全新卫星双向时间比对调制解调器设计

摘要

Two-way satellite time and frequency transfer (TWSTFT) is general used in high-precision time and frequency transfer,the key equipment of TWSTT system is the modem.Nowadays,a new time transfer modem for TWSTFT has been developed at BIRMM.The direct sequence spread spectrum(DSSS) and binary phase shift keying (BPSK) modulation techniques are used to generate a pseudo-random noise (PRN) signal.A fast Fourier transform (FFT) parallel algorithm is applied to achieve fast acquisition of the PRN modulated receiving signal.A 2ndorder frequency lock loop (FLL) assisted 3m order phase lock loop (PLL) is designed to keep both of the performance of loop dynamic stress and carrier phase tracking accuracy,and a 2nd order delay lock loop DLL is used to track and measure the code phase.A short baseline TWSTFT experiment was done with two 1.2m very small aperture terminal (VSAT) earth stations and a commercial geosynchronous orbit communication satellite to evaluate the modem's performance.The result shows very low noise with the standard deviation (lo-) equal to 0.13ns at a 2.5MChip/s code rate.%卫星双向时间频率传递是目前被广泛应用的远距离高精度时间频率量值传递方法,其核心组成设备是双向时间比对调制解调器.文章介绍了由北京无线电计量测试研究所研制的卫星双向时间比对调制解调器,该设备采用直接序列扩频(DSSS)和二进制相移键控(BPSK)方式完成时间信号的调制,采用快速傅里叶变换(FFT)算法实现对信号的快速搜索和捕获;利用二阶锁频辅助三阶锁相环路达到动态性能和跟踪精度的平衡;采用二阶延迟锁定环(DLL)来实现对码相位的精密跟踪和测量.采用两个1.2m口径天线的双向比对地球站进行短基线卫星双向时间比对试验,试验结果表明当系统工作在2.5MChip/s码速率时,该调制解调器的时间比对精度(标准偏差(1σ))能够达到0.13ns.