Methods for Improving PPP Accuracy in Urban Canyons

Y. Kubo, Y. Suzuki, M. Ozaki, M. Ohashi, S. Sugimoto

Abstract:	In this paper, practical methods for improving PPP (Precise Point Positioning) accuracy in urban canyons are presented. Several techniques to improve PPP quality are proposed and they are integrated into a PPP algorithm which is available in case that there are few (only two or three) visible satellites from automobiles moving on the street in urban canyons. We have already developed PPP algorithms based on GR (Gnss Regression) models [3]-[6].Our PPP algorithm achieved the positioning accuracy in decimeter level.The algorithm does not require the real-time transmitted correction information. Therefore our PPP algorithm can be easily implemented without any external online received data.However, in order to maintain high precision positioning and navigation with GNSS in urban canyons, detection of cycle slips and multipathis naturally very important.Moreover, in such sever environment, the number of visible satellites available for the position calculation may decrease to less than four. Thus, in [6], we had presented the methods (a) detecting cycle slips and multipathbased on the statistical test of innovation processes in Kalman filtering, (b) fixing or constraining the height (altitude)of the vehicle in the position calculationby using digital map data, (c) modeling the dynamics of the automobile, i.e. accelerations in the horizontal axes and the velocity in the vertical axis are modeled by the first order Markov process,(d) utilizing the Dopplerdata effectively, (e) identifying the dynamics of receiver clock error based on the maximum likelihood estimation. By integrating these methods, the positioning accuracy in the skyscrapers of Tokyo, Japan was considerably improved. In this paper, we try to extend and more improve the above PPP algorithm. Especially in the method (b) of the above paragraph, the height information obtained from the digital map was utilized as the measurement of vehicle’s height in Kalman filter with the assumption that the vehicle was running in a flat area, i.e. the height information was fixed to the height of the center point of the running area. On the other hand, the digitalmaps with height information at grid points of 5-meter intervals in urban area are available to the public in Japan.Therefore, in this paper, we present a method to effectively and adaptively utilize the digital map height information. The height information is regarded as a new additional measurement in Kalman filter and the digital map height information can be obtained from the predicted horizontal position of the vehicle. With the above method, the additional height information can be taken into account in the position estimation even when the number of visible satellites greatly decreases. However, because the height of digital map is basically the height of the terrain, it is sometimes incorrect when the vehicle runs on elevated roads, overpass and so on. Therefore, in this paper, a low-cost barometric pressure sensor is applied observe the vertical variation of the vehicle. In this research, the digital pressure sensor BMP085 of BOSCH which is low-cost (about $5) and can provide height information with high resolution (0.03hPa, 0.25m). Generally, the sensor should be properly calibrated with the reference altitude and surrounding air temperature to obtain the sea level altitude. To avoid the calibration problem, in this paper, the pressure sensor is utilized to provide only the vertical variation of the successive measurement epochs. The vertical variation information is regarded as the vertical velocity measurement in Kalman filter. There exist a lot of researches that utilize the IMU (Inertial Measurement Unit) to keep the continuous navigation. However, if the IMU is utilized the signal processing procedure may be quite complex. Contrary to the use of IMU, the proposed method can be easily implemented because only two additional measurements should be utilized in Kalman filter. The proposed methods are integrated into the PPP algorithm, and experimental results of the data received by the automobile on the road as well as on the street in the urban area, Shinjuku, Tokyo, are shown for the feasibility and usefulness of ourRTK-PPP algorithms using GNSS Observables from few satellites. References: [1] Y. Kubo, K. Sone and S. Sugimoto: Cycle Slip Detection and Correction for Kinematic GPS Based on Statistical Test of Innovation Processes, Proc. of 17th Int. Tech. Meeting of the Satellite Div.of the Institute of Navigation (ION GNSS 2004), pp. 1438-1447, Long Beach, CA, 21-24 Sept. (2004). [2] M. Kamimura, R. Tomita, T. Nagano, A. Chabata, Y. Kubo and Sueo Sugimoto: Detection of Cycle Slips and Multipath in GNSS RTK Precise Point Positioning, Proc. 24th Int. Tech. Meeting of the Satellite Division of the Institute of Navigation (ION GNSS 2011), pp. 1056-1067, Portland, Oregon, Sept., 2011. [3] S. Sugimoto and Y. Kubo: GNSS Regressive Models and Precise Point Positioning, Proc. 36th ISCIE International Symposium on Stochastic Systems Theory and Its Applications, pp. 159-164, Saitama, Japan, Oct., 2004. [4] S. Sugimoto and Y. Kubo: Unified Methods of Point and Relative Positioning Based on GNSS Regression Equations, Proc. 19th Int. Tech. Meeting of the Satellite Division of the Institute of Navigation (ION GNSS 2006), pp. 345-358, Fort Worth, Texas, Sep., 2006. [5] S. Sugimoto and R. Shibasaki (Eds.): GPS Handbook (in Japanese), Asakura-Shoten, Tokyo (2010). [6] A. Chabata, Y. Suzuki, Y. Kubo and S. Sugimoto: RTK-PPP Algorithms using GNSS Observables fromFew Satellites, Proc. 25th Int’l. Tech. Meeting of the Satellite Division of the Institute of Navigation (ION GNSS 2012), pp. 3696-3707, Nashville, TN, Sep., 2012.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1659 - 1664
Cite this article:	Kubo, Y., Suzuki, Y., Ozaki, M., Ohashi, M., Sugimoto, S., "Methods for Improving PPP Accuracy in Urban Canyons," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1659-1664.
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