In underwater acoustic communication,because the available bandwidth of the channel is severely limited,the direct-sequence spread-spectrum scheme can only be realized at low bit rates.To improve the transmission spee...In underwater acoustic communication,because the available bandwidth of the channel is severely limited,the direct-sequence spread-spectrum scheme can only be realized at low bit rates.To improve the transmission speed,a multicode spread-spectrum scheme is considered.However,in this case,due to the rapid time-variability of the underwater channel,and the influence of inter-symbol interference(ISI)and inter-channel interference(ICI),the conventional rake receiver may fail to function.The hypothesis-feedback equalization algorithm has been proposed for the direct-sequence spread-spectrum system[1].By updating coefficients at chip rate and feeding back hypothesized chips,it can track time-variability and combat ISI effectively.However,for a multicode system,its performance will be degraded by ICI.An improved algorithm is proposed in this paper,which combines parallel interference cancellation(PIC)with hypothesis-feedback equalization(HFE),with the capabilities of tracking the time-varying channel and suppressing the ISI and ICI at the same time.Simulation results prove that the proposed algorithm can significantly improve the performance of a multicode system.展开更多
文摘In underwater acoustic communication,because the available bandwidth of the channel is severely limited,the direct-sequence spread-spectrum scheme can only be realized at low bit rates.To improve the transmission speed,a multicode spread-spectrum scheme is considered.However,in this case,due to the rapid time-variability of the underwater channel,and the influence of inter-symbol interference(ISI)and inter-channel interference(ICI),the conventional rake receiver may fail to function.The hypothesis-feedback equalization algorithm has been proposed for the direct-sequence spread-spectrum system[1].By updating coefficients at chip rate and feeding back hypothesized chips,it can track time-variability and combat ISI effectively.However,for a multicode system,its performance will be degraded by ICI.An improved algorithm is proposed in this paper,which combines parallel interference cancellation(PIC)with hypothesis-feedback equalization(HFE),with the capabilities of tracking the time-varying channel and suppressing the ISI and ICI at the same time.Simulation results prove that the proposed algorithm can significantly improve the performance of a multicode system.
