An Error Overbounding Method Based on a Gaussian Mixture Model with Uncertainty Estimation for a Dual-Frequency Ground-Based Augmentation System

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%.

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) 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.

Ground‐based augmentation systems (GBASs) are widely used augmentation systems using satellite navigation. GBAS can improve the performance of BeiDou navigation satellite system (BDS) in civil aviation application. Evaluation is necessary before using a GBAS. On the basis of the flight trials conducted at the Dongying airport, evaluation results show that based on both the global positioning system (GPS) L1 signal and BDS B1I signal, ground accuracy designators (GADs) of four reference receivers are consistent with GAD‐C levels. The improvement in accuracy obtained with GBAS differential process is ∼60%, and the differential position error based on the BDS B1I signal is 40% greater than that of the GPS L1 signal, because currently incomplete BDS satellites distribution is worse than that of GPS. Airborne protection levels assessments show that the approach trials based on the BDS B1I signal exhibit several false alarm events. Further analysis indicates that BDS vertical protection levels were larger because of larger pseudoinverse S result from low elevation angle and unsatisfactory geometric distribution of BDS satellites. Besides, monitors show that BDS B1I signal is more affected by ionospheric delay than GPS L1 signal, which can also contribute to false alarm events.

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.

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.

The ground-based augmentation system (GBAS) is a system for receiving supplementary information directly from a ground-based transmitter using the global navigation satellite system (GNSS). The GBAS is also used for precise approach and landing of aircraft. The antenna used for transmission and reception exhibits the quadrangular array structure of a dipole antenna having linear polarization with VHF data broadcast (VDB). However, in the case of a VDB antenna, signal cancellation and interference among individual elements may occur.In this paper, we describe an omni-directional microstrip antenna that can replace the VDB antenna used in GBAS. The proposed design reduces the ground plane in a λ/4 folded microstrip antenna in order to have omni-directional characteristics and to radiate without affecting the ground plane itself. To miniaturize the physical size of the antenna, a metal plate is added between the openings using a perturbing effect.The designed antenna is verified through simulation. The size of the radiating element is 318 mm (0.12λ) × 100 mm (0.038λ) × 221 mm (0.083λ), whereas the size of the radiating element of a λ/4 folded microstrip antenna is 568 mm (0.214λ) × 100 mm (0.038λ) × 608 mm (0.23λ). Thus, the size of the radiating element is reduced by 79.7%. As a result of the electrical characteristics of the designed antenna, S 11 is −37.1 dB, the −10-dB bandwidth is 0.56 MHz, and its gain is 1.09 dBi at a center frequency of 113 MHz. The radiation pattern shows the desired omni-directional characteristic. It is thus confirmed that the proposed antenna can replace the existing VDB antenna used in GBAS.

The integrity evaluation of satellite navigation ground based augmentation system (GBAS) is the key of the whole performance evaluation process. Aiming to solve the problems of large sample demand and low evaluation accuracy in the integrity evaluation using frequency estimation method. This paper presents a method of GBAS integrity evaluation based on the extremum distribution model. This method starts from the integrity protection mechanism, uses the positive correlation between navigation positioning error and protection level to fuse data and takes the fusion data as the evaluation sample to improve the accuracy of evaluation. Then the feasibility of using the extremum distribution model to evaluate the integrity under the condition of limited samples is analyzed based on the extremum theory and integrity risk. Further, an error controlled fusion data extremum distribution model is established and the distribution parameters are estimated by the maximum likelihood estimation criterion. Finally, the integrity risk value of GBAS in the single approach guidance is derived from the distribution model. The processing result of Beidou GBAS sample data verifies the validity of this method.

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.

Ionospheric fronts pose a significant threat to single frequency ground based augmentation systems (GBAS) for airplane precision approach. Here, we show our implementation of two ionospheric threat models in the DLR MASTER GNSS Simulator, a modified Spirent GSS7780/779. These threat models include the standard GBAS ”front” threat model as required for CAT-1 certification and a simplified plasma bubble model intended to represent equatorial conditions. These models can now easily be simulated at the German Aerospace Center's facilities. As an example, we simulate a GBAS ground facility (with a code carrier divergence monitor) affected by both a plasma bubble with a constant differential delay of −2 m and fronts of various gradients and speeds. Results confirm that a plasma bubble can lead to worst case position biases that may cause misleading and hazardously misleading information to be used by an approaching aircraft. Moreover, we confirm that ionospheric fronts at a speeds close to the airplane approach speed and propagating into the approach direction cause the most severe range biases. These, mapped to the position domain, can also cause hazardously misleading information.

