Use of Multiple GPS Antennas And A Low Cost IMU for Reliable And Continuous Urban Navigation

R. A. Nayak, M. E. Cannon, C. Wilson and G. Zhang

Abstract:	This paper focuses on the integration of differential GPS (DGPS) and a low cost IMU for reliable and effective navigation in an urban vehicular environment, which is motivated by the significant accuracy degradation that can exist due to satellite shading and multipath effects. A series of tests were conducted in and around Calgary whereby the shading effects ranged from open sky to significant shading to about 30 degrees in elevation. Four GPS NovAtel receivers and antennas along with a low cost IMU (MotionPak) were mounted on the roof of the vehicle. Another NovAtel receiver was sited at the University of Calgary so that differential processing in post-mission could be performed. The IMU is a three-axis inertial measurement unit from Systron Donner, which has micro-machined solid-state accelerometers and gyroscopes, that can measure acceleration and angular rates with a resolution of 5mG and 1.0 deg/s, respectively, in analog mode at 50 Hz. A Kalman filter is presented which integrates data from up to four GPS antennas with the IMU so that a reliable and continuous trajectory can be estimated. The resulting integrated positions are computed and compared to a digital road map of Calgary and accuracy statistics are presented. Subsets of the antennas (i.e. one, two and three antennas) are used with the IMU to determine the performance as a function of the number of GPS receivers utilized. In addition, the ability of the IMU to bridge GPS outages, poor geometry, and significant multipath is also assessed. The overall performance as a function of the shading environment (open sky versus urban) is computed and the effectiveness of the IMU to aid GPS is described. The test results show that the position accuracies vary significantly with the number of antennas used, the reliability test and also with inertial aiding. The augmentation of GPS with INS resulted in improved availability of position. Availability improvement of 10% is observed by limiting the prediction interval to 20 s and 100% availability is achievable, with reduced accuracy improvement resulting from the poor quality of sensors used.
Published in:	Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000) June 26 - 28, 2000 The Catamaran Resort Hotel San Diego, CA
Pages:	44 - 53
Cite this article:	Nayak, R. A., Cannon, M. E., Wilson, C., Zhang, G., "Use of Multiple GPS Antennas And A Low Cost IMU for Reliable And Continuous Urban Navigation," Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000), San Diego, CA, June 2000, pp. 44-53.
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