Hypothesis-feedback equalization for multicode direct-sequence spread spectrum underwater communications

In this paper, multicode direct-sequence spread spectrum is considered to achieve high-speed data transmission in underwater acoustic channel, where extended multipath and rapid time-variability is encountered and the conventional RAKE receiver usually fails to function. To track and compensate the channel distortion, a decentralized hypothesis-feedback equalization (HFE) algorithm [1] which updates coefficients at chip rate is a promising method and has been used in multi-user underwater communication. But for multicode system, its performance is degraded by inter-channel interference (ICI). For this reason, a parallel interference cancellation hypothesis-feedback equalization (PIC-HFE) algorithm is proposed, which combines the capabilities of tracking the time-varying channel and suppressing the ICI. Simulation results proved that the proposed algorithm could significantly improve the performance of multicode system.