Airborne Users Research Articles

Reinforcement Learning-Based Energy-Efficient Data Access for Airborne Users in Civil Aircrafts-Enabled SAGIN

Airborne users are always dreaming of enjoying a good Internet access experience while in the air. However, due to long propagation delay and limited network coverage, the existing data communication methods utilized in space and ground communications not only fail to ensure the quality-of-service (QoS) of airborne users, but also incur significant energy consumption to process content requests. In this paper, we introduce the aeronautical ad hoc network (AANET) as a new method of network access and design an energy-efficient data access scheme in civil aircrafts-enabled space-air-ground integrated networks (CAE-SAGIN). In order to minimize the energy consumption, we propose a service selection scheme based on reinforcement learning and formulate a joint optimization problem of resource allocation and request distribution. Leveraged by the Lyapunov optimization method, the optimization problem can be solved by the proposed joint optimization algorithm. Extensive simulations are conducted to confirm the stability of the CAE-SAGIN, and demonstrate that the proposed data access scheme can effectively reduce both the energy consumption and the processing delay. Moreover, the advantages of using AANET are becoming more obvious when higher data rate is required.

Development and Assessment of Improved Global Pressure and Temperature Series Models

Global pressure and temperature (GPT) series models can provide the underlying meteorological parameters for tropospheric corrections without any other meteorological observations, which allows them to be widely used for a series of geodetic as well as meteorological and climatological purposes. Due to the height difference between the empirical model height and user location, a vertical correction of meteorological parameters is inevitable, particularly for airborne users. Unfortunately, the GPT series models have limitations on the vertical correction. We explored the temperature lapse rate for the vertical adjustment using 10 years of reanalysis data provided by the National Centers for Environmental Prediction (NCEP), and extended the GPT models to improved global pressure and temperature (IGPT) series models by introducing a new temperature lapse rate model and a new formulation of pressure reduction. An evaluation of the IGPT models expression determines that the IGPT models have better accuracy than the GPT models, particularly under large height differences, which is attributed to their ability to consider the real behavior of temperature in the atmosphere and adiabatic effects on air pressure. The performance of the IGPT models in zenith tropospheric delay (ZTD) estimations was also evaluated by comparison with the fifth-generation European Centers for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA5) data and International GNSS Service (IGS) data. The results confirm that our new models can effectively improve the accuracy of ZTDs, particularly at larger altitude differences between the target height and the corresponding four grid points of the model, not only enhancing the performance of the model in complex terrain but also extending the feasibility of the IGPT models from the Earth's surface to higher altitudes.

Signal deformation fault monitors for dual‐frequency GBAS

<h3>Abstract</h3> This paper proposes a new dual-frequency signal deformation fault monitor, which can effectively reduce the time delay at the Ground-Based Augmentation System (GBAS) airborne user from the airborne filter initialization to the time when it incorporates ground corrections and user measurements for navigation, assuring the system integrity at the same time. The new monitor is applied together with the existing Honeywell signal deformation monitor and Code-Carrier Divergence monitors to protect the airborne users against the signal deformation faults. In addition, the probability of missed detection of the monitors is assessed for the GBAS Approach Service Types (GAST) F, which supports the Category (CAT) II and III precision approaches based on the multifrequency and multiconstellation. As a result, the proposed monitor together with the Honeywell and the CCD monitors is able to assure the system integrity for all fault cases within the threat space. The result also shows that the addition of the proposed monitor can reduce the time delay by 80%; moreover, it can even reduce the recommended time delay below 50 s. Consequently, it can avoid the unnecessary delays for the use of newly available satellites at the airborne.

Ionospheric delay prediction and code-carrier divergence testing for GBAS using neural network and GPS L1

This paper presents a Neural Network (NN) model for predicting Ionospheric Delay (ID) which is used particularly in the Ground Based Augmentation System (GBAS) as a new and alternative approach. It is vital to have positioning solutions exhibiting high levels of performance in terms of navigation for aircraft to counter systematic errors in broadcast correction ranging measurements associated with GBAS, such as ID when using a Global Positioning System (GPS) L1 frequency receiver. In principle, ID can be simply estimated with the aid of dual frequency receivers (GPS L1 and L2) or a new GPS signal (L5). However, the GBAS relies only on the L1 frequency as the L2 frequency is not protected by Aeronautical Radio Navigation Service (ARNS) and L5 is not fully functional. In this context, the NN model is proposed to predict the ID from only GPS L1 pseudorange measurements. Benchmarking performed between prediction and conventional dual frequencies (GPS L1 and L2) illustrates the validity of the proposed method. In addition, divergence tests are performed to assess the effectiveness of predicted ID on the code-carrier. The possibility that ID type systematic and temporal errors in GBAS ranging measurements can be predicted accurately with only GPS L1 measurements is investigated. NN can also be used in the GBAS to reduce the code-carrier divergence effects between ground and airborne users.

