How Does a GPS Receiver Determine the Distance Between You and the Satellites

Are you curious to know how does a GPS receiver determine the distance between you and the satellites? The level of accuracy of these readings will depend on the kind of GPS device that you have.

GPS technology is now widely used in gathering data that was not readily available before. For one, the accuracy of GPS reading is crucial for scientists in their quest to learn more about volcanic activity, the tectonic plates of the earth, and the movement of the northern ice sheets.

Then again, most smartphones also have their own built-in GPS feature, which makes it easy for them to receive precise navigating instructions. Some smartphones also have the ability to provide exact street names and landmarks while you travel either on foot or while inside a vehicle.

What Is GPS?

GPS or Global Positioning System is a group of at least 30 satellites that are evenly positioned in space. These satellites orbit the earth, making it possible for those who have ground receivers to determine their exact geographical location.

The GPS is under the ownership and management of the US Department of Defense. However, it is available for use by anyone and everyone who has a GPS receiver.

Common GPS Terms

  • Pseudorange

Calculated by the receiver, this is the measurement of the distance between the receiver and the satellite by getting the difference between the receiver’s time and the GPS’ signal timestamp. The difference will then be multiplied to the speed of light.

  • GNSS

This acronym means Global Navigation Satellite System. It is the generic name for a group of satellites that make up our planet’s navigation system. These satellites include the European GALILEO, the Russian GLONASS, the Chinese Beidou, and of course, the US GPS.

  • Almanac

This is a set of information that each GPS satellite sends, such as the status of the whole GPS constellation and a rough data of the satellite’s orbit.

  • Ephemeris

This is the name for the exact orbital information of astronomical objects and artificial satellites circling above the planet.

How Does a GPS Receiver Determine the Distance Between You and the Satellites?

There are 21 satellites and three spares that are in constant orbit around the earth. The satellites are spaced evenly so that there will always be four of them circling the planet at any point in time.

Each satellite has its own atomic clock, radio, and a computer. The satellite’s changing time and position are being broadcasted continuously to the earth. Each satellite also checks its time and location once a day with a ground station to know if there are minor adjustments that need to be made to its program.

Any GPS receiver on the ground has its own computer system that determines its own position by getting information from three of the four satellites above. This data is the geographic position of the receiver and is measured by latitude and longitude within a 100-meter radius.

This geographic position can also be seen on a map if the GPS receiver has a map display screen. The fourth satellite is the one sending the altitude reading. If the GPS receiver is on the move, the direction and the speed of travel can also be given, as well as the estimated time of arrival to a specific location.

GPS Accuracy

How can we validate the accuracy of a GPS reading? Every GPS satellite sends a signal with a pseudorandom code and the geographical position of the satellite. The same signal is produced by the GPS receiver.

Upon comparison of the two signals, the one from the satellite will be slower compared to the one coming from the receiver. This is because of the travel time consumed during the process.

To put simply, each satellite sends details about its current position at that specific time interval on a regular basis. Now, these transmissions, when caught by the receiver, estimate the distance of each satellite depending on the time the signal was received. It usually takes 12.5 minutes for the satellite data to be obtained and be locked to a precise location.

There are superior GPS engines that have been added to a VBOX for a much better positional accuracy. The majority of errors can be eliminated if another GPS engine is added in a fixed position.

That is how base stations work. Because it stays in a fixed location, it can send correction messages to a wandering VBOX that can result in a more accurate reading.

Will GPS Work Anywhere?

Now that we have learned the basics of how a GPS works and how it determines our exact location, will it work anywhere? There is no denying that having a GPS device that works in any environment is essential to our daily activities, whether we are using it while walking or driving a vehicle.

GPS devices use different applications with specific features depending on the kind of activity we need it for. Hikers use a GPS device to help them stay on track and sometimes to be able to communicate with other hikers or emergency personnel by providing their exact location.

Drivers also use a GPS device to help them navigate the streets more efficiently and to be able to have a rough estimate on when they will arrive in their chosen destination. Law enforcers also use this technology to perform their jobs better and respond to emergency situations quickly.

We can safely assume that the GPS device will work properly if and when the location has been pinpointed correctly and that the surrounding area is clear of any interference.

Conclusion

Have you ever wondered how does a GPS receiver determine the distance between you and the satellites? That is what trilateration does. It measures the distance from three satellites from a fixed position. Those three GPS satellite signals are caught by a GPS receiver and then calculate those readings for precise location data.

While the use of GPS devices makes our daily lives convenient and a lot easier, these devices are not yet perfect and still in constant testing to achieve a much better version that would be beneficial for all of us.

In the end, remember that measuring the distance of a satellite from a precise location using GPS receivers will always depend on several factors, like the kind of device used and the condition of the surroundings around you.

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