| Global Navigation Satellite System（GNSS）such as GPS and Beidou has highprecision positioning function in the visible range,and has been widely used in various fields.However,in application scenarios such as dense forests,mountains,canyons,and indoors,the number of visible satellites in the positioning area is less than the number required for positioning due to factors such as object occlusion and weather changes,resulting in low GNSS positioning accuracy.At the same time,if the satellite navigation in the positioning area If the signal is completely rejected,the positioning function cannot be realized.In order to realize high-precision positioning and navigation functions under the condition of satellite navigation accuracy degradation or rejection,and to make up for the technical and application defects of GNSS systems,ground-based pseudolite radio navigation and positioning systems have been widely studied.This thesis systematically studies the architecture,working mechanism and key technologies of the ground-based radiolocation system,and mainly designs and implements the baseband circuit and signal processing of the ground-based pseudolite navigation terminal,which meets the requirements of the ground-based navigation integrated system.The main work and research contents are as follows:1.Research and analyze the background of ground-based pseudolite radiolocation technology and the research status at home and abroad,and systematically study the working mechanism of ground-based pseudolite radiolocation and navigation system architecture,signal structure,time synchronization,signal synchronization and positioning algorithm.The signal system suitable for the ground-based pseudolite radiolocation system is proposed above,the baseband signal processing acquisition and tracking strategy is designed,and the signal pseudo-code synchronization and carrier separation functions are realized.2.Complete the overall scheme of the baseband hardware circuit of the ground-based pseudolite navigation terminal,and design the baseband circuit based on the FPGA+ARM architecture.A digital-to-analog conversion circuit with a dual-channel DAC with a sampling rate of 500 Msps as the core and an analog-to-digital conversion circuit with a dual-channel ADC with a sampling rate of 250 Msps are designed to realize the conversion of the RF front-end analog signal and digital signal;When realizing the functions of RF front-end circuit configuration,positioning algorithm,time synchronization,etc.,the required FPGA logic resources and I/O pins,combined with the requirements of DAC/ADC and DDR for data rate and level standards,complete the baseband processing Chip related circuit design.Finally,a complete ground-based pseudolite navigation terminal baseband hardware schematic and PCB layout are drawn.3.Complete the baseband signal processing design of the ground-based pseudosatellite navigation terminal.Completed the baseband bpsk spread-spectrum modulation signal design according to the signal system of the ground-based navigation system;According to the characteristics of ground-based pseudo-satellite positioning signals,the demodulation end capture tracking loop is designed,and the influence of signal-to-noise ratio,noise bandwidth and Doppler frequency difference on the capture tracking loop is simulated and analyzed,and the results show that the capture tracking loop can work stably > 6 d B of signal-to-noise ratio at the loop input.The programming implementation of the baseband signal processing module was completed on the FPGA+ARM platform.4.Completed the baseband signal processing test verification of ground-based pseudo-satellite navigation terminal,including ADC receive module,DAC transmission spread spectrum modulation module,capture module,tracking loop and other tests.The test results show that the capture trace module is able to synchronize the symbols into one sampling cycle and complete the carrier trace at a maximum frequency difference of 100 KHz. |
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