What is GPS and how does it work?
Published on May 22, 2020 in Most Popular by John Kyes | 7 minute read
Table of contents
Discover everything you need to know about GPS and how it is used today.
Discover everything you need to know about GPS and how it is used today.
GPS, or the Global Positioning System, is a global navigation satellite system that provides location, velocity and time synchronisation.
GPS is everywhere. You can find GPS systems in your car, your smartphone and your watch. GPS helps you get where you are going, from point A to point B. What is GPS? Read this article to learn more about how it works, its history and future advancements.
What is GPS and how does it work?
The Global Positioning System (GPS) is a navigation system using satellites, a receiver and algorithms to synchronise location, velocity and time data for air, sea and land travel.
The satellite system consists of a constellation of 24 satellites in six Earth-centred orbital planes, each with four satellites, orbiting at 13,000 miles (20,000 km) above Earth and travelling at a speed of 8,700 mph (14,000 km/h).
While we only need three satellites to produce a location on earth’s surface, a fourth satellite is often used to validate the information from the other three. The fourth satellite also moves us into the third dimension and allows us to calculate the altitude of a device.
What are the three elements of GPS?
GPS is made up of three different components, called segments, that work together to provide location information.
The three segments of GPS are:
- Space (Satellites) — The satellites circling the Earth, transmitting signals to users on geographical position and time of day.
- Ground control — The Control Segment is made up of Earth-based monitor stations, master control stations and ground aerial. Control activities include tracking and operating the satellites in space and monitoring transmissions. There are monitoring stations on almost every continent in the world, including North and South America, Africa, Europe, Asia and Australia.
- User equipment — GPS receivers and transmitters including items like watches, smartphones and telematic devices.
How does GPS technology work?
GPS works through a technique called trilateration. Used to calculate location, velocity and elevation, trilateration collects signals from satellites to output location information. It is often mistaken for triangulation, which is used to measure angles, not distances.
Satellites orbiting the earth send signals to be read and interpreted by a GPS device, situated on or near the earth’s surface. To calculate location, a GPS device must be able to read the signal from at least four satellites.
Each satellite in the network circles the earth twice a day, and each satellite sends a unique signal, orbital parameters and time. At any given moment, a GPS device can read the signals from six or more satellites.
A single satellite broadcasts a microwave signal which is picked up by a GPS device and used to calculate the distance from the GPS device to the satellite. Since a GPS device only gives information about the distance from a satellite, a single satellite cannot provide much location information. Satellites do not give off information about angles, so the location of a GPS device could be anywhere on a sphere’s surface area.
When a satellite sends a signal, it creates a circle with a radius measured from the GPS device to the satellite.
When we add a second satellite, it creates a second circle, and the location is narrowed down to one of two points where the circles intersect.
With a third satellite, the device’s location can finally be determined, as the device is at the intersection of all three circles.
That said, we live in a three-dimensional world, which means that each satellite produces a sphere, not a circle. The intersection of three spheres produces two points of intersection, so the point nearest Earth is chosen.
Here is an illustration of satellite ranging:
As a device moves, the radius (distance to the satellite) changes. When the radius changes, new spheres are produced, giving us a new position. We can use that data, combined with the time from the satellite, to determine velocity, calculate the distance to our destination and the ETA.
What are the uses of GPS?
GPS is a powerful and dependable tool for businesses and organisations in many different industries. Surveyors, scientists, pilots, boat captains, first responders, and workers in mining and agriculture, are just some of the people who use GPS on a daily basis for work. They use GPS information for preparing accurate surveys and maps, taking precise time measurements, tracking position or location, and for navigation. GPS works at all times and in almost all weather conditions.
There are five main uses of GPS:
- Location — Determining a position.
- Navigation — Getting from one location to another.
- Tracking — Monitoring objects or personal movement.
- Mapping — Creating maps of the world.
- Timing — Making it possible to take precise time measurements.
Some specific examples of GPS use cases include:
- Emergency Response: During an emergency or natural disaster, first responders use GPS for mapping, following and predicting weather, and keeping track of emergency personnel. In the EU and Russia, the eCall regulation relies on GLONASS technology (a GPS alternative) and telematics to send data to emergency services in the case of a vehicle crash, reducing response time.
- Entertainment: GPS can be incorporated into games and activities like Pokémon Go and Geocaching.
- Health and fitness: Smartwatches and wearable technology can track fitness activity (such as running distance) and benchmark it against a similar demographic.
- Construction, mining and off-road trucking: From locating equipment, to measuring and improving asset allocation, GPS enables companies to increase return on their assets.
- Transportation: Logistics companies implement telematics systems to improve driver productivity and safety. A lorry tracker can be used to support route optimisation, fuel efficiency, driver safety and compliance.
Other industries where GPS is used include: agriculture, autonomous vehicles, sales and services, the military, mobile communications, security, and fishing.
How accurate is GPS?
GPS device accuracy depends on many variables, such as the number of satellites available, the ionosphere, the urban environment and more.
Some factors that can hinder GPS accuracy include:
- Physical obstructions: Arrival time measurements can be skewed by large masses like mountains, buildings, trees and more.
- Atmospheric effects: Ionospheric delays, heavy storm cover and solar storms can all affect GPS devices.
- Ephemeris: The orbital model within a satellite could be incorrect or out-of-date, although this is becoming increasingly rare.
- Numerical miscalculations: This might be a factor when the device hardware is not designed to specifications.
