Characterizing GNSS Multipath at Different Antenna Mounting Positions on Vehicles

This document presents an analysis of antenna performance as a function of installation position on a vehicle. Each of three antennas is evaluated at three different installation locations on top of a car: front, middle, and rear along the car center-line (see Fig. 2).The equipment and experimental procedures are described in Section II. GPS measurement models are reviewed in Section III. Performance is analyzed by two methods. The first analysis approach uses differential GPS (DGPS) estimated position relative to a ground truth antenna position. The second analysis approach directly analyzes the statistics of the estimated multipath signal for each satellite. The methodology for each analysis approach is described in Sections IV and V. The experimental results are presented in Section VI.The method for determining ground truth for the DGPS anal- ysis approach is presented in Appendix A. The method for estimating Ionospheric delay for the multipath signal analysis is presented in Appendix B. Example Ionospheric delay calculations are include in Appendix C. The elevation and signal strength thresholds used to select the epochs to be included in this study are discussed in Appendix D.The conclusions related to performance are as follows. Among the antennas, the Sharkfin consistently performed worse than the other two antennas. Between the single and multi-band patch antennas, the performance was similar with the multi- band antenna performing better by some measures (e.g. position estimation histogram and standard deviation) and the single-band antenna performing better by other measures (e.g., multi-path standard deviation). The rear antenna location yielded slightly better performance, but the differences in performance between the three mounting locations was not large and therefore some- what inconclusive.