Basic Principles of Satellite Navigation

Satellite Navigation Systems all use the same basic principles to determine coordinates:
• Satellites with a known position transmit a regular time signal.
• Based on the measured travel time of the radio waves (electromagnetic signals travel through space at the speed of light c = 300’000km/s) the position of the receiver is calculated.
We can see the principle more clearly using a simple model. Imagine that we are in a car and need to determine our position on a long and straight street. At the end of the street is a radio transmitter sending a time signal pulse every second. Onboard the car we are carrying a clock, which is synchronized to the clock at the transmitter. By measuring the elapsed travel time from the transmitter to the car we can calculate our position on the street .

GPS Intro

GPS (the full name of the system is: NAVigation System with Timing And Ranging Global Positioning System, NAVSTAR-GPS) is intended for both civilian and military use. The civilian signal SPS (Standard Positioning Service) can be used freely by the general public, while the military signal PPS (Precise Positioning Service) is available only to authorized government agencies. The first satellite was placed in orbit on February 22, 1978, and it is planned to have up to 32 operational satellites orbiting the Earth at an altitude of 20,180 km on 6 different orbital planes. The orbits are inclined at 55° to the equator, ensuring that a least 4 satellites are in radio communication with any point on the planet. Each satellite orbits the Earth in approximately 12 hours and has four atomic clocks onboard.
During the development of the GPS system, particular emphasis was placed on the following three aspects:
1. It had to provide users with the capability of determining position, speed and time, whether in motion or at rest.
2. It had to have a continuous, global, all-weather 3-dimensional positioning capability with a high degree of accuracy.
3. It had to offer potential for civilian use.

Introduction To Satellite Navigation

Satellite Navigation is a method employing a Global Navigation Satellite System (GNSS) to accurately determine position and time anywhere on the Earth. Satellite Navigation receivers are currently used by both private individuals and businesses for positioning, locating, navigating, surveying, and determining the exact time in an ever-growing list of personal, leisure and commercial applications.
Using a GNSS system the following values can accurately be determined anywhere on the globe

1. Exact position (longitude, latitude and altitude co-ordinates) accurate to within 20 m to approx.1 mm.
2. Exact time (Universal Time Coordinated, UTC) accurate to within 60ns to approx. 5ns.
Speed and direction of travel (course) can be derived from these values, which are obtained from satellites orbiting the Earth.