【摘要】 在扩频信号数字化后采用相关、视频累积和DLL延迟锁相环求累积值的基础上,提出了一种改进的伪随机码(PN码)跟踪环.利用DLL延迟锁相环S型签相曲线中间部分的线性特点,采用最小二乘法,通过极大似然参数估计进一步消除随机噪声对伪码相位差估计的影响,得到精确伪码相位差从而实现伪码精确同步及伪码精确测距.该方法实现简单,同步精度高,并且跟踪环伪码相位差门限和精度不受信噪比影响.即使在极限信噪比下也可以准确估计伪码相位差.论述了该方法在某直扩系统中的应用,给出了伪码精确同步部分的FPGA实现方案.系统已通过测试,伪码相位差估计精度可达10ns级,通过后端信号处理进一步平均滤波后精度可达ns级.更多还原

【Abstract】 An improved pseudorandom code-tracking loop, which eliminates the influence on the estimation of the phrase difference of the pseudorandom codes, was described, based on the approach of the digitized spread-spectrum signals′ correlation, video one and digital delay locked loop. This loop was improved by the least square method through the maximum likelihood estimation, referring to the linear character of the midst of the delay licked loop (dll) S-like curve of phrase locked. The accurate synchronization of the pseudorandom codes and the pseudorandom ranging was achieved by the exact phrase difference estimation. The method is precision adequate and the threshold of the phrase difference of the pseudorandom code-tracking loop is impervious to the conditions of different SNR, even under the limited condition of SNR. The implementation of accurate code synchronization on FPGA in some ds/ss was done by using the cyclone device of Altera Corporation. The system was tested, the phrase difference error of the pseudorandom codes being about ten ns. After the following data signal processing, the error could be down to less than ten ns.更多还原