| The Global Navigation Satellite System(GNSS)can provide users with accurate navigation and positioning services throughout the day.However,in indoor,tunnel,valley and other obstructed environments,GNSS signal attenuation is serious,resulting in reduced positioning accuracy or even unable to locate.Pseudolite technology can solve the above problems well and improve the quality of positioning service.Pseudolites can not only enhance the GNSS system and expand the application area,but also can be independently networked to realize the seamless connection between indoor and outdoor positioning.However,the application and promotion of pseudolite positioning system is still restricted by some difficulties,such as near-far effect,clock synchronization,etc.In this dissertation,an independent distributed pseudolite positioning system was designed and implemented.,which can use the existing commercial GNSS satellite receiver for positioning.At the same time,the key technical problems of the pseudolite positioning system are studied,and the relevant applied technologies are verified.The main contents are as follows:Firstly,according to the application requirements of pseudolite positioning,the system structure of distributed pseudolite positioning system is determined.Combined with the technical requirements of pseudolite,the overall scheme of pseudolite transmitter is designed,and the signal system of GNSS satellite is analyzed in detail.On the basis of ensuring the system compatibility,the signal structure and navigation message format of pseudolite transmitter are determined.The key problems of the pseudolite system are analyzed and the corresponding solutions are put forward.Secondly,in accordance with the requirements of the technical solution,the hardware platform of the pseudolite positioning system is designed using the software defined software radio thought.The hardware was divided into four units according to functions:control,baseband,clock and radio frequency.According to the circuit characteristics of each unit,the selection of related chips and devices was carried out,and the communication interface and power supply scheme was determined.The schematic diagram and PCB design were completed,and the hardware platform of the pseudolite system was designed and developed.According to the technical requirements,the software design of the relevant functional modules is completed on the hardware platform of the pseudolite system and the correctness of the functions is verified by simulation.GPS/BDS baseband signal processing function,clock synchronization control function and various RF functions based on pulse modulation are realized.And then,aiming at the problem of internal transmission delay of the pseudolite transmitter,a method of relative transmission delay measurement of pseudolite is proposed and a system error correction model is designed.In accordance with the characteristics of pseudolite signal generation and transmission,the time delay measurement system of pseudolite is composed of high precision clock source,pseudolite transmitter and receiver,radio RF transmission cable,etc.A common receiver and transmission cable are adopted,and one of the pseudolites is taken as the test benchmark.The relative transmission delay is obtained by differential calculation of the time delay measurement data of other pseudolites.Then,according to the relative time delay correction parameters,the error correction of the positioning solution model is carried out,so as to improve the accuracy of the pseudolite positioning system.Finally,testing and verification of pseudolite positioning system.Complete the joint debugging and assembly of the hardware and software of the pseudolite transmitter,then the test scheme is formulated,the test and verification environment is built,the performance of each functional module and the whole machine of the pseudolite is tested,and the correctness of the function of the pseudolite transmitter is verified.Four pseudolite transmitters were assembled into an indoor pseudolite positioning system.U-blox satellite receiver and its receiving evaluation software were used to evaluate the performance of pseudolite positioning signal acquisition and tracking.The correctness and rationality of the positioning design of the pseudolite system are verified by using the carrier phase observation data collected by the receiver.The experiment and test show that the design is correct and reasonable and meets the technical requirements. |
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