Block-adaptive decision feedback equalization with integral error correction for underwater acoustic communications

This paper presents recent experimental results for an underwater acoustic communications receiver based on a block-adaptive implementation of a decision feedback equalizer (DFE). Block-encoded QPSK acoustic data was transmitted from a moving UUV to a stationary platform. The receiver algorithm implemented soft decision decoding within the equalizer decision feedback loop in order to intercept decision errors and improve low SNR performance. Block adaptation of the the DFE was achieved with a Block Recursive Least Squares adaptive mechanism coupled with an integral phase tracking loop. A quaternary block code was used in this case to facilitate receiver implementation such that block decoding was done directly on the QPSK data symbols. Results from Narragansett Bay, Rhode Island show approximately 3 dB performance improvement over a non-coded system.