Table of Contents
Advertisement
1 Introduction
1.2 GPS AND GLONASS OVERVIEW
The Global Positioning System (GPS) and the Global Navigation Satellite System (GLONASS) are satellite
systems capable of providing autonomous and highly accurate timing and positioning information. GPS and
GLONASS provide 24-hour, all-weather, worldwide coverage. See Table 1.1, Page 14, for a summary of their
characteristics. Refer to Figure 1.1, Page 10, for a representation of the GPS and GLONASS combined satellite
orbit arrangement.
Figure 1.1 View of GPS and GLONASS Combined Satellite Orbit Arrangement
1.3 GPS SYSTEM DESIGN
The system uses the NAVSTAR (NAVigation Satellite Timing And Ranging) satellites which consists of 24
operational satellites to provide a GPS receiver with six to twelve-satellite coverage at all times depending on the
receiver model. A minimum of four satellites in view allows the GPSCard to compute its current latitude, longitude,
altitude with reference to ellipsoid mean sea level and the GPS system time.
The GPS system design consists of three parts:
•
The Space segment
•
The Control segment
•
The User segment
All these parts operate together to provide accurate three dimensional positioning, timing and velocity data to users
worldwide.
1.3.1 THE SPACE SEGMENT
The space segment is composed of the NAVSTAR GPS satellites. The final constellation of the system consists of
24 satellites in six orbital planes, inclined 55° from the equator, with four satellites in each plane. The orbital period
of each satellite is approximately 12 hours at an altitude of 20,183 km. This provides a GPS receiver with six to
twelve satellites in view from any point on earth, at any particular time.
The GPS satellite signal identifies the satellite and provides the positioning, timing, ranging data, satellite status
and ephemerides (orbit parameters) of the satellite to the receiver. The satellites can be identified either by the
Space Vehicle Number (SVN) or the Pseudorandom Code Number (PRN). The PRN is used by the NovAtel
GPSCard.
The GPS satellites transmit on two L-band frequencies; one centered at 1575.42 MHz (L1) and the other at 1227.60
MHz (L2). The L1 carrier is modulated by the C/A code (Coarse/Acquisition) and the P code (Precision) which
is encrypted for military and other authorized users. The L2 carrier is modulated only with the P code. Please refer
to the following figure for a representation of the GPS satellite orbit arrangement.
10
GPS/GLONASS Receiver User Manual Rev 1
Advertisement
Table of Contents
