Zeller, Emma2023-11-302023-11-302023-07https://hdl.handle.net/11299/258850University of Minnesota M.S. thesis. July 2023. Major: Aerospace Engineering and Mechanics. Advisor: Kirsten Strandjord. 1 computer file (PDF); vii, 69 pages.GPS has been a key positioning tool since it was first introduced, and improved space and control segments have led users to expect accurate positioning. However, there are still uncertainties and errors in the user segment that can’t be fully accounted for upfront due to challenges specific to each user. GPS positioning in urban environments is challenging as tall buildings often block, reflect, or diffract signals. When signals reflect off buildings or other surfaces they reach the receiver via a non-line-of-sight (NLOS) path. Multipath is a phenomenon that occurs when a signal from a single satellite reaches the receiver via both a direct-line-of-sight (DLOS) and NLOS path. When a strong reflected signal reaches the receiver at a delay less than ~300m relative to the direct path signal, the interference due to the combination of both signals causes errors in the computed position solution. Many techniques in conventional software defined radios (SDRs) equipped to detect multipath attempt to mitigate the resulting errors by removing the NLOS component or the entire signal. However, very few approaches attempt to utilize both the DLOS and NLOS signals as additional measurements to aid in positioning. The approach discussed in this work uses urban mapping to predict visibility and specularity at any location of interest within the mapped environment, as well as the Multipath Estimating Delay Lock Loop (MEDLL) to characterize multipath signals. These are then incorporated into Direct Position Estimation (DPE), an alternative positioning approach that directly computes a multi-dimensional spatial correlogram from the individual satellite correlations, rather than individually tracking each to get a navigation solution. Experimental data from both a stationary and driving experiment done in Denver, CO are used to test the different methods. When positioning results using DPE integrating visibility and specularity predictions from both urban mapping and MEDLL are compared to standard SDR positioning, improvements are seen.enDirect Position EstimationGPSMEDLLMultipathNavigationPositioningThesis or Dissertation