Hypothesis feedback equalization for M-ary parallel combinatory communication in deep water

Direct-sequence spread spectrum (DSSS) is a candidate technique for long range acoustic communications (LRAC) in deep water. However, its data rate is quite low. To achieve a higher data rate, M-ary parallel combinatory communication (MPCC) scheme is adopted in this paper. The major obstacle encountered for LRAC is extended multipath propagation, which would cause severe inter-symbol interference (ISI). Many classical techniques, such as decision feedback equalization (DFE) and hypothesis feedback equalization (HFE), cannot be directly applied to MPCC scheme. In order to suppress ISI, we propose a new hypothesis feedback equalization method called MPCC-HFE. This method has a superior performance of ISI suppression at the price of increased computational complexity. To reduce its computational complexity, we present an optimized algorithm. Experimental results demonstrate that the proposed equalization method has a quite low bit error rate (BER) for LRAC in deep water.