The IFFT-based SQM method against digital distortion in GNSS signals

Global navigation satellite systems (GNSS) signal deformations could threaten the position accuracy and integrity of GNSS, especially for safety critical applications. Digital distortion is an important kind of deformations caused by failures inside the baseband generation unit onboard the GNSS satellites. Multi-correlator technique, as a prevalent signal quality monitoring (SQM) method, was developed to reliably detect the signal anomaly and therefore protect airborne users from this integrity threat. However, the conventional multi-correlator technique is unable to estimate the degree of distortion quantitatively, while another SQM method, the chip domain observable, has a poor real-time capability so that it could not meet the stringent time to alarm requirements. To solve the above problem, we derived the spectrum form of the conventional Threat Model A first and proposed a IFFT-based SQM algorithm. This new method can perform SQM easily by analyzing the impulses after PSD division and IFFT: Detect the presence of digital distortion by judging whether there is an impulse after IFFT and estimate the degree of distortion by computing the offset of the impulse. The results show that the IFFT-based method can not only detect digital distortion real-timely but also estimate the digital distortion degree quantitatively.

Enhanced Positioning Algorithm of ARPS for Improving Accuracy and Expanding Service Coverage.

The airborne relay-based positioning system (ARPS), which employs the relaying of navigation signals, was proposed as an alternative positioning system. However, the ARPS has limitations, such as relatively large vertical error and service restrictions, because firstly, the user position is estimated based on airborne relays that are located in one direction, and secondly, the positioning is processed using only relayed navigation signals. In this paper, we propose an enhanced positioning algorithm to improve the performance of the ARPS. The main idea of the enhanced algorithm is the adaptable use of either virtual or direct measurements of reference stations in the calculation process based on the structural features of the ARPS. Unlike the existing two-step algorithm for airborne relay and user positioning, the enhanced algorithm is divided into two cases based on whether the required number of navigation signals for user positioning is met. In the first case, where the number of signals is greater than four, the user first estimates the positions of the airborne relays and its own initial position. Then, the user position is re-estimated by integrating a virtual measurement of a reference station that is calculated using the initial estimated user position and known reference positions. To prevent performance degradation, the re-estimation is performed after determining its requirement through comparing the expected position errors. If the navigation signals are insufficient, such as when the user is outside of airborne relay coverage, the user position is estimated by additionally using direct signal measurements of the reference stations in place of absent relayed signals. The simulation results demonstrate that a higher accuracy level can be achieved because the user position is estimated based on the measurements of airborne relays and a ground station. Furthermore, the service coverage is expanded by using direct measurements of reference stations for user positioning.

Ionospheric threat simulation for GNSS using the Spirent hardware signal simulator

Ionospheric disturbances present a considerable hazard to single-frequency satellite navigation systems for airborne users. We discuss our implementation of three ionospheric threat models in the DLR "multi-output advanced signal test environment for receivers" global navigation satellite system simulator, which is based on Spirent GSS 7780/7790 signal generator. These threat models include the standard front-based threat model developed for the integrity assessment of ground-based augmentation systems (GBAS), a simplified plasma bubble model, and ionospheric scintillation, which can be combined with either of the two previously mentioned models. These effects can now straightforwardly be simulated at the German Aerospace Center's research facilities. As an example, we simulate a GBAS ground facility with code–carrier divergence monitoring, affected by an ionospheric front, and we show the results of a simulation with coincidental occurrence of a plasma bubble and scintillation with an S 4 index of 0.4.

Worldwide Vertical Guidance of Aircraft Based on Modernized GPS and New Integrity Augmentations

In the 2020 time frame, the Global Positioning System (GPS) will be fully modernized, and other satellite navigation systems will be operational. With an additional layer of fault detection, these systems will provide vertical guidance worldwide. This capability will be born of three important technologies. First and foremost, avionics will receive signals on two frequencies: L1/E1 and L5/E5a. This frequency diversity will do much to obviate the impact of ionospheric storms that troubles aviation use of GPS today. Secondly, a multiplicity of data broadcasts will be available to convey integrity information from the ground to the airborne users. These will include the navigation satellites themselves, geostationary satellites, and possibly terrestrial transmitters. However, the most important change will be the most subtle. The fault monitoring burden will be split between the aircraft and the supporting ground systems in a new way relative to the fault-detection techniques used in 2008. This new integrity allocation and the associated architectures are the subject of this paper.

