H序沃尔什快速变换及其在水声扩频通信中的应用

严重的多途衰落、多普勒频偏是水声通信中引起误码的主要原因,扩频通信技术的抗多途、抗干扰性能使之适合用于水声通信。然而,要想较好地解决多途衰落和多普勒频偏问题,须对接收信号进行多途分量的提取和多普勒频率搜索。这将使程序的运算量大为增加,一般的相关算法无法满足数据处理的实时性。沃尔什快速变换能够快速的实现矢量和矩阵的相关运算,将其应用到水声扩频通信中的扩频编解码、频率搜索和多途分集,可以保证接收信号的实时处理。从而,在信道多途比较严重、环境噪声较强的浅海信道中,能够实现长距离、低信噪比、低误码率、高保密性的实时扩频通信。通过湖试和海试,验证了此水声扩频通信系统的上述优良性能。

Fast H-order Walsh transform and its applications in underwater acoustic spread-spectrum communication

The main causes of bit-error-rate in underwater acoustic communication are multipath and Doppler shift. Good anti-multipath and anti-jamming performances of spread-spectrum communication technique are suitable for underwater acoustic communication. In order to deal with multipath and Doppler shift, it is necessary to separate multipath components and search carrier frequency of the received signals. These lead to significant increase of processing burden, and real-time processing cannot be realized with conventional correlation techniques. Fast Walsh transform can be used to implement fast correlation between vector and matrix. Therefore, real-time processing of received signals can be achieved by applying fast Walsh transform in underwater spread-spectrum communication, for example spread-spectrum coding and decoding, frequency search and multipath collection. Thus, real-time spread-spectrum communication with long distance, low SNR, low bit-error-rate and high secrecy can be realized in shallow sea channel with severe multipath and ambient noise. Good performances of this system are shown in lake-trial and sea-trial.