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The Global Positioning System

Today GPS is mostly known as a device that shows your location on a map, in your phone, or in a car. But GPS has many more "jobs” then you might notice at first glance. Here we shall mention just a few.

It makes the mobile telephony networks and electricity networks work because GPS can tell very precisely the time (or frequency). It enables landing of airplanes, navigation of ships in tight ports. Also satellites can be positioned and oriented towards Earth because GPS can provide precision of centimeters. Even precision of millimeters can be achieved by special GPS receivers, allowing to monitor the motion of bridges, buildings even mountains or continents. Not many other technologies can compete with GPS in these areas.

Often we do not notice it in our daily life, but GPS makes our life easier, more convenient and safer. These days new jobs are being created for GPS that have nothing to do with telling where you are on a map. For example GPS can be used for meteorology, to measure how stormy the sea is or how much water there is in the soil.

 

GPS, and other GNSS

GPS is a satellite based positioning system that provides reliable location and timing information, with new applications emerging every day. It uses a constellation of  32 satellites which orbit the Earth twice a day. GPS works in any weather conditions, anywhere in the world, 24 hours a day and  it is freely accessible by anyone with a GPS receiver.

Although GPS was initially designed for US military purposes, the number of civilian applications has by far surpassed the military ones.

Contradictory to popular belief, the GPS satellites don’t actually track the receiver, the receiver tracks the signals form GPS satellites. Here you can read more how GPS works...

GPS, which is maintained by the U.S. Government is not the only system of its kind. Other systems are available or are under development like the European Galileo, the Russian Global Navigation Satellite System (GLONASS), Chinese COMPASS or a dozen of other Global Navigation Satellite Systems or closely related systems. Read more about these systems here...

 

Typical and not so typical GPS applications

The GPS relies on the precise atomic clocks and time maintenance. This feature allows GPS to be used for precise time transfer, having applications in time synchronization and precise frequency generation (syntonation). Although the initial purpose of the system was, as the name implies, for positioning, a lot of new applications have been or are under development, which have little to do with indication of position or time.

  • Atmospheric measurements can be done because GPS radio signals are affected by temperature and humidity changes in atmosphere.
  • Geo-encryption (location-based encryption) is a method of encryption in which the encrypted information can be decrypted only at a specific location. 
  • Earthquake detection/prediction can be done by GPS based monitoring of tectonic plate movements.
  • Sea roughness (wave height) can be estimated by analysis of reflected GPS signals.
  • Amount of moisture in the soil can be also estimated by analysis of GPS signals that reflect from the ground.
  • Other GPS applications: investigation of the ionosphere and troposphere, entertainment (GeoCaching games), art, tracking, charting, environmental studies, transportation, road pricing, and many other, that you can read about here.

Enhancements to Standard GPS

Along the years multiple technologies and systems have been developed to aid the GPS system to obtain better precision, improve reliability, robustness and to minimize time to the first position output.

GPS (GNSS) Receivers

GPS (or GNSS) receiver is a very special kind of a radio. It can receive from 12 to 70 or more signals in parallel from all visible satellites. It needs to maintain the time and to do time measurements very precisely. A one microsecond error would cause a 300m distance measurement error.

The traditional GNSS receivers rely on hardware based channels to process the received signals. The introduction of Software Defined Radio (SDR) technology opens new ways to do GNSS based positioning. 

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Danish GPS Center, Fredrik Bajers Vej 7C, DK-9220 Aalborg Ø, Denmark, Tel +45 9940 8362, E-mail: gpscenter(at)gps.aau.dk