一种改进延迟锁相环跟踪系统的FP GA实现

摘要

直接序列扩频(DSSS)是通信数据链中广泛采用的一种信号调制方法,而实现伪随机码(PN码)同步是直接序列扩频通信系统正常工作的前提.从分析伪随机码的结构出发,研究了一种采用改进延迟锁相环的伪随机码跟踪方法,在传统延迟锁相环的基础上,将改进坐标旋转数字(CORDIC)算法应用到数控振荡器(NCO)中,极大减少了对于硬件资源的占用.基于最小二乘法直线拟合的原理,提出了一种本地PN码和输入扩频信号的相位差算法,能够实现更加精确的同步.改进后的延迟锁相环跟踪系统在硬件实现上更为简单,通过Quartus II和ModelSim软件进行仿真,验证了这种改进方案的可行性.%Direct Sequence Spread Spectrum ( DSSS) is a generally used signal modulation method in the communication data link. The synchronization of pseudorandom-noise code is a precondition for DSSS system's normal work. The structure of PN code is analyzed and a tracking method using the delay locked loop is studied. It uses modified CORDIC algorithm in NCO to reduce occupation of hardware resources. Based on the least-squares method curve fitting, an algorithm for phase difference between the local PN code and the input DSSS signal is proposed. It could achieve more accurate synchronization. This modified delay locked loop is more simple for hardware implementation and the feasibility is proved by Quartus II and ModelSim simulation.