TABLE OF CONTENTS Elliott D. Kaplan and Joseph L. Leva
The MITRE Corporation
Dennis Milbert
NOAA (retired)
Mike S. Pavloff
Raytheon Company
GPS utilizes the concept of TOA ranging to determine user position. This concept entails measuring the time it takes for a signal transmitted by an emitter (e.g., foghorn, radiobeacon, or satellite) at a known location to reach a user receiver.
This time interval, referred to as the signal propagation time, is then multiplied by the speed of the signal (e.g., speed of sound or speed of light) to obtain the emitter-to-receiver distance. By measuring the propagation time of the signal broadcast from multiple emitters (i.e., navigation aids) at known locations, the receiver can determine its position. An example of two-dimensional positioning is provided next.
Consider the case of a mariner at sea determining his or her vessel s position from a foghorn. (This introductory example was originally presented in [1] and is contained herein because it provides an excellent overview of TOA position determination concepts.) Assume that the vessel is equipped with an accurate clock and the mariner has an approximate knowledge of the vessel s position. Also, assume that the foghorn whistle is sounded precisely on the minute mark and that the vessel s clock is synchronized to the foghorn clock. The mariner notes the elapsed time from the minute mark until the foghorn whistle is heard. The foghorn whistle propagation time is the time it took for the foghorn whistle to...
