Periodic Reporting for period 1 - EDGAR (EGNSS DFMC for GBAS bAsed opeRations)
Reporting period: 2024-01-01 to 2024-12-31
In the currently standardized Ground-based augmentation system (GBAS), a Ground Station (GS) calculates differential corrections and associated integrity data for the GNSS satellite signals received by the ground subsystem and broadcasts this information to GBAS -equipped aircraft in the vicinity of an airport. GBAS enables for GNSS based precision landing capabilities in all-weather conditions. The GBAS approach services are differentiated into several types, namely GBAS Approach Service Types (GAST), which are available when the GBAS airborne equipment and ground station match their performance and functional requirements to enable those service types. Currently GAST C is deployed in several airports supporting CAT I operations (and CAT II using ionospheric monitoring on ground from SBAS), and GAST D has been designed and standardized to support landing operations in lower visibility conditions including CAT III operations. The currently standardized GASTs are based on augmenting GNSS satellite SF (Single Frequency) signals.
The EDGAR (EGNSS DFMC for GBAS bAsed opeRations) project aims to support the development of an improved GBAS solution based on Dual-Frequency Multi-Constellation (DFMC) GBAS, focused on GPS and Galileo.
Hence, the main objectives of this proposal are: to further develop and validate the GBAS DFMC solution so as to modernize and improve air operations, with emphasis on providing safety, availability, and robustness in all situations, including during challenging ionospheric conditions; to analyze the distinguishing features of Single-Frequency Multi- Constellation, or SFMC, GBAS brought by the addition of Galileo; and to facilitate CAT II service to GAST C airborne users based on a GAST D ground station with European Global Navigation Satellite System (EGNSS) integration (from Galileo or EGNOS).
Two concepts were still competing for the DFMC GBAS when the project was proposed, the so-called GAST F (based on transmitting corrections for the signals) and the GAST X (based on the transmission of raw ground station pseudorange and carrier phase measurements for the differential corrections to be computed onboard by the avionics). However, during grant preparation, a convergence between both concepts at ICAO level led to the selection of a different approach, known as GAST E. Consequently, the project activities have been adapted to take into account this decision.
The EDGAR (EGNSS DFMC for GBAS bAsed opeRations) project aims to support the development of an improved GBAS solution based on Dual-Frequency Multi-Constellation (DFMC) GBAS, focused on GPS and Galileo.
Hence, the main objectives of this proposal are: to further develop and validate the GBAS DFMC solution so as to modernize and improve air operations, with emphasis on providing safety, availability, and robustness in all situations, including during challenging ionospheric conditions; to analyze the distinguishing features of Single-Frequency Multi- Constellation, or SFMC, GBAS brought by the addition of Galileo; and to facilitate CAT II service to GAST C airborne users based on a GAST D ground station with European Global Navigation Satellite System (EGNSS) integration (from Galileo or EGNOS).
Two concepts were still competing for the DFMC GBAS when the project was proposed, the so-called GAST F (based on transmitting corrections for the signals) and the GAST X (based on the transmission of raw ground station pseudorange and carrier phase measurements for the differential corrections to be computed onboard by the avionics). However, during grant preparation, a convergence between both concepts at ICAO level led to the selection of a different approach, known as GAST E. Consequently, the project activities have been adapted to take into account this decision.
The activities performed during the reporting period 1 can be clustered and summarized as follows:
Research on open points and definition of requirements:
• Analysis of primary and fallback DFMC GBAS modes based on performance simulations for the processing modes and tests with real measurements.
• Consolidation of assumptions to perform simulations to assess the integrity, availability and continuity of the GAST E proposed architecture.
• Regarding operational aspects, analysis of the impact of VDB transmission rate on sigma ground, trade-offs on aircraft performance, and study of GCID/APD potential coding issues.
• Identification of possibilities of using EGNSS to provide CAT II to GAST C users and assessment of their feasibility.
• Regarding the integrity and continuity allocation for DFMC GBAS, investigation of the ranging source integrity monitoring requirements.
• Initiation of the theoretical formulation of potential scintillation detection strategies.
• Development of a set up for the assessment of robustness of DFMC GBAS against unintentional RFI to see the influence of receiver specific design parameters. A first round of simulations has been run, and the results are being analyzed.
• Start of the modelling of the ionospheric storms, including scintillation, to simulate them and study how they affect GNSS satellites and DFMC GBAS CAT III availability.
