Broadcast Ephemeris Data Research Articles

Evaluation and Anomaly Detection Methods for Broadcast Ephemeris Time Series in the BeiDou Navigation Satellite System

Broadcast ephemeris data are essential for the precision and reliability of the BeiDou Navigation Satellite System (BDS) but are highly susceptible to anomalies caused by various interference factors, such as ionospheric and tropospheric effects, solar radiation pressure, and satellite clock biases. Traditional threshold-based methods and manual review processes are often insufficient for detecting these complex anomalies, especially considering the distinct characteristics of different satellite types. To address these limitations, this study proposes an automated anomaly detection method using the IF-TEA-LSTM model. By transforming broadcast ephemeris data into multivariate time series and integrating anomaly score sequences, the model enhances detection robustness through data integrity assessments and stationarity tests. Evaluation results show that the IF-TEA-LSTM model reduces the RMSE by up to 20.80% for orbital parameters and improves clock deviation prediction accuracy for MEO satellites by 68.37% in short-term forecasts, outperforming baseline models. This method significantly enhances anomaly detection accuracy across GEO, IGSO, and MEO satellite orbits, demonstrating its superiority in long-term data processing and its capacity to improve the reliability of satellite operations within the BDS.

Analysis of Post-Processed Pseudorange-Based Point Positioning with Different Data Sources for the Current Galileo Constellations.

The Galileo satellite navigation system now provides initial services. With further satellite launches, the performance of Galileo will gradually improve, and new services will be introduced. This study aims to provide a comprehensive analysis of Galileo Single Point Positioning (SPP) using different broadcast ephemeris data sources. This study investigates the completeness of Galileo navigation message records from different institutions. The results show that IGS provides the best completeness across different data sources (ECR > 70%), while IGN exhibits the lowest completeness. Analyze the proportions of different data sources within the Galileo navigation message in the broadcast ephemeris files provided by IGS during the study period. The proportions of FNAV_258, INAV_513, INAV_516, and INAV_517 during the study period are 25.83%, 24.76%, 23.61%, and 25.80%, respectively, suggesting better data completeness for FNAV_258 and INAV_517 and poorer completeness for INAV_513 and INAV_516. Finally, this study explores SPP solutions for GPS and Galileo systems using different data sources. The results indicate that a higher ECR corresponds to better positioning performance. Although GPS exhibits smaller error fluctuations and smoother positioning results, Galileo's SPP positioning accuracy surpasses that of GPS. The introduction of dual-frequency observations effectively reduces data dispersion and enhances vertical positioning accuracy.

BDS-3 Broadcast Ephemeris Orbit Correction Model Based on Improved PSO Combined with BP Neural Network.

During the operation of navigation satellites, errors in the broadcast ephemeris orbits are caused by the influence of ingress factors and other factors. To address this phenomenon, this paper examines the use of the computational intelligence (CI) methods to implement track correction and to develop an optimized BP neural network model based on an improved particle swarm algorithm. The model improves the inertia weights and learning factor parameters of the particle swarm optimization (PSO) algorithm to improve the global optimization capability and accelerate the convergence speed. The improved PSO (IPSO) algorithm is used to perform a global optimization search for the hyperparameters of the BP neural network, and then the neural network model is trained by broadcast ephemeris Keplerian root number and regression parameters. The model is validated using the broadcast ephemeris data of the BDS-3 MEO and IGSO satellites, and the mean square error correction rate of multiple satellites with different correction models shows that the error correction rate of the IPSO-BPNN model can reach 70.2–84% and the error correction rate can be improved by 14.2–56.8% compared with the PSO-BPNN model. The proposed algorithm provides an important reference for BDS-3 and other global navigation satellite systems for improving the accuracy of satellite orbit determination.

Real-Time Detection of Orbital Maneuvers Using Epoch-Differenced Carrier Phase Observations and Broadcast Ephemeris Data: A Case Study of the BDS Dataset.

The orbital maneuvers of the global navigation satellite system (GNSSs) have a significant influence on the performance of the precise positioning, navigation, and timing (PNT) services. Because the Chinese BeiDou Navigation Satellite System (BDS) has three types of satellites in the geostationary orbit (GEO), inclined geosynchronous orbit (IGSO), and medium earth orbit (MEO) maneuvers occur more frequently. Thus, it is essential to determine an effective approach for the detection of orbital maneuvers. This study proposes a method for the detection of orbital maneuvers using epoch-differenced carrier phase observations and broadcast ephemeris data. When using the epoch-differenced velocity estimation as a basic data solution model, the time discrimination and satellite identification factors are defined and used for the real-time detection of the beginning and the pseudorandom noise code (PRN) of satellites. The datasets from four GNSS stations (WUH1, BJF1, POHN, CUT0) from the year 2016 were collected and analyzed. The validations showed that the beginning, the PRN of the orbital maneuver of the satellite can be precisely detected in real time for all GEO, IGSO, and MEO satellites, and the detected results also showed good consistency, with the beginning time at a difference of 1–2 min across different stations. The proposed approach was observed to be more sensitive, and the detected beginning time was about 30 min earlier than the single point positioning approach when the high-precision carrier phase observation was used. Thus, orbital maneuvering can be accurately detected by the proposed method. It not only improves the utilization of the collected data but also improves the performance of PNT services.

