Precise Real-Time Positioning in WADGPS Networks

The main component of Global Positioning System (GPS) positioning error results from time and space varying conditions of radio wave propagation, which depend on atmospherics, disturbances in the satellite constellation, orbit stability, and also due to the U. S. military intentionally such as Selective Availability (SA), among other things. The error caused by the transmitter and receiver operation precision or time-measurement accuracy is negligible. A method for GPS precision enhancement commonly used by civil users is the Differential GPS (DGPS). If DGPS service is interrupted, it will lead to the degraded navigation performance. This paper focuses on applying a Π-Σ Neural Network (PSNN) model to predict Pseudo-Range Corrections (PRC) for DGPS. A low cost commercial module (Rockwell single-frequency GPS receiver) is employed to represent the improvement in DGPS. Experimental results show the proposed NN can online predict the PRC precisely when the PRC signal is lost for a short period of time.

The United States Coast Guard is responsible for the design, procurement, installation, and operation of reference stations, broadcast facilities, monitor sites, and control stations to provide a Differential GPS (DGPS) service for coastal and other critical waterways of the United States. The DGPS service is intended to support a number of applications where system accuracy, reliability, and integrity are all critical to safe and efficient navigation. As part of the design effort, the Coast Guard has analyzed the accuracy, reliability, and integrity requirements of four DGPS applications: harbor and harbor approach navigation, vessel traffic service (VTS) surveillance, aids to navigation (ATON) positioning, and exclusive economic zone (EEZ) surveying. This paper provides an overview of the DGPS design efforts, and describes the analysis methodologies used to derive the DGPS reliability and integrity requirements.

Integrating Passive Millimeter Wave camera (PMMW), Global Positioning System (GPS), and Differential Global Positioning System (DGPS) provides a pilot with a visual precision approach and landing in inclement weather conditions conceivably down to CAT III conditions. A DARPA funded, NASA Langley managed Technology Reinvestment Program (TRP) consortium consisting of Honeywell, TRW, Boeing, and Composite Optics Corporations is demonstrating the PMMW camera. The TRW developed PMMW camera displays the runway through fog, smoke, and clouds in day or night conditions. The Global Air Traffic Program Office entered into a Cooperative Research and Development Agreement (CRDA) with Honeywell to demonstrate DGPS. The Honeywell developed DGPS provides precision navigational data to within 1 m error where GPS has 100 m of error. In inclement weather the runway approach is initiated using GPS data until a range where DGPS data can be received. The runway is presented to the pilot using the PMMW image viewed via a Heads Up Display (HUD) or Head Mounted Display (HMD). At a range where DGPS data is available, a precise runway and horizon symbology is computed in the Flight Display Computer and overlaid on the PMMW image. Image processing algorithms operate on the PMMW image to identify and highlight obstacles on the runway. The integrated system provides the pilot with an enhanced situation awareness of the runway approach in inclement weather. When a DGPS ground station is not available at the landing area, image processing algorithms (again operating on the PMMW image) generate the runway and horizon symbology. GPS provides the algorithm with initial conditions for runway location and perspective. The algorithm then locates and highlights the runway and any obstacles on the runway. Honeywell Technology Center is performing research in the area of integrating the PMMW, DGPS, and GPS technologies to provide the pilot with the most necessary features of each system; namely: visibility, accuracy, obstacle detection, runway overlay, horizon symbology and availability.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The difference in ionospheric delay between paths to the reference and mobile stations for differential GPS has been quantified for equatorial region. This small additional ionospheric error can be evaluated and predicted for the mobile station by means of a determined differential delay along the baseline so that accurate correction can be made for the most precise positioning. In this paper we studies the ionospheric delay on the Global Positioning System (GPS) signal due to the variation of elevation angle and variation in total electron content (TEC) and ionospheric profiles utilizing the Modified Jones 3D Ray Tracing method. The differential delay can be determined for any azimuth angle of propagation and for any baseline direction, providing the approximate difference in line-of-sight (LOS) between the stations. Result show that the variations of elevation angle and TEC give effects on the difference in delay between the two stations in differential GPS (dGPS). This analysis determined the difference in ionospheric delay expected over a short baseline so that a more accurate differential GPS correction can be made.