Design of integrity monitors:
• An appropriate ionospheric gradient monitoring scheme that leverages the availability of the second navigation frequency and the additional signals from the Galileo constellations was pursued to improve observability.
• For the airborne DSIGMA (Dual Solution Ionospheric Gradient Monitoring Algorithm) monitor, one of the main ionospheric monitors for the DFMC GBAS fallback modes, the derivation of a threshold for GAST D2 (L5/E5a) has been investigated using both ground collected and airborne real data. The potential change of the threshold with different ground data transmission rates is also being analyzed.
• Preliminary studies have been performed to determine the feasibility of facilitating CAT II service to GAST C airborne users based on a GAST D ground station with European Global Navigation Satellite System (EGNSS) integration.
• Potential concepts for an improvement of the ephemeris monitoring have been studied.
• Ongoing the review of approach and aircraft assumptions and FTE/NSE trade-off based on the touchdown requirements in the landing box with the objective to reduce some monitoring thresholds (e.g. the maximum range error or the maximum vertical position error).
Development of new error characterization models for GAST E:
• With the objective of understanding the limits and bound the antenna induced errors at L1/E1 and L5/E5a, the Multipath Limiting Antennas (MLAs) have been characterized to the best state-of-art techniques in an anechoic chamber and a digital twin is underway.
• Extension of airborne multipath models for GAST E to take into account the introduction of different processing methods on board the aircraft.
A series of validation activities, to support the DFMC GBAS concept with the purpose of evaluating its expected system performance, including the robustness against identified threats (such as ionospheric anomalous conditions and RFI), are being defined.
Research on open points and definition of requirements:
• Analysis of primary and fallback DFMC GBAS modes based on performance simulations for the processing modes and tests with real measurements.
• Consolidation of assumptions to perform simulations to assess the integrity, availability and continuity of the GAST E proposed architecture.
• Regarding operational aspects, analysis of the impact of VDB transmission rate on sigma ground, trade-offs on aircraft performance, and study of GCID/APD potential coding issues.
• Identification of possibilities of using EGNSS to provide CAT II to GAST C users and assessment of their feasibility.
• Regarding the integrity and continuity allocation for DFMC GBAS, investigation of the ranging source integrity monitoring requirements.
• Initiation of the theoretical formulation of potential scintillation detection strategies.
• Development of a set up for the assessment of robustness of DFMC GBAS against unintentional RFI to see the influence of receiver specific design parameters. A first round of simulations has been run, and the results are being analyzed.
• Start of the modelling of the ionospheric storms, including scintillation, to simulate them and study how they affect GNSS satellites and DFMC GBAS CAT III availability.
Design of integrity monitors:
• An appropriate ionospheric gradient monitoring scheme that leverages the availability of the second navigation frequency and the additional signals from the Galileo constellations was pursued to improve observability.
• For the airborne DSIGMA (Dual Solution Ionospheric Gradient Monitoring Algorithm) monitor, one of the main ionospheric monitors for the DFMC GBAS fallback modes, the derivation of a threshold for GAST D2 (L5/E5a) has been investigated using both ground collected and airborne real data. The potential change of the threshold with different ground data transmission rates is also being analyzed.
• Preliminary studies have been performed to determine the feasibility of facilitating CAT II service to GAST C airborne users based on a GAST D ground station with European Global Navigation Satellite System (EGNSS) integration.
• Potential concepts for an improvement of the ephemeris monitoring have been studied.
• Ongoing the review of approach and aircraft assumptions and FTE/NSE trade-off based on the touchdown requirements in the landing box with the objective to reduce some monitoring thresholds (e.g. the maximum range error or the maximum vertical position error).
Development of new error characterization models for GAST E:
• With the objective of understanding the limits and bound the antenna induced errors at L1/E1 and L5/E5a, the Multipath Limiting Antennas (MLAs) have been characterized to the best state-of-art techniques in an anechoic chamber and a digital twin is underway.
• Extension of airborne multipath models for GAST E to take into account the introduction of different processing methods on board the aircraft.
A series of validation activities, to support the DFMC GBAS concept with the purpose of evaluating its expected system performance, including the robustness against identified threats (such as ionospheric anomalous conditions and RFI), are being defined.
By now only initial results are being produced. They are being the object of dissemination activities to get feedback from relevant stakeholders and to contribute to the definition of the GBAS DFMC concept and development baseline at ICAO level.