Space State Representation Corrections as an Aid in Pseudolite Positioning.

In the presented study, the authors deal with the problem of transmission of pseudolite coordinates to the receiver. Nowadays, there is no uniquely specified method that would provide data about the position of the pseudolite to the GNSS receiver. There is also no technical standard that defines the explicit way of performing such transmission. Solutions presented in the literature are usually tailored to the described system, which is then suited to the specific situation. The article shows that the universal methods, involving the modification of transmitted broadcast ephemeris data, cannot be universally used. The modifications could not have been introduced due to the low resolution of the quantities that are transmitted in the ephemeris data, in relation to the values that would have to be sent by the pseudolite. To overcome the implementation problems, the authors propose two solutions. The first solution presented is the modification of the RTCM SSR frame. This approach allows replacing one of the existing satellites in space with the pseudolite, while the second method involves the use of new RTCM frame for sending the pseudolite position. Finally, a numerical example of the proposed solutions is presented. At the end of the manuscript, their advantages and implementation possibilities are discussed.

Rectification of GNSS-based collaborative positioning using 3D building models in urban areas

GNSS collaborative positioning receives great attention because of the rapid development of vehicle-to-vehicle communication. Its current bottleneck is in urban areas. During the relative positioning using GNSS double-difference pseudorange measurements, the multipath effects and non-line-of-sight (NLOS) reception cannot be eliminated, or even worse, both might be aggregated. It has been widely demonstrated that 3D map aided GNSS can mitigate or even correct the multipath and NLOS effects. We, therefore, investigate the potential of aiding GNSS collaborative positioning using 3D city models. These models are used in two phases. First, the building models are used to exclude NLOS measurements at a single receiver using GNSS shadow matching positioning. Second, the models are used together with broadcast ephemeris data to generate a predicted GNSS positioning error map. Based on this error map, each receiver will be identified as experiencing healthy or degraded conditions. The receiver experiencing degraded condition will be improved by the receiver experiencing the healthy condition, hence the aspect of collaborative positioning. Five low-cost GNSS receivers are used to conduct experiments. According to the result, the positioning accuracy of the receiver in a deep urban area improves from 46.2 to 14.4 m.

Self-Assisted First-Fix Method for A-BDS Receivers with Medium- and Long-Term Ephemeris Extension

As a sensor for standalone position and velocity determination, the BeiDou Navigation Satellite System (BDS) receiver is becoming an important part of the intelligent logistics systems under rapid development in China. The applications in the mass market urgently require the BDS receivers to improve the performance of such functions, that is, shorter Time to First Fix (TTFF) and faster navigation signal acquisition speed with Ephemeris Extension (EE) in standalone mode. As a practical way to improve such functions of the Assisted BDS (A-BDS) receivers without the need for specialized hardware support, a Self-Assisted First-Fix (SAFF) method with medium- and long-term EE is proposed in this paper. In this SAFF method, the dynamic Medium- and Long-Term Orbit Prediction (MLTOP) method, which uses the historical broadcast ephemeris data with the optimal configuration of the dynamic models and orbit fitting time interval, is utilized to generate the extended ephemeris. To demonstrate the performance of the MLTOP method used in the SAFF method, a suit of tests, which were based on the real data of broadcast ephemeris and precise ephemeris, were carried out. In terms of the positioning accuracy, the overall performance of the SAFF method is illustrated. Based on the characteristics of the medium- and long-term EE, the simulation tests for the SAFF method were conducted. Results show that, for the SAFF method with medium- and long-term EE of the BeiDou MEO/IGSO satellites, the horizontal positioning accuracy is about 12 meters, and the overall positioning accuracy is about 25 meters. The results also indicate that, for the BeiDou satellites with different orbit types, the optimal configurations of the MLTOP method are different.

