Per Enge

Bio: Per Enge is an academic researcher from Stanford University. The author has contributed to research in topics: Global Positioning System & GNSS applications. The author has an hindex of 47, co-authored 479 publications receiving 11520 citations. Previous affiliations of Per Enge include Worcester Polytechnic Institute.

Global Positioning System: Signals, Measurements, and Performance

Abstract: The Global Positioning System (GPS) is a satellite-based navigation and time transfer system developed by the U.S. Department of Defense. It serves marine, airborne, and terrestrial users, both military and civilian. Specifically, GPS includes the Standard Positioning Service (SPS) which provides civilian users with 100 meter accuracy, and it serves military users with the Precise Positioning Service (PPS) which provides 20-m accuracy. Both of these services are available worldwide with no requirement for a local reference station. In contrast, differential operation of GPS provides 2- to 10-m accuracy to users within 1000 km of a fixed GPS reference receiver. Finally, carrier phase comparisons can be used to provide centimeter accuracy to users within 10 km and potentially within 100 km of a reference receiver. This advanced tutorial will describe the GPS signals, the various measurements made by the GPS receivers, and estimate the achievable accuracies. It will not dwell on those aspects of GPS which are well known to those skilled in the radio communications art, such as spread-spectrum or code division multiple access. Rather, it will focus on topics which are more unique to radio navigation or GPS. These include code-carrier divergence, codeless tracking, carrier aiding, and narrow correlator spacing.

Global Positioning System: Theory and Applications, Volume II

Abstract: Volume I: GPS Fundamentals Introduction and Heritage and History of NAVSTAR, the Global Positioning System Overview of the GPS Operation and Design GPS Signal Structure and Theoretical Performance GPS Navigation Data Satellite Constellation and Geometric Dilution of Precision GPS Satellite and Payload Fundamentals of Signal Tracking Theory GPS Receivers GPS Navigation Algorithms GPS Operational Control Segment GPS Performance and Error Effects GPS Error Analysis Ionospheric Effects on GPS Tropospheric Effects on GPS Multipath Effects Foliage Attenuation for Land Mobile Users Ephermeris and Clock Navigation Message Accuracy Selective Availability Introduction to Relativistic Effects on the Global Position System Joint Program Office Test Results Interference Effects and Mitigation Techniques

Weighted RAIM for Precision Approach

Abstract: The use of differential GPS is becoming increasingly popular for real-time navigation systems. As these systems migrate to safety-of-life applications (e.g. precision approach and landing), their integrity becomes more important than their accuracy. One method for increasing both accuracy and integrity is the use of weighting in the navigation solution. This method uses a priori information to weight certain satellites (e.g. those at higher elevation) over other satellites. The accuracy increases because we better use the information available. The integrity increases because satellites that are more likely to introduce error contribute less to the solution. A weighted position solution by itself does not provide sufficient integrity to support precision approach. However, this method can be combined with a weighted form of Receiver Autonomous Integrity Monitoring (RAIM) to increase the level of integrity. RAIM uses redundant measurements to check the consistency of an overdetermined solution. This check is crucial because only a user can detect certain error types (e.g. severe airframe multipath or local interference). A differential reference station can detect many types of errors. However, it is only at the user where all the information is combined. The use of RAIM (or some form of integrity at the user) must be combined together with integrity checking at the reference station to provide the overall safety of the system. Weighted RAIM is investigated for application to Category I precision approach as supported by a Wide Area Augmentation System (WAAS). This paper details how to implement weighted RAIM and how to use geometry selection to guarantee a certain level of protection. Also, we provide information on the availability of these geometries. The results are based upon analysis, Monte Carlo simulation and actual data collected from Stanford University’s wide-area differential GPS network.

Wide area augmentation of the Global Positioning System

Abstract: The Wide Area Augmentation System (WAAS) is being deployed by the Federal Aviation Administration (FAA) to augment the Global Positioning System (GPS). The WAAS will aid GPS with the following three services. First, it will broadcast spread-spectrum ranging signals from communication satellites. The airborne WAAS receiver will add these new ranging signals to the GPS constellation of measurements. By so doing, the augmented position fix will be less sensitive to the failure of individual system components, thus improving time availability and continuity of service. Second, the WAAS will use a nationwide ground network to monitor the health of all satellites over our airspace and flag situations which threaten flight safety. This data will be modulated on to the WAAS ranging signals and broadcast to the users, thereby guaranteeing the integrity of the airborne position fix. Third, the WAAS will use the ground network to develop corrections for the errors which currently limit the accuracy of unaugmented GPS. This data will also be included on the WAAS broadcast and will improve position accuracy from approximately 100 m to 8 m. When complete, the augmented system will provide an accurate position fix from satellites to an unlimited number of aircraft across the nation. It will be the primary navigation system for aircraft in oceanic routes, enroute over our domestic airspace, in crowded metropolitan airspaces, and on airport approach.