The capabilities of Ashtech XII for differential GPS (Global Positioning System) are discussed. Differential algorithms and communication protocols to exchange differential information between receivers are included in the internal software of the receiver. Hence, there is no need for external computers to provide the protocol link. The all-in-view capability of the receivers makes them suitable for reference stations as well as remotes. Integration of ASHTECH XII with the vehicle tracking system (VTS) is presented. Differential GPS messages are transferred via the VTS communication link. The integration of the VTS and differential GPS has resulted in an accurate vehicle tracking and positioning system called differential GPS/VTS.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

One of the main tasks of geodesy is to determine coordinates with high accuracy using GNSS-observations. To perform such tasks in geodesy usually use the relative method of determining the coordinates in static mode. The technique of the relative method is based on determining the coordinates of an unknown point relative to a known one. The coordinates of the base point must be known, often precisely specified on the basis of the State Geodetic Networks. Static mode of observation is most often used to build geodetic networks, because it has the highest accuracy. In this study, the base points were active reference stations, the coordinates of which are set from the weekly combined solution of the GNSS-network. The purpose of the work is to investigate the accuracy of the application of the method of determining the coordinates according to GNSS-observations with reference to the network of active reference stations. Methodology. The data of GNSS-observations performed at the triangulation points of the State Geodetic Network and data of reference stations are used in the work. Based on these data, conditional GNSS-networks were formed for their processing in the software package, which consisted of three reference stations and one triangulation point. The data processing process assumed that the nearest reference stations were taken as a control point, the specified coordinates of which were recorded as control and set in the ETRS2000 system. The obtained sets of coordinates of the same points and stations were transformed into the USK2000 system. The accuracy of the coordinates determined in this way was analyzed on the basis of coordinate differences and their standard deviations. Differences for reference stations were determined relative to the refined weekly coordinates, and for triangulation points relative to the mean. Results. The obtained differences at the points of the state network are within 1–2 cm, acquiring both positive and negative values. The only exception is the fifth observation session, where the differences are 2–4 cm with a positive sign. At the KOVL reference station, the coordinate differences vary from –1.2 cm to +1.8 cm, and at the MEL2 station from 0 cm to 5.4 cm. Coordinate changes at triangulation points were estimated by standard deviations of 2.1 cm, 1.1 cm, and 1.9 cm for XYZ, respectively. The accuracy of all other coordinates of the reference stations is 0.3–1.6 cm, with an average range from –2.7 cm to +1 cm. Scientific novelty and practical significance. The paper shows the method of determining the coordinates in the system USK2000 according to GNSS-observations with reference to the network of active reference stations. The proposed technique allows the use of satellite methods to determine the coordinates in the state system USK2000 with an accuracy of 1–2 cm, as well as significantly speed up and speed up the process of field work.

The Global Positioning system (GPS) is used for navigation and associated tasks in wide variety of applications. One of the primary modes of GPS operation is differential GPS. Differential GPS allows more accurate positioning than stand-alone GPS. Many new applications are possible because of the increased accuracy obtained through differential GPS. In this paper the techniques and methods of differential GPS along with the algorithms are discussed which are providing more accurate and precise positioning in recent trends of communication. The purpose of the paper is to introduce the principles of differential GPS theory, and to provide a background for more advanced material.

Differential GPS (DGPS) and Real-Time- Kinematic (RTK) solutions are widely accepted meth- ods for accurate positioning and navigation. Initially these methods were based on single reference stations. A big breakthrough in performance and accuracy was achieved by the introduction of network solutions. To- day, the use of the Virtual Reference Station method is a standard technology applied in a large number of regional RTK networks all over the world, to pro- vide a positioning service with centimetre accuracy. DGPS techniques are used for marine, airborne and land applications and provide accuracies in the sev- eral decimetre range. The DGPS and RTK methods are based on regional reference station networks or nearby single stations. In contrast, the Precise Point Position- ing (PPP) method is providing position accuracy of several centimetres to decimetres based on a globally distributed tracking network. Precise satellite orbit and clock information is derived from the network process- ing. The achievable accuracy with PPP is impressive, but this method suffers from long convergence times of the order of more than 20-30 min to achieve acceptable

