To combat severe intersymbol interference incurred by multipath propagation of sound waves in the underwater acoustic\nenvironment, we introduce an iterative equalization and decoding scheme by iteratively exchanging soft information between a\nlow-density parity check (LDPC) decoder and a decision feedback equalizer.We apply extrinsic information transfer (EXIT) charts\nto analyze performance of LDPC codes over the acoustic multipath channel. Furthermore, using differential evolution technique,\nwe develop an EXIT-aided method to optimize LDPC codes for the underwater acoustic channel. Design examples are presented\nfor two different realizations of the underwater acoustic channel that are generated by an acoustic ray tracing model. Computer\nsimulations show that the optimized LDPC codes outperform its regular counterpart or Turbo codes under the same coding rate\nand block length, with gains of 1.0 and 0.8 dB, respectively, at the bit error rate of 10âË?â??5.
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