Have you ever thought of locating yourself on the blue planet (Earth)? This might be a tough question if you are residing in a new place.
But don’t worry, the answer is simple, the GPS. GPS is a tiny device used as a navigation receiver in ships, and aviator, smartphones and many more.
In this tutorial, you will know the working and applications of GPS employed in various fields. We will start with basics of GPS and elements of a navigation system.
GPS is the abbreviated form of Global Positioning System introduced by the Department of Defense (United States) for the military crew. This satellite navigation system is named NAVSTAR (Navigational Satellite Timing and Ranging).
Later, GPS receivers has been developed to find out the accurate position of a particular location and in weather navigation applications.
The GPS system consists of 24 satellites placed 20,000 Km above the earth in various orbits, commonly called GPS constellation.
These satellites revolves round the earth for every 12 hours periodically. They will keep track of worldwide position, velocity and time.
GPS satellite broadcast the information (Date, time, position, and astronomical data) related to all the satellites in the constellation.
The GPS satellites in the space are designed in such a way that receivers captures the information 4 satellites at any time. It gets the calculated distance from the satellite. In order to receive the GPS signals, the sky has to be unclouded.
Each satellite transmits low power RF signals with unique range codes (Coarse/Acquisition code and Precision code). Coarse/Acquisition code is free for every user but the precision code is restricted for military purpose.
Satellites transmit at two frequencies, 1.57542 GHz, and 1.2276 GHz. GPS also known as Global Navigation Satellite System (GNSS) is not a single subsystem and it is divided into 3 main components. They are Space Segment, Control Segment, and User Segment.
Space Segment consists of Satellites rotating around the earth and passing information (latitude, longitude, and altitude) to the GPS receivers. Moreover, it determines the UTC (Universal Coordinated Time).
This unit supervises the status of satellite and sends back the error and rectification data. The data is corrected and send back to the satellite.
User Segment comprises the GPS receivers that collect the satellite information.
There are numerous satellites in the space developed by many countries. Some of them are GLONASS (Russia), IRNSS (India), BDS (China), and Galileo (Europe).
How GPS works?
The GNSS satellite works by the following principle. Satellites are built with high precision atomic clocks operating at a frequency of 10.23 MHz. These clocks helps in calculating the position of the receiver.
The crystal used in the satellite is the most important element in determining the almanac data. The accuracy of a crystal is measured in terms of PPM (Parts per Million). Generally, the ppm used in a satellite is in the order of 1ppm. This ppm varies with the temperature and responsible for shifting of frequency. Hence it is necessary to design and use accurate crystal.
The errors may occur not only due to clock errors. It may be due to ionosphere and troposphere delays, number of visible satellites, receiver clock timing.
As you know the satellite generates two carrier frequencies (L1 and L2) located in L-band. L1 carrier is transmitted at a frequency of 1575.42 MHz and L2 carrier wave at 1227.60 MHz’.
This carrier waves are modulated with C/A code and P-code. This modulated wave is called radio wave.
Now the distance is equal to the time taken for the radio wave to travel from the satellite to the GPS receiver multiplied with the speed of the radio wave.
Distance = Speed of Radio wave X Travelling time of the radio wave
Applications of GPS
GPS has been used in many areas of industry for serving mankind. Some of the GPS application are:
- Fault measurement of Earthquakes.
- To eradicate the terrorism activities.
- Weather-based data acquisition device uses GPS to track the date, time, latitude and longitude.
- Self-navigation robots for determining the latitude, longitude, speed and time in military applications.
- In automotive cars and aerial vehicles
- Farmers make use of GPS for seasonal tracking of field mapping, soil evaluation, and yield analysis.
- Used in space and astronomical fields.
- In marine industry for shipping navigation.
Right from our smartphones to high speed aerial vehicles make use of GPS for tracking and locating of unknown places. This revolutionized technology is implemented in internet of things, wearables etc.
I hope, you have understand the basics of GPS and its applications. You will explore more in the coming tutorials about GPS receivers and their implementation.