Research On Differential GNSS With Multiple Antennas

Differential Global Navigation Satellite System(DGNSS)technique is used to implement high-accuracy positioning with the assistance of reference signals.It generally requires reference stations to be deployed appropriately and provide the raw signal measurements or the corrections to the raw pseudorange measurements.Nevertheless,ground reference station service is not free and in certain special environments such as on the sea and in deserted country deploying reference stations is challenging or not cost effective.Hence,the dynamic reference station is developed which,however,needs to accompany the rover's movement to provide accurate reference signals.To improve the positioning accuracy without reference stations and any other assistant methods,in this thesis,we propose a multi-antenna and geometry based differential GNSS positioning method.Multiple independent antennas which track the same satellites simultaneously are connected to the receiver by cables and form a given geometry.Carrier phases of the signals received by those antennas are measured and differenced at the receiver.The phase cycle integer ambiguities are solved by exploiting the geometry formed by the antennas,and then the positions of multiple antennas are derived simultaneously by using the differenced phase measurements.Fusing the measured antenna positions based on the geometry formed by the receiver and antennas will find the receiver position.Regularization method is employed to solve the ill-conditioned problem produced by the geometry formed.Considering that the initial positions of antennas are obtained by the pseudorange based positioning,whereas the accuracy of pseudorange positioning is low,we further propose a differential evolution algorithm based pseudorange positioning method.The pseudorange based positioning problem is transformed into a multi-objective optimization problem through the geometric structure constraints formed by the antenna positions.Then the differential evolution algorithm is used to search the optimum pseudoranges from satellites to the antennas.Both searching space and searching time are compressed by aid of the correlation of pseudorange measurement errors in time and space.Kalman filter can further smooth the positioning results and mitigate the influence of outliers.In this thesis,the performance of multi-antenna positioning system is analyzed theoretically and verified by simulations.Positioning errors are analyzed according to the antenna and the receiver positioning solution,and the error upper bound is derived.In addition,the impact of various factors on the feasibility of positioning system solution is analyzed,and the factors include the number of satellites,antennas,frequencies and epochs.