Improving multicode spread spectrum underwater communication with PIC-HFE algorithm

Multicode spread spectrum underwater communication is rather complicated. To our best knowledge, the still unsolved major problems are time-variability, ISI (inter-symbol interference) and ICI (inter-channel interference). We now present PIC-HFE (parallel interference cancellation hypothesis feedback equalization) algorithm to reduce to a minimum the degradation of performance of multicode spread spectrum underwater communication due to time-variability, ISI and ICI. In the paper, we explain in detail how to reduce such degradation to a minimum. We proposed two topics of explanation: (A) the model of multicode spread spectrum system; (B) description of PIC-HFE algorithm; under topic A, Figs. 1 and 2 in the full paper give the schematic of the model of multicode spread spectrum system; under topic B, we derive eqs. (10) through (14); by updating coefficients at chip rate and feeding back hypothesized chips, it can track time-variability and combat ISI effectively; by combining parallel interference cancellation with hypothesis-feedback equalization, PIC-HFE is capable of suppressing ICI. Simulation results, given in Figs.4 and 5 in the full paper, prove preliminarily that the proposed algorithm can significantly improve the performance of multicode system.