星座组网中直扩信号快速同步改进算法

An Improved Fast Synchronization Algorithm for DSSS Signals in Constellation Networking

基于直扩体制的时分多址(TDMA)卫星星座组网,信号帧前导段长度越短、净荷长度越长,数据传输的效率就越高。但是,直扩体制信号帧前导段长度越短意味着接收信号捕获增益就越低,捕获概率就越低。另外,前导段长度越短要求锁相环信号跟踪收敛速度越快。星座组网整网数据传输效率受到卫星信号同步算法性能的制约。为了提高直扩信号同步算法的性能,从捕获与跟踪两个部分对同步算法进行了改进,提出了一种直扩信号快速同步改进算法。针对捕获部分,分析了前置低通滤波器带宽对扩频信号的自相关函数的影响,通过选择滤波器参数在保证相关主峰无明显恶化情况下提升1/4码片偏差相关峰能量1 d B以上。针对跟踪部分,提出了一种调整闭环控制系统的零极点分布优化锁相环时域响应的锁相环设计方法,给出了基于控制理论优化锁相环闭环系统的零极点分布的四点原则,利用该方法设计的锁相环能大大降低信号跟踪的收敛时间。仿真结果表明,所提改进算法与传统同步方法相比能有效提高信号的捕获概率,加快信号跟踪的收敛速度,明显减少信号的同步时间。

During satellite constellation networking based on time division multiple access( TDMA),the shorter the preamble length and the longer the payload length of the signal frame,the higher the efficiency of data transmission is. However,the shorter preamble length means that the gain for the received signal is lower and the probability of capture is lower. Also,the shorter preamble length means that the faster the convergence rate of phase locked loop( PLL) signal tracking is. The data transmission efficiency of constellation networks is limited by the performance of satellite signal synchronization algorithm. In order to improve the performance of direct sequence spread spectrum( DSSS) algorithm,two improvements are made from capture and tracking and a fast synchronization algorithm for DSSS signals is proposed in this paper.For capturing part,the influence of the bandwidth of the low-pass prefilter on the autocorrelation results is analyzed. By selecting filter parameters,which not only ensures that the main peaks are not obviously deteriorated,but also enhances the 1/4 chip bias related peak energy more than 1 d B. For tracking part,an optimized PLL design method is proposed,which adjusts the zero pole distribution of closed loop control system to change the time response of PLL. Four principles for optimizing zero pole distribution of closed loop system of PLL based on zero pole distribution in PLL system based on Control Theory are presented.The convergence time of signal tracking is greatly reduced based on the optimize PLL parameters. Compared with traditional synchronization method,the simulation results show that the proposed schemes can improve the acquisition probability effectively,accelerate convergence rate of DSSS signal tracking greatly,and reduce the signal synchronization time obviously.