TABLE OF CONTENTS Arthur J. Dorsey and Willard A. Marquis
Lockheed Martin Corporation
Peter M. Fyfe
The Boeing Company
Elliott D. Kaplan and Lawrence F. Wiederholt
The MITRE Corporation
GPS is comprised of three segments: satellite constellation, ground-control/monitoring network, and user receiving equipment. Formal GPS JPO programmatic terms for these components are space, control, and user equipment segments, respectively. The satellite constellation is the set of satellites in orbit that provide the ranging signals and data messages to the user equipment. The control segment (CS) tracks and maintains the satellites in space. The CS monitors satellite health and signal integrity and maintains the orbital configuration of the satellites. Furthermore, the CS updates the satellite clock corrections and ephemerides as well as numerous other parameters essential to determining user PVT. Finally, the user receiver equipment (i.e., user segment) performs the navigation, timing, or other related functions (e.g., surveying). An overview of each system segment is provided next, followed by further elaboration on each segment starting in Section 3.2.
The space segment is the constellation of satellites from which users make ranging measurements. The SVs (i.e., satellites) transmit a PRN-coded signal from which the ranging measurements are made. This concept makes GPS a passive system for the user with signals only being transmitted and the user passively receiving the signals. Thus, an unlimited number of users can simultaneously use GPS. A satellite s transmitted ranging signal is modulated with data that includes information that defines the...
