Low-Complexity Turbo Equalization for MIMO Underwater Acoustic Communications

Underwater acoustic communication (UAC) suffers from inter-symbol interference (ISI) due to multipath propagation, multiple-input-multiple-output (MIMO) UAC also suffers from co-channel interference (CCI) among data streams transmitted by different antennas. In this paper, we propose a low-complexity turbo equalization (LCTEQ) scheme for MIMO UAC. Turbo equalization in MIMO systems is applied to combat both inter-symbol interference (ISI) and CCI. The proposed MIMO LCTEQ structure includes a time reverse mirror (TRM), a decision feedback equalizer (DFE) and a SISO mapper/demapper, from the point of view of reducing the number of filters and the length of filters, we embed the time reverse mirror (TRM) technology into the LCTEQ scheme. In a N×M MIMO system, only N filters are needed instead of N×M filters, the residual ISI length is greatly shortened by using the focusing effect of the TRM, so the computational complexity of the TEQ is greatly reduced. The performance of the MIMO LCTEQ has been verified through the undersea experimental in 2019.