Research On Correction Method Of Pseudorange Multipath In Urban Area

In recent years,with the improvement of GNSS receiver performance and the rapid construction of multi-constellation navigation systems,GNSS has been greatly expanded in the application of urban environments.However,for urban areas,the block of a large number of buildings,the complex path of signal propagation,the generation of reflected multipath effects and non-line-of-sight have always affected the highprecision positioning in urban areas.In order to improve the positioning accuracy of urban areas,and lay the foundation for subsequent lane-level navigation,unmanned vehicle,emergency rescue,social applications and other applications,this paper takes GPS system as the basic research object,and focuses on the processing method of pseudo-multipath in urban areas.The followings are discussed:1.The paper defines meanings of three kinds of signals: "NLOS" refers to non-lineof-sight,"reflective multipath" refers to the coherent error between direct signal and reflected signal,and "multipath" includes non-line-of-sight and reflected multipath.Then the composition of GPS system,basic principle of pseudo-range positioning and error analysis,GPS positioning algorithm and precision analysis,differential positioning principle,and the generation and characteristics of reflected multipath are introduced,which lay the foundation for the following topics.2.Two common methods of handling with non-line-of-sight(NLOS)in pseudorange positioning are introduced: receiver autonomous integrity monitoring(RAIM)and Urban Trench.The improvement of positioning accuracy,the scope of application,the advantages and disadvantages of two methods are compared and analyzed.Both methods could improve the positioning accuracy.RAIM is simple to operate but couldn't deal with all multipath signals,the improvement of accuracy is poor;urban Trench is highly targeted for the correction of NLOS,but the reflected multipath signal cannot be identified and corrected.Besides,the three-dimensional model is must for Urban Trench.3.Because of the high requirements for 3D city model of the Urban Trench,and the incomplete deletion of multipath of RAIM,a multipath correction method using spatial repeatability of multipath is proposed.The method is based on the Multipath Hemisphere Map(MHM).The current MHM is only applicable to the synchronization,dual antenna device,it's universality is weak.This paper proposes to implement the MMH method to ordinary short baseline area by using the Zero Differences method.Finally it is further combined with the RAIM method,to achieve better positioning accuracy in urban high-density area.4.Based on L5 band data with good quality after GPS modernization,the L1L5 dualfrequency fusion multipath suppression method on low-cost mobile phone positioning is evaluated.The results show that the L5 signal can suppress multipath effect of L1 signal,and the positioning accuracy has a significant improvement.