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Fault detection algorithms (such as advanced RAIM) developed for aviation can be applied in situations where the probabilities of fault are arbitrarily high. However, with large probabilities, the user receiver needs to protect against a large number of fault modes (which results from the combination of simultaneous independent faults). In baseline ARAIM algorithms, the user receiver must compute a fault-tolerant position solution for each fault mode (computed using the subset of the available measurements that would not be affected by the fault mode), or at least its error covariance. After showing how to use a solution separation algorithm without computing the fault-tolerant position solutions, we present a technique to obtain upper bounds on the subset error covariance for a given subset size. This upper bound does not require the computation of every subset error covariance and can be computed without additional matrix inversions. We evaluate the potential of this technique by applying it to ARAIM scenarios. [ABSTRACT FROM AUTHOR]

Due to the ever-growing threat of GPS spoofing, it has become necessary for the aviation sector to develop an effective means of detection. This article focuses on two complementary spoofing-detection techniques that are available on commercial GPS receivers and thus require no additional hardware to operate. The primary methodology for detection is using a combination of radio power monitoring metrics, levering both automatic gain control and C/N0 measurements, along with multiple correlations for signal distortion to provide a best practices spoofing-detection algorithm, which is able to distinguish between interference and spoofing. The article first assesses nominal statistics for both metrics compiled from more than 250 h of nominal data collected from multiple wide area augmentation system stations. These data are compared to previous collections to validate the thresholds and false alarms rates and establish a complete testing methodology. These tests and thresholds are then assessed with the Texas spoofing test battery series of GPS spoofing data sets to confirm detection capabilities. Finally, these tests and thresholds are applied to assess the GPS signal of six extended flights over the United States to assess the performance on an aircraft. [ABSTRACT FROM AUTHOR]

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]

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]