Omni-directional Microstrip Antenna for GBAS

Ground based augmentation system (GBAS) is the only global navigation satellite system (GNSS) with augmentation that can support category III precision approach and landing for aircrafts in the near future. The State Key Laboratory of Air Traffic Management System and Technology has developed a GBAS prototype that based on the Beidou Navigation Satellite System (BDS). Here, an assessment of BDS GBAS performance during position domain trials has been given with respect to requirements for the GBAS approach service type C (GAST C), which permits aircraft approach and landing down to the zero visibility conditions of category I approaches. The experimental results show that the accuracy of the airborne terminal is sub-meter level after the pseudorange has been corrected, and the availability of the BDS GBAS for GAST C is greater than 0.99999. The BDS GBAS is implemented within the required accuracy, integrity and availability standards for GAST C. However, due to the poor distribution of satellites geometry in some time periods, the availability of the BDS GBAS cannot meet the required criteria for GAST-D approaches. In the future, a dual-frequency and dual-constellation GBAS based on the BDS and GPS will be developed to improve the integrity and availability of the system.

Ground-Based Augmentation System (GBAS) is concerned with the aircraft positioning correction for precision landing. The ionospheric irregularity is a major impediment of the performance of GBAS. When an airport has at least 2 Global Navigation Satellite System (GNSS) stations, the ionospheric delay gradients can be obtained by using the dual-frequency GNSS stations. If there is only 1 GNSS station in the area, the time step-method can be used. Normally, the baseline from the time-step method is varied according to the sampling rate of GNSS data. Although the sampling rate of the GNSS receiver is a constant value, the baseline varies due to the speed of the GNSS satellite, observed from the ground reference, which can be up to 20 difference km. This paper proposes the dynamic Time-Step method which designates the baseline by adjusting the time between 2 snapshots. The results show that the range of baseline from the reference time-step method, which is set to 1 minute of the sampling rate, can be reduced to 0.5-km variation.

The ground-based augmentation system (GBAS) is the cornerstone for enabling automated landings without the instrument landing system (ILS). Currently, GBAS is evolving to GBAS approach service type-D (GAST-D) for category III landings. This development toward GBAS GAST-D extends GBAS via the use of multiple frequencies (L1/L2 and L5) and the use of multiple global navigation satellite system constellations. GBAS requires correction data to be broadcast to aircraft, which is currently handled via the VHF data broadcast (VDB) datalink. However, VDB has several known shortcomings: 1) low throughput, 2) small area of operation, and 3) no cyber-security measures. In this article, we propose the use of the L-band digital aeronautical communications system (LDACS) for broadcasting GBAS correction data to address these shortcomings. In flight experiments conducted in 2019, we set up an experimental GBAS installation using LDACS. Broadcast data are secured using the timed efficient stream loss-tolerant authentication (TESLA) broadcast authentication protocol. Our results indicate that cryptographically secured GBAS data via LDACS can provide GAST-C and GAST-D services with high availability if cryptographic parameters are chosen appropriately.

The Ground Based Augmentation System (GBAS)is a landing system for aircraft based on Global NavigationSatellite Systems (GNSS). It consists of a reference station at anairport that generates corrections and integrity parameters thatare transmitted to arriving aircraft. The broadcast is currentlyaccomplished via a VHF data broadcast (VDB). In recent years itturned out that proper siting and frequency planning for theVDB is a challenging task in an operational environment.Coverage, as well as signal power issues, especially at large andcomplex airports have led to a number of considerations thathave to be taken into account when installing VDB transmissionantennas. Furthermore, current GBAS only broadcastcorrections for the L1 frequency of GPS satellites. Availabilityissues, mainly due to ionospheric effects in equatorial regions,however, drive the development of expanding GBAS from asingle frequency single constellation system towards a dualfrequency multi constellation architecture. Transmittingadditional corrections and integrity parameters at the sameupdate rate is challenging due to the limited capacity of the VDBdata link. Finally, transmission should offer the potential toprovide secure transmissions with an authenticated signal inorder to be robust also from a security perspective. For all thesereasons it can be envisioned to provide the GBAS messages viaLDACS which is currently in the process of standardization. Thiscould resolve the issues mentioned and thus support GBASimplementation in the future. This paper provides an overview ofthe expected benefits mentioned above and provides a firstperformance estimation of GBAS over LDACS.

