An intelligent Differential GPS using Π-Σ Neural Network

In recent years the importance of real-time positioning and navigation with the Global Positioning System (GPS) has grown rapidly. Starting from the establishment of differential GPS (DGPS) reference stations for marine and land navigation, new users and applications have emerged that resulted in a high demand for the establishment of a high-density network of reference stations around the world. Many countries have established their own DGPS service, which is either governmentally or commercially owned. These services are referred to as Local Area DGPS Systems (LADGPS). However, the costs for the establishment and maintenance of a dense network of reference stations are very high. Therefore Wide Area DGPS Systems (WADGPS) are being developed to overcome the main drawbacks of LADGPS. In this case, only a few reference stations are used to cover a large area, such s a continent like Europe. To achieve high positioning accuracies, real-time modeling of the main error sources for long-range baselines is required as errors in the satellite orbit and ionospheric refraction do not cancel entirely in double differencing. In this article, a real-time correction model based on the Kalman filter for WADGPS and networked LADGPS services is discussed and results of field tests in a WADGPS network in Europe are presented. © 2000 John Wiley & Sons, Inc.

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 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.

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>

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.

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.

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.

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.

Differential Global Positioning System (DGPS) techniques are frequently used to correct for ranging errors common to two receivers, one of which is at a known position. One such source of error is selective availability (SA). A time delay (latency) is inherent between the generation of pseudo-range corrections and their application by the user, and can result in large residual errors. The data latency of the DGPS correction is a fundamental limitation on DGPS performance accuracies. These corrections can be predicted for relatively short periods of time. In this paper, an innovative methodology is developed which predicts the corrections and compensates the GPS data in real time. It also takes care of any transients in the DGPS data and/or GPS data in real time. This methodology has been applied to automobile navigation and tested in a DGPS/INS system. For these experiments, we used a 12-channel Ashtech XII GPS receiver. The INS system included a 3-axis Hitachi HGA-D fiber-optic gyro, a 3-axis 177 2g accelerometer by NeuwGhent Technology, Inc., and a Vector 2x electronic compass by Precision Navigation.

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.

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.

Many organizations would benefit from the ability to continuously locate the position of individuals as they move throughout a facility. Early tracking and direction finding was achieved using directional antennas or pseudo Doppler array techniques. It was developed for outdoor use over relatively long ranges. The reliability and accuracy fell short of current personnel tracking needs. Today, Global Positioning System (GPS) service is ubiquitous. Differential GPS provides sufficient accuracy for most personnel tracking applications. Recent cost reductions in OEM grade GPS receiver printed circuit assemblies have made GPS solutions feasible for personnel tracking. Bidirectional LEOs based satellite location systems are under development which can be applied to personnel location as well. The paper examines the practical and technical issues confronting personnel tracking systems in today's target markets. Potential approaches to personnel tracking are presented and compared. We then introduce an alternative RF location technique utilized by the PALS (Personal Alarm Location System) from Dominion Wireless, Inc. The theory of operation of PALS is presented. Early designs and their performance are summarized. Current implementations are discussed and the capabilities and limitations are reviewed as observed in actual deployed systems. Finally, the future plans for the refinement and advancement of PALS are presented and projections of enhanced performance supplied

This is the second part of a two-part discussion, in which we will provide an overview of the use of GIS and GPS in environmental analysis and enforcement. Geographic Information Systems (GIS) describes a system which manages, analyses and displays geographic information. Environmental applications include analysis of source, extent and transport of contaminants, nonpoint runoff modeling, flood control, and emergency response support. The ability to examine spatial relationships between environmental observations and other mapped and historical information, and to communicate these relationships to others, makes GIS valuable in environmental forensics. The US Environmental Protection Agency currently requires the inclusion of locational information with all other environmental data that is collected. Geographic Information Systems is a complex tool that requires careful planning and design to be successfully implemented. Choices in hardware, software and data development must be based on evaluation of project objectives, analytical requirements, data availability and data development considerations. Data sets must be evaluated and documented with metadata. The Global Positioning System (GPS) is a satellite-based system which provides highly accurate, three-dimensional position information anywhere on the earth's surface. Using portable radio receivers, field analysts can easily record the positions of spill sites, sampling locations and other environmental features. Spatial accuracy of GPS ranges from 20-30 m (single receiver) to 1-5 m (differential GPS) for navigation-grade instruments, and down to millimeter level accuracy for geodetic units. Global Position Systems can be used not only to capture spatial information into a GIS system, but also to evaluate and quantify the spatial accuracy of existing digital map data, and to provide control points for existing aerial photographs and other remotely-sensed data.

This project was undertaken to develop a system to map salinity with a towed electromagnetic induction meter (EM) and to position the meter with the Global Positioning System (GPS). The characteristics of the GPS are reviewed and the differential GPS (DGPS) mode of positioning, as applied to the EM meter positioning case, is explained. An EM38 salinity meter was time synchronized to GPS through a field portable personal computer (PC) and mounted on a non-magnetic toboggan for this purpose. The PC was also used to record all data for post-processing and analysis. The system was towed at velocities of up to 25 km h−1 during the field measurements. Continuous positioning of the system was achieved with an accuracy of 1–3 m. Salinity and GPS measurements were integrated and recorded on a field portable PC laptop. The results from a 30-ha site near Brooks are presented as well as those from a 100-ha site near Stettler, AB, which was surveyed in 3 h yielding 6000 salinity measurements. In order to test the repeatable accuracy of the system, the survey at Stettler was repeated the following day. The agreement is of the order of 1 dS m−1 which is satisfactory for most applications. The effect of measurement spacing on accuracy is also analysed using various scenarios. Key words: Soil electrical conductivity, salinity, satellite navigation, Global Positioning System, positioning, precision farming

Fast and precise relative positioning for baselines can be achieved using dual-frequency Global Positioning System (GPS) receivers. While the Differential GPS (DGPS) technique enhances GNSS accuracy by mitigating certain errors, it cannot entirely eliminate orbital, ionospheric, and tropospheric errors. This study explores the application of accurate relative positioning for processing GPS data, discussing its advantages and limitations, and compares the outcomes with relative positioning results obtained using the Mecca permanent GPS observation network. The results and analysis of the integrated system are presented. The findings conclude that utilizing precise ephemeris from the International GPS Services (IGS) Network in combination with the Klobuchar ionospheric model and either the Hopfield or Saastamoinen tropospheric model significantly improves the accuracy of DGPS measurements.