A frequency domain adaptive coded decision feedback equalizer for a broadband UWA COFDM system

A novel modulation scheme for UWA (underwater acoustic) communications is presented which uses coherent pseudorandom-phase carrier COFDM modulation. A feature of the system is the use of a new form of frequency domain equalizer that is specifically designed for the parallel structure of the COFDM system. The equalization algorithm is based upon the least-squares auto-regressive model and the singular value decomposition algorithm for the estimation of a minimum mean-square-error channel transfer function. In order to allow adaptive signal equalization, a coded decision feedback receiver system configuration has also been developed. By virtue of the frequency domain equalization and maximum-likelihood Viterbi decoding, the system is shown to have high stability, capable of operating under multipath/Doppler channels at low SNRs.