Development Of GPS Multi-channel If Signal Source

At present, the world has formed the coexistence pattern of the four global satellite navigation systems which are the GPS of the United States, the Galileo of Europe, the GLONASS of Russia, and the BeiDou of China. At the same time, the application fields of the satellite navigation are also continue to expand, and in the mobile terminal, location-based services(LBS) have also been deeply into every corner of our daily life. Because of the broadening of the application fields, the satellite navigation receivers’ working environment is more and more complex, and the demand for the receivers’ performance and position precision is constantly improving. Meanwhile, it also gives the signal source broader demand and higher requirements which is used for performance test of the satellite navigation receiver.Based on above, this paper has carried on the research work for the relevant theories of GPS signal simulation and hardware implementation.In this paper, the main work is as follows:Research on mathematics model of GPS intermediate frequency(IF) signal and the overall design for GPS IF signal source’s hardware. According to GPS signal’s structure and the analyses for the space propagation’s influence on GPS signal, the mathematical model of GPS IF signal is derived. Based on the signal model, and combined with the application requirements for the signal source, the overall architecture for the signal source is designed,and the DSP + FPGA scheme is adopted.The design and realization of the DSP subsystem. Make the functional planning for the DSP subsystem which is one of the two main subsystems to form the signal source, and design the operation process of the DSP according to the signal model and the requirements of the function realization. Based on the operation process, the models of the visible satellite calculation, signal propagation delay time calculation, doppler frequency shift calculation and the navigation message generation are implemented in turn. The simulation results show that the models can correctly complete calculations of the signal parameters. The interface and the data interaction logic between the DSP and the FPGA are designed and implemented.Meanwhile, the method of changing the signal propagation delay time and the doppler shift parameters to the channel control words of FPGA is studied. The test result shows that the DSP can sent the control words to FPGA correctly.The design and realization of the FPGA subsystem. Make the functional planning for the FPGA subsystem which is the other one of the two main subsystems to form the signal source and design the internal block scheme of the FPGA. The five key modules of FPGA, including bus interface module, carrier NCO module, code module, navigation message buffer moduleand epoch counter module are studied especially. These modules are implemented using Verilog HDL in Quartus II and simulated in ModelSim-Altera. The results show that each module works in line with expectations and all logic functions are implemented correctly.System verification and testing. To validate the working condition of the signal source, the output signal’s waveform and spectrum, the acquisition and tracking results of the software GPS receiver are tested respectively.The practical test results show that waveform and spectrum of the IF signal generated by the signal source is in line with GPS signal specification and the IF signal can be acquired and tracked correctly by software receiver. The signal source has good real-time performance and scalability with controllable cost, which is able to be effectively used in the lab for the performance test of the receiver.