Research on accuracy performance evaluation technology of Beidou GBAS reference receiver

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 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 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 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.

According to Sheridan and Verplank's classification of levels of automation, taxiing on an airport still has a very low automation level. Key element for increased automation in taxi guidance is a precise and reliable navigation capability. As a Ground Based Augmentation System (GBAS) can fulfill the stringent requirements for a precision approach, it can play an important role in providing the required navigation performance during taxiing as well. This paper will explain the use of GBAS for taxi guidance. It presents, how the required navigation performance for automatic taxiing can be provided using GBAS. Besides the highly precision position service provided via Differential GPS, the Terminal Area Path (TAP) messages will be used to provide the aircraft with accurate and reliable information about the taxi route. Taxi trials with DLR's A320 research aircraft ATRA (Advanced Technology Research Aircraft) and the GBAS ground station at airport Braunschweig-Wolfsburg (EDVE) showed that over the whole maneuvering area the received VHF signal level was adequate for transmitting such a “Ground-TAP”. These tests were performed with an antenna on the aircraft located at a height of 8ft, which is lower than the actual required coverage minimum of 12ft defined in ICAO Annex 10. Together with a redefined voice communication structure and a list of predefined routes the use of GBAS for taxi routing functionalities of an Advanced Surface Movement Guidance & Control System (A-SMGCS) is feasible. Due to the independency from an on-board database the combination of such a message broadcast and the GNSS based positioning can be the key enabler for a future auto taxiing functionality.

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.

This study proposes a new set of processing procedures based on the strain model and the Kalman filter (SM-Kalman) to obtain high-precision three-dimensional surface deformation time series from interferometric synthetic aperture radar (InSAR) and global navigation satellite system (GNSS) data. Implementing the Kalman filter requires the establishment of state and observation equations. In the time domain, the state equation is generated by fitting the pre-existing deformation time series based on a deformation model containing linear and seasonal terms. In the space domain, the observation equation is established with the assistance of the strain model to realize the spatial combination of InSAR and GNSS observation data at each moment. Benefiting from the application of the Kalman filter, InSAR and GNSS data at different moments can be synchronized. The time and measurement update steps are performed dynamically to generate a 3-D deformation time series with high precision and a high resolution in the temporal and spatial domains. Sentinel-1 SAR and GNSS datasets in the Los Angeles area are used to verify the effectiveness of the proposed method. The datasets include twenty-seven ascending track SAR images, thirty-four descending track SAR images and the daily time series of forty-eight GNSS stations from January 2016 to November 2018. The experimental result demonstrates that the proposed SM-Kalman method can produce high-precision deformation results at the millimeter level and provide two types of 3-D deformation time series with the same temporal resolution as InSAR or GNSS observations according to the needs of users. The new method achieves a high degree of temporal and spatial fusion of GNSS and InSAR data.

Ground based augmentation system (GBAS) is one of the core infrastructures of future air traffic management system based on performance navigation, and the calculation of the B-values in the multiple reference consistency check (MRCC) algorithm is the core algorithm for the integrity monitoring of the GBAS ground station. In view of the traditional B-values processing algorithm cannot effectively distinguish between the receiver faults and the satellite faults, a new fault detection algorithm by calculating the S-values of the difference values of the pseudorange has been proposed, and the threshold of the S-values is determined by Gaussian overbounding method. So, the failure satellites and receivers can be marked out by combining the B-values detection algorithm and the S-values detection algorithm, and then the set of available satellites and receivers can be obtained. Taking the GBAS platform built in the laboratory as the object of study, the MRCC algorithm which is based on S-values auxiliary information is verified and analyzed. The experimental results show that the new algorithm proposed here can effectively eliminate the fault satellites, enhance the integrity of the GBAS, and thus improve the availability of the navigation system.

The Quasi-Zenith Satellite System (QZSS), which offered positioning signals into your navigation system of devices such as cars and smartphones started service as a four-satellite system from November 2018. They are expected a widespread various innovative services with highly precise positioning. In this study, we describe the development of information processing technology in utilizing Global Navigation Satellite System (GNSS) data in view of the trend of human sensing technology on a wide area outdoor environment. The practical case of target is a human behavior of a skier in ski resort which is case of sports field by GNSS data capture experiment. The behavior of the skier is not only when skiing. There are various actions such as taking a break and ride on a ski lift. That is to say, it is necessary to separate skiing data and other data. In order to realize this, we analyzed the features of the raw GNSS data. We described an analysis of three-dimension GNSS data that is latitude, longitude, high data. As a result, we considered characteristic noise detection results of the data, and extracted of the ski lift ride situation about human behavior analysis.

