How GPS Works
The GPS (Global Positioning System) consists of 24 medium earth orbit satellites developed by the US Department of Defense and currently managed by the US Air Force 50th Space Wing. Each satellite transmits microwave signals to the earth. GPS receivers on the earth use these signals to determine their locations, speed, direction, and time. A typical GPS receiver must have line-of-sight with satellites to calculate its position using signals from four or more GPS satellites. Four satellites are needed since the process needs a very accurate local time for the device to determine its time as well as position. These signals are then processed by the receiver to determine latitude/longitude, speed, altitude, and time. For fleet management systems, this set of data is transmitted over a wireless network to a server. The server then takes the data and uses it to provide the end user with locations of their devices.
History of GPS
GPS is based on technology similar to radar, which was developed during WWII. In 1957, A group of scientists monitoring Sputnik (the first ever space vehicle launched by the Soviet Union) found that they could determine the satellite’s approximate location because radio signals from it would get stronger as it approached a certain point and would become weaker after it passed due to the Doppler effect. They used this concept to theorize that signals from a group of satellites could be measured to determine the precise location of a receiver based on earth. Over the next 2 decades, the US military experimented with several types of satellite navigation systems to aid them in guiding aircraft, submarines and missiles. Finally, in 1978, the first GPS satellite was launched, with the remaining to follow throughout the 1980’s and 1990’s. Much like the original version of the Internet, the US used GPS as a defense tool. It helped the U.S. government determine the positions of enemy nuclear warheads and any nuclear test explosions that were in violation of any existing treaties. Until 1983, the global positioning system was exclusively used by the US military.
However, in 1983, the Soviet government accidentally shot down Korean Airlines Flight 007. Immediately afterward, President Ronald Regan made the system available for civilian use as a means to avoid any similar catastrophes in the future. However, the US enabled a protocol called Selective Availability (SA) which gave the government the ability to severely reduce the accuracy of the system or disable it all together for non-military users at anytime. This was a means of limiting the ability for enemies to use the system to attack the US in times of war or during any other perceived threat. The current version of the global positioning system was finally completed in 1993.
In 2000, Selective Availability was eliminated by President Bill Clinton, making the system available at no cost to all civilian users world-wide at all times. Other satellite navigation systems do exist across the world. GLONASS was developed by the Soviet government, but fell into disrepair during the early 1990’s when the government collapsed. As of 2008, it is still not fully operational. The European Union is planning the launch of their version of GPS (Galileo) during the next 10 years. Finally, China and India are developing their own versions of space-based navigation systems.
GPS has since become a widely used navigation aid worldwide. It has been used for map-making, land surveying, asset tracking, and many other applications.
With fleet management products, GPS receivers determine their locations using the previously mentioned methods from signals broadcast by the GPS satellites. They must then transmit this location data wirelessly to a server so that the fleet management system can provide the location data to the end users.
1. Global Positioning Satellites (GPS) constantly broadcast signals to earth. A GPS device located inside a vehicle or asset receives these signals. The device then determines its location location based on geometric calculations from the incoming satellite signals.
2. Optional inputs such as a message display terminal, personal navigation device, PTO sensors connect to the device to provide additional messaging capabilities.
3. The device then acts as a wireless modem and transmits location, speed, heading, and other messaging information through the cellular network.
4. The incoming information is then processed and stored on servers.
5. The user logs into a website to view the current and past locations and activities of vehicles and assets.