Research On Multipath Effect Restrain And Cycle Slip Detection Based On Beidou Short Baseline Positioning

The multipath effects and the cycle slip are the main factors which affects the positioning accuracy in short baseline differential positioning of Beidou satellites.Because multipath effects are random errors,it is difficult to eliminate them by conventional differential methods and mathematical models.In the thesis,aiming at the above technical problem in short-baseline differential positioning,a new nonlinear non-stationary signal processing method named empirical wavelet transform is applied to restrain multipath effects by taking data post-processing measure.Combined with the method of improved differential,we can detect and repair the cycle slip.Through setting up an experimental platform,the collected data are simulated to verify the effectiveness of the method,compared with empirical mode decomposition and ensemble empirical mode decomposition,which provides a new idea for Beidou data post-processing method.Firstly,the basic theory of empirical wavelet transform is studied.The development of nonlinear non-stationary signal processing is introduced systematically,including the basic theories and algorithm flows of EMD and EEMD.After that,we introduce the divided method of spectrum in EWT algorithm and the construction of empirical wavelet filter bank.To compare with EEMD method,we simulate two typical non-linear non-stationary signals.The experimental results show that EWT can extract clearer model components with physical meaning than EEMD,and the results of filtering and the time of calculation are better than EEMD.Secondly,focus on the problem of cycle slip consists in positioning data which makes a large error in observed data,the thesis elaborates the definition and occurrence of the cycle slip.Afterwards,we introduce some detection methods,such as the differential detection method,the phase minus pseudorange method and the wide-lane phase minus narrow-lane pseudorange method.Through the experiments,we prove the validity of the above methods to detect cycle slip and different methods' applied scope,then based on the characteristics of Beidou observation data,we improve the above three methods to enhance the detective rate of cycle slips.Finally,the thesis takes Beidou antennas,ATGM332D dual-mode positioning module and Arduino Mega 2560 microcontroller to build a dual sampling experimental platform for short baseline.Then we use EWT filter and improved differential method to restrain multipath effect and detect different size of cycle slips in short baseline differential observation data measured by Beidou.The experimental results show that the proposed method can restrain multipath effect by 43%and detect cycle slips in short-baseline positioning effectively,so that it may be useful to improve the differential positioning precision in Beidou satellite short-baseline.After that,we simulate deformation monitoring experiment,and results show that the EWT algorithm is suitable for deformation monitoring situation around 1?10Hz.