直扩水声通信机的码同步技术研究

Research on Code Synchronization Technology of Direct Sequence Spread Spectrum Underwater Acoustic Communication

为了降低扩频码同步技术对硬件的依赖,提高水声通信机的性能,对传统直接序列扩频码同步技术进行了一些改进。扩频码同步技术包括码捕获和码跟踪两个阶段,在码捕获阶段,采用双倍补零法扩展接收信号与接收机本地扩频码序列,使两者满足基二快速傅里叶变换运算的要求;在控制逻辑部分采用蓄水池抽样算法来确定范围内载波频偏值的计算顺序,无需按照固定顺序遍历范围内的载波频偏值,从而减少了计算量。在码跟踪阶段,采用了全时间超前-滞后非相干相关同步跟踪回路,采用双Δ值延迟锁相环的设计,扩大了跟踪范围,降低了失锁概率。最后基于DSP平台实现了直接序列扩频水声通信系统,该系统通过了水箱实验环境的测试。

In order to reduce the dependence of spread spectrum code synchronization technology on hardware and improve the performance of underwater acoustic communication machine,this paper makes some improvements on the basis of traditional spread spectrum code synchronization technology.The synchronization of spread spectrum code includes two stages:code acquisition and code tracking.In the code acquisition stage,the double zero filling method is used to expand the received signal and the local spread spectrum code sequence of the receiver to meet the requirements of radix-2 fast fourier transform operation;In the control logic part,the reservoir sampling algorithm is used to determine the calculation order of carrier frequency offset within the range,without traversing the carrier frequency offset within the range in a fixed order,so as to reduce the amount of calculation.In the code tracking stage,this paper adopts the full-time lead-lag incoherent correlated synchronous tracking loop and the design of doubleΔvalue delay phase-locked loop,which expands the tracking range and reduces the probability of losing lock.Finally,a direct sequence spread spectrum underwater acoustic communication system is realized based on DSP platform,which has passed the test of water tank experimental environment.