一种用于多码扩频水声通信的假设反馈均衡算法

Improving Multicode Spread Spectrum Underwater Communication with PIC-HFE Algorithm

在水声通信中,受到信道带宽的限制,直接序列扩频传输的数据率较低,为提高系统数据率,对多码扩频的应用进行研究。但在此情况下,受到信道快速时变以及码间干扰与子通道间干扰的影响,传统RAKE接收机可能无法完成正确解调。一种应用于直接序列扩频的假设反馈均衡器采用码片级的自适应均衡以及对假设序列的反馈,能够有效地跟踪补偿信道时变与码间干扰,但是对于多码扩频系统,由于未对子通道间干扰进行抑制,直接应用将导致系统性能损失。为此,提出一种改进的假设反馈均衡算法,它引入并行干扰消除结构并将其与假设反馈均衡相结合,能够同时实现时变信道跟踪以及码间干扰与子通道间干扰抑制。仿真结果表明采用此算法可以显著提高多码扩频系统的性能。

Aim. 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 full paper, we explain in detail how to reduce such degradation to a minimum; in this abstract, we just add some pertinent remarks to the 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.