Research On High-Precision Single Frequency Multi-System GNSS Positioning Utilizing Ambiguity-Free Method

The Global Navigation Satellite System(GNSS)has a wide range of applicability in positioning,which can provide the full range,all-weather,and all-time navigation and positioning information for countless users at the same time.With the increasing global development trends such as digitalization,big data,artificial intelligence,and the Internet of Things(Io T),the demand for high-precision positioning services is increasing.The research is still focused on providing high-precision navigation and positioning solutions for the mass market through single-frequency receivers.The carrier phase measurement is the most accurate ranging method,and the ambiguity problem is the primary problem that must be solved to achieve a high precision positioning.In the meantime,the cycle slips often occur in the carrier phase measurements,expecially for single frequency receivers used in cities,canyons and jungles,which seriously affects their positioning performance.In this paper,the ambiguity-free search method for high precision single frequency multi-system GNSS positioning is studied,focusing mainly on four aspects:relative tracking and positioning based on relative motion vector repair,multi-epoch cooperative positioning under low-precision initial search points,single-frequency and single-epoch positioning based on loosely constrained initial baseline vector,and real time dynamic high-precision positioning based on position domain search.Giving full play to the advantages that the positioning accuracy of the position domain search algorithm is not affected by the cycle slips in the carrier phase observation.It can achieve high-precision positioning through far fewer epochs or even single epoch observation to meet the high-precision navigation and positioning performance requirements of single-frequency receiver users in the severe cycle slip environment.The main work of this paper is summarized as follows:(1)While using single-frequency carrier phase observation,aiming at the problem that the accuracy of long-term relative tracking and positioning is easily affected by the cycle slips in the carrier phase observations,an improved relative motion tracking and positioning algorithm is proposed.Relying on the integer ambiguity is constant between adjacent epochs,the integer ambiguity term is eliminated by constructing double-difference observation model between adjacent epochs,and the accurate relative motion vector solution is obtained.The positioning result of relative motion tracking is given by using the Dead Reckoning algorithm.By exploring the change of clock drift solution caused by cycle slip,combined with speed constraint information,the verifying method of relative motion vector solution is put forward,and the wrong vector solution is repaired.The static and dynamic experimental results show that the proposed method can accurately give out the relative motion vector between receivers,and the vector solution is not affected by cycle slips in the carrier phase observations or recovered from it more quickly.The computational efficiency analysis shows that the proposed method has a lower computational resource occupation rate and is more suitable to be transplanted to a low-cost single-frequency positioning module with limited resources to realize a long-term high-precision relative tracking and positioning.(2)An improved ambiguity function approach based on segmented simulated annealing optimization is proposed to solve the positioning precision of position domain search methods easily affected by the wrong position solution while the initial search point’s accuracy is low.The optimal segmentation interval distance is given by exploring the relationship between the segmentation interval distance in the position domain and the success rate of obtaining the correct position solution.Relying on the false position solutions is uncorrelated in each observation epoch.The probability density value of candidate optimal solutions is given based on the kernel density function method,and the influence of pseudo-global optimal solutions on the positioning accuracy is removed by the multi-epoch collaborative computing method.The static and dynamic experimental results show that the proposed method can achieve high-precision positioning based on less epoch observation data while the initial search point is low in precision.(3)In order to solve the problem that the position domain search algorithm needs to be provided a high-precision prior baseline vector constraints while performing the high-precision single frequency and single epoch positioning,this paper proposes a single epoch position domain search positioning algorithm based on ant colony optimization.With the advantage of fewer peak values utilizing the improved ambiguity function approach,the accuracy requirement of initial baseline vector value is reduced.Through experimental analysis,the precision threshold requirement of prior baseline vector accuracy is given,and the influence of pseudo-global optimal position solution on single epoch positioning accuracy is eliminated.A single epoch high-precision position solution is calculated out by updating and judging the pheromone value of ant colony.The experimental results show that the proposed method can significantly reduce the accuracy requirement of the initial baseline vector value utilizing the single epoch position domain search method and is more suitable for applying single frequency receivers in deformation monitoring under the severe cycle slips observation environment.(4)Aiming at the problem that the position domain search algorithm is constrained by the objective function’s multi-peak phenomenon and has low computational efficiency;it cannot achieve a real-time dynamic high-precision positioning.In this paper,an improved ambiguity function approach based on particle swarm optimization based on genetic mutation optimization is proposed.Relying on the particle swarm optimization algorithm has global optimization ability.The optimal global solution is given in the optimal position search domain utilizing the improved ambiguity function approach,which improves the position domain search and location algorithm’s computational efficiency.Genetic mutation algorithm is used to keep the diversity of particle swarm optimization and prevent the positioning result from falling into the local optimal position solution.A dynamic positioning method based on position domain search is given by combining the relative motion vector tracking method.The experimental results show that the proposed method can achieve a real-time dynamic high-precision positioning based on position domain search.The positioning accuracy is not affected by the cycle slip in the carrier phase observation,which meets the real-time dynamic high-precision positioning performance requirements of single-frequency receiver users in the severe cycle slip environment.