The fusion of global navigation satellite system (GNSS) and interferometric synthetic aperture radar (InSAR) deformation data can leverage the advantages of GNSS high temporal resolution and InSAR high spatial resolution, and obtain more abundant deformation data for constraints on geophysical structural and mechanical parameters. Existing studies seldom consider the spatial heterogeneity of largescale deformation data, which easily leads to obvious spatial aggregation of errors in the results of fusion. Here, we propose a novel multiresolution segmentation fusion (MRSF) method that uses a multiresolution segmentation algorithm to automatically classify the spatial heterogeneity of InSAR deformation data with similar deformation characteristics. We applied the MRSF method to the fusion of GNSS and InSAR deformation data covering the central valley aquifer system (CVAS) in southern California to verify its precision and robustness. Results show that the MRSF method can accurately reflect spatiotemporal evolution characteristics of displacement data and reliably estimate deformation for the times and locations of missing data. We then tested this method for geophysical parameter estimation by constructing three different sets of data, including dense GNSS sites, sparse GNSS sites, and sparse GNSS sites fused with InSAR data using MRSF, to invert the slip distribution of the Cascadia subduction zone. Results show that the inverted slip of the fused InSAR and GNSS data is comparable to that of the dense GNSS sites. Therefore, the MRSF method can obtain deformation results with high precision and high spatiotemporal resolution and effectively compensate for the lack of data caused by sparse GNSS sites during the geophysical inversion process.

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.

Temporal mass variations within the Earth’s system can be detected on a regional/global scale using GRACE (Gravity Recovery and Climate Experiment) and GRACE Follow-On (GRACE-FO) satellite missions’ data, while GNSS (Global Navigation Satellite System) data can be used to detect those variations on a local scale. The aim of this study is to investigate the usefulness of national GNSS CORS (Continuously Operating Reference Stations) networks for the determination of those temporal mass variations and for improving GRACE/GRACE-FO solutions. The area of Poland was chosen as a study area. Temporal variations of equivalent water thickness ΔEWT and vertical deformations of the Earth’s surface Δh were determined at the sites of the ASG-EUPOS (Active Geodetic Network of the European Position Determination System) CORS network using GRACE/GRACE-FO-based GGMs and GNSS data. Moreover, combined solutions of ΔEWT were developed by combining ΔEWT obtained from GNSS data with the corresponding ones determined from GRACE satellite mission data. Strong correlations (correlation coefficients ranging from 0.6 to 0.9) between detrended Δh determined from GRACE/GRACE-FO satellite mission data and the corresponding ones from GNSS data were observed at 93% of the GNSS stations investigated. Furthermore, for the determination of temporal mass variations, GNSS data from CORS network stations provide valuable information complementary to GRACE satellite mission data.

The study of climate change is an important field of research. Monitoring of atmospheric variability especially the tropospheric precipitable water vapor (PWV) is a powerful way to investigate climate change. Global navigation satellite systems (GNSS) provide a good tool for studying atmospheric parameters as GNSS signals along its path from the satellites to the ground based receivers suffer a significant delay due to the refractivity of earth’s atmosphere. GNSS signals are not only delayed but also refracted in the neutral atmosphere. The zenith wet delays (ZWD) caused by the troposphere can be estimated during the geodetic processing of GNSS signals. Since the ZWD is tightly correlated to the PWV, GNSS observations can be used to study the changes of PWV. In this study GNSS data from the Egyptian permanent GNSS network (EPGN), International GNSS Service (IGS), EUREF Permanent Network (EPN) and Scripps Orbit and Permanent Array Center (SOPAC), for the years 2013 and 2014, were used. These GNSS stations provided a good geometrical coverage over the respective region. All GNSS data were processed using Bernese V 5.2 software. The needed product from GNSS data processing is the tropospheric zenith total delay (ZTD) over each GNSS site. The ZTD is divided based on physical parameters into zenith hydrostatic delay (ZHD) and zenith wet delay (ZWD). The ZWD is the basic observable used to calculate PWV. The values of the PWV were calculated and its variation over the study area was investigated. The quality of calculated PWV values from GNSS data evaluated against traditional Radiosonde (RS) measurements. The results of GNSS PWV showed good agreement with RS PWV when the PWV values were low, but this agreement became worse at high PWV values as the differences between the two techniques increased. The correlation coefficient between RS PWV and GNSS PWV varied from 0.31 to 0.84. Standard deviation of the differences between RS PWV and GNSS PWV ranged from 2.369 to 5.973 mm. The PWV estimated from GNSS observations had annual cycle, and its cycle in 2013 was different from that in 2014. The PWV differences between the 2 years clarified that the water vapor content over the east Mediterranean in most of 2014 days was higher than that in 2013. Furthermore, PWV variations were noted on both temporal and spatial scales. The highest temporal variation value was 25.41 mm whereas the maximum value of the spatial variation was 19.67 mm. The present study illustrated the importance of using geodetic networks to provide atmospheric information.

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.