Global Positioning System

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GPS

Are you looking for a coffee house near your location or trying to find the best restaurant in an unknown city? All of this is no longer a big deal. Now, you do not have to go around asking people or following manual maps. No, you do not even need highly specialized systems like sextants or chronometers to get to an unknown place. The global positioning system is here to easily help you out in the form of just a tiny GPS chip inside your mobile device. It is the same system that guides your pizza delivery guy to get your pizza on time.


GPS or global positioning system is a common system that most of us use every single day to reach from location A to B. The GPS or Global Positioning System can tell you the ground location of any object.


The GPS systems are made up of a network of satellites that are constantly sending coded information in the form of radio signals. The receivers then interpret the transmitted information from the satellites to locate the position on earth accurately.


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This satellite positioning system is an electronic system that can be used to locate vehicles, ships, people., etc. You use GPS everywhere, it is there in your car, smartphones, and even your watch has it. This GPS satellite system is a conglomeration of 29 Navstar satellites situated at almost 20,000 kilometres above the Earth’s surface. The satellites are located at 6 earth-centred orbital planes and travel at a speed of 14,000 km/hr.


This system is available in most parts of the world and available 24 hours a day. You will learn all the necessary facts about the GPS system in this article.


When was GPS First Used and Who Owns This System?

The USDD (U.S Department of Defense) has launched the GPS satellites starting from 1978 till 1994. USDD had initially put the satellites in orbit for military purposes. In the 1980s, the GPS was made available by president Ronald Regan for civilian use when a Korean airline strayed off due to navigational errors and was shot down by the Soviet fighters.


The U.S government still owns the GPS and the Air Force operates the satellites. But it is available for use by anyone who has a GPS receiver. Few interesting facts about GPS:

  • GPS was first used in combat during the Gulf wars.

  • The early military GPS receivers (handheld ones) weighed 35 pounds.

  • The first cell phones, which were GPS-enabled, came out in 2004.

  • GPS has two levels of services:

  • Standard positioning services - This service is free worldwide.

  • Precise Positioning services - This service is restricted to the U.S. armed forces, selected allies and federal agencies.

GPS Architecture

GPS has three units:

  • GPS Space Segment:

These are the satellites in space circling the earth every 12 hours. The space segment mainly does two things:

  • Route the radio signals.

  • Store the radio signal and retransmit it to the receiver unit.

The satellites have atomic clocks on them to control the signals. There are enough satellites which ensure that at any time there are 4 satellites in view from Earth’s surface.

  • GPS Control Segment:

There are one master control station and 5 monitor stations which form the GPC control segment. The monitor stations monitor the signals from satellites. Then the qualified signals are sent to the master station that revises the abnormalities and checks the operational specifications before sending the revised signals back to the satellites.

  • GPS Receiver or User Segment:

This forms all the GPS receivers like mobile phones, PCs, laptops and other devices that receive GPS signals and determines its distance from each satellite.


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The Working Mechanism of the GPS

All the three elements of the GPS described above work in tandem to accurately determine the position of any object. GPS works on the “Trilateration mathematical principle”. This principle uses distances to points at known coordinates to locate an object’s position. Trilateration needs 3 ranges to 3 known points whereas a GPS needs 4 pseudo-ranges to 4 satellites.


Each GPS satellite broadcasts a message which consists of the satellite’s current position, exact time, and orbit. A GPS receiver then calculates its exact position by combining the broadcasts from multiple satellites.


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In the image above, the 4 satellites around the receiver on the earth determine the man’s position. It is the 4th satellite that confirms the target location, the other 3 satellites are used to trace the location.


Types of GPS systems

The mobile phone industry has numerous different GPS systems:

  • A-GPS:

This is the assisted GPS that is used to speed up the start-up time taken by GPS based positioning systems. With an A-GPS, the receiver would get a lock when there is a weak signal. This kind of GPS requires a network connection in the mobile phone since A-GPS needs assistance servers to acquire the lock. A GPS lock is something that makes positioning accurate and depends on the movement of the tracker.

  • S-GPS:

The simultaneous GPS type enhances the reporting ability of the satellite to the network carrier. With S-GPS, one can receive both voice data and GPS at the same time so that network providers can give services depending on the location.

FAQ (Frequently Asked Questions)

Q1. What are Some of the Applications of a GPS Positioning System?

Ans: The global positioning satellite was initially developed to help the U.S. military but it is now used worldwide for many purposes. There are five main jobs that a GPS performs:

  • Determine a location.

  • Navigation i.e. moving from one point to another.

  • Tracking i.e. monitoring the movement of objects.

  • Mapping i.e. creating world maps.

  • Timing i.e. telling the world about precis time.

Based on these features of the GPS, it is used in many fields, some of them are mentioned below:

  • Astronomy

  • Cartography

  • Mobile phones

  • Fleet tracking

  • Geofencing

  • Geotagging

  • GPS Aircraft tracking

  • Disaster relief

  • Emergency services

  • Navigation of vehicles

  • Surveying

  • Robotics

  • Tectonics

Q2. Mention Some of the Sources of a GPS Error.

Ans: Many sources may affect the accuracy of positions that the GPS computes. The travel time of GPS satellite signals are affected by the following factors:

  • Atmospheric Effects - A GPS signal is refracted while passing from the ionosphere to the troposphere. This causes the speed of the GPS signal to differ from the GPS signal in space.

  • Noise or Distortion of the Signal - There could be errors inherent in the GPS receiver itself that can cause electrical interference. This will ultimately give the wrong position information.

  • Small Variations in the Atomic Clocks - A clock error of even 1 nanosecond can cause huge position errors of 1 foot to 0.3 meters in determining the position on the ground.

  • Multipath Effect - Sometimes satellite signals can bounce off a reflective surface before they reach the receiver’s antenna. This causes a multipath error effect where the receiver gets the signal in the straight-line path and also in the delayed path. This causes the same effect as a double image on a TV set.