The Impact of Measurement Biases on Availability for Category III LAAS

original error description for the Local Area Augmentation System (LAAS) assumed unbiased measurement errors. In practice, however, satellite ranging errors may exhibit nonzero means. The LAAS error bound must account for these biases. This requirement places a particularly stringent demand on Category III (CAT III) LAAS, a future LAAS variant that will enable safe automated landing through rollout. This paper examines the availability impact of biases on CAT III LAAS. To provide an upper limit for tolerable LAAS biases, the paper first considers an improved LAAS messaging structure and asks, for this ideal case, what maximum level of bias is tolerable. Even in the ideal case, the maximum bias at worst-case CONUS airports is only 4-8 cm. This baseline case assumes a nominal LAAS error distribution and a relaxed Vertical Alert Limit (VAL) of 10 m. To tolerate larger biases, improvements to the nominal LAAS are required. For instance, a dual-frequency LAAS implementation can tolerate biases as high as 14-30 cm, even with a tighter VAL of 5.3 m. Tolerable biases for nonideal bounding algorithms are also considered. In order to achieve ideal performance, the LAAS message must be changed to transmit bias parameters to the airborne user. Preferably, the biasprotection algorithm would not require modification of the existing LAAS specification. Sigma inflation methods represent an alternative to bias-parameter transmission that requires no LAAS specification change but, consequently, that delivers somewhat lower bias tolerance. Performance varies widely for different classes of sigma inflation. Simulations indicate that the bestperforming sigma inflation method (real-time positiondomain inflation) nearly matches the bias tolerance possible with bias-parameter transmission. Unlike biasparameter transmission, however, the bias tolerance for sigma-inflation methods depends strongly on possessing precise knowledge of the airborne error, sair, at the LAAS ground facility (LGF).

Measurement Errors in GPS Observables

Airborne users of GPS may benefit from differential (relative) navigation to the extent that the errors in their measurements of pseudorange and/or delta range to each satellite are correlated with observation errors for the same satellite signals received at a reference site. This paper describes some results of an experiment to characterize the measurement errors of one airborne GPS user equipment. The results suggest that pseudorange errors are dominated by slowly varying systematic processes that are likely to be highly correlated from user to user, whereas delta-range errors appear to be zero-mean processes that are dominated by user generated noises, especially clock jitter and tracking errors.

Survey of Worldwide OMEGA Users*

This paper provides a status report on a Worldwide OMEGA Users Survey which has been in progress over the last two years. Phase One of this Survey involved sending out a questionnaire to manufacturers of OMEGA equipments to determine what organizations had purchased OMEGA sets. From this initial effort, over 3500 airborne user sets and 1300 marine sets were identified. The second phase of this survey involved contacting specific users to determine what sets they had and how they were using them. Fifty letters were sent out and 36 replies were received. In addition 15 separate requests were sent out by ONSOD and to user monitoring agencies such as the FAA, the British CAA and the Japanese Maritime Agency. This status report will present a listing of OMEGA users identified to date and provide an analysis of the types of sets, location, and application.

A concept for wide band global communications

The Global Communication Network (GCN) is a new concept that uses polar‐orbiting satellites to provide communications services that are unavailable otherwise from existing satellite systems. These services are becoming essential to perform the kind of global science that has been proposed for the 1990s and beyond by the ocean, atmosphere, and earth processes science communities. Existing communications services over the oceans and particularly over the polar regions are severely constrained. Service Argos provides worldwide data collection capability at low rates and for limited quantities of data, but it makes no provisions for interrogation or for wide band, high‐volume data [see In Situ Ocean Science Working Group, 1985]. Other geostationary satellite systems, such as the Geostationary Operational Environment Satellite (GOES), require an amount of transmission power that is prohibitive for most mobile, floating, or airborne users [see Hughes Aerospace Corporation, 1980].

Automation in Marine Navigation

Automation has proceeded much further in connection with air navigation and air traffic control than it has in comparable aspects of the maritime service. There are many factors to account for this. By its nature, air travel involves risks which are greater and more urgent than those of sea travel and which, in focal areas, are high in all conditions of weather; its passenger/cargo ratio is vastly greater and this inevitably stresses the need for every possible aid to safety. These characteristics and others more obvious lead to ground control, control leads to centralization and uniformity and thus to the ready introduction of advanced developments and their imposition where appropriate on the airborne user.