The dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) should be able to provide a vertical protection level in the range of 10---12 m, which is sufficient to support Category I precision approach operations. Because of the limited data rate of the SBAS signal and the need to augment 91 satellites simultaneously, DFMC SBAS does not broadcast equivalent terms for fast pseudorange corrections in legacy L1-only SBAS. An analysis of the wide area augmentation system (WAAS) suggests that the range error after applying long-term satellite error corrections, known as satellite clock---ephemeris (SCE) corrections in DFMC SBAS, is not accurate enough for Category I operations. Thus, it is necessary to improve the accuracy of these SCE corrections. With the construction of DFMC SBAS, there is an opportunity to upgrade the SCE correction algorithm. Based on the fact that the Global Navigation Satellite System SCE parameter-fitting error constitutes the majority of the SCE error, we propose a method of computing the SCE corrections by combining a priori knowledge of the SCE parameter-fitting error with real-time measurements. A comparison of the user range error after applying WAAS SCE corrections and fast corrections indicates that the proposed method extends the period when a satellite is augmented by 22.9 % and reduces the root mean square error by 27 %.

Computation of satellite clock---ephemeris corrections using a priori knowledge for satellite-based augmentation system

Statistical multipath model comparative analysis of different GNSS orbits in static urban canyon environment

Cooperative positioning is attracting an increasing amount of attention due to its ability to enhance the accuracy and availability of positioning performance. Current algorithms for cooperative positioning are sensitive to the initial guess as a result of their nonconvex objective functions, which is especially true in hybrid wireless networks. Perfect a priori information about the locations is needed, which is rather problematic in many scenarios. With strong convergence, the iterative parallel projection method (IPPM) is extended to hybrid wireless networks (H-IPPM) in this paper. Motivated by the fact that normal weighted methods cannot achieve the optimal solution, the position uncertainty is modeled, and two distributed weighted parallel projection algorithms, namely, an inexact weighted algorithm called the HBFW-IPPM and an exact weighted algorithm called the HCPW-IPPM, are developed when considering both the range measurement errors and position uncertainty. Experiments in a realistic outdoor scenario are conducted. The results indicate that the exact weighted algorithm HCPW-IPPM shows superior and robust performance in both warm-start and cold-start conditions, and this is true even when non-line of sight (NLOS) measurements and weight estimation errors are taken into account.

Robust Hybrid Cooperative Positioning Via a Modified Distributed Projection-Based Method

Emerging applications, such as improved all-weather safety for self-driving vehicles, require public positioning precision and reliability beyond the capability of open global navigation satellite system (GNSS) services. To meet these requirements, next-generation public positioning, navigation, and time (PNT) services should: 1) deliver ubiquitously available differential corrections and assistance information for massive numbers of concurrent users with fixed delay, indoor penetration and stable bit rate signals and 2) have navigation signals that are extremely enriched against challenging scenarios. The dilemma is that the free-of-charge public PNT service makes it a formidable challenge to build a dedicated information infrastructure. In this context, a natural question arises: where should we seek next-generation public PNT services in the age of Internet of Things? In this paper, we propose GNSS augmentation by FM radio symbiosis. Specifically, we propose GNSS augmentation-optimized digital data broadcasting for which the signal symbiotically co-exists with the analog FM radio in band and in channel without sensibly affecting the existing FM service. With this symbiotic digital data broadcasting, we then propose a GNSS augmentation system that can: 1) broadcast real-time kinematics correction to massive numbers of concurrent GNSS receivers to achieve outdoor precision at the centimeter-level; 2) deliver fine time GNSS assistance for significantly improved receiver sensitivity; and 3) provide common-view timing to enable GNSS independent ground positioning beacon signals. A prime challenge therein is to separate the symbiotic digital signal from the much stronger, spectrum-overlapping co-channel FM signal; this challenge represents a non-orthogonal de-multiplexing problem that is solved by a novel modulation structure. A prototype was designed, and field tests by authorized third parties were conducted with excellent results.

GNSS Augmentation by FM Radio Symbiosis

Advancements in information technology and communication systems enabled the development of a wide variety of location based applications and services. The global navigation satellite systems are among the fundamental localization solutions. In harsh environments (e.g., urban canyons and indoor areas), these solutions do not provide a good accuracy or even become unavailable. In order to offer accurate and ubiquitous localization solutions, wireless communication systems have been considered, where several location dependent parameters of the transmitted signals can be measured and exploited (e.g., the time-of-arrival (ToA), the received signal strength (RSS)). In this work, the topic of wireless localization is explored from a statistical signal processing perspective with a focus on two axes. The first axis is cooperative localization applied to ad-hoc networks, where the nodes perform pair-wise ranging measurements (i.e., ToA or RSS) between each other in order to simultaneously estimate their positions. The unique solvability conditions are studied based on the two approaches of graph rigidity and semidefinite programming, and the identifiability conditions are derived. Location estimation solutions are considered with a focus on probabilistic estimation and its application in Markov random fields using the nonparametric belief propagation (NBP) algorithm. The second axis is mobile terminals tracking based on RSS measurements. These measurements are affected by a shadowing phenomenon. The improvement brought by the knowledge of the shadowing maps to the position estimation accuracy is studied. The classical solution for obtaining these maps is fingerprinting, which can be costly in time and effort. Solutions are developed to overcome these difficulties. Several solutions are proposed and investigated via Monte Carlo simulations in different deployment and application scenarios, and several theoretical and practical results are derived.

https://tel.archives-ouvertes.fr/tel-00787543/document

Some Signal Processing Techniques for Wireless Cooperative Localization and Tracking

This paper describes space-based augmentation for global navigation satellite systems (GNSS). Space-based augmentations increase the accuracy and integrity of the GNSS, thereby enhancing users' safety. The corrections for ephemeris, ionospheric delay, and clocks are calculated from reference station measurements of GNSS data in wide-area master stations and broadcast via geostationary earth orbit (GEO) satellites. This paper discusses the clock models, satellite orbit determination, ionospheric delay estimation, multipath mitigation, and GEO uplink subsystem (GUS) as used in the Wide Area Augmentation System developed by the FAA.

M. S. Grewal

Papers

Space-based augmentation for global navigation satellite systems