低声能辐射下的两种水声跳频通信方法对比研究

Comparison of two underwater acoustic frequency-hopping communication schemes under low sound energy condition

水声信道是一个极其复杂的时变-空变-频变信道,因而进行水声通信,必须克服时变多途干扰等困难。将抗干扰能力强的跳频通信技术应用于水声通信领域,对于隐蔽性、保密性要求高的系统来说,该体制有着卓越的特性。在仿真环境下,对比研究了m序列和基于二维logistic映射的混沌序列的相关性、平衡性、功率谱特性、多址性等性能。构建了一种在低声能条件下的水声跳频通信系统,给出了系统编解码技术的实现方法。发射的帧信号由激活信号、同步信号、时延信号和三组(15,11)汉明码循环3次组成,采用了时间与频率的双分集技术进行纠错解码,从而增强了系统的保密性。通过外场试验,验证了利用m序列和混沌序列进行水声跳频通信的可行性,并对试验结果进行了对比研究。由于混沌序列的数量巨大且性能优异,非常适用于水声组网通信和保密性要求高的水声通信系统。因此,混沌序列在今后的水声跳频通信领域应有更广阔的应用前景。

Underwater acoustic （UWA） channel is a complex channel that is time-varying, space-varying and frequency-varying. UWA communications suffer from interferences due to multi-path, ambient noise and Doppler shift. Frequency hopping spread-spectrum （FH-SS） provides good performance to UWA communications that require strict security and interference immunity. In a simulation environment, correlation, balance, power spectrum and multi-address of m-sequence and chaotic sequence based on two-dimension mapping have been studied. An UWA communication framework utilizing FH-SS under low sound energy condition is proposed. Implemetation of coding and decoding has been presented. The system is composed of activated signal, synchronization signal, time delay signal and three groups of （15, 11） Hamming code. Dual diversity is employed both in time and frequency for decoding and error correction. System security is improved and error rate reduced. Field experiments show that both m-sequence and chaotic sequence are feasible in UWA FH-SS communications. Comparison has also been made. As the number of chaotic sequences is enormous and they perform excellently in terms of correlation, they are suitable to be applied to multi-access communications and UWA communications requiring high security. Therefore chaotic sequences have good prospects in UWA communication.