User Range Error Research Articles

User Range Error Analysis of Multiple Satellite Navigation System

User range error (URE) is widely used to measure the effects of satellite orbit error and clock error on user positioning. A detailed calculation method of URE was brought forward including the partitions of the ground coverage of the MEO satellites and the calculation methods of the projection parameters of URE. The different URE performance of multiple Satellite navigation system was analyzed. Simulation results show that the radial direction projection parameters are basically the same, but the horizontal direction projection parameters are different among GPS, Galileo and BDS. The higher the satellite orbit, the smaller the horizontal direction projection parameters.

An information fusion algorithm for integrated autonomous orbit determination of navigation satellites

This paper focuses on the information fusion problem of integrated autonomous orbit determination using the observations from inter-satellite-link (ISL), X-ray pulsars and star sensors. A step Kalman filter structure is proposed to solve the information fusion problem of multiple subsystems that have greatly different filtering precision. The subsystems are grouped according to their measurement accuracy and the state parameters and covariance matrix of a group can be calculated using the federated filter structure and propagated to the next group step-by-step. Simulation results show that the mean user range error (URE) of the constellation will be less than 1.5m in 60 days using the step Kalman filter structure for information fusion. And it has better performance than the federated structure in dealing with information fusion of the astronomical observations and the ISL ranging measurements in integrated autonomous orbit determination.

A New Algorithm for Onboard Autonomous Orbit Determination of Navigation Satellites

Autonomous orbit determination of a navigation constellation is the process by which the orbit parameters of navigation satellites are autonomously calibrated onboard the satellites without the need for external aids. It commonly uses a satellite onboard data processing unit and a filtering method to process the measurements of inter-satellite ranges. The onboard data processing unit is the main module of autonomous navigation systems. In this paper, the two main factors that affect the accuracy of autonomous orbit determination for a navigation constellation are discussed first, and then a distributed onboard algorithm for autonomous orbit determination of navigation satellites is proposed. This method is based on a long-term ephemeris prediction and is suitable for the satellite hardware capability. The main feature of this method is that both the distributed computing method and an onboard analytical state transition matrix are used to process inter-satellite range measurements. One of the main advantages of this approach is high-speed computing since the amount of calculations needed is significantly less than that of the centralised computing method and those distributed methods that need to use an onboard numerical integrator. Another advantage of this approach is that the use of the onboard analytical state transition matrix algorithm can save a great amount of resources for both ground-to-satellite data transmissions and data storage units in satellites’ hardware. This could result in substantial cost reduction for space missions. Finally, a simulation method used for testing the proposed algorithm is presented. Results of tests over a period of 90 days show that the user range error of autonomous orbit determination derived from the proposed method is less than three metres.

GPS Orbit and Clock Error Distributions

Integrity is one of the most important requirements for civilian aviation. One method of achieving the required integrity for supplemental Global Positioning System (GPS) navigation is the use of Receiver Autonomous Integrity Monitoring (RAIM), and for primary means of navigation, Receiver Autonomous Integrity Monitoring and Exclusion (RAIME). The RAIM(E) algorithm parameters depend on the assumed probability of a satellite fault condition (anomaly) and on the fault-free standard deviation of a normal distribution that over-bounds the actual user range error distribution. In this paper, GPS clock and orbit errors are calculated based on the broadcast ephemeredes and truth data obtained from online sources for the three year period starting in June 2005. Anomalous satellite behavior is identified and removed from the data set. The remaining fault-free data are analyzed statistically. A table of anomalies, cumulative distributions, and normal distribution standard deviation overbounds are provided by satellite Block Type.

Statistical characterization of composite protection levels for GPS

A statistical characterization is presented of Global Positioning System (GPS) user range error as a normally distributed random variable with non-zero mean over the length of the aircraft precision approach operation, correlated from one GPS measurement epoch to another and from one satellite to another. This leads directly to modeling GPS error in the position domain as multivariate normal with non-zero mean. Based on this model, a vertical composite protection level VPLc and a horizontal composite protection level HPLc are each calculated as scalar values from a univariate normal distribution displaced from the origin by the worst-case position domain bias combination possible, given the maximum possible individual satellite bias magnitudes and the satellite geometry. A method is then presented by which exact values--that is, values accurate to a user-defined error tolerance and consistent with statistical assumptions--of VPLc and HPLc are obtained, and by which computationally efficient approximations may be evaluated. A statistical quadratic form under the multivariate normal distribution is used to derive a new class of protection levels based on the probability enclosed within a radius defined in two or more dimensions. A central Chi-square representation of this quadratic form is also presented and is incorporated into a six-step computational procedure for the two-dimensional composite radial protection level RPLc. This procedure is extended to the spherical protection level (SPLc) and the ellipsoidal protection level (EPLc).