- Artificial interference: These include GPS jamming devices or spoofs.
Accuracy tends to be higher in open areas with no adjacent tall buildings that can block signals. This effect is known as an urban canyon. When a device is surrounded by large buildings, like in downtown Manhattan or Toronto, the satellite signal is first blocked, and then bounced off a building, where it is finally read by the device. This can result in miscalculations of the satellite distance.
Fortunately, many critical issues facing GPS technology have been identified and are nearing resolution. High-quality receivers provide better than 2.2 metre horizontal accuracy in 95% of cases, and better than 3 metre accuracy in 99% of cases.
A brief history of GPS
Humans have been practising navigation for thousands of years using the sun, moon, stars, and later, the sextant. GPS was an advancement of the 20th century made possible by space-age technology.
GPS technology has been used globally throughout history. The launch of Russia’s Sputnik I satellite in 1957 ushered in the possibility of geolocation capabilities and soon after, the U.S. Department of Defence began using it for submarine navigation.
In 1983, the U.S. government made GPS publicly available, but still kept control of the available data. It wasn’t until 2000 that companies and the general public gained full access to the use of GPS, eventually paving the way for greater GPS advancement.
Global Navigation Satellite Systems (GNSS)
A GPS is considered to be a Global Navigation Satellite System (GNSS) — meaning it is a satellite navigation system with global coverage. As of 2020, there are two fully operational global navigation satellite systems: the U.S. navigation signal timing and ranging (NAVSTAR) GPS and Russia’s Global Navigation Satellite System (GLONASS). The NAVSTAR GPS consists of 32 satellites owned by the U.S. and is the best-known and most widely utilised satellite system. Russia’s GLONASS consists of 24 operational satellites with three remaining as spares or in testing.
Illustration of GLONASS, GPS and Galileo Satellites.
Other countries are also racing to catch up. The EU, for example, has been working on Galileo, which is expected to reach full operation capacity by the end of 2020. China is also building the BeiDou Navigation Satellite System, with 35 satellites planned to be in orbit by May 2020. Japan and India are also well on their way with their own regional systems, the Quasi-Zenith Satellite System (QZSS) and the Indian Regional Navigation Satellite System (IRNSS), respectively.
GPS vs GNSS Devices
Though GPS is a subset of GNSS, receivers are differentiated as GPS (meaning GPS-only) or GNSS. A GPS receiver is only capable of reading information from satellites in the GPS satellite network, while the typical GNSS device can receive information from both GPS and GLONASS (or more than these two systems) at a time.
A GNSS receiver has 60 satellites available for viewing. While a device only needs three satellites to determine its location, accuracy is improved with a larger number of satellites. The chart below shows an example of the number of satellites available (shown in green), along with its signal strength (height of the column), to a GPS receiver. In this case, 12 satellites are available.
Typical GPS-only test board showing 12 satellite signals (green), using U-Center software.
A GNSS device can see more satellites, which helps improve device accuracy. In the chart below, there are 17 available satellites. Green bars are part of GPS and blue bars are part of GLONASS.
Typical GNSS test board showing 17 satellite signals (GPS = green; GLONASS = blue), using U-Center software.
A larger number of satellites providing information to a receiver enables the GPS device to calculate location with greater precision. More satellites give a device a better chance of getting a positional fix when the receiver has calculated the location of the user.
That being said, GNSS receivers have some drawbacks:
- The cost of GNSS chips is higher than those of GPS devices.
- GNSS uses a wider bandwidth (1559-1610 MHz) than GPS (1559-1591 MHz). This means standard GPS radio frequency components, such as aerials, filters and amplifiers, cannot be used for GNSS receivers, resulting in a greater cost impact.
- Power consumption would be slightly higher than with GPS receivers as it connects to more satellites and runs the calculations to determine location.
The future of GPS
Countries continue to build and make improvements to their GPS systems. Efforts worldwide are being made to increase accuracy and improve reliability and GPS capabilities. For example:
- GNSS receivers are expected to become smaller, more accurate and more efficient, and GNSS technology is set to penetrate even the most cost-sensitive GPS applications.
- Scientists and rescue workers are finding new ways to use GPS technology in natural disaster prevention and analysis in the event of an earthquake, volcanic eruption, sinkhole or avalanche. For the COVID-19 pandemic, researchers are looking at using mobile phone location data to assist with contact tracing in order to slow down the spread of the virus.
- The launch of new GPS III satellites will refine GPS accuracy to 1-3 metres, improve navigation abilities, and longer-lasting components as early as 2023. By broadcasting on the L1C civilian signal for interoperability with other satellite systems.
- The next generation of GPS satellites will include better signal protection, decreased susceptibility to signal jamming and more manoeuvrability to cover dead zones.
- The National Aeronautics and Space Administration’s (NASA) Deep Space Atomic Clock is set to use a powerful onboard GPS satellite to help provide better consistency in time for future astronauts embarking on deep space journeys.
The future of GPS tracking will likely be far more accurate and effective for both personal and business use.
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John Kyes is a Manager, Test & Automation Engineering for Geotab.
Geotab's blog posts are intended to provide information and encourage discussion on topics of interest to the telematics community at large. Geotab is not providing technical, professional or legal advice through these blog posts. While every effort has been made to ensure the information in this blog post is timely and accurate, errors and omissions may occur, and the information presented here may become out-of-date with the passage of time.
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