How Global Positioning System works: GPS Information

High-precision GPS is now available for free!

• The Global Positioning System (GPS) is a precise satellite-based navigation system providing three dimensional positioning, velocity and time information all on a twenty four hour basis. GPS can be used in all types of weather, any place in the world. It offers better performance than any other navigation system available now or in the foreseeable future.

A GPS Unit installed in any vehicle consist of a small
box with an antenna, both properly hidden into the vehicle

• Once you install a Personal-GPS Unit into your vehicle, you can monitor its position YOURSELF from your PC or laptop and enjoy the great accuracy and simplicity of this system.

• IF YOU ARE ON THE AVL BUSINESS, you can build a HunterPro-GPS Base Station for monitoring yours or third party vehicles. One feature of HunterPro-GPS is that you can add an unlimited number of vehicles to your Base Station.
  
  Standard and Precise Positioning Service

• Its principal system is operated by the United States Department of Defense (DOD). The GPS is transmitted in two different levels of service. Firstly, a Standard Positioning Service (SPS) is transmitted for general public use and secondly, an encoded Precise Positioning Service (PPS). The PPS is transmitted and intended to be primarily used by the Department of Defense.

Using the existing cellular communications infrastructure with
GPS has many advantages: low operational costs and wide coverage

• The technology involved into a GPS receiver is enormous and thanks to all the satellites in orbit and the human efforts to build such a project, the security systems can really take part on its benefits.
  
  Free! The Public System

• SPS signal accuracy WAS intentionally degraded (dithered) for national security reasons. This signal degradation, or dithering, was known as Selective Availability (SA). Selective availability essentially controlled the availability of the system’s full accuracy capability. In the present the SA was removed in order to increase the accuracy for commercial applications. Now we can enjoy greater accuracy than with the previous system.

• At the present the accuracy without Differential GPS (DGPS) correction is usually within 15 meters (with the effects of SA removed). Reports by people who use GPS frequently report accuracy of 10 to 20 meters most of the time. With Differential correction users can achieve sub-meter precision which enable other applications like remote measuring, precision 3D robot control, industry automation, etc.
  
  Three segments GPS: space segment, control station and user

• The GPS Unit installed in any vehicle will only consist of a small box with an antenna. But this unit will be getting info from a high-tech moving lab in outer space: the space segment.

• 1. The space segment consists of twenty-four (24) operational satellites in six circular orbits that are about 10,900 nautical miles above the earth’s surface. These satellites are spaced in orbit so that at any time six satellites will be in view anywhere in the world at any given time. The satellites broadcast their position and time data to users in view of a set of satellites anywhere in the world.

• 2. The control station consists of a master control station in Colorado Springs, with five monitor stations and three ground antennas located throughout the world. The monitor stations track all GPS satellites in view and collect ranging information from the satellite broadcasts. The monitor stations then send the information they collect from each of the satellites back to the master control station, which then computes the precise satellite’s positioning and their orbits. This information is then formatted into updated navigation messages for each satellite. The updated information is transmitted to each satellite via the ground antennas, which also transmit and receive satellite control and monitoring signals.

• 3. The user segment of the GPS system consists of the receivers, processors, and antennas that allow land, sea or airborne operators to receive GPS satellite broadcasts to compute their position, velocity and time. The user’s receiver measures the time delay for the signal to reach the receiver, which is the direct measurement of the apparent distance to a satellite. All of the measurements collected simultaneously from the "visible" satellites are processed to solve the three dimensions of position, velocity, and time. This provides the GPS receiver the necessary data for it to compute and display your position in latitude and longitude.
  
  Receiver Types

• There are two categories of GPS units, they being multiplexing receivers and parallel channel receivers. Multiplexing and parallel refers to how a GPS unit receives information from the satellites. A GPS receiver must lock onto the signals of at least three individual satellites in order to have the data necessary to do position reporting. This acquisition is called "Triangulation".

• The Multiplexing receiver only temporarily establishes contact with one to two satellites and rotates to different satellites to get all the information it needs. Multiplexing receivers can tend to have more problems finding and maintaining satellite contact than the parallel channel receivers. Parallel Channel receivers lock on and stay with the satellites required to accomplish triangulation. This feature offers the most dependable up to date information possible.

• HunterPro GPS receivers are state-of-the-art, latest technology in Parallel Channel receivers which are capable of tracking 12 satellite vehicles at the same time. Its high sensitivity and antenna gain makes it a standard for AVL with an unbelievable cost.