Analysis of GPS Measurement Delays in Low-Cost INS/GPS Navigation Systems

C. Eck, M. Kottmann, H.P. Geering

Abstract:	For many kinds of civil and military applications unmanned aerial vehicles are appropriate alternatives to manned aircraft (O'Neill et al., 1998; Amidi, 1996). Driving functions are often questions of cost or availability of aircrafts. Latest developments in the ?eld of unmanned aerial vehicles have shown a wide variety of ?ying systems with similar navigation units that are quite often based on INS/GPS ?ltering technology (Eck, 2001; Gavrilets et al., 2000). The complemental advantages of GPS (Global Positioning System) and INS (Inertial Navigation System) have been extensively discussed in various publications (Litmanovich et al., 2000; Farrell and Barth, 1999; Grewal et al., 2001; Rogers, 2000). However, the target to achieve a good and reliable navigation performance, i.e., drift compensation and increased navigation bandwidth with lowcost inertial sensors and single GPS receivers is still a question of optimal data fusion or the ?ltering technology applied. Furthermore, there are often limitations in computational power and data storing capabilities onboard the aerial vehicle as the overall avionics should be more and more cost-e?ective (Eck et al., 2003). Within this publication, the main aspects of GPS measurement delays and its compensation methods are being discussed. The motivation is given by the ?eld experience with INS/GPS navigation. In general, the INS/GPS navigation unit performs well as long as GPS is available, but the inclusion of GPS measurement delays as well as GPS dropouts decline the navigation performance notably. The outline of the paper is as follows. First, the test environment to record INS/GPS data is described in Sect. 2. This includes an unmanned helicopter and an unmanned ?xed-wing aircraft. Both ?ight vehicles are equipped with an INS/GPS unit to record ?ight data of different ?ight maneuvers. In Sect. 3 this data will be analyzed in more detail to determine the delays of the GPS velocity and position measurements. Based on the measurement delays obtained within this section a simulation environment (Eck et al., 2001) has been adapted to the real ?ight data, including measurement noise and measurement delays. Within Sect. 4 two methods to compensate for the GPS measurement delays will be described in more detail. Various simulation results are shown to compare the ?ltering solutions. A short summary and conclusion is given within Sect. 5. Finally, the list of references concludes the paper.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2408 - 2416
Cite this article:	Eck, C., Kottmann, M., Geering, H.P., "Analysis of GPS Measurement Delays in Low-Cost INS/GPS Navigation Systems," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2408-2416.
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