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.

Wide area augmentation of the Global Positioning System

Consensus is growing that the flexibility gained with the introduction of programmable, electronic cockpit displays in the 1980s must be exploited to the full extent. An important candidate to become the primary flight display of future flight decks is the tunnel-in-the-sky display, a perspective flight-path display that shows the reference trajectory to be flown in a synthetic three-dimensional world. The usefulness of the tunnel display in the pilot manual aircraft control task is the subject of this thesis. The mainstream of tunnel display research is confined to empirical comparisons of the tunnel display with conventional displays. The approach taken in the present theoretical and experimental study is original and new as it is conducted from the perspective of cybernetics. A four-stage methodology is developed to study the fundamental characteristics of pilot/display interaction, based on a theoretical analysis of information, in particular the information used for control. The information analysis is conducted within the context of Gibson's ecological approach to visual perception. The information analysis provides novel insights into how the tunnel display geometric design variables can affect pilot behavior. To examine the validity of the theoretical hypotheses, six experiments have been conducted. Three experiments examined the effects of manipulating some of the main display design variables, such as the tunnel size, the viewing volume and the presence of guidance symbology. Another three experiments investigated the fundamental characteristics of the tunnel geometrical design in the tasks of following a trajectory that is either straight or circular, and in the task of conducting a curve-interception maneuver. The experiments show that the cybernetic, information-centered approach is indeed very successful in pin-pointing the important characteristics of pilot/display interaction. The experimental methodology employed in this thesis aimed at integrating the model-based approach with the common approach of collecting mainly performance-related data. It is described in detail how experiments can be designed with the objective of conducting a control-theoretic analysis. The limitations of some non-parametric identification methods in multi-axis, multiple loop tracking tasks are described. The use of criterion functions, in both the frequency and the time domain, in the parametric identification methods is also exemplified.

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Cybernetics of Tunnel-in-the-Sky Displays

Autonomous vehicles require precise knowledge of their position and orientation in all weather and traffic conditions for path planning, perception, control, and general safe operation. Here we derive these requirements for autonomous vehicles based on first principles. We begin with the safety integrity level, defining the allowable probability of failure per hour of operation based on desired improvements on road safety today. This draws comparisons with the localization integrity levels required in aviation and rail where similar numbers are derived at 10^-8 probability of failure per hour of operation. We then define the geometry of the problem, where the aim is to maintain knowledge that the vehicle is within its lane and to determine what road level it is on. Longitudinal, lateral, and vertical localization error bounds (alert limits) and 95% accuracy requirements are derived based on US road geometry standards (lane width, curvature, and vertical clearance) and allowable vehicle dimensions. For passenger vehicles operating on freeway roads, the result is a required lateral error bound of 0.57 m (0.20 m, 95%), a longitudinal bound of 1.40 m (0.48 m, 95%), a vertical bound of 1.30 m (0.43 m, 95%), and an attitude bound in each direction of 1.50 deg (0.51 deg, 95%). On local streets, the road geometry makes requirements more stringent where lateral and longitudinal error bounds of 0.29 m (0.10 m, 95%) are needed with an orientation requirement of 0.50 deg (0.17 deg, 95%).

Localization Requirements for Autonomous Vehicles.

Localization Requirements for Autonomous Vehicles

Strong ionospheric scintillation due to electron density irregularities inside the ionosphere is commonly observed in the equatorial region during solar maxima. Strong amplitude scintillation causes deep and frequent Global Positioning System (GPS) signal fading. Since GPS receivers lose carrier tracking lock at deep signal fading and the lost channel cannot be used for the position solution until reacquired, ionospheric scintillation is a major concern for GPS aviation in the equatorial area. Frequent signal fading also causes frequent reset of the carrier smoothing filter in aviation receivers. This leads to higher noise levels on the pseudo-range measurements. Aviation availability during a severe scintillation period observed using data from the previous solar maximum is analyzed. The effects from satellite loss due to deep fading and shortened carrier smoothing time are considered. Availability results for both vertical and horizontal navigation during the severe scintillation are illustrated. Finally, a modification to the upper bound of the allowed reacquisition time for the current Wide Area Augmentation System (WAAS) Minimum Operational Performance Standards (MOPS) is recommended based on the availability analysis results and observed performance of a certified WAAS receiver.

Availability Impact on GPS Aviation due to Strong Ionospheric Scintillation

A methodology to determine the required navigation performance (RNP) for aircraft precision approach and landing under instrument meteorological conditions (IMC) is described. The RNP in turn defines an aircraft containment surface about the nominal flight path, called a tunnel, which specifies the allowed approach and landing flight path limits. If the aircraft and its navigation system satisfy the RNP, then the aircraft will successfully traverse the tunnel, terminating in a safe landing. The tunnel is defined by four RNP parameters: accuracy, integrity, continuity, and availability.

J. M. Davis

Papers

Required navigation performance (rnp) for precision approach and landing with gnss application