Space-based augmentation for global navigation satellite systems
03 Apr 2012-IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control (IEEE)-Vol. 59, Iss: 3, pp 497-503
TL;DR: 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 are discussed.
Abstract: 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.
Citations
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TL;DR: A method of computing the S CE corrections by combining a priori knowledge of the SCE parameter-fitting error with real-time measurements is proposed, which extends the period when a satellite is augmented by 22.9 % and reduces the root mean square error by 27 %.
Abstract: 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 %.
13 citations
Cites methods from "Space-based augmentation for global..."
...WAAS was first introduced by Enge et al. (1996), and enhancements to its system architecture and algorithms were briefly discussed in Grewal (2012)....
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TL;DR: GNSS multipath channel characteristics research and modeling is an important but not well-solved topic, and a series of on-field research experiments from June 2015 to August 2017 at Shanghai Lujiazui area in China yields insights that will be helpful for the design of both GNSS receivers and simulators.
11 citations
TL;DR: 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.
Abstract: 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.
7 citations
TL;DR: This paper proposes GNSS augmentation by FM radio symbiosis for which the signal symbiotically co-exists with the analog FM radio in band and in channel without sensibly affecting the existing FM service.
Abstract: 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.
6 citations
Cites background from "Space-based augmentation for global..."
...• Deliver real time RTK differential correction for centimeter level outdoor positioning and fine time GNSS aiding for improved indoor sensitivity to unlimited number of simultaneous users [5]....
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Dissertation•
16 Nov 2012TL;DR: The topic of wireless localization is explored from a statistical signal processing perspective with a focus on two axes, where location estimation solutions are considered with afocus on probabilistic estimation and its application in Markov random fields using the nonparametric belief propagation (NBP).
Abstract: 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.
6 citations
Cites background from "Space-based augmentation for global..."
...External information can be delivered either by a satellite-based augmentation system (SBAS) in which messages are broadcast by additional satellites [9], or by a ground-based augmentation system (GBAS) in which messages are broadcast by terrestrial wireless networks [10]....
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References
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24 Sep 1993
TL;DR: In this article, a Kalman-type filter and random walk process noise are used to generate TEC maps at 1 hour or less intervals, and the maps utilize a locally supported vertical TEC function (called "TRIN") based on tessellation of the sphere into 1280 spherical triangles.
Abstract: The global positioning system satellites and a world-wide
network of dual-frequency GPS receivers can be used to
measure ionospheric total electron content (TEC) on
global scales. A new method for generating global TEC
maps is described. This method uses a Kalman-type filter
and random-walk process noise to generate TEC maps at
time intervals of one hour or less. The maps utilize a
locally-supported vertical TEC function (called “TRIN”)
based on tessellation of the sphere into 1280 spherical
triangles. The 642 vertices of the triangles are assigned a
TEC value estimated from the data and the TEC within
each tile is computed by linearly interpolating between
vertex TEC values. The previous approach used a single-
batch filter requiring an averaging time of 6-12 hours
before a map could be obtained; the TEC data was fitted to
a surface harmonic expansion which did not follow local
TEC variations accurately. Both approaches use a
spherical thin-shell elevation mapping function to convert
all station-to-satellite TEC measurements to equivalent
vertical TEC at a unique shell intersect point. The new
maps follow diurnal TEC variations over a single site to
within a few TECU as measured by established single-site
GPS calibration techniques. In a global-scale simulation
using the Bent ionosphere model, the TRIN fit reproduces
the simulated data set to within 5 TECU over 70 percent
of the globe. Errors exceeding 10 TECU are seen in the
daytime-peak regions within the equatorial bulge.
Methods for improving the accuracy of the maps are
discussed.
256 citations
"Space-based augmentation for global..." refers background in this paper
...The actual computation of the interfrequency biases and ionospheric delay involves both l1l2 and Iono filters [5]–[7]....
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TL;DR: It is expected that improvements in smoothing and editing techniques for the dual-frequency user will yield better positions than those yielded for single-frequency users during peak solar activity.
Abstract: This paper describes the system architecture, algorithms, and results from an operating Wide Area Differential GPS (WADGPS) system spanning the continental United States (CONUS). With single-frequency GPS user equipment and improved positioning algorithms, real-time root mean square (RMS) user position accuracy is typically better than 25 cm in the horizontal components and 50 cm in the vertical with current levels of ionospheric activity. Dual-frequency users have a slightly degraded accuracy of 35 cm horizontal and 75 cm vertical. There may be some degradation in single-frequency positioning during solar maximum or ionospheric storms. We expect that improvements in smoothing and editing techniques for the dual-frequency user will yield better positions than those yielded for single-frequency users during peak solar activity. In addition to commercial applications, the software for estimation of the WADGPS corrections is being adapted for use in the Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) and will be installed in the FAA's National Satellite Test Bed (NSTB).
42 citations
"Space-based augmentation for global..." refers background in this paper
...space-based augmentation systems (sBas) include the United states’ Wide area augmentation system (Waas), the European Union’s European Geostationary navigation overlay service (EGnos), Japan’s Multifunctional Transport satellite augmentation system (Msas), canada’s canadian Waas (cWaas), china’s satellite navigation augmentation system (snas), and India’s GPs and GEo augmented navigation (GaGan) [1]–[3]....
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Book•
28 Oct 201725 citations
15 Sep 1995
TL;DR: This solution to the ionospheric correction problem is self-calibrating, since GPS transmitter inter-frequency biases are obtained as a byproduct of the mapping procedure, which contrasts with other techniques in which bias values must be provided from sornc additional source.
Abstract: A powerful approach for generating ionospheric
corrections in wide area differential GPS applications has
been developed, that can be applied to the Federal
Aviation Administration’s Wide Area Augmentation
System (WAAS). This approach has been used to support
ionospheric calibration for NASA’s Deep Space Network
and will be supporting real-time operations for global
ionospheric specification and, possibly, single-frequency
satellite altimeter calibration. It is a real-time, grid-based
technique relying on a computationally efficient Kalman-
type filter to produce accurate, smoothly varying
ionospheric correction maps over the coverage area.
Formal error maps are also computed, providing vertical
delay errors over the WAAS grid, which are useful in
integrity monitoring. This solution to the ionospheric
correction problem is self-calibrating, since GPS
transmitter inter-frequency biases are obtained as a by-
product of the mapping procedure. This contrasts with
other techniques in which bias values must be provided
from some additional source.
Simulated data were generated for the proposed
configuration of 24 WAAS reference GPS stations, using
a well-tested climatological ionosphere model (Bent) to
compute ionospheric total electron content (TEC) during
conditions typical near the peak of the solar cycle. Slant
TEC delays often exceed 30 meters over the continental
US (CONUS) during solar maximum, but the simulations
indicate that the corrections are accurate to 0.25-0.5 meter
over the CONUS. Alaska and Hawaii (this includes any
errors in estimating the transmitter biases). Our technique
is therefore useful for en-route navigation and precision
approach, the latter requiring 1.5 meter correction
accuracy.
15 citations
"Space-based augmentation for global..." refers background in this paper
...The actual computation of the interfrequency biases and ionospheric delay involves both l1l2 and Iono filters [5]–[7]....
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19 Sep 1997
5 citations
"Space-based augmentation for global..." refers methods in this paper
...The error signal input is the difference between the l1 doppler frequency from the Waas GPs receiver and the estimated range rate (converted to a doppler frequency) from the Kalman filter [8], [10]–[12]....
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