Satellite Selection Methodology for Horizontal Navigation and Integrity Algorithms

With the new upcoming GNSS constellation in the future it might no longer be possible to use all satellites in view for navigation due to limited tracking channels. This is in particular true in the context of Advanced Receiver Autonomous Integrity Monitoring (ARAIM), where the use of dual frequency is favorable to mitigate ionospheric disturbances. To address the issues of limited channels we propose two different satellites selection strategies adapted for Horizontal ARAIM in this paper. First a bare geometric approach which comes with almost no additional computation effort at the cost of less stable results. And second a heuristic optimization which improves selection results significantly while adding additional computational effort. Both approaches are compared to brute force selected best sets in terms of resulting protection levels, computational cost and achieved ARAIM availability. Results show the general applicability of both presented selection methods in Horizontal ARAIM. Using limited sets instead of all satellites in view can still provide global availability. Depending on the method more or less satellites are necessary to ensure sufficiently small and stable protection levels

Satellite selection in the context of an operational GBAS

When incorporating multiple constellations into future ground based augmentation systems (GBAS), a problem with limited VDB (VHF data broadcast) capacity might arise. Furthermore, the number of airborne receiver tracking channels could be insufficient to use all visible satellites. One way to cope with these issues is to perform a satellite selection to limit the number of used satellites with minor impact on performance. This paper investigates different factors that constrain the approach of simply selecting "the best set in every epoch" and shows how to overcome some limitations. These constraints include limitations in satellite visibility, loss of satellites during approach (i.e. in curves), and convergence times in the airborne processing until satellites are usable. Various protection level simulations are performed to show the influence of the named factors on the nominal performance. Taking into account all these contextual influences, results show satellite selection is still applicable in GBAS ground stations

Combined multilateration with machine learning for enhanced aircraft localization

In this paper, we present an aircraft localization solution developed in the context of the Aircraft Localization Competition and applied to the OpenSky Network real-world ADS-B data. The developed solution is based on a combination of machine learning and multilateration using data provided by time synchronized ground receivers. A gradient boosting regression technique is used to obtain an estimate of the geometric altitude of the aircraft, as well as a first guess of the 2D aircraft position. Then, a triplet-wise and an all-in-view multilateration technique are implemented to obtain an accurate estimate of the aircraft latitude and longitude. A sensitivity analysis of the accuracy as a function of the number of receivers is conducted and used to optimize the proposed solution. The obtained predictions have an accuracy below 25 m for the 2D root mean squared error and below 35 m for the geometric altitude

Localization of interrogators with a 1030/1090 MHz spectrum monitoring system

We present a new method for localizing Mode S Secondary Surveillance Radar (SSR) interrogators, which compared to previous work only requires the reception of aircraft transponder replies using one receiver on the ground. Because too high interrogation loads can lead to the suppression of targets, there is an interest in localizing unknown interrogators. To test the proposed localization method a proof-of-concept spectrum monitoring system based on Software Defined Radio (SDR) receivers was implemented. Results obtained from data recorded with the spectrum monitoring system show that Mode S SSRs at distances of up to ca. 320 km could be localized with a distance error <3.5 km, based on a recording of 5 s duration. Additionally, we also present results for load monitoring of aircraft transponder reply rate

