CHAPTER 1:  SYSTEM OVERVIEW

1.1  GENERAL DESCRIPTION

The Navstar Global Positioning System (GPS) is a space based radio positioning and time 

transfer system.  GPS provides accurate position, velocity, and time (PVT) information to an

unlimited number of suitably equipped ground, sea, air and space users.  Passive PVT fixes are

available world wide in all weathers in a world wide common grid system.  Normally GPS

contains features which limit the full accuracy of the service only to authorized users and

protection from spoofing (hostile imitation).

GPS comprises three major system segments, Space, Control, and User (see Figure 1

 1).

Figure 1 1.  Navstar GPS Major Segments

The Space Segment consists of a nominal constellation of 24 Navstar satellites.  Each satellite

broadcasts RF ranging codes and a navigation data message.  The Control Segment consists of a

network of monitoring and control facilities which are used to manage the satellite constellation

and update the satellite navigation data messages.  The User Segment consists of a variety of

radio navigation receivers specifically designed to receive, decode, and process the GPS satellite

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