The ionosphere has been the most challenging source of error to mitigate within the community of global navigation satellite system (GNSS)-based safety-critical systems. Users of those systems should be assured that the difference between an unknown true position and a system-derived position estimate is bounded with an extremely high degree of confidence. One of the major concerns for meeting this requirement, known as integrity, is ionosphere-induced error or discontinuity of GNSS signals significant enough to threaten the safety of users. The potentially hazardous ionospheric anomalies of interest in this article are ionospheric spatial decorrelation and ionospheric scintillation under disturbed conditions. As the demand of safety-critical navigation applications increases with the rapid growth of the autonomous vehicle sector, ionospheric monitoring and mitigation techniques become more important to support such systems.

A multi‐unmanned aerial vehicle (UAV)‐based stereo vision system is proposed to assist global path planning of an unmanned ground vehicle (UGV) even in GPS‐denied environments. The proposed system can optimally generate the depth map of ground objects and robustly detect obstacles. The proposed multi‐UAV‐based system with a movable baseline overcomes the limitations of a single‐UAV‐based stereo vision system with a fixed baseline. Thus, the performance of the proposed system does not degrade significantly based on the altitude of UAVs. The relative position and altitude estimation, multi‐agent formation control and image processing techniques are considered to implement a prototype system. The experimental results demonstrate the performance of the implemented system for various baseline conditions between UAVs.

The position accuracy of Global Navigation Satellite System (GNSS) modules is one of the most significant factors in determining the feasibility of new location-based services for smartphones. Considering the structure of current smartphones, it is impossible to apply the ordinary range-domain Differential GNSS (DGNSS) method. Therefore, this paper describes and applies a DGNSS-correction projection method to a commercial smartphone. First, the local line-of-sight unit vector is calculated using the elevation and azimuth angle provided in the position-related output of Android’s LocationManager, and this is transformed to Earth-centered, Earth-fixed coordinates for use. To achieve position-domain correction for satellite systems other than GPS, such as GLONASS and BeiDou, the relevant line-of-sight unit vectors are used to construct an observation matrix suitable for multiple constellations. The results of static and dynamic tests show that the standalone GNSS accuracy is improved by about 30%–60%, thereby reducing the existing error of 3–4 m to just 1 m. The proposed algorithm enables the position error to be directly corrected via software, without the need to alter the hardware and infrastructure of the smartphone. This method of implementation and the subsequent improvement in performance are expected to be highly effective to portability and cost saving.

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.

The vulnerability of global positioning system (GPS) receivers to jammers is a major concern owing to the extremely weak received signal power of GPS. Researches have been conducted on a variety of antenna array techniques to be used as countermeasures to GPS jammers, and their antijamming performance is known to be greater than that of single antenna methods. However, the application of antenna arrays remains limited because of their size, cost, and computational complexity. This article proposes and experimentally validates a novel space-time-polarization-domain adaptive processing for a single-element dual-polarized antenna (STPAPS) by focusing on the polarization diversity of a dual-polarized antenna. The mathematical models of arbitrarily polarized signals received by the dual-polarized antenna are derived, and an appropriate constraint matrix for dual-polarized-antenna-based GPS antijam is suggested. To reduce the computational complexity of the constraint matrix approach, the eigenvector constraint design scheme is adopted. The performance of STPAPS is quantitively and qualitatively evaluated through experiments as follows. First, the carrier-to-noise-density ratio (C/N ₀ ) of STPAPS under synthetic jamming is demonstrated to be higher than that of the previous minimum mean-squared error (MMSE) or minimum variance distortionless response (MVDR) based dual-polarized-antenna methods. Second, the strengths and weaknesses of STPAPS are qualitatively compared with those of the previous single-element dual-polarized-antenna methods that are not based on the MMSE or MVDR algorithms. Finally, the characteristics of STPAPS (in terms of the directions and polarizations of the GPS and jamming signals) are compared with those of the conventional two-element single-polarized-antenna array method, which has the same degree of freedom as that of STPAPS. This is a GPS L1 C/A-code proof-of-concept study, although STPAPS will extend to higher chipping-rate modernized global navigation satellite system signals.

After a series of intentional Global Positioning System (GPS) jamming attacks impacted a large area of South Korea, the Ministry of Oceans and Fisheries of South Korea considers long-range navigation (Loran) and enhanced Loran (eLoran) as a maritime backup navigation system. Despite its robustness to signal jamming, the positioning accuracy of Loran/eLoran is lower than that of GPS. Because the signal delay due to the land path, which is called the additional secondary factor (ASF), is the largest unknown component of Loran/eLoran, it is necessary to account for temporal and spatial ASF errors to ensure high accuracy. The generation of ASF maps based on ASF survey data in a service area is the most convenient way to mitigate spatial ASF error, but the quality of ASF maps depends on the applied interpolation algorithm. It is desirable to generate high-quality ASF maps based on ASF measurements at only a few survey points, because extensive ASF surveys are expensive and time-consuming and require considerable effort. This paper proposes kriging methods for satisfying this objective and shows their superior performance during a field test in Incheon, Korea. In particular, universal kriging with the proposed drift model showed a better performance than linear interpolation, inverse distance weighing, and ordinary kriging when the test vehicle was close to a coastline. The positioning accuracy with the ASF maps generated by the proposed universal kriging along a 5-km route during the field test was 25.24 m (95%). The land vehicle used for the test experienced significant signal-to-noise ratio (SNR) degradation owing to the noise caused by its engine. A vessel without such SNR degradation is expected to achieve higher accuracy.