Standardization of New Airborne Multipath Models

In aeronautical navigation the use of Global Navigation Satellite Systems (GNSS) is becoming ever more important. GNSS are one of the cornerstones of the performance based navigation (PBN) concept. They are currently used for navigation en-route, as well as during arrival procedures and for lateral approach guidance. Together with satellite-based or ground-based augmentation systems (SBAS, GBAS) satellite navigation can provide precision approach guidance down to CAT-I minima. In order to ensure sufficient global availability of these services and enable new services, such as Advanced Receiver Autonomous Integrity Monitoring (ARAIM) for providing services with higher performance levels, including in regions with active ionospheric conditions, existing integrity concepts and augmentation systems are upgraded to incorporate not only GPS but multiple GNSS constellations and also navigation signals on a second frequency. On the side of GNSS, all GPS satellites since the Block IIF generation with currently 12 operational satellites provide signals in the L5 band (in addition to the most commonly used signals in the L1 band), a second frequency band usable for aeronautical applications. The Galileo constellation has currently 22 operational satellites in orbit that all provide signals on the E1 and E5a frequency bands. Other constellations, such as Glonass and BeiDou are also launching further satellites so that a large number of navigation satellites are available to users. The use of dual-frequency and multi constellation techniques will mitigate the impact of most ionosphere-related disturbances, significantly increasing service availability. All GNSS-based navigation methods have in common that they need appropriate integrity concepts safely bounding any residual errors that may prevail in the position solution. With the ionospheric errors largely addressed by dual-frequency and multi-constellation methods, the residual noise and multipath becomes the most significant contributor to the residual errors. In order to bound these errors, standardized error models are used. The existing multipath model was developed based on extensive data analysis, however, using only the legacy GPS signal in the L1 band. Galileo is using a different modulation for the E1 signals which is less susceptible to multipath. The GPS and Galileo signals in the L5/E5a band are using a 10-times higher chipping rate than the L1/E1 signal. Therefore, also for these signals, the multipath envelope is significantly smaller, potentially allowing to have smaller error models for these signals. When using dual-frequency methods to remove the ionospheric delay, the receiver tracking noise and multipath error from the signals on both frequencies are combined. For all these cases the existing model is not well suited for error modelling. Within the frame of the DUFMAN project funded by the European Commission new multipath models for the new signals are developed in order to be able to exploit the potential benefits for aviation users. Previous papers on the project were addressing the methodology, described the results of the studies and the influence of the antenna. This paper explains the standardization activities and discusses choices that were made in setting up the data collection campaign and the subsequent steps to standardized models. Regarding standardization, the International Civil Aviation Organization (ICAO) is producing Standards and Recommended Practices (SARPS) for DFMC SBAS which will make use of the DFMC multipath models. Further requirements on the hardware exist e.g. in form of Minimum Operational Performance Standards (MOPS) that specify performance of certain components, such as the airborne antenna. A variety of antennas differing significantly in performance is available on the market. Furthermore, the airborne receiver hardware may use different correlator spacing and receiver bandwidth settings which may also have an impact on the results. In the effort to characterize the multipath errors, hardware and processing choices had to be made taking into account all those requirements and the impact on the final models. The paper discusses the interdependency between different standards and explains the choices that were made in the project, as well as results in terms of standardization

Concept for a Dual Frequency Dual Constellation GBAS

This paper proposes one possible concept for a dual frequency dual constellation GBAS architecture. It is based on a single frequency L5/E5a mode as primary processing scheme for best standard performance, a switch to an ionosphere free combination in case of ionospheric disturbances and supporting also classical GBAS approach service types (GAST) C and D for single frequency GPS-based CAT I and CAT II/III modes. The concept is supported by a proposal of how to transmit the required corrections in the existing capacity limited VDB broadcast and is backwards compatible to legacy GBAS. A discussion about the benefits and remaining issues of the proposed architecture concludes the paper

GNSS jamming and its effect on air traffic in Eastern Europe

Global navigation satellite systems technology is at the core of modern air traffic navigation. Aircraft use it to estimate their position, while air navigation service providers rely on services such as automatic dependent surveillance broadcast which have been enabled by this technology. Since satellite signals are very low in power, they are susceptible to radio frequency interference activities, which can have a significant impact on aviation. This paper illustrates how crowd-sourced automatic dependent surveillance data transmitted by aircraft can be used to gain situational awareness about radio frequency interference and how air traffic over Eastern Europe has been impacted by interference activities over a period spanning from February to August 2022. The results suggest that satellite navigation signals were subject to interference of varying strength and duration. We observed several days when more than 1000 flights were affected, representing 60% of the daily traffic in the analysed area. Furthermore, the extent of the interference impact on aviation depends on the altitude of the aircraft, as low-flying aircraft tend to be less affected by interference than the ones flying at higher altitudes. Consequently, this paper contributes to a better understanding of how civil aviation is affected by radio frequency interference and where such disturbances may occur

Impact of GNSS-band radio interference on operational avionics

GNSS outages due to intentional jamming affecting the airspace over the Eastern Mediterranean have received significant attention in recent years. In an effort to better understand the phenomenon and its impact on aviation hardware, DLR sent a data collection flight to the area. The flight was conducted in an Airbus 320, which allowed a study of the behavior of regular avionics and aviation-grade GNSS receivers under jamming conditions. Part of the experimental instrumentation included a high-definition radio-frequency recording device, which allows in-depth pre-correlation analysis of the radio spectrum around the main GPS and Galileo carrier frequencies. The results confirm that the observed outages likely stem from man-made radio interference. They also provide an in-situ opportunity to study the behavior of commercial avionics under GNSS interference conditions