estimation, an algorithm of combining soft iterative channel and phase estimation for turbo equalization is proposed based on channel mode of time-varying transversal filter and phase rotation. The algorithm adopts soft iterative fast self-optimized LMS to get transversal filter coefficients vector for every symbol and combing it and second-order phase-locked loop for optimization. Through simulation, the proposed algorithm is better than conventional hard decision channel and phase estimation algorithm. As to performance of phase estimation, the proposed algorithm is better than soft iterative channel estimation raised in other references. During the sea experiment, underwater acoustic communication distance is 5 m, approximately in vertical direction and the fuctuation period of receiver array is 10 s. The algorithm is adopted for single-channel Turbo equalization on sea experiment data, which can output error-free symbols. The result verifies the advantage of all of the algorithms in the soft channel estimation.