The positioning accuracy and integrity of the Ground-Based Augmentation System (GBAS) are impacted by the abnormal troposphere and ionosphere conditions resulting from extreme weather and intense radiation. Non-nominal troposphere error will increase the residual tropospheric uncertainty between the GBAS ground facility and aircraft. The plasma bubbles may induce signal scintillations while passing across a signal path, which could result in a loss of lock or a cycle slip. However, existing methods cannot deal with the threats caused by abnormal meteorological conditions. To reduce the impact of these conditions on GBAS, this paper describes an optimization method. By reassessing the weight matrix W in the calculation of the Vertical Protection Level (VPL), satellites that suffer from bigger pseudorange errors are assigned less importance in the positioning solution. Therefore, the positioning accuracy and integrity of GBAS are improved. Initially, we evaluate the Geometric Dilution of Precision and VPL for both single GPS and GPS+BDS constellations under abnormal meteorological conditions. The performance of different orbiting satellites in such conditions is then evaluated to further analyze their benefits in future Multi-Constellation Dual Frequency (MCDF) GBAS. The results show that the proposed optimization method can effectively reduce the influence of abnormal meteorological conditions and improve the positioning accuracy and integrity of MCDF GBAS. Moreover, mixed orbiting satellites provide more robustness against abnormal meteorological conditions and can significantly enhance the performance of MCDF GBAS.

The ground based augmentation system (GBAS) uses ground subsystems including reference receivers to provide differentially correction Global Navigation Satellite System (GNSS) data to improve the overall accuracy and integrity of the system. The accuracy of the GBAS ground subsystem is measured in the pseudo-range domain, so it is necessary to perform pseudo-range domain accuracy testing of the GBAS ground equipment. Based on the B-value method, this paper presents the evaluation process of GBAS pseudo-range domain accuracy based on the BDS-3 new frequency points of B1C and B2a. The B-value methodology is based on broadcast pseudo-range correction data, which covers the differential correction data of all reference stations and considers ground system monitoring, and can reflect the impact of the multipath synthesis effect of different receiver combinations on the accuracy of the pseudo-range domain. The real-collected data shows that the built test system can reach a GAD-B3 accuracy level, and the B-value method can effectively evaluate the pseudo-range domain accuracy of BDS-3 GBAS reference receivers.

Nowadays one can use four global navigation satellite systems (GNSS). Two of them are complete constellations (GPS, Glonass) and two (Beidou, Galileo) are already usable and will be finish in the near future. Additionally satellite based augmentation systems (SBAS) like WAAS, EGNOS, GAGAN or QZSS complement the GNSS service. However, within all systems one can observe changes, modifications, and updates every year. This can be related to satellite renewables leading to signal property changes. Especially, for safety critical applications using GNSS, like advanced receiver autonomous integrity monitoring (ARAIM) or ground-based augmentation systems (GBAS) the new or changed signal properties are of high interest. With the help of detailed information about the signal deformation and the received signal power it is possible to calculate realistic error bounds and consequently realistic protection level for these kinds of safety critical applications. This paper presents an overview of the findings according new signals or signal configurations of GPS, Beidou and QZSS of the last two years. After a brief introduction of the measurement facility the paper will introduce basic analysis about the quality of the signal shape in spectral and modulation domain. Using our precise calibrated measurement facility, we will also present an analysis of the transmitted satellite signal power including estimates about the power sharing among individual signal components within each band. Considering the measured power in relation to the boresight angle of the satellite one can derive a cut through the antenna pattern of the satellite and can assess the antenna symmetry properties. Examples for different satellites will be presented. Finally, we will end with a conclusion regarding the considered signal developments and its impact on GNSS users.

The Ground-Based Augmentation System (GBAS) is a navigation system for aircraft designed to be used for precision approaches and landings. GBAS improves the accuracy of the satellite navigation system significantly. However, some flight accidents still occur occasionally due to lack of availability and it makes more stringent requirements on availability that CAT II/III precise approach is trying to introduce GBAS. Therefore, it is necessary to find an effective prediction algorithm for GBAS. The protection level is a key parameter in the process of evaluating the availability. There are three relevant parameters: quantile K represents the fault-free missed detection multiplier; projection matrix S is the vertical projection factor in the along-track coordinate system; variance of measurement noise is the standard deviation of the uncertainties of the residual differential error, which consists of the root sum square of uncertainties introduced through ionospheric and tropospheric decorrelation as well as the contribution of the ground and airborne multipath and noise. Some researchers have found that the model for the standard deviation of GBAS pseudo-range correction error is conservative, which causes decline of prediction accuracy. However, it is hard to explicitly model this parameter. We made a reevaluation based on support vector machine and improved the prediction algorithm for availability. We developed the simulation software and make practical measurement. Considering the influence of different distributions of based stations of GBAS, the availabilities of EWR, GIG and IAH are evaluated, and the results were compared with the actual values. The result shows that the prediction errors are 3.17%, 1.96% and 0.98% respectively.

