Navigating with a Paper Clip, Antennas do Matter in Urban Enviroments

Abdul Khalique, Arthur Alfonso, and Andrew Christie

Abstract: The paper presents a study into the effects of antenna performance on commercial GNSS receivers. The purpose of the study is to show although the receiver largely determines the performance of a GNSS Device, ultimately the antenna determines which Satellites are received. The authors have determined which antenna parameters are most critical to produce accurate GPS performance in small portable devices. The experiments used drive testing of complete GNSS receiver systems, logging NMEA data over a standard test route. The input variables were the antenna type, vehicle type (Thermal coated vs standard), time of day and location (latitude/longitude). Drive tests were conducted over a range of typical environments including countryside, suburban, clustered urban areas and inner city urban canyons. During the study the Authors developed a reliable method for evaluating devices. Some key findings were: Devices should be evaluated using dynamic tests (Drive testing) as static tests do not accurately recreate these conditions. Although HDOP is a good indicator of the antennas 2D fix accuracy, it is not completely reliable. In conditions with significant multi-path HDOP can misrepresent the 2D accuracy. Instead we should consider the RMC statement in the NMEA data or to plot the data on a map. Using these techniques it was possible to determine common areas where antennas fail. One of the most likely areas for antennas to lose fix is traveling around corners. The authors have shown this is due to a non omnidirectional antenna pattern. It can be shown that the Azimuth plots of the antenna correlate closely with the devices ability to track in these conditions. Nulls in low elevation angle Azimuth plots should be avoided for good navigation performance. By reviewing the typical Satellite constellations, a GNSS receiver will observe most Satellites at low elevations. The Satellites used in a fix will be positioned at an elevation less than 60 above the horizon. This finding led the authors to the conclusion that zenith gain is much less important than antenna beam-width.
Published in: Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007)
April 23 - 25, 2007
Royal Sonesta Hotel
Cambridge, MA
Pages: 555 - 571
Cite this article: Khalique, Abdul, Alfonso, Arthur, Christie, Andrew, "Navigating with a Paper Clip, Antennas do Matter in Urban Enviroments," Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007), Cambridge, MA, April 2007, pp. 555-571.
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