Yang T C, Yang Wen-Bin
Naval Research Laboratory, Washington, DC 20375, USA.
J Acoust Soc Am. 2008 Dec;124(6):3632-47. doi: 10.1121/1.2996329.
Direct-sequence spread spectrum is used for underwater acoustic communications between nodes, at least one of which is moving. At-sea data show that the phase change due to source motion is significant: The differential phase between two adjacent symbols is often larger than the phase difference between symbols. This poses a challenge to phase-detection based receiver algorithms when the source or receiver is moving. A pair of energy detectors that are insensitive to the phase fluctuations is proposed, whose outputs are used to determine the relationship between adjacent symbols. Good performance is achieved for a signal-to-noise ratio (SNR) as low as -10 dB based on at-sea data. While the method can be applied to signaling using short code sequences, the focus in this paper is on long code sequences for the purpose of achieving a high processing gain (at the expense of a low data rate), so that communications can be carried out at a low input SNR to minimize the probability of detection (P(D)) by an interceptor. P(D) is calculated for a typical shallow water environment as a function of range for several source levels assuming a broadband energy detector with a known signal bandwidth.
直接序列扩频用于节点间的水声通信，其中至少有一个节点处于移动状态。海上数据表明，源运动引起的相位变化很显著：两个相邻符号之间的差分相位通常大于符号之间的相位差。当源或接收器移动时，这对基于相位检测的接收器算法构成了挑战。提出了一对对相位波动不敏感的能量检测器，其输出用于确定相邻符号之间的关系。基于海上数据，在低至-10 dB的信噪比下也能实现良好性能。虽然该方法可应用于使用短码序列的信令，但本文重点关注长码序列，以实现高处理增益（以低数据速率为代价），从而能在低输入信噪比下进行通信，以最小化拦截器的检测概率（P(D)）。针对典型的浅水环境，假设使用具有已知信号带宽的宽带能量检测器，计算了几个源级别的P(D)作为距离的函数。
