OFDM in deep water acoustic channels with extremely long delay spread

Deep water horizontal channels usually have very long delay spreads relative to shallow water channels. The delay spread can be several hundreds of milliseconds, which covers several blocks of orthogonal frequency division multiplexing (OFDM) transmissions, leading to severe inter-block-interference (IBI). There are usually two significant well-separated clusters, one from direct paths and the other from surface reflections. Viewing the signals arrived along the two clusters as from two virtual users, we develop a multiuser based OFDM receiver to address IBI, where both channel estimation and data detection algorithms are presented. This receiver can effectively combine signals from multiple senors with different delay spread structures, where each block is decoded in the presence of interference from multiple different blocks. Experimental data from the Atlantic Undersea Test and Evaluation Center (AUTEC) environment are used to validate the performance of the proposed receiver.