Ambiguity fixing in Precise Point Positioning (PPP) has been extensively studied in recent years. The provision of uncalibrated hardware delays (UHDs) to the PPP algorithm, on top of precise orbits and clocks, allows the recovery of the integer values of the carrier-phase ambiguities. Experimental results show that integer ambiguity resolution increases the accuracy in the position domain. Most of the research so far has been done on GPS, where the wide-and narrow-lane approach for ambiguity resolution has proven successful. In the context of multi-GNSS PPP, the aim of this study is to extend the method to Galileo. Initial results for UHD estimation for Galileo satellites are presented. The contribution of ambiguity-fixing to GPS + Galileo PPP is assessed. Copyright # 2016 Institute of Navigation It has been recently proven that all these approaches are equivalent [7]. Essentially, the ionosphere-free ambiguity is separated into a wideand a narrow-lane ambiguity. Wide-lane ambiguity resolution is based on the Melbourne-Wübbena geometry-free approach, while the narrow-lane ambiguity resolution is achieved via a geometry-based approach. Integer ambiguity resolution in PPP then becomes feasible when UHDs are estimated in a network adjustment and transferred to the end-user. This method has been successful in increasing accuracy in GPS-based PPP. The aim of this study is to provide initial experimentation for the extension of the method to Galileo. There are four in-orbit validation (IOV) satellites in orbit, launched in October

For precise positioning in arctic regions with Global Navigation Satellite Systems (GNSS), such as GPS and Glonass, there are a number of issues to be resolved or taken into account. The most important ones are satellite geometry, ionospheric effects and distribution of correction data. Precise Point Positioning (PPP) is currently the standard for precise offshore positioning. PPP requires a sparse global network of GNSS reference stations to estimate precise satellite orbit and clock parameters in real-time. These parameters are transmitted to users, who can compute their position with an accuracy of 0.1 m using code and carrier observations. The main disadvantage of PPP is that in general it takes a long time to converge to this accuracy, about 30–45 minutes. GNSS carrier observations are similar to pseudo ranges, but have an additional bias which needs to be estimated. Under certain conditions, these biases are integer. This property is used in what is generally referred to as Real-Time Kinematic (RTK) positioning, a technique which uses corrections generated at reference stations to make sure these ambiguities are integer. Integer Ambiguity Resolution (IAR) results in RTK accuracies of 0.01–0.03 m or better and short convergence times, ranging from instantaneous to several minutes for long inter-station distances. The disadvantage is the limited area of applicability, because RTK in general does not use precise orbits and clocks. Current research focuses on the combination of PPP and RTK techniques. The main goal is to achieve cm accuracy with a sparse network of reference stations. Another goal is to reduce convergence time. Applications are in the field of precise real-time offshore positioning in general, and subsidence monitoring and tidal estimation in particular. Results will be presented from standard PPP and PPP combined with IAR for arctic regions and from a test bed in the Gulf of Mexico. These results, although preliminary, indicate centimeter level accuracy is indeed possible, also in the arctic. We will also look at further improvements, mainly in convergence time, using all operational satellites and signals from current and future navigation systems.

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In order to achieve high-accuracy positioning, either Real-Time Kinematic (RTK) or Precise Point Positioning (PPP) techniques can be used. While RTK normally delivers higher accuracy with shorter convergence times, PPP has been an attractive technology for maritime applications, as it delivers uniform positioning performance without the direct need of a nearby reference station. Traditional PPP has been based on ambiguityfloat solutions using GPS and Glonass constellations. However, the addition of new satellite systems, such as Galileo and BeiDou, and the possibility of fixing integer carrier-phase ambiguities (PPP-AR) allow to increase PPP accuracy. In this article, a performance assessment has been done between RTK, PPP and PPP-AR, using GNSS data collected from two antennas installed on a ferry navigating in Oslo (Norway). RTK solutions have been generated using short, medium and long baselines (up to 290 km). For the generation of PPP-AR solutions, Uncalibrated Hardware Delays (UHDs) for GPS, Galileo and BeiDou have been estimated using reference stations in Oslo and Onsala. The performance of RTK and multiconstellation PPP and PPP-AR are presented.