Abstract:The blind adaptive decision feedback equalizer (BADFE) is more useful than the decision feedback equalizer (DFE) in underwater acoustic (UWA) communications. However, in severe time-varying UWA channels, the BADFE has problems in mean-square error convergence as well as in switching between the starting mode and the tracking mode, and its function is degraded. Soft decision approaches for the BADFE are investigated. The modified equalizer, called SD-BADFE, has better performance than that of ordinary DFE and BADFE. Simulation results show that the SD-BADFE has good convergence rate and low bit error rate even in the severe transmission environments.