| At present,the GNSS navigation and positioning system based on satellite communication technology develops rapidly and gradually plays an important role in people’s daily life,which further promotes the development of multi-system navigation receivers.As an auxiliary test equipment,the GNSS signal simulator can generate virtual satellite signals and provide a good experimental environment for the development and testing of navigation receivers.It can also be used as a signal source to effectively control unmanned equipment such as "black flying" drones,and maintain social order and national defense security.Therefore,the GNSS signal simulator has high research value.This thesis takes the GNSS multi-system satellite signal simulator as the core topic to carry out research,and the main work is as follows:1.This thesis deeply studies the structure,pseudo code and navigation message of GPS,BDS and GLONASS navigation signals,and uses MATLAB to carry out corresponding simulation verification,and finally introduces the technical principle of space satellite positioning.2.Aiming at the inconsistency of space-time benchmarks of multiple navigation systems,this thesis summarizes the space-time conversion formulas among GPS,BDS,and GLONASS systems,and designs a distribution scheme that can align navigation messages according to the conversion formulas.Aiming at the complex problem of GLONASS ephemeris calculation,this thesis designs a GLONASS ephemeris fitting method based on the Hermite interpolation algorithm.After MATLAB simulation verification,the fitting error in a short period of time is only small,ensuring that the GLONASS ephemeris fitting Accuracy is improved while improving computational efficiency.Aiming at the complex problem of GLONASS ephemeris calculation,this thesis designs a GLONASS ephemeris fitting method based on Hermite interpolation algorithm,which improves the calculation efficiency while ensuring the correct fitting of GLONASS ephemeris.Aiming at the problem of poor authenticity of traditional simulated satellite signals,this thesis delves into the error delay simulation technology and digital frequency synthesis technology in the propagation process of GNSS signals.The Klobuchar ionospheric delay model and Modify-Hopfield tropospheric delay model are mathematically modeled and simulated to improve the positioning accuracy of satellite signals.3.This thesis designs the overall implementation scheme of GNSS multi-system satellite signal simulator,writes DSP algorithms responsible for navigation data processing and FPGA logic responsible for digital signal generation.The DSP algorithm realizes the calculation of user motion trajectory,pseudo range,frequency control word and other data,and completes the encoding and transmission of multiple navigation systems’ messages.FPGA logic has achieved pseudo code,carrier generation,and message modulation of various navigation signals,achieved signal power control for a single channel,and completed data interaction between the upper computer and DSP.The upconversion module achieved mixing and amplification of satellite intermediate frequency signals,and ultimately successfully generated GNSS satellite signals.4.This article designs a testing plan and process for the GNSS multi-system satellite signal simulator,including spectrum characteristics testing of GNSS satellite intermediate frequency signals,MATLAB capture and tracking testing,positioning performance testing in static and dynamic scenarios,comparative testing with the National Defense University NSS 6000 simulator,and system power control testing.The above test results indicate that:The GNSS satellite intermediate frequency signal generated by this system is correct and can be captured normally by MATLAB.The radio frequency signal power of the satellite is controllable.Its accuracy is winthin 1 m under static positioning and about 2 m under Dynamic positioning,which is smaller than the NSS 6000,but the stability of the receiver for long-term positioning is weaker than that of the NSS 6000.In summary,all indicators of this system have met the requirements of theoretical design. |
