Review of PPP–RTK: achievements, challenges, and opportunities

Abstract

The PPP–RTK method, which combines the concepts of Precise of Point Positioning (PPP) and Real-Time Kinematic (RTK), is proposed to provide a centimeter-accuracy positioning service for an unlimited number of users. Recently, the PPP–RTK technique is becoming a promising tool for emerging applications such as autonomous vehicles and unmanned logistics as it has several advantages including high precision, full flexibility, and good privacy. This paper gives a detailed review of PPP–RTK focusing on its implementation methods, recent achievements as well as challenges and opportunities. Firstly, the fundamental approach to implement PPP–RTK is described and an overview of the research on key techniques, such as Uncalibrated Phase Delay (UPD) estimation, precise atmospheric correction retrieval and modeling, and fast PPP ambiguity resolution, is given. Then, the recent efforts and progress are addressed, such as improving the performance of PPP–RTK by combining multi-GNSS and multi-frequency observations, single-frequency PPP–RTK for low-cost devices, and PPP–RTK for vehicle navigation. Also, the system construction and applications based on the PPP–RTK method are summarized. Moreover, the main issues that impact PPP–RTK performance are highlighted, including signal occlusion in complex urban areas and atmosphere modeling in extreme weather events. The new opportunities brought by the rapid development of low-cost markets, multiple sensors, and new-generation Low Earth Orbit (LEO) navigation constellation are also discussed. Finally, the paper concludes with some comments and the prospects for future research.

A Two-Step Regional Ionospheric Modeling Approach for PPP-RTK

“…where C 0 is a nugget, C is a partial sill, C 0 + C is a sill; h is the distance between stations, and 3a is the range, which reflects the distance at which the variogram tends to be stable. Through the fitted semi-variogram, the weight of sampling points can be calculated by Equation (8).…”

“…In PPP-RTKs, the quality of ionospheric products has a direct impact on the users' positioning performance [8]. As a publicly available product from the International GNSS Service (IGS), the global ionospheric map (GIM) can be used to constrain ionospheric parameters, to shorten the initialization time of PPP.…”

The Implementation of Precise Point Positioning (PPP): A Comprehensive Review

“…Nevertheless, ambiguity-fixed PPP, or PPP-AR, has the advantages of shorter initial convergence time and improved accuracy, especially in the east direction [7,68]. PPP-RTK is a state-of-the-art technique that combines the complementary characteristics of PPP and RTK to achieve centimeter-level positioning in a short time [69].…”

Designing and Testing an IoT Low-Cost PPP-RTK Augmented GNSS Location Device

“…Robustelli et al [ 29 , 30 ] obtained interesting results in terms of the time needed to resolve the phase ambiguity at integer values along with good accuracy and precision in a static test using the u-blox Point Perfect commercial PPP-RTK data correction service. Although there is an extensive literature on PPP-RTK theoretical approaches and implementation methods, as described in [ 31 ], the literature on the design of IoT location devices based on GNSS-sourced signals remains limited, as do case studies involving real-world testing. The development of engineered devices has room for improvement; hence, in this work we report the design and implementation of an Internet of Things (IoT) GNSS device developed with low-cost hardware that leverages a commercial PPP-RTK data correction service targeting horizontal and vertical decimetre level accuracies in static and kinematic tests.…”