| Precision point positioning(PPP)technology has the advantages of low equipment cost,simple operation and high computational efficiency.With enhanced information support,it can obtain centimeter-level real-time dynamic positioning accuracy,which has great potential in the field of large-scale real-time disaster monitoring.However,traditional centimeter-level PPP requires dual-frequency or tri-frequency receiver with a price of over 10,000 yuan,so this technology cannot be popularized on a large scale.With the introduction of the hundred yuan level u-blox multi-system single-frequency high-precision positioning module,the real-time centimeter-level PPP algorithm based on low-cost single-frequency receiver has become a research hotspot.However,the current low-cost single-frequency receiver PPP technology has poor positioning reliability and low real-time positioning accuracy in the occlusion environment.Based on this,this paper first analyzes and discusses the influence of different occlusion environments on multi-system PPP,and proposes a base station enhanced PPP algorithm based on u-blox low-cost receiver,and derives and implements the seamless handover model of the base station enhanced PPP algorithm.The main research results and innovations of the thesis are as follows:(1)Using GNSS observation data from multiple stations to simulate three kinds of occlusion environments: ambient occlusion(urban environment),unilateral occlusion(canyon environment)and headspace occlusion(large bridge subgrade environment).The positioning service performance of multi-system PPP technology is comprehensively analyzed from five aspects: available satellite number,PDOP value,available epoch rate,positioning accuracy and convergence time.The results show that compared with the GPS PPP positioning results,the multi-system PPP technology improves the available satellite number,PDOP value,available epoch rate,positioning accuracy and convergence time by 300%,40%,2%,20% and 50% in the unobstructed environment,and 300%,60%,25%,39% and 52% in the occlusion environment.(2)Low-cost single-frequency PPP technology has problems such as long convergence time and poor positioning accuracy.Based on this,the base station enhanced PPP technology is proposed to improve the positioning performance of low-cost receivers.The related algorithm model is deduced,and the dynamic and static measured data of u-blox single-frequency receiver is taken as an example.The GPS and GPS/BDS combined positioning modes are used for experimental calculation.The results of the example show that,in static environment,the GPS/BDS combination position converges to the centimeter level takes about 3 minutes,which is 64% shorter than the GPS result,the positioning accuracy is(3.2cm,2.7cm)in the plane and elevation directions,which is(47%,59%)better than the GPS.In the dynamic environment,the GPS/BDS needs about 4 minutes to converge to the centimeter level,which is 59% higher than the GPS,and the positioning accuracy is(3.1cm,5.9cm),which is(34%,43%)higher than the GPS.(3)Aiming at the problem of positioning instability and precision loss caused by base station replacement in the base station enhanced PPP algorithm,the seamless replacement model of the base station enhanced PPP is derived and proposed.The model can achieve smooth switching of the base station,and can maintain high-precision positioning performance before and after switching,effectively avoiding the impact of the base station switching on the positioning accuracy.The results of the example show that the base station switching model can maintain the horizontal single-frequency PPP accuracy better than 5cm in the horizontal direction and 8cm in the elevation direction before and after the switching,which can provide users with a stable centimeter-level positioning service. |
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