We address the differences in the ways the Instrument Landing System (ILS) and Ground-Based Augmentation System (GBAS) offer approach guidance, and their principles and methods. We perform comparative analysis of the accuracy of deviation between the GBAS Landing System (GLS) and ILS by means of flight tests, using the flight inspection aircraft at Gimpo International Airport. Our results show that the ILS deviation error increases as the distance between the threshold of runway and the aircraft increases; on the other hand, the GLS deviation error is stable, within the range of ±0.5 to ±2 m lateral and vertical deviation, respectively. We also analyze the alignment accuracy of the ILS and GLS based on the evaluation criteria of Category I of the Federal Aviation Administration, and our analysis results confirm that both systems satisfy the requirements (lateral: ±0.1°, vertical: ±0.05°).

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.

Civil aviation transportation equipment is more convenient and faster than other transportation tools and is an essential part of intelligent transportation. It is significant to study the reliability of positioning information and enhance traffic safety. Advanced receiver autonomous integrity monitoring (ARAIM) can provide vertical guidance during the different navigation stages in civil aviation fields. The traditional multiple hypothesis solution separation (MHSS) algorithm distributes the probability of hazardous misleading information (PHMI) and probability of false alarm (PFA) uniformly over all visible satellites resulting in reduced global availability of ARAIM. Aiming at this problem, we proposed an adaptive simulated annealing particle swarm optimization (ASAPSO) algorithm to redistribute integrity and continuity risks and establish a protection level optimization model. Based on the real BeiDou navigation satellite system/global positioning system (BDS/GPS) data, the experimental results show that the optimized algorithm can reduce the vertical protection level (VPL), and the ARAIM global availability of BDS/GPS is improved by 1.73%∼2.73%. The optimized algorithm can improve the availability of integrity monitoring at different stages of the navigation system and provide a basis for ensuring the reliability of the positioning results.

Predictability is a necessity in today's commercial flight operations if delays are to be minimized. Possible mitigations, such as the implementation of continuous descent arrivals (CDAs), may help generate the required procedural predictability to curtail these delays. However, on the basis of its individual avionics suite, each aircraft follows a different barometric vertical descent path; furthermore, the aircraft may be given additional level-off segments by air traffic control to compensate for possible deviations in the vertical profile. Therefore, aircraft flying the current descent profiles are too unpredictable and thus the procedures cannot be implemented in complex airspace structures or when traffic is moderate to high. This study introduces a mitigation to this problem by taking the global positioning system (GPS) one step further by integrating the GPS-based ground-based augmentation system (GBAS) into the new optimized continuous decent arrival procedure, subsequently, allowing for the introduction of a geometrical vertical guidance, namely, the GBASCDA, which will make the aircraft flying the descent profile predictable. With the increase in availability of GBAS aircraft equipage, specifically the GPS landing system (GLS), and the approaching amendment of the Appendix E of the Minimum Operational Performance Standards for GPS Local Area Augmentation System Airborne Equipment–RTCA DO-253D, this idea of the integration of the GBAS on the arrival/descent segment as a viable solution may be finally coming within reach.

A sharp yet conservative overbound for heavy-tailed error distributions is essential in integrity monitoring applications due to availability and continuity constraints. This article proposes the principal Gaussian overbound (PGO) for heavy-tailed error distributions by leveraging the characteristics of the Gaussian mixture model. The overbounding property of the PGO is proved to be preserved through convolution, which makes it possible to derive pseudorange-level requirements from the position domain integrity requirements. Experimental results on two datasets show that the PGO provides the most competitive bounding performance for heavy-tailed differential global navigation satellite system (GNSS) pseudorange errors when compared to the two-step Gaussian overbound and Gaussian-Pareto overbound, yielding a sharp bound in both the core and tail parts of the error distribution. The proposed method reduces the mean vertical protection level (VPL) by more than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$78\%$</tex-math></inline-formula> compared to the two-step Gaussian overbounding method on the urban dataset. In addition, the mean computation time of VPL is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.08 \,\,\mathrm{s}$</tex-math></inline-formula> with 15 measurements by employing fast Fourier transforms, suggesting the substantial potential of the PGO in GNSS applications with strict integrity and real-time requirements. Furthermore, the feasibility of the PGO in fault detection is discussed.