Mitigation of Dominant Channel Propagation Effects in GNSS-based Positioning

Global Navigation Satellite Systems (GNSSs) have significantly changed the landscape of positioning. The development of the first GNSS, Global Positioning System (GPS), has been a major milestone in the history of navigation; not only because of its technological superiority over the existing positioning technologies of that time but also because it has turned the access to positioning signals from a privilege of a few into a public utility. In addition, the modern advancements in mobile devices have revolutionized the way positioning information is used; besides navigation, location information is used in a wide spectrum of applications such as to track people or goods, authenticate individuals, facilitate fleet management, optimize farming activities, find the nearest restaurant, assist elderly or disabled people, etc. While GNSS-based positioning has several advantages over other positioning technologies, such as global coverage and high availability, it also has its challenges. Most of these are related to the physical channel which consists of various error sources that affect the quality of the received satellite signals, and degrade the receiver’s positioning performance. In this dissertation, the focus is placed on the dominant propagation effects that take place in GNSS-based positioning. Precisely, these are the (1)ionospheric and the (2) multipath propagation effects. The former depends on the electron content along signal’s route and the latter, on the arrangement of the objects surrounding the GNSS receiver. For example, both effects introduce delays which make the satellite-receiver distance to appear longer than in reality and consequently, decrease the positioning accuracy. To mitigate such unwanted effects, an algorithmic approach is followed. Specifically, this dissertation studies the impact of multipath errors in the estimation of the ionosphere-corrected range and suggests a new algorithm for estimating the ionosphere-corrected range in dual-frequency receivers. The proposed algorithm achieves higher range estimation accuracy than alternative dual-frequency methods in the presence of multipath errors without raising the implementational complexity. Furthermore, this dissertation proposes new code and carrier tracking algorithms for improving directly the receiver’s tracking accuracy under multipath propagation effects. These methods yield better code and carrier tracking performance in exchange for higher complexity. Moreover, this thesis suggests novel algorithms for distinguishing two Carrier to Noise Ratio (CNR) ranges, such as those characterizing indoor and outdoor environments, and for estimating the CNR. Both methods are based on the level crossing rate information of the averaged cross-correlation function and can be used to improve the receiver’s code or carrier tracking performance, for example by adjusting certain parameters or switching between different algorithms. This dissertation is a collection of nine publications which include detailed descriptions of the proposed algorithms, comparison with state of the art methods and performance analysis. In addition, this thesis contains an introductory part which provides readers with a beginning knowledge on the principles of GNSS-based positioning, the error sources that degrade receiver’s positioning performance and a literature overview on the methods developed for mitigating the dominant environmental effects caused by ionosphere and multipath propagation.