RADAR: an in-building RF-based user location and tracking system

Abstract: The proliferation of mobile computing devices and local-area wireless networks has fostered a growing interest in location-aware systems and services. In this paper we present RADAR, a radio-frequency (RF)-based system for locating and tracking users inside buildings. RADAR operates by recording and processing signal strength information at multiple base stations positioned to provide overlapping coverage in the area of interest. It combines empirical measurements with signal propagation modeling to determine user location and thereby enable location-aware services and applications. We present experimental results that demonstrate the ability of RADAR to estimate user location with a high degree of accuracy.

Understanding GPS : principles and applications

Abstract: Fundamentals of Satellite Navigation. GPS Systems Segments. GPS Satellite Signal Characteristics and Message Formats. Satellite Signal Acquisitions and Tracking. Effects of RF Interference on GPS Satellite Signal Receiver Tracking. Performance of Standalone GPS. Differential GPS. Integration of GPS with other Sensors. Galileo. The Russian GLONASS, Chinese Bediou, and Japanese QZSS Systems. GNSS Markets and Applications.

Survey of Wireless Indoor Positioning Techniques and Systems

Abstract: Wireless indoor positioning systems have become very popular in recent years. These systems have been successfully used in many applications such as asset tracking and inventory management. This paper provides an overview of the existing wireless indoor positioning solutions and attempts to classify different techniques and systems. Three typical location estimation schemes of triangulation, scene analysis, and proximity are analyzed. We also discuss location fingerprinting in detail since it is used in most current system or solutions. We then examine a set of properties by which location systems are evaluated, and apply this evaluation method to survey a number of existing systems. Comprehensive performance comparisons including accuracy, precision, complexity, scalability, robustness, and cost are presented.

GPS-less low-cost outdoor localization for very small devices

Abstract: Instrumenting the physical world through large networks of wireless sensor nodes, particularly for applications like environmental monitoring of water and soil, requires that these nodes be very small, lightweight, untethered, and unobtrusive. The problem of localization, that is, determining where a given node is physically located in a network, is a challenging one, and yet extremely crucial for many of these applications. Practical considerations such as the small size, form factor, cost and power constraints of nodes preclude the reliance on GPS of all nodes in these networks. We review localization techniques and evaluate the effectiveness of a very simple connectivity metric method for localization in outdoor environments that makes use of the inherent RF communications capabilities of these devices. A fixed number of reference points in the network with overlapping regions of coverage transmit periodic beacon signals. Nodes use a simple connectivity metric, which is more robust to environmental vagaries, to infer proximity to a given subset of these reference points. Nodes localize themselves to the centroid of their proximate reference points. The accuracy of localization is then dependent on the separation distance between two-adjacent reference points and the transmission range of these reference points. Initial experimental results show that the accuracy for 90 percent of our data points is within one-third of the separation distance. However, future work is needed to extend the technique to more cluttered environments.

Global Positioning System: Signals, Measurements, and Performance

Abstract: The Global Positioning System (GPS) is a satellite-based navigation and time transfer system developed by the U.S. Department of Defense. It serves marine, airborne, and terrestrial users, both military and civilian. Specifically, GPS includes the Standard Positioning Service (SPS) which provides civilian users with 100 meter accuracy, and it serves military users with the Precise Positioning Service (PPS) which provides 20-m accuracy. Both of these services are available worldwide with no requirement for a local reference station. In contrast, differential operation of GPS provides 2- to 10-m accuracy to users within 1000 km of a fixed GPS reference receiver. Finally, carrier phase comparisons can be used to provide centimeter accuracy to users within 10 km and potentially within 100 km of a reference receiver. This advanced tutorial will describe the GPS signals, the various measurements made by the GPS receivers, and estimate the achievable accuracies. It will not dwell on those aspects of GPS which are well known to those skilled in the radio communications art, such as spread-spectrum or code division multiple access. Rather, it will focus on topics which are more unique to radio navigation or GPS. These include code-carrier divergence, codeless tracking, carrier aiding, and narrow correlator spacing.