Research And Design Of Beidou Baseband Signal Simulator

The Beidou Navigation Satellite System(BDS)is widely used in various fields such as national defense,military industry,intelligent transportation,and logistics,and it plays an important role in national economic construction and social development.With the continuous development of the Beidou Navigation Satellite System,users have put forward higher requirements for the positioning accuracy of satellite navigation signal receivers.In the process of receiver research and development and testing,the real satellite signals may be affected by factors such as atmospheric conditions and geographical locations,which may prevent the receiver from receiving high-quality and stable satellite signals for testing.Moreover,when testing the performance of the receiver in various scenarios such as high dynamics,urban areas,and mountainous regions,it is difficult to reproduce the natural environment,and conducting actual tests consumes a significant amount of time and resources.Therefore,this thesis designs a Beidou baseband signal simulator based on STM32 and FPGA to simulate various motion scenarios of the receiver and the transmission environment of satellite signals.It provides a high-precision signal source for the research and development and performance testing of Beidou receivers,while also providing a testing environment for navigation positioning algorithms.Firstly,this thesis introduces the basic principles of BDS positioning,the structure of BDS satellite signals,and the mathematical model of Beidou baseband signals.Secondly,it delves into the key technologies involved in the Beidou baseband signal simulator,including spatial coordinate system conversion,signal propagation delay calculation,satellite motion trajectory modeling,and real-time pseudorange calculation.Furthermore,considering the computational complexity of satellite signal parameters and the real-time requirements of multi-channel signals,a Beidou baseband signal simulator based on STM32 and FPGA is designed.In this simulator,the STM32 module handles the conversion between spatial coordinate systems,determines satellite visibility,and compiles navigation messages.An algorithm for calculating the propagation delay of satellite signals is developed to simulate the transmission environment.The synchronization of navigation messages and pseudorange codes is achieved using the emission time of satellite signals.To simulate the Doppler effect on satellite signals,the frequency control word is calculated in real-time based on the rate of change of pseudorange within the satellite signal parameter update interval,enabling precise control of carrier frequency and code frequency.Leveraging the FPGA development platform,the hardware circuit design of various modules such as digital carrier generation,pseudorange code sequence generation,BCH error correction coding,navigation message calculation,and signal modulation is implemented using Verilog HDL.The functionality of each module is verified using the Modelsim simulation tool.To facilitate data interaction between modules in the simulator,a UART module is designed for communication between STM32 and FPGA.Finally,this thesis tested the BDS baseband signal produced by the BDS baseband signal simulator using a software and hardware receiver.Firstly,the Doppler frequency shift values and code phases captured by the receiver were compared with the preset values,and the error reasons were analyzed.Then,the tracking results of the receiver were analyzed.Finally,the positioning results were given:(1)Under stationary conditions,the positioning error of the receiver is within ±6 m.(2)Under constant velocity motion,the BDS baseband signal generated by the BDS baseband signal simulator is consistent with the preset trajectory.