A Novel Positioning and Integrity Monitoring Algorithm for a Multiple Constellation Receiver

Shaojun Feng, Carl Milner, Altti Jokinen and Washington Ochieng, Chris Hide, Terry Moore and Chris Hill, Marek Ziebart, Mojtaba Bahrami, Paul Groves and Ziyi Jiang

Abstract:	With an increasing number of navigation satellites, full operation of multiple constellations is on the horizon. This will bring both opportunities and challenges for user level positioning and integrity monitoring. The opportunities will be facilitated by amongst others, more satellites, frequencies, message types, and better signal design and geometry. The challenges are not only to deal with the differences among satellite navigation systems but also to maximize the benefit from the similarity of multiple constellation signals to develop, for example, low cost, high performance receivers for mass market applications. The current methods for positioning using multiple constellations focus on dealing with differences especially those associated with the time reference. This is dealt with either by the use of information broadcast by the systems or treatment as an unknown to be estimated as part of the solution. This paper proposes a novel positioning and integrity monitoring algorithm for multiple constellation receivers. The positioning method is based on single differences of pairs of measurements from two constellations, for example, the difference between the measurements from a GPS satellite and one or more Galileo satellites. The single difference removes the real receiver clock bias and drift error. Therefore, the inter-system time difference appears as common bias, and is estimated as a virtual receiver clock error. In addition, a carefully selected pair can also mitigate correlated un-modeled errors, thus improving the quality of the positioning solution. One approach to forming the single difference (i.e. basic pairs) is to use satellites in different constellations that are in close proximity. The degree of closeness depends on the user location, time, configuration and status of constellations. For example, signals from the paired satellites with similar elevation and azimuth should help mitigate un-modeled and correlated errors. The corresponding integrity monitoring is similar to the standard code or carrier receiver integrity monitoring methods. The novelties are in the determination of error standard deviations of the new observation pairings and potential multiple common biases in pairs when one satellite involved in more than one pair. In case of more than two constellations, the proposed method can be applied in multiple stages. The proposed technique benefits more from multiple constellations than the existing methods by addressing the problem of inter-constellation differences (e.g. time) while benefiting from similarities (e.g. elevation and azimuth). Test results from the two currently operating constellations, GPS and GLONASS, are presented. The results show that the proposed method results in a higher positioning accuracy than the other three methods including GPS only, GLONASS only and GPS plus GLONASS where the system time difference is estimated. Furthermore, the protection level is lower than the other three methods for a given integrity risk, and therefore, has the potential to support more stringent services with stringent requirements.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2681 - 2688
Cite this article:	Feng, Shaojun, Milner, Carl, Jokinen, Altti, Ochieng, Washington, Hide, Chris, Moore, Terry, Hill, Chris, Ziebart, Marek, Bahrami, Mojtaba, Groves, Paul, Jiang, Ziyi, "A Novel Positioning and Integrity Monitoring Algorithm for a Multiple Constellation Receiver," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2681-2688.
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