Global navigation satellite system (GNSS) can realize global time synchronization with tens of nanoseconds precision. For more precise time synchronization applications, two-way satellite time and frequency transfer is commonly used despite its high cost and requiring a geostationary satellite. Considering the high cost, people started to use the GNSS signals to realize high accuracy time transfer, named common-view or all-in-view, which can achieve several nanoseconds according to the analyses and verifications of previous studies. However, time transfer cannot realize real-time timing in a large area as a common GNSS one-way timing receiver does. In such a timing system, a highly stable reference and a matched high-precision timing receiver system are necessary. To solve this problem, we have established a one-way timing system based on a ground-based augmentation system. The system estimates real-time high-precision satellite clocks using the ground-based augmentation network as the time reference. Moreover, the time reference is transferred to the terminal through real-time precise point positioning (PPP). Finally, the timing receiver synchronizes its local clock to the reference by real-time clock adjustment, resulting in high-precision timing. We present the details of this system, including the time reference, the PPP algorithm, and the timing receiver technologies. Finally, we give the precision and stability evaluation of the whole system, especially for one pulse per second (1 PPS) outputs of the terminal. The results show that the stability of the 1 PPS output is better than 1 ns in a day.

This article presents analysis results from a long-term multi-site Global Navigation Satellite System (GNSS) Radio Frequency Interference (RFI) monitoring campaign in the context of Ground Based Augmentation System (GBAS) Dual Frequency Multi Constellation (DFMC) concept operation. GBAS resilience against unintentional RFI is an important area for investigation as the ground station receivers often must operate adjacent to high-traffic roads where chances of being affected by RFI are high. To be able to develop algorithms and reaction strategies necessary to ensure continuity and availability of service, knowledge of interference signal characteristics and frequency band/bands affected, as well as relative occurrence rates between the considered frequencies and frequency combinations, is necessary. The analysis presented in the article covers the prevalence and properties of the RFI events observed on the GPSs L1 and L5 and the Galileo E1 and E5a frequency bands that are considered by the on-going DFMC GBAS concept development initiatives. Due to being spectrally adjacent, the observed event analysis is also carried out for the Galileo E5b and GLONASS G1 frequency bands. The article also addresses the issue of spectral occupancy distribution of the observed events and presents new interesting RFI event types captured during the considered monitoring period.

The Gaussian mixture model (GMM) is commonly used to model the heavy tail of the ground-based augmentation system (GBAS) range error distribution. In practice, Gaussian over-bounding based on a GMM is used to over-bound the heavy tail of the ranging errors, but the GBAS protection levels (PLs) based on the Gaussian over-bounding tend to be overestimated. Based on the idea of solution separation and overcoming the shortcoming of its direct reference to GBAS, this paper analyses the constraint conditions and objective functions of the optimal protection level based on solution separation under a GMM distribution, and proposes that multi-hypothesis solution set classification can effectively reduce the computational complexity. At the same time, least squares optimization and dynamic allocation of integrity risk are used to further reduce the protection level. This paper verifies the validity of the parameters of the GMM based on actual airport GBAS data, performs simulation verification of the typical scenarios of CAT I and CAT II/IIIa global GBAS under the Beidou 3 constellation, and analyses the performance improvement effect under different solution set traversal depths. The results show that when the traversal depths of CAT I and CAT II/IIIa are 4 and 6, the vertical protection level component of the ground ranging error is reduced by 14% and the total vertical protection level is reduced by 10%.

This paper explores the potential of integrating Global Navigation Satellite System (GNSS) Avionics Based Integrity Augmentation (ABIA) functionalities in Unmanned Aerial Systems (UAS) to perform mission planning and real-time trajectory optimisation tasks. In case of mission planning, a pseudo-spectral optimization technique is adopted. For real-time trajectory optimisation a Direct Constrained Optimisation (DCO) method is employed. In this method the aircraft dynamics model is used to generate a number of feasible flight trajectories that also satisfy the GNSS integrity constraints. The feasible trajectories are calculated by initialising the aircraft dynamics model with a manoeuvre identification algorithm. The performance of the proposed GNSS integrity augmentation and trajectory optimisation algorithms was evaluated in representative simulation case studies. Additionally, the ABIA performance was compared with Space-Based and Ground-Based Augmentation Systems (SBAS/GBAS). Simulation results show that the proposed integration scheme is capable of performing safety-critical UAS tasks (CAT III precision approach, UAS Detect-and-Avoid, etc.) when GNSS is used as the primary source of navigation data. There is a synergy with SBAS/GBAS in providing suitable (predictive and reactive) integrity flags in all flight phases. Therefore, the integration of ABIA with SBAS/GBAS is a clear opportunity for future research towards the development of a Space-Ground-Avionics Augmentation Network (SGAAN) for UAS SAA and other safety-critical aviation applications.

