Experimental Evaluation for Road User Charging of GPS/GLONASS/MEMS OBU

M. Azaola, C. Moriana, P. Navarro, D. Valdés, L. Bonardi, M. Toledo, J. Cosmen

Abstract:	Accurate and reliable positioning, navigation and timing in harsh environments is a key enabler for an increasing number of applications. Specifically, a wide range of so-called liability-critical applications like on-street parking pricing or road user charging are waiting for technological readiness of a suitable solution which fulfills their demanding requirements in terms of accuracy, integrity, availability and cost-efficiency. These are the key performance parameters of a liability-critical application: availability (of navigation) and accuracy contribute to service availability, a wider concept which requires both a position solution and an associated uncertainty which is small enough for the intended application; in turn, availability of service ensures that only very few liabilities (charges, fines, etc.) will be lost; finally, and even more critical, integrity ensures that no liabilities will be applied to the wrong user. And all these requirements must be met with a rather cheap piece of equipment as far as large user volumes are to be reached. Since recently, both the Russian constellation and the associated user receiver technology have improved to the point of enabling low-cost and high sensitivity GPS/GLONASS navigation. This, together with an ever-improving, ever-cheapening inertial sensor technology market, is opening the door to the long-awaited cost-efficient solution. Having access to a second GNSS constellation dramatically increases satellite availability in urban environments, which not only diminishes the dilution of precision (DOP) factor but also adds enough measurement redundancy for fault detection/exclusion (FDE) algorithms to perform decently. This in turn improves accuracy as long as the DOP factor does not increase too much after measurement rejection. Adding an inertial measurement unit (IMU) into the loop significantly increases the ability to identify degraded measurements while paying a relatively low price in terms of DOP increase (if we let DOP account also for the extra observability added by the IMU). On the other hand, the advantages of inertial aiding with regard to navigation availability are clear, enabling position computation even when too few GNSS observations (or even none) exist to carry out GNSS standalone navigation. Furthermore, inertial aiding provides a powerful means to implement anti-spoofing (another key aspect of integrity) as it allows to check the consistency between the IMU data and the (possibly spoofed) GNSS signal. Hence, multi-constellation GNSS aided with inertial sensing results in a powerful combination with regard not only to navigation accuracy but also to integrity and availability. In this work we present a low-cost automotive-grade on-board unit (OBU) by GMV whose GPS/GLONASS/IMU navigation engine has been specifically designed for road pricing applications in harsh environments. Based on very-low-cost commercial components (high-sensitivity GPS/GLONASS module and 6 DoF inertial module which together amount to just a few dollars when ordered in medium to large volumes) customized with embedded GMV software (proprietary GMV algorithms for GPS/GLONASS/IMU navigation and integrity, including Protection Level computation), our solution is among the most cost-efficient in the road pricing market while delivering a high performance navigation solution. In this article we describe the high-level design of our solution, discuss some of the key design decisions (such us the level of coupling in the data fusion), analyze the results of an extensive experimental campaign carried out in the city of Madrid and present conclusions on the suitability of this technology for demanding applications in harsh environments, also considering foreseeable improvements in the near future.
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:	656 - 666
Cite this article:	Azaola, M., Moriana, C., Navarro, P., Valdés, D., Bonardi, L., Toledo, M., Cosmen, J., "Experimental Evaluation for Road User Charging of GPS/GLONASS/MEMS OBU," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 656-666.
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