Initial orbit determination of BDS-3 satellites based on new code signals

For the two newly launched satellites (PRN number 27 and 28) of the future global BeiDou navigation satellite system (BDS-3), there is no available broadcast ephemeris data and other initial orbit information, but the initial orbit is the fundamental of the comprehensive analysis of the satellites and their signals. Precise orbit determination (POD) also requires determination of a priori initial value with a certain precision in order to avoid problems such as filter divergence during POD. Compared with the Newton iteration method, which relies on the initial value, this study utilizes the Bancroft algorithm to directly solve the nonlinear equations with the advantage of numerical stability. The initial orbits of these two satellites are calculated based on new code signals, and their results are analyzed and discussed. The experimental results show that, with the exception of very few epochs, when the new code signal is utilized, the median and robust variance factor of the observed residuals computed using pseudo-range observations and the solved initial orbits are less than 4 and 2 m, respectively. It also shows that this solution can be used for rapid initial orbit recovery after maneuvers of the new BeiDou satellites.

A fast cold-start method of GPS receiver based on satellite orbit prediction

Time to first fix (TTFF) is one of the crucial indicators to evaluate the performance of a GPS receiver. In this paper, an orbit prediction algorithm to reduce the TTFF of GPS receivers without a network connection is presented. Satellite orbit is predicted by numerically integrating the satellite’s equation of motion. Satellite’s initial position and velocity value, as well as the Earth’s polar motion parameters, used in prediction correspond to the locally collected previous broadcast ephemeris. As the solar radiation pressure (SRP) is one of the most critical factors causing orbit prediction error, an empirical SRP model with two parameters that change with the movement of satellite and Earth is also described. The presented algorithm is verified by GPS satellites using the initial conditions divided from three groups of broadcast ephemeris data. Simulation results show that, with the SRP model described in this paper the satellite’s position error limited to 30 meters within 7 days prediction.

Application of IGS Products for Air Navigation

Abstract Single Point Positioning (SPP) method is widely used in air, marine, and land navigation to determine the user’s position in real time and post factum. A typical accuracy for this method of determining the user’s position in the static mode is approximately 10 meters. In air operations, the SPP method accuracy can be several times lower and that may cause problems with precise positioning of an aircraft. The authors of this article presented preliminary results of research concerning aircraft positioning in the kinematic mode based on GPS observations. For this purpose, an in-flight experiment, in which a Cessna 172 aircraft was used, was performed at the airport in Mielec, Poland. The aircraft was equipped with a dual-frequency Topcon TPS HiperPro receiver, which was recording satellite observations with 1-second interval. The aircraft position was determined using the least-squares method (LSM) in the RTKLIB (RTKPOST module) software. Two research tests were performed within the scope of the experiment, i.e. in test I the aircraft position was determined on the basis of raw GPS observations and the broadcast ephemeris data whereas in test II precision products of the IGS were used, such as: precise ephemeris SP3, DCB hardware delay, clock bias data of GPS satellites and receivers in the CLK format, data of the ionosphere maps based on IONEX format, and phase center calibration of GPS satellites and receivers in the ANTEX format. The use of the IGS precision products improved the accuracy of the X coordinate to 1 m, Y to 0.7 m and Z to 1.3 m. On the basis of tests I and II, an additional RMS-3D parameter was determined, whose mean value was 4 m.

Method and Analysis of Medium and Long Term Satellite Orbit Prediction Based on Satellite Broadcast Ephemeris Parameters

Given the lag of IGS precise ephemeris and complexity of dynamic models, in order to solve the problem of long-term satellite orbit prediction in autonomous orbit determination, a new medium and long term orbit prediction method that based on satellite broadcast ephemeris parameters has been put forward. This method is that forecasting the orbit parameters firstly according to broadcast ephemeris history data, and then calculating satellite position according to the forecast ephemeris parameters. In order to verify the feasibility of this method, using 40 days of broadcast ephemeris data, adopting ARMA model combined with sliding window model to predict broadcast ephemeris orbit parameters value in 25 days. Analyzed the parameters prediction error and the influence of parameters prediction error to satellite orbit accuracy, 25 days of orbit prediction error can be controlled in 150 meters. The results show that the predictability of orbit parameters has certain application value for satellite orbit prediction, the medium and long term orbit prediction that based on the satellite broadcast ephemeris parameters is a new and feasible method of orbit prediction.

Differential Code Bias Estimation using Multi-GNSS Observations and Global Ionosphere Maps

Measurements of Global Navigation Satellite System (GNSS) receivers are affected by systematic offsets re- lated to group and phase delays of the signal generation and processing chain. The resulting code and phase biases depend on the transmission frequency and the employed signal modulation. Within this study differential code biases (DCBs) of legacy an d modernized GNSS signals are derived from pseudodrange observations of a global multi-GNSS receiver network. Global ionosphere maps (GIMs) are employed for th e correction of ionospheric path delays. Satellite and receiver-specific contributions are separated based on the a ssumption of additive biases and a zero-mean condition for the satellite biases within a constellation. Based on 6 months of data collected within the Multi-GNSS Experiment (M GEX) of the International GNSS Service (IGS), DCBs for the publicly available signals of GPS, Galileo and BeiDou have been deter- mined. The quality of the resulting DCB estimates is as- sessed and compared against group delay parameters transmitted by the GNSS providers as part of the broad- cast ephemeris data.

