Research On Differential Beidou System Based Indoor Positioning

With the successful application of the GNSS outdoor positioning,there is a strong desire for indoor emergent rescue,positioning navigation,and object tracking,etc.Therefore,studies have been widely conducted on indoor positioning technologies including ultrasound,Wi-Fi,Bluetooth,A-GPS,and GNSS repeater based systems.In this thesis,GNSS repeater based indoor positioning techniques are studied.Considering signals from one repeater as the reference signals,a differential indoor positioning method is proposed.First,the Extended Kalman Filter based positioning algorithm is studied.The single differential delay of repeaters and single differential ambiguity are estimated when the single differential carrier phase measurement and single differential pseudorange are considered as observations.In order to further improve the positioning accuracy,the optimum integer phase ambiguity is searched by using the classical LAMBDA algorithm.Thus,the accurate receiver position can be obtained.In order to improve the slow convergence of extended Kalman filter,the multi-time-measurement based positioning algorithm is proposed.In two consecutive measurement times,the receiver's movement will make the topology formed by the repeaters and receiver change.Thus,the varied topology can be used to find the phase ambiguity.In the thesis,considering single differential ambiguity are found through Newton iteration method.Then,the integer least square method is employed to obtain the integer single differential ambiguities,which are used to further update the receiver position at those two measurement times.Multi-frequency combination is more suitable for real time accurate positioning than regular ambiguity search based method because it is free of the complex ambiguity search process.Thus the multi-frequency combination based indoor positioning algorithm is studied to improve the positioning performance.It is analyzed that the traditional Cascade Integer Resolution is not suitable for solving the phase ambiguity for indoor positioning because its probability of determining the ambiguity correctly is only 0.766.Thus,for the repeater based indoor positioning model,the enhanced CIR algorithm is proposed.First,the coefficients for the multi-frequency combination with long wavelength and small errors are selected.Then,the probabilities of determining the ambiguity correctly with different combination coefficients are calculated,and the impact of the determined phase ambiguity on the accuracy of distance measurement is analyzed.Third,the optimum combination coefficients are decided.Through the proposed five-step cascade stages,the phase ambiguity can be found.With the proposed enhanced algorithm,the probability of determining the phase ambiguity correctly will be 0.9881 and it supports the high-accuracy positioning.The indoor positioning approached proposed in this thesis is featured by convenient deployment and high positioning accuracy,and they require the receiver make no modification in the hardware.