Orbit determination and prediction accuracy analysis for a regional tracking network

China’s COMPASS satellite navigation system relies on a regional tracking network to provide navigation services. Limited by its geographic border, the regional network is able to cover only 30% of the medium-earth-orbits (MEO). Accuracy of determined and predicted orbits is not able to satisfy system requirements if the tracking data processing strategy for global tracking network processing is used for the regional network. Two major error sources for orbital prediction are accuracy of initial orbital elements and dynamical modeling. To achieve better prediction accuracy, we propose a two-step orbit determination and prediction strategy. For step 1, only solar radiation pressure (SRP) parameters are estimated along with the orbital elements and other parameters; for step 2, all parameters are estimated but the SRP parameters are tightly constrained to their step 1 estimates. Experimenting with data from a regional GPS network, we conclude for orbital prediction using the proposed two-step strategy, the average user range error (URE) for 24-h prediction arcs is better than 0.6 m.

Autonomous Navigation of Global Positioning System Satellites Using Cross-Link Measurements

The Global Positioning System (GPS) Block IIR satellites, which will replace the current Block II/IIA satellites, will have satellite-to-satellite communication capabilities that will allow intersatellite ranging between the Block IIR satellites. The cross-link pseudorange measurements will be used by onboard computers to update the stored navigation messages, which are based on trajectories predicted over an extended period of time, by ground-based processing of tracking data. During normal operations, the cross-link pseudorange measurements will provideimproved satellite states, which then can be broadcast to theusers. One oftheerrorsourcesin the updated navigation messages, which cannot be corrected by cross-link measurements, is found in the Earth orientation parameter (EOP) errors. As a consequence, as the age of the Earth rotation parameter increases, the performance of the autonomous navigation system will degrade. The effect of this error source on the Block II GPS autonomous navigation accuracy is described. This work is based on simulated cross-link pseudorange measurements. Realistic force, measurement, and reference frame models are used in the analysis to account for additional major error sources. Cross-link measurementsfora period of oneday, generated at the end ofeach of three different prediction intervals, are used to update the predicted trajectory. The estimated solutions then are compared to true solutions to evaluate the effect of prediction errors. With the current EOP prediction errors, the user range errors (URE), computed from improved trajectories and clock differences for a 90-day prediction, exceed 9 m, and for a 180-day prediction, they exceed 17 m. Finally, results of processing measurements from ground stations, instead of cross links, are discussed wherein the URE for the 180-day prediction case are shown to be about 3.1 m.

Results of the GPS JPO's GPS Performance Baseline Analysis: The GOSPAR Project*

The GPS Operational Control System (OCS) Performance Analysis and Reporting (GOSPAR) project was initiated by the GPS Joint Program Office (JPO) to establish an in-depth definition of current GPS Precise Positioning Service (PPS) performance characteristics. This paper provides a description of the key findings of the GOSPAR project to date. Specifically, the following topics are addressed: project overview, performance metric review, how GPS is doing, why GPS is doing so well, and bottom line to users. The results of the GOSPAR project have established a GPS performance baseline and set the stage for development of the next-generation GPS OCS. The next-generation OCS has as an objective to reduce GPS PPS user range errors (UREs) to 1.5 m root mean square (RMS) or better.

INMARSAT integrity channels for global navigation satellite systems

The transmission of integrity information using a signal format compatible with the Global Positioning System (GPS) and relayed through a geostationary satellite repeater, which will be critical in achieving high integrity and availability of global navigation by satellite is discussed. The inclusion of navigation repeaters designed to fulfil this function, the next generation of INMARSAT spacecraft, INMARSAT-3 is examined. The global navigation satellite system (GNSS) integrity channel (GIC) will employ pseudorandom codes in the same family as, but distinct from, the codes reserved by GPS. The data format of the basic integrity channel is designed to convey user range error information for 24 to 40 satellites. A closed-loop timing compensation technique will be used at the uplinking Earth station, to make the signal's clock and carrier Doppler variations identical to those that would result from an onboard signal source. Therefore, the INMARSAT-3 satellites will increase the number of useful navigation satellites available to any user, and can also function as sources of precise timing. There is also a possibility that wide area differential corrections can be carried on the same signal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GPS Satellite-to-User Range Accuracies: A Calibration Experiment

From 20 October to 17 November 1986, three Contracting and three Government institutions took part in a cooperative evaluation of the accuracy of the Global Positioning System (GPS). In effect, acting as independent GPS users employing CIA-code single-frequency or P-code dual-frequency receivers, each organization computed satellite-to-user range prediction errors. Each institutional user computed statistical summaries of these User Range Errors (URE). The root-mean-square (rms) of the URE’s across all satellites, and over all 30-days of the test, as reported by each user ranged from a high of 4.8 meters to a low of 3.1 meters. The C/A-code users experienced the largest rms URE. The GPS is required to provide 6 meter rms URE. For the same test period, the GPS Operational Control System (OCS) computed URE performance measures of 2.0 meters (rms) and 2.5 meters (rms). This suggests that these GPS performance measures might be improved. Throughout the 30 day test, users reported that the daily rms URE were approximately steady-state. However, just prior to the test, the rms URE did appear correlated over several days with rms values near 6 meters. This URE degradation appeared to improve as NAVSTARS 3,6, and 10 were less and less eclipsed by the Earth shadow.