Augmenting GPS RTK with Regional BeiDou in North America

J. Dou, K. O'keefe

Abstract:	The BeiDou Navigation Satellite System (BeiDou system) Signal-In-Space Interface Control Document (ICD) was published in December 2012 and deployment of the initial BeiDou regional navigation satellite system consisting of 14 satellites was completed. The BeiDou regional navigation satellite system is also known as the first phase of the BeiDou global navigation satellite system. A considerable amount of research has been conducted to evaluate the performance of the BeiDou system. However, the focus has been generally on pseudorange measurements, thus limiting obtainable positioning accuracy to the order of tens of meters. Moreover, most of the research has been with respect to the Asia Pacific region which fails to illustrate the performance of the regional BeiDou system globally. In contrast, the real time kinematic (RTK) positioning capability (i.e., centimeter-level) of the BeiDou system has not received as much attention, even though many applications require, or could benefit from, such high positioning accuracy. Some potential benefits of RTK positioning include precise relative positioning of two vehicles, precise relative motion over time and enhanced personal navigation accuracy. Unfortunately, RTK positioning is effectively impossible using the standalone BeiDou system anywhere outside the Asia Pacific region (e.g., North America) due to the limited number of visible BeiDou satellites. According to current BeiDou ephemeris, during limited times, three or four Medium Earth Orbit (MEO) satellites can be simultaneously tracked in North America while none of the Geostationary (GEO) satellites are visible. This is in contrast to the Asia Pacific region, where typically ten BeiDou satellites are visible at any given time. However, RTK positioning based on both the Global Positioning System (GPS) and the BeiDou system could be attempted in North America and has some advantages over using GPS alone. The purpose of this paper is to assess and demonstrate the usefulness of GPS/BeiDou combined RTK for users in North America by analyzing availability and accuracy, then demonstrating GPS/BeiDou RTK with real data. In this paper, the BeiDou regional system is introduced briefly. Geometry-based carrier phase position and float ambiguity estimation algorithms using stand-alone GPS and the combined GPS/BeiDou system are described in detail. In both cases, ambiguity resolution is accomplished using the well known LAMBDA approach. Definitions and measures of availability and accuracy are reviewed and clarified. These include Dilution of Precision to assess solution geometry, ambiguity dilution of precision to assess ambiguity observability, estimated position and float ambiguity co-variances, and real position and ambiguity errors obtained from real data. Real data will be obtained using a software receiver developed at the University of Calgary that has just recently been modified to track BeiDou INSERT BANDS HERE signals. Results of the test conducted in an open sky environment will be presented and analyzed to compare GPS and the combined GPS/BeiDou system. Additional data will be collected in kinematic scenarios during May and June 2013 with the aim to demonstrate the usefulness of 2-3 additional BeiDou satellites in urban and suburban parts of the city of Calgary, Canada. Preliminary results indicate the enhanced availability of the combined GPS/BeiDou system. The final results will serve as a counterpoint for the analysis of the BeiDou system that is currently being conducted in the Asia Pacific region by others and will play an important role in evaluating the global performance of the combined GPS/BeiDou system for high precision applications.
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:	3205 - 3213
Cite this article:	Dou, J., O'keefe, K., "Augmenting GPS RTK with Regional BeiDou in North America," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3205-3213.
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