Global Positioning System

Global Positioning System is a navigation system based on satellites. The system works on a network of 24 satellites. The U.S. Department of Defense (DOD) launched this system and is responsible for placing these satellites into orbit along their regular maintenance. Accurate positioning, reliable navigation, and timing services to worldwide users on a continuous basis are the main purpose of global positioning system.

Initially the U.S Department of Defense implemented this system for military use. But later the same was open for civilian use also. Now the system provides critical capabilities to military, commercial, and civil users all around the world.

In addition to GPS, other systems which are in use or under development are:

•        GLONASS: The Russian Global Navigation Satellite System
•          European Union Galileo positioning system
•         Indian Regional Navigation Satellite System, India
•        China's BeiDou Navigation Satellite System  
•         Japanese Quasi-Zenith Satellite System

A GPS receiver must receive signal of at least 3 satellites for calculating the 2-D position (latitude and longitude) and track movement. With four or more locked satellites signal in view, the receiver can determine the user's 3-D position (latitude, longitude and altitude). Upon determining the accurate position, the GPS unit can also calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.

How GPS works

The current GPS consists of three major segments. These are: a space segment, a control segment and a user segment. The GPS works on the concept of time and the known position of specialized satellites. Each satellite carries very stable atomic clocks. These clocks are synchronized to each other and to clocks on Earth. The satellite time is compared with the ground clocks and if there is any drift, the same is corrected on daily basics. Likewise, the satellite locations are also known with great precision. GPS receivers have clocks as well and these clocks are not synchronized with true time, and therefore are less stable.

GPS satellites continuously share their current position and time. A GPS receiver monitors multiple satellites and solves mathematical equations to determine the exact position of the sender and its deviation from true time. For finding out the location and time, at a minimum, signal from four satellites must be in the view of the receiver. The receiver then computes the four unknown quantities (three position coordinates: latitude, longitude, and altitude and clock deviation from satellite time).

Applications of GPS

Throughout the world, GPS has become a mainstay of transportation systems, providing navigation for ground, aviation and maritime operations. Location and timing capabilities of GPS are used in Disaster relief and emergency services in their life saving missions. Everyday activities such as banking, mobile phone operations, and even the control of power grids are facilitated by the accurate timing that GPS provides. Farmers, surveyors, geologists and countless others perform their work more efficiently, safely and economically.

GPS can work in any weather conditions, anywhere in the world, 24 hours a day. One must utilize the services offered by GPS as there are no subscription fees or setup charges to use GPS.

Ms. Snehlata
Assistant Professor
Deptt. of Information Technology