Galileo Signal and Positioning Performance Analysis Based on Four IOV Satellites

With the availability of Galileo signals from four in-orbit validation (IOV) satellites, positioning with Galileo-only observations has become possible, which allows us to assess its positioning performance. The performance of the Galileo system is evaluated in respect of carrier-to-noise density ratio (C/N0), pseudorange multipath (including noise), Galileo broadcast satellite orbit and satellite clock errors, and single point positioning (SPP) accuracy in Galileo-only mode as well as in GPS/Galileo combined mode. The precision of the broadcast ephemeris data is assessed using the precise satellite orbit and clock products from the Institute of Astronomical and Physical Geodesy of the Technische Universität München (IAPG/TUM) as references. The GPS-Galileo time offset (GGTO) is estimated using datasets from different types of GNSS receivers and the results indicate that a systematic bias exists between different receiver types. Positioning solutions indicate that Galileo-only SPP can achieve a three-dimensional position accuracy of about six metres. The integration of Galileo and GPS data can improve the positioning accuracies by about 10% in the vertical components compared with GPS-only solutions.

CODE coefficients based Single frequency Ionospheric Error Correction Model to improve GPS Positional Accuracy of the Low-latitude regions

GPS (Global Positioning System) is a satellite based navigation system which provides reliable positioning information to its users (receivers) based on the concept of Time of Arrival (TOA) of the signal at the receiver. The positional accuracy of GPS is affected by several sources such as atmosphere, multipath and satellite-receiver geometry etc., of which ionosphere is one of the major sources of error for single frequency GPS user. When GPS signal propagates through the ionosphere, due to the change in refractive index in atmospheric layers, the signal bends which causes a delay in the arrival of the signal at the receiver. This delay of the signal introduces an error in ranging measurements at the receiver which in turn leads to an error in positioning information. Hence, to improve the positional accuracy, it is necessary estimate the delay of the signal in ionosphere during its transit from satellite to receiver. As this delay is caused by the electron content of the ionosphere, it is also necessary to estimate the Total Electron Content (TEC) in the signal path. The only way of estimating the ionospheric delay for single frequency receivers is by using Klobuchar algorithm which is based on the GPS broadcast ephemeris data. But this algorithm is optimized for mid latitudes and is very poor in high and low latitude regions. Hence it is required to have a model that is suitable for low latitude regions and near-equatorial regions such as Indian subcontinent. In this paper, low latitude suitable CODE coefficients based Klobuchar algorithm is implemented and is validated. The paper aims to investigate the performance of the CODE based Klobuchar algorithm by estimating the ionospheric delay using the CODE coefficients for data due to a low-latitude receiver data i.e. IGS station (HYDE: Lat/Long: 17°24'39N/78°33'4E) located in Hyderabad, Andhra Pradesh, India. This CODE based ionospheric delay is compared with delay due to Klobuchar model using the broadcast ephemeris data of the IGS receiver (HYDE). The model performance is validated with the ionospheric delay computed using the IONO-Lab data for the IGS station (HYDE). The CODE based algorithm is implemented, compared and validated for several days data of the IGS receiver (HYDE) and in this paper, it is presented for a typical day i.e. 11 th September 2014. The work yields the conclusion that Klobuchar model is simple due to short

Precise regional baseline estimation using a priori orbital information

A solution using GPS measurements acquired during the CASA UNO campaign has resulted in 3–4 mm horizontal daily baseline repeatability and 13 mm vertical repeatability for a 729 km baseline, located in North America. The agreement with VLBI is at the level of 10–20 mm for all components. The results were obtained with the GIPSY orbit determination and baseline estimation software and are based on five single‐day data arcs spanning the 20, 21, 25, 26, and 27 of January, 1988. The estimation strategy included resolving the carrier phase integer ambiguities (bias fixing), utilizing an optimal set of fixed reference stations (fiducials), and constraining GPS orbit parameters by applying a priori information (derived from initial multi‐day trajectory fits to broadcast ephemeris data). A multi‐day (January 20–27) GPS orbit and baseline solution has yielded similar 2–4 mm horizontal daily repeatabilities for the same baseline, consistent with the constrained single‐day arc solutions. The application of weak constraints to the orbital state for single‐day data arcs produces solutions which approach the precise orbits obtained with unconstrained multi‐day arc solutions. This work suggests that the general availability of nominal ephemerides based on many days of global tracking data would be very valuable and practical for regional geodesy, allowing for high precision with single‐day network solutions when combined with a continental scale fiducial network.