Nexteq's Integer Ambiguity-Resolved Precise Point Positioning System

Landon Urquhart, Yufeng Zhang, Suen Lee, Jianping Chan

Abstract:	To obtain high accuracy results using the global positioning system (GPS), real-time kinematic (RTK) and precise point positioning (PPP) technologies are commonly used. Traditional RTK technologies are limited to baseline lengths of less than 50 km and do not take full advantage of the information contained in a network of reference receivers. On the other hand, while the accuracy of PPP has been widely demonstrated, the full adoption of this technique has been limited by its long convergence time. With the development of new PPP technologies, Nexteq has been targeting high accuracy GNSS users who have traditionally relied on RTK or differential GPS solutions. Currently, Nexteq offers Freedom and i-PPP positioning solutions which enable global sub-meter to sub-foot real-time accuracy for consumer and professional grade single frequency chipsets with virtually no initialization time. These technologies have been able to reduce the cost and logistics required for survey grade geographic information systems (GIS) operations which in the past typically required a base station and/or post-processing to achieve a comparable level of accuracy. For users requiring high accuracy, Nexteq offers dual frequency PPP technology which can achieve 10 cm horizontal RMS in real-time. However, as with all high accuracy PPP systems, typical convergence times vary from tens of minutes, up to an hour depending on local conditions (such as multipath and atmospheric effects). In the past few years, researchers have been able to improve both the convergence and accuracy of the PPP technique by resolving the integer nature of the carrier phase ambiguities. In order to achieve this, the fractional biases which exist on the carrier phase and pseudorange observations must be explicitly modeled using a network of continuously operating receivers. In this contribution, we describe the development of a PPP system which enables ambiguity resolution at a remote receiver. This includes a description of the system architecture, as well as the technology supporting the state-space corrections, determination of the fractional biases and end user algorithm. Using these corrections, the improvement in accuracy and convergence of the ambiguity-resolved PPP solutions with respect to traditional float PPP solutions are shown. Additionally, the impact of the network size on the quality of the fractional biases will also be discussed.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3046 - 3054
Cite this article:	Urquhart, Landon, Zhang, Yufeng, Lee, Suen, Chan, Jianping, "Nexteq's Integer Ambiguity-Resolved Precise Point Positioning System," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 3046-3054.
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