论述了GPS模拟器中频信号数学模型,并着熏介绍了GPS模拟器中频信号生成采用的直接数字频率合成技术(DDS技术),针对用硬件FPGA实现GPS中频信号生成时的杂散误差问题,提出并在FPGA上实现了一种抑制GPS中频信号载波杂散的方法,同时研究了在C/A码生成过程中的码相位误差修正方法,及导航电文和C/A码完成调制中信号同步的关键技术;经仿真实验,该方法能明显抑制信号杂散问题,并提高信号同步精度;最后在FPGA+DSP硬件平台上完成了GPS中频信号的设计和验证。
The intermediate--frequency (IF) signal mathematical model of Global Position System (GPS) simulator is discussed in this paper with focus on the direct digital frequency synthesis (DDS technology) used in IF signal generation of GPS simulator. A method is proposed to eliminate spu- rious error which is generated by DDS in hardware FPGA implement. Research is given on the phase error correction of C/A code in the process of gen- erating code, as well as signal synchronization key technology of the navigation data and C/A code modulation. Finally the GPS IF signal design and simulation using QuartusII 9. 1 and modelsim ae6.5 are realized on the FPGA and DSP hardware platform.