| At present,with the development of industries such as intelligent driving,mobile mapping,and smart cities,the demand for high-precision and high-reliability positioning technology in urban environments is becoming increasingly urgent.In July 2020,the Beidou-3 network was completed,providing users with higher quality all-weather,all-day and high-precision positioning,navigation and timing(PNT)services.By combining GPS,GLONASS and other navigation and positioning systems,the positioning accuracy and credibility in complex urban environments have been greatly improved.Carrier phase differential positioning,as the most widely used and mature satellite positioning technology,can provide users with centimeter-millimeter-level positioning services.However,in the complex dynamic environment,satellite signals are easily affected by the obscuring environment,and the reliability of the positioning results cannot be guaranteed.To address the above issues,this thesis conducts in-depth research on differential positioning technology in complex environment application scenarios,with a focus on breakthroughs in key technologies such as cycle jump detection and repair and ambiguity fixing,and establishes a set of precision positioning technical services based on Beidou and compatible with other GNSS systems in complex environment.The main contents and achievements of the thesis are as follows:(1)This thesis systematically summarizes the development and existing problems of BeiDou/GNSS relative positioning technology,and elaborates and introduces the basic theory of GNSS relative positioning in detail from the aspects of function model,stochastic model,parameter estimation of GPS/BDS/GLONASS systems.Based on a set of short baseline data,the multi-system fusion localization experiment was conducted for seven positioning methods(G,B,R,G+B,G+R,G+R,G+B+R).The results show that the multi-system fusion positioning scheme is better than the single-system and dual-system schemes in terms of the number of available satellites,the fixed rate of ambiguity and the positioning accuracy.(2)The detection and repair of cycle slips in GNSS dynamic positioning are easily affected by strong multipath environments.Satellite signals can experience cycle slips due to the strong multipath effect,and more severely,signal loss.The determination of cycle slip estimation is not accurate due to the influence of the rapidly changing pseudorange multipath residuals between epochs,which makes it difficult for traditional dual-frequency MW combination cycle slip detection models to accurately detect them.Regarding the accurate detection and reliable correction of cycle slips in strong multipath environments,this chapter presents a new method for AMG cycle slip detection and correction using BDS dual-frequency observations as an example.An AR model-assisted cycle slip test quantity is developed,and evaluation metrics for cycle slip detection false alarm rate and missed detection rate are provided.The results show that the AMG method for cycle slip detection and correction reduces the effect of pseudorange multipath on cycle slip detection,effectively resolving issues with cycle slips in strong multipath environments.Compared to traditional methods,the AMG combination has an improved cycle slip correction rate of 36%,and the false alarm rate and missed detection rate for cycle slips decrease by 64.5%and 42.0%,respectively.(3)In the dynamic environment,due to the vulnerability of GNSS signals,the ambiguity is easily affected by the sheltered or semi-sheltered environment,which can result in a fixed failure and cause significant errors in differential positioning results.Therefore,in order to improve the effectiveness of ambiguity fixing,a partial ambiguity fixing method that takes into account posterior residual+altitude Angle information is proposed to eliminate the adverse effects of low-level satellite observations on ambiguity fixing,improve the fixed performance of ambiguity in complex urban situations,and bring more possibilities for high-precision and highly reliable positioning.The experimental results show that fixed partial ambiguity method effectively improve the estimation performance of navigation parameters.Compared with the traditional full ambiguity fixing method,the ambiguity fixing rate is improved by 5%,and the accuracy of the three directions N,E,and U is improved by 29%,50.4%,and 3.1%,respectively.(4)This section takes a set of car-mounted measured data as an example to analyze the feasibility and accuracy of differential positioning methods in complex environments.In the single system,the BDS system has completed the positioning solution,but there is a maximum error of meters.In the dual-system,the GPS+BDS system has the best positioning results.The multi-system further improves the positioning accuracy of the dual-system,with a 40%improvement in the N-direction,43%in the E-direction,and 36%in the U-direction.Compared with the conventional full ambiguity fixing strategy,the partial ambiguity fixing strategy has improved the positioning accuracy by 53%in the N-direction and 59%in the E-direction,2%in the U-direction.The experimental results show that the dynamic partial ambiguity fixing algorithm in three special scenarios significantly improves the reliability and positioning accuracy of differential positioning in complex environments compared to full ambiguity fixing strategies,both in terms of the number of epoch solutions and positioning accuracy. |
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