Principles of GPS
Everything You Need To Know About Global Navigation Satellite Systems
First developed by the United States military, the Global Positioning System (GPS) relies on a network of satellites and synced atomic clocks to provide positioning, navigation, and timing (PNT) services. There are three components or elements that make the system work for individual users: 1) the space segment, 2) the control segment, and 3) the user segment. The first two of those three segments are the responsibility of the United States Air Force. Let’s look at each segment more closely.
How Many GPS Systems Are There?
Department of Defense GPS Constellation
The space component or segment is the satellite arm of the system, utilizing a minimum of 24 orbiting and operational satellites. Each of these satellites transmits a one-way radio signal that included an encoded sequence relating to the atomic clock time; the one-way radio signal also includes information about the current GPS satellite position.
The control component or segment is the worldwide system of monitoring and control stations that help maintain satellites in their proper orbits, including making any clock adjustments or orbit manipulations. These command centers track each of the satellites, upload navigational data as it is freshly updated, and maintain the health and status of the constellation. These are critical components of GPS that assist with precision timing and time difference.
Finally, the user segment is your end and consists of GPS receiver equipment. Your GPS receiver takes the one-way radio signal from the satellite and uses that transmitted information to determine the distance from each satellite. Using a method known as trilateration (which we’ll discuss in greater detail in just a moment), the receiver can then determine location information for positioning and navigation purposes. Your GPS receiver can also use the satellite info to determine the time. Your hiking GPS tracker will utilize each of those functions to help keep you from getting lost.
Even better, all three of these components and the services they enable have been available for civilian service, which is available freely and on a continuous basis all over the world since the Selective Availability Act. Additionally, some applications are available that can help augment GPS systems and techniques.
GPS User Equipment Velocity And Timing
Have you ever wondered how a GPS device provides exact longitude, latitude, positions, and time? GPS user equipment (whether it be GPS tracking or GPS navigation solution) receives satellite signals with the ground antennas. The low-level radio signals from satellite constellations determine your position on Earth, arrival times, speed, altitude, and other data that can be helpful in vehicle tracking and additional consumer/business applications.
Trilateration: How Does GPS work?
If it helps, think of your receiver as the center of a three-circle Venn diagram. When your receiver gets a signal from a satellite, it can calculate the distance to the satellite, helping draw a circle of all possible locations that distance from the satellite. When you add the signal from a second satellite, you suddenly have a couple of intersection areas. A third satellite helps narrow it down further yet, and a fourth helps ensure that you also know the elevation data of the point at which you are currently located. That’s obviously a gross oversimplification, but you get the general idea of how GPS works in your hiking GPS tracker.