Global Positioning System (GPS) signals experience ranging errors due to propagation through the neutral atmosphere. These range delays consist of a hydrostatic component, dependent on air pressure and temperature, and a wet delay dependent on water vapour pressure and temperature. Range delays arising from the hydrostatic component can be computed with accuracies of a few millimeters using existing models, provided that surface barometric or meteorological data are available. By using a regional network of GPS reference stations, it is possible to recover estimates of the Slant Wet Delay to all satellites in view. Observations of the Slant Wet Delay (SWD) can be used to model the vertical and horizontal structure of water vapour over a local area. These techniques are based on a tomographic approach using the SWD as input observables, where 4-D models of the wet refractivity may be derived. This method allows improved resolution of water vapour estimates for precise positioning applications and assimilation into Numerical Weather Predictions (NWP). In this paper we present strategies for real-time modeling of wet refractivity, with simulations and preliminary results of data processing for a regional GPS network in Southern California.

In order to resolve the problem that DGPS (differential global positioning system) can not be used in the HIL (hardware-in-loop) simulation of aerocraft, but only simulated by math modeling, a method how to use DGPS in HIL simulation was brought forward on the base of GSS7700GPS simulator and NovAtel DGPS receiver. The DGPS simulation system configuration fig of aerocarft was shown.The trial data of single GPS and DGPS was acquired and plotted in the table. Comparing single GPS trial data with DGPS trial data, it improved that DGPS has more positioning accuracy than single GPS. The method realized that the whole DGPS out-of-doors running process could be simulated realistically in static environment of laboratory. The accuracy and reliability of DGPS simulation of aerocraft were improved greatly by using the method.

FAA and NASA have established a joint program to evaluate the technical feasibility of using guidance from the satellite-based NAVSTAR Global Positioning System (GPS) for Category I11 (CAT 111) precision approaches. A combination of analyses, simulation tests and flight tests will be used to evaluate Differential GPS (DGPS) techniques for CAT I11 applications. Emphasis will be placed on meeting accuracy and integrity requirements for a complete DGPS-based CAT I11 autoland capability. Contractors will be requested to supply the ground and airborne equipment for computing the DGPS-based aircraft position and velocity. Contractors will also provide their own aircraft completely equipped with a DGPS-based capability. Feasibility will be demonstrated by meeting either sensor accuracy requirements for Instrument Landing System (ILS) CAT I11 applications or Total System Error (TSE) requirements currently under development. Additionally, the existing FAA Advisory Circulzus for CAT 11, CAT I11 and autoland approaches should be used as a guide for system development. It is expected that meeting TSE requirements would place less demand on the performance of the DGPS-based sensor than meeting ILSwves an based navigation sensor requirements. This paper ,' overview of the DGPS CAT I11 system architecture, requirements and demonstration program.

A real-time integrated navigation system with 2-cm position accuracy was developed using commercial off-the shelf (COTS) equipment including inertial sensors and differential Global Positioning System (GPS) receivers, and was demonstrated for transportation applications with an emphasis on lane departure detection. A 900-MHz radiofrequency communications link transmits GPS base station range and carrier phase measurements to a GPS receiver on the vehicle. The GPS receiver calculates the vehicle position relative to the surveyed base location. The loosely coupled eight-state extended Kalman filter with 10-Hz navigation aids provides smoothed position information between 2-Hz GPS updates and provides graceful degradation in the presence of GPS blockages or communication dropouts. Currently, the navigation aids include anti-lock braking system wheel turns, electronic compass heading and pitch, and map vertical height. Data acquisition and Kalman filtering systems were developed to handle real-time processing and recording of all instrument data for further post-test system evaluation to determine the optimum configuration. An accurate rapid survey and map representation approach for measuring lane boundaries was validated using a vehicle, demonstrating inherit repeatability by the GPS positioning system. Real-time lane departure monitoring was developed. A video camera was installed to assist in accurate surveying and real-time system validation. This GPS-based positioning system is suitable for highway speeds during all weather conditions. It can be extended to other collision avoidance, drowsy driver awareness, advanced curve or intersection warnings, SOS, tracking, automated control, fast precision road mapping, and traffic management applications.

