TABLE OF CONTENTS The Global Positioning System (GPS) consists of three segments: the space segment, the control segment, and the user segment, as shown in Fig. 1. The control segment tracks each satellite and periodically uploads to the satellite its prediction of future satellite positions and satellite clock time corrections. These predictions are then continuously transmitted by the satellite to the user as a part of the navigation message. The space segment consists of 24 satellites, each of which continuously transmits a ranging signal that includes the navigation message stating current position and time correction. The user receiver tracks the ranging signals of selected satellites and calculates three-dimensional position and local time.
This chapter is designed to provide a summary discussion of the GPS. Later chapters develop the details. All segments of the system, along with a detailed discussion of the signal and the multiple applications of the GPS, are covered in separate chapters.
[*]Ph.D., Chairman of the Board.
[ ]Professor, Department of Aeronautics and Astronautics, and Director, GPS Program.
The key performance objectives of the GPS system can be summarized as follows:
