GPS: Technology for the Military and Civilians
GPS, which stands for Global Positioning System, was developed by the US
military. Funded by the US Department of Defense, GPS allows receivers to
calculate position, velocity and time from satellite signals, making it possible
for GPS to be used as a Satellite Navigation System. Today, GPS is used not only
by the military but by civilians.
Space segment, Control segment and User segment are three users of GPS
technology. Space segments consist of space vehicles used for transmitting radio
signals from space. A Control segment, on the other hand, consists of several
tracking systems positioned in different parts of the world. GPS receivers and
GPS users make up the User segment. GPS receivers convert signals that come from
the Space segment into time, velocity and position estimates.
GPS is mainly used for 3D navigation. Ships, airplanes, ground vehicles and hand
held devices are equipped with navigation receivers. Astronomy,
telecommunications and laboratories are some areas that have used special
purpose GPS receivers. In research studies, GPS has been used to calculate
atmospheric pressure.
There are two types of GPS: the Precise Positioning System and the Standard
Positioning Services. The US military and selected government agencies use the
Precise Positioning System. This type of GPS has accuracy of 22 meters latitude
and 22.7 meters longitude. It also has a 200-nanosecond time accuracy.
The Standard Positioning Services, on the other hand, is the type of GPS that is
used by civilians. This particular GPS is free and has unrestricted. Most GPS
receivers can receive and use this GPS type. However, Standard Positioning
Services is not very accurate. It has a 100-meter horizontal accuracy, 156-meter
vertical accuracy and 340-nanosecond time accuracy. This slight inaccuracy was
intentionally done by the US Department of Defense.
Timed data bits make up the GPS Navigation Message. Timed data bits mark
transmission time for each sub-frame as they are sent across by space vehicles.
Noise, biases and blunders are some of the common factors that affect accuracy
of timed data bits.
If you're in the market for GPS receivers, you will discover that their prices
vary depending on their capabilities. GPS receivers with greater capabilities
and more robust features can cost a few thousand dollars. However, you can get a
small GPS receiver that can accept differential corrections for under $200. |
