Error Analysis of Two GPS Receivers in a High Dynamic Flight Environment

Brian J. Bohenek, Todd Levine, Tom Buter

Abstract:	Flight-test position and velocity data from two Global Positioning System receivers were collected and compared to a baseline Global Positioning System/Inertial Navigation System (GPS/INS) system. The effects of acceleration and jerk on receiver performance were examined by a USAF TPS team over 34 different turning and non-turning flight maneuvers in a T-38A aircraft. Emphasis was placed on receiver performance during high dynamic maneuvering (maneuvers up to 6.0g with accelerations in excess of 200 ft/sec 2 ). The two receivers evaluated were the Rockwell Collins 5-channel Precision Lightweight GPS Receiver (PLGR+96) and the Navstar 12-channel C/A Code Receiver (CACR). The baseline system against which test receiver performance was compared was the GPS Aided Inertial Navigation Reference (GAINR). The CACR unit was flown 6 times and the PLGR+96 unit was flown 3 times. CACR performance was examined both with and without differential corrections incorporated. Position error analysis for the uncorrected CACR navigation solution could not be completed due to the effects of Selective Availability. Uncorrected velocity error varied linearly with aircraft acceleration. Initial analysis uncovered a latency in the CACR-derived velocity message of approximately 0.75 seconds. Application of a 0.75- second time shift to the CACR data reduced the observed velocity error to values commensurate with advertised receiver performance. The PLGR+96 position errors were observed to be most dependent upon vertical accelerations for non-turning maneuvers. Positive accelerations exhibited greater position errors than negative accelerations. Aircraft bank angle exhibited the greatest affect on velocity error. An analysis of satellite Geometric Dilution of Precision (GDOP) for the maneuvers evaluated did not show significant dependence of position or velocity errors on GDOP. The velocity error was also observed to be a function of jerk for all maneuvers evaluated. Both test receivers performed better under high dynamics than expected with the 12- channel CACR unit maintaining lock for a greater number of high dynamic maneuvers, including a 6.0-g wind up turn. Previous flight test and simulations have noted some of the challenges associated with flight testing of GPS hardware; the current study revealed some promising techniques for addressing many of these issues.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	2253 - 2260
Cite this article:	Bohenek, Brian J., Levine, Todd, Buter, Tom, "Error Analysis of Two GPS Receivers in a High Dynamic Flight Environment," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 2253-2260.
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