Soft-Decision Feedback Turbo Equalization for LDPC-Coded MIMO Underwater Acoustic Communications

In this paper, a low-complexity turbo-detection scheme is proposed for single-carrier multiple-input-multiple-output (MIMO) underwater acoustic (UWA) communication systems that employ low-density parity-check (LDPC) channel coding. The proposed iterative soft-decision feedback equalization (SDFE) algorithm offers a novel approach to combat error propagation by utilizing the past soft decisions to mitigate intersymbol interference. In addition, we utilize an iterative data detection and channel estimation scheme to reduce the pilot overhead used in the data communication system. Performance of the proposed detection scheme is demonstrated through extensive communication data from two undersea experiments. The results show that the proposed SDFE algorithm provides robust detection for MIMO UWA communications with different modulations and different symbol rates, at different transmission ranges.