Key Techniques For High Accuracy Positioning Of Beidou Pseudolite System

Around 2020,China's self-developed BD-3 global positioning and navigation system will be put into use,and at that time,the Beidou system will show its tremendous superiority and play an important role in the military and economic fields.However,the Beidou satellites are very far away from the earth ground,and the navigation signal's transmission environment is very complex,in some areas,users cannot receive more than four satellites signals.At this time,we need to use pseudolites to assist Beidou system in positioning or even replace it to establish a pseudolite positioning system,so it is of great significance to study the Beidou pseudolite high accuracy positioning algorithm.For the pseudolite positioning system,this thesis proposes a pseudolite layout optimition strategy,an integer ambiguity solution method and pseudo-range and carrier phase Kalman filtering method,and finally obtain the high accuracy positioning result.The main contents of this thesis are as follows,1.An overview of the principles of pseudolite positioning and error sources are given in this thesis.Firstly,the meaning of the pseudo-range and the methods to obtain it are introduced.Then,the pseudo-range positioning algorithm and the establishment method of the pseudolite coordinate system are discussed.And then this thesis simulates the common errors of the pseudolites system and analyses their influences,at the same time,proposes the corresponding solutions to these errors;2.A pseudolite optimization layout strategy based on PSO algorithm is proposed in this thesis.Firstly,the model of the positioning error is established,which shows that the positioning errors of the pseudolite system are related to the pseudolite layout and the system measurement errors.Then,the concept and the solving method of the system GDOP are analyzed.Then,according to the tetrahedron volumn method,the classical layout is obtained,and then based on the classical layout,a pseudolite optimization layout strategy based on the PSO algorithm is proposed,and under the same measurement condition,this thesis simulates the positioning results of classical and optimal layout.The simulation results show that the layout optimization method reduces the GDOP value by 15.5%,and reduces the mean and variance of positioning error by 14.4% and 50.8%,respectively.3.Some related algorithms based on carrier phase positioning are studied in this thesis.Firstly,the meaning of the carrier phase measurement value and the solution method are analyzed.Then,a common solution algorithm of the integer ambiguity which is called the least cost funtion method is discussed.Then,the Kalman filtering methods EKF and UKF are used to measure the pseudoranges,at the same time,the pseudo-range algorithm is used to obtain more accurate pseudo-range positioning value.Then the integer ambiguity is obtained by using the least cost function,and combined with the carrier phase measurement value,the high precision user position is obtained by using the carrier phase positioning algorithm.Finally,simulations are performed for specific experimental scenarios.The simulation results show that EKF and UKF increase the pseudo-range positioning performance by 59.05% and 65.14,respectively.At the same time,if we only consider using EKF for filtering,the carrier phase positioning performance is increased by 17.98% relative to the pseudo-range positioning algorithm.