A Control survey is a survey operation that is carried out in order to establish position of points with a high degree of accuracy in order to support activities like mapping and map revisions, property boundary surveys, construction projects and so on. Control densification is a continuous exercise in the field of geomatics. This forms the basis upon which other geomatics and engineering activities geared toward development are referenced. This study is aimed at determining the coordinates of existing control points network along Ayetoro / Egbeda Atuba road using dual frequency GPS and Total Station with a view to comparing the accuracies of DGPS and Total Station using statistical analysis to determine which one has better accuracy. The Objectives of the study are to locate the existing control points, to collect the information/coordinates of the existing control points, and to carry out the observation using DGPS and Total station and process/compute the final coordinates and compare the results by using statistical analysis. The methodology that are adopted for this project is Satellite Positioning Technology using Differential Global Positioning System (DGPS) and Total Station. And the acquired data was processed and adjusted. The statistical analysis was used to compare the result obtained from DGPS and Total Station with the data collected from the Ministry of Land and Housing. The result of the analysis shows that DGPS has better accuracy. It is recommended that whenever more suitable and accurate method of measurement is to be employed, the DGPS method should be selected as this study has demonstrated and compared the accuracy of the two methods and showed that the DGPS method is better.

For precise positioning in arctic regions with Global Navigation Satellite Systems (GNSS), such as GPS and Glonass, there are a number of issues to be resolved or taken into account. The most important ones are satellite geometry, ionospheric effects and distribution of correction data. Precise Point Positioning (PPP) is currently the standard for precise offshore positioning. PPP requires a sparse global network of GNSS reference stations to estimate precise satellite orbit and clock parameters in real-time. These parameters are transmitted to users, who can compute their position with an accuracy of 0.1 m using code and carrier observations. The main disadvantage of PPP is that in general it takes a long time to converge to this accuracy, about 30–45 minutes. GNSS carrier observations are similar to pseudo ranges, but have an additional bias which needs to be estimated. Under certain conditions, these biases are integer. This property is used in what is generally referred to as Real-Time Kinematic (RTK) positioning, a technique which uses corrections generated at reference stations to make sure these ambiguities are integer. Integer Ambiguity Resolution (IAR) results in RTK accuracies of 0.01–0.03 m or better and short convergence times, ranging from instantaneous to several minutes for long inter-station distances. The disadvantage is the limited area of applicability, because RTK in general does not use precise orbits and clocks. Current research focuses on the combination of PPP and RTK techniques. The main goal is to achieve cm accuracy with a sparse network of reference stations. Another goal is to reduce convergence time. Applications are in the field of precise real-time offshore positioning in general, and subsidence monitoring and tidal estimation in particular. Results will be presented from standard PPP and PPP combined with IAR for arctic regions and from a test bed in the Gulf of Mexico. These results, although preliminary, indicate centimeter level accuracy is indeed possible, also in the arctic. We will also look at further improvements, mainly in convergence time, using all operational satellites and signals from current and future navigation systems.

Information communication technology related vehicle services need to support location and the transmission of communication and traffic information between vehicles, or between vehicles and infrastructure. In particular, the technology for the measurement of the accurate location of a vehicle is dependent on location-determination technology like Global Positioning System, and this technology is very important for vehicle driving and location services. If, however, a vehicle is in a Global Positioning System radio-shadow area, neither a Global Positioning System nor a Differential Global Positioning System can accurately measure the corresponding location because of a high error rate caused by the shadowing intervention. Even an Inertial Measurement Unit could provide inaccurate location data due to sensor drift faults around corners and traffic-road speed dumps. Vehicles, therefore, need an absolute location to prevent the provision of inaccurate vehicle-location data that is due to radio-shadow areas and relational Inertial Measurement Unit positions. To achieve this, we assume that vehicle-to-infrastructure communication is possible between a vehicle and roadside unit in Vehicular Ad hoc Networks. We used iBeacon at the roadside unit and revised its Universally Unique Identifier so that it generates absolute Global Positioning System location data; that is, moving vehicles can receive absolute Global Positioning System data from the roadside unit-based iBeacon. We compared the proposed method with current Global Positioning System and Inertial Measurement Unit systems for the following two cases: one with a radio-shadow area and one without. We proved that the proposed method generates location data that are more accurate than those of the other methods.