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Two critical parameters for advanced receiver autonomous integrity monitoring are the probability of satellite fault and the probability of constellation fault. This paper provides specific definitions for each of these fault types. We describe how these faults are evaluated and how to estimate their probability occurrence. Providing a precise definition of what constitutes a fault is essential so that all observers are able to agree on whether or not one has occurred. [ABSTRACT FROM AUTHOR]

We describe a simple method to determine a Global Navigation Satellite System (GNSS) position estimator for advanced receiver autonomous integrity monitoring (RAIM) that improves availability upon the commonly used least squares estimator. The idea consists in searching the estimator among all affine combinations of the all-in-view least squares estimator and a fault-tolerant estimator?the one corresponding to the most difficult fault to mitigate. Availability simulations show a significant improvement in vertical guidance coverage levels for a dual constellation scenario. [ABSTRACT FROM PUBLISHER]

Multipath and jamming interference affects the accuracy, availability, and continuity of global navigation satellite systems. The U.S. Global Positioning System and the Russian Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) are being joined by the European Galileo and the Chinese BeiDou. An increasing number of satellites in multiple constellations enable users to use high-mask-angle antennas (HMAAs) to mitigate interference signals coming from a low-elevation angle. This paper studies the optimal antenna mask angle that maximizes the suppression of interference but still maintains the performance of a single constellation with a low-mask-angle antenna. This paper first proves a novel lower bound on the expectation of dilution of precision (DOP) and derives closed-form formulas that relate the lower bound to the antenna mask angle and the number of satellites. Then, through extensive simulations, a variety of optimal mask angles are obtained with respect to different constellation settings, different DOP metrics, and different assumptions of range accuracy. The numerical results highly agree with our theory. Both of them show that two constellations can match the performance of one constellation with a 5 ^\circ–14 ^\circ higher mask, and three constellations can match the performance of one constellation with an 11 ^\circ–23 ^\circ higher mask, depending on the DOP metric and the range error model used. The numerical results also show that using HMAAs is more beneficial to users interested in positioning accuracy than to users interested in time transfer accuracy. [ABSTRACT FROM PUBLISHER]

GPS technology is essential for future intelligent air transportation systems such as the Next Generation Air Transportation System (NextGen) of the United States. However, observed deep and frequent amplitude fading of GPS signals due to ionospheric scintillation can be a major concern in expanding GPS-guided aviation to the equatorial area where strong scintillation is expected. Current civil GPS airborne avionics track signals at a single frequency (L1 frequency) alone because it was the only civil signal available in the frequency band for aviation applications. The first GPS Block IIF satellite was launched in May 2010. This next-generation satellite transmits a new civil signal at the L5 frequency, which can be used for air transportation. This paper investigates a possible improvement in the availability of GPS-based aircraft landing guidance down to 200 ft above the runway, which is also known as Localizer Performance with Vertical Guidance (LPV) 200, under strong ionospheric scintillation when dual-frequency signals are available. Based on the availability study, this paper proposes and justifies a GPS aviation receiver performance standard mandating fast reacquisition after a very brief signal outage due to scintillation. In order to support a temporary single-frequency operation under a single-frequency loss due to scintillation, a new vertical protection level (VPL) equation is proposed and justified. With this new performance requirement and new VPL equation in place, 99% availability of LPV-200 would be attainable, rather than 50% at the current standards, even under the severe scintillation scenarios considered in this paper. [ABSTRACT FROM PUBLISHER]

Knowledge of the Global Positioning System (GPS) signal-in-space (SIS) anomalies in history has a great importance for not only assessing the general performance of GPS SIS integrity but also validating the fundamental assumption of receiver autonomous integrity monitoring (RAIM): at most one satellite fault at a time. The main purpose of this paper is to screen out all potential SIS anomalies in the last decade by comparing broadcast ephemerides and clocks with precise ones. Validated broadcast navigation messages are generated from 397,044,414 navigation messages logged by on average 410 International GNSS Service (IGS) stations during the period 6/1/2000?8/31/2010. Both IGS and National Geospatial-Intelligence Agency (NGA) precise ephemerides/clocks are used as truth references. Finally, 1256 potential SIS anomalies are screened out. These anomalies show an improving SIS integrity performance in the last decade, from tens or hundreds of anomalies per year before 2003 to on average two anomalies per year after 2008. Moreover, the fundamental assumption of RAIM is valid because never have two SIS anomalies or more occurred simultaneously since 2004. [ABSTRACT FROM AUTHOR]

Satellite navigation has been used for aircraft navigation for more than 50 years. In the last ten years, the capabilities of satellite navigation have been expanded to more demanding phases of flight, in particular vertical guidance down to 200 ft, thanks to the implementation of augmentation systems. In this paper, we attempt to predict the state of satellite navigation in the next 15 years. We will start by reviewing the challenges that must be addressed by satellite navigation for aircraft guidance. Then, we will describe the current techniques that enable satellite navigation for aviation and the level of performance they achieve today. This will be followed by a description of the upcoming changes to satellite navigation, which include the launch of new constellations and the introduction of new civil signals. Despite these developments, satellite navigation is inherently vulnerable to radio-frequency interference so that backup navigation systems are still necessary. Nonetheless, these improvements will have a great impact on the availability and level of service achieved by satellite navigation, in particular enabling worldwide coverage of vertical guidance. [ABSTRACT FROM PUBLISHER]

Strong ionospheric scintillation due to electron density irregularities inside the ionosphere is commonly observed in the equatorial region during solar maxima. Strong amplitude scintillation causes deep and frequent Global Positioning System (GPS) signal fading. Since GPS receivers lose carrier tracking lock at deep signal fading and the lost channel cannot be used for the position solution until reacquired, ionospheric scintillation is a major concern for GPS aviation in the equatorial area. Frequent signal fading also causes frequent reset of the carrier smoothing filter in aviation receivers. This leads to higher noise levels on the pseudo-range measurements. Aviation availability during a severe scintillation period observed using data from the previous solar maximum is analyzed. The effects from satellite loss due to deep fading and shortened carrier smoothing time are considered. Availability results for both vertical and horizontal navigation during the severe scintillation are illustrated. Finally, a modification to the upper bound of the allowed reacquisition time for the current Wide Area Augmentation System (WAAS) Minimum Operational Performance Standards (MOPS) is recommended based on the availability analysis results and observed performance of a certified WAAS receiver. [ABSTRACT FROM PUBLISHER]