Global Navigation Satellite Systems (GNSS) can support the development of low-cost and high performance navigation and guidance architectures for Unmanned Aircraft Systems (UAS) and, in conjunction with suitable data link technologies, the provision of Automated Dependent Surveillance (ADS) functionalities for cooperative Sense-and-Avoid (SAA). In non-cooperative SAA, the adoption of GNSS can also provide the key positioning and, in some cases, attitude data (using multiple antennas) required for automated collision avoidance. A key limitation of GNSS for both cooperative (ADS) and non-cooperative applications is represented by the achievable levels of integrity. Therefore, an Avionics Based Integrity Augmentation (ABIA) solution is proposed to support the development of an Integrity-Augmented SAA (IAS) architecture suitable for both cooperative and non-cooperative scenarios. The performances of this IAS architecture were investigated in representative simulation case studies by testing the ability of the SAA system to exploit the predictive (caution) and reactive (warning) integrity flags generated by ABIA. Additionally, the ABIA False Alarm Rate (FAR) and Detection Probability (DP) performances were examined and an initial evaluation of the complementarity with Space-Based and Ground-Based Augmentation Systems (SBAS/GBAS) was accomplished. Simulation results show that the proposed IAS architecture is capable of performing high-integrity conflict detection and resolution when GNSS is used as the primary source of navigation data and there is a clear synergy with state-of-the art SBAS/GBAS in all applicable flight phases.

Purpose The purpose of this paper is to present the problem of implementation of the differential global navigation satellite system (DGNSS) differential technique for aircraft accuracy positioning. The paper particularly focuses on identification and an analysis of the accuracy of aircraft positioning for the DGNSS measuring technique. Design/methodology/approach The investigation uses the DGNSS method of positioning, which is based on using the model of single code differences for global navigation satellite system (GNSS) observations. In the research experiment, the authors used single-frequency code observations in the global positioning system (GPS)/global navigation satellite system (GLONASS) system from the on-board receiver Topcon HiperPro and the reference station REF1 (reference station for the airport military EPDE in Deblin in south-eastern Poland). The geodetic Topcon HiperPro receiver was installed in Cessna 172 plane in the aviation test. The paper presents the new methodology in the DGNSS solution in air navigation. The aircraft position was estimated using a “weighted mean” scheme for differential global positioning system and differential global navigation satellite system solution, respectively. The final resultant position of aircraft was compared with precise real-time kinematic – on the fly solution. Findings In the investigations it was specified that the average accuracy of positioning the aircraft Cessna 172 in the geocentric coordinates XYZ equals approximately: +0.03 ÷ +0.33 m along the x-axis, −0.02 ÷ +0.14 m along the y-axis and approximately +0.02 ÷ −0.15 m along the z-axis. Moreover, the root mean square errors determining the measure of the accuracy of positioning of the Cessna 172 for the DGNSS differential technique in the geocentric coordinates XYZ, are below 1.2 m. Research limitations/implications In research, the data from GNSS onboard receiver and also GNSS reference receiver are needed. In addition, the pseudo-range corrections from the base stations were applied in the observation model of the DGNSS solution. Practical implications The presented research method can be used in a ground based augmentation system (GBAS) augmentation system, whereas the GBAS system is still not applied in Polish aviation. Social implications The paper is destined for people who work in the area of aviation and air transport. Originality/value The study presents the DGNSS differential technique as a precise method for recovery of aircraft position in civil aviation and this method can be also used in the positioning of aircraft based on GPS and GLONASS code observations.

Augmentation System (GBAS) in equatorial and low latitude regions. The ionosphere affects the propagation of GPS signals and can reduce the positioning accuracy in the equatorial and low-latitude regions. Auxiliary systems have been developed to meet the safety requirements of aviation. In this context, GBAS provide higher accuracy for differential corrections. To evaluate the performance of a GBAS, a simulation model of the GPS L1 signal-in-space has been developed, considering ionospheric delay based on statistical distributions of vertical Total Electron Content residuals obtained from IRI model and Rede Brasileira de Monitoramento Contnuo estimates, in combination with amplitude ionospheric scintillation simulated based on - probability distributions, as well as phase scintillation, generated according to empirical relationships between the indices 4 and . The GPS L1 signal model also considers clock and random errors, tropospheric delays, ambiguity, and multipath, for a complete description.