Investigation Of The Methods For Mitigating Multipath And NLOS Errors In Urban Area

Multipath greatly affects the GNSS positioning accuracy in urban area.Unlike atmospheric errors or clock bias,this effect cannot be eliminated by differencing signals.The thesis explores multipath errors on different GNSS signals and the methods for reducing multipath effects in various scenarios.The features of multipath errors for different constellations are analyzed.Three navigation systems – GPS,Galileo,GLONASS,are simulated in the same orbits.Therefore,all systems have the same GDOP value and number of visible satellites.The respective performance of If EN receiver and ubloxF9 P with different discriminators is evaluated.As Non-Line-Of-Sight(NLOS)situation contributes to poor GNSS accuracy,the thesis has come up with a method for NLOS exclusion and compared it with traditional Receiver Autonomous Integrity Monitoring(RAIM)techniques.Multi-GNSS is applied,as the number of LOS-available satellites decreases after NLOS exclusion.Finally,positioning algorithms are introduced and evaluated.Single Point Positioning(SPP),Differential GNSS(DGNSS)and Real-Time Kinematic(RTK)positioning solutions are compared and analyzed,so as to investigate how these methods perform with multipath errors.