GPS, or the Global Positioning System, is a global navigation satellite system that uses at least 24 satellites, a receiver and algorithms to provide location, velocity and time synchronization for air, sea and land travel. The satellite system consists of six earth-centered orbital planes, each with four satellites. GPS works at all times and in almost all weather conditions. This post answers "What is GPS?" and explains how it works.
In general, there are five key uses of GPS:
GPS is extremely relevant today and used in numerous industries for preparing accurate surveys and maps, taking precise time measurements, tracking position or location, and navigating. Some examples of GPS applications include:
Other industries that use GPS include: agriculture, autonomous vehicles, sales and services, military, mobile communications, security, drones, and fishing.
GPS technology is also being used in new and innovative ways, such as the tracking of endangered species and the mistreatment of animals. For example, to stop the illegal trade market, GPS devices are being placed in artificial ivory so that law enforcement can track and find illegal traders and save endangered wildlife.
Initially put into place by the U.S. Department of Defense, GPS often refers to the American navigation system known as NAVSTAR. It shouldn’t be confused with the term global navigation satellite system (GNSS), GLONASS, or a GPS receiver (which is most commonly referred to as a GPS).
In 1957, the Soviet Union launched Sputnik I satellite, making satellite a possible solution for developing better geolocation technology. In 1960, the U.S. Navy begins tracking submarines with satellite navigation, which led to the invention of the TRANSIT system.
For a long time, GPS was only available for governmental use. In the early 1970s the United States Department of Defense initiated the Navigation System with Timing and Ranging (NAVSTAR) project that would become a more reliable method of location.
By 1978, the launch of NAVSTAR Block I GPS took place. Only four satellites were launched at the time. It wasn’t until 1983 that GPS became available for civilians. Even then, the government controlled signal and made GPS devices less accurate — this was called selective availability (SA).
In the early 1990s, GPS services were originally partitioned into the Standard Positioning Service (SPS) intended for the public, and the Precise Positioning Service (PPS) for military use. Despite some of the limitations in coverage and accuracy, GPS played a significant role in military operations such as the Gulf War in 1990-91. In 1993, 24 satellites became operational and full capacity was declared two years later.
Selective availability was discontinued by the U.S. Government in 2000 and in 2004, Qualcomm successfully completed tests of live assisted GPS on a mobile phone. In 2008, Block II satellites were launched followed by GPS IIF satellite in 2016.
See a timeline of GPS here: History of GPS Satellites and Commercial GPS Tracking
A series of satellites orbiting the earth send a unique signal that is then read and interpreted by a GPS device, situated on or near the earth’s surface. In order 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 time, a GPS device can read the signals from six or more satellites, but there needs to be at least four.
A single satellite broadcasts a microwave signal, which a GPS device picks up and uses to calculate the distance from GPS device to the satellite. Since a GPS device only gives information about the distance from a satellite, a single satellite doesn’t provide much information in terms of location. Satellites don’t give off information about angles, which means the location of a GPS device could be anywhere along a sphere’s surface area— with the satellite being the center and the radius being the distance of the GPS device from the satellite.
To better understand this, we could use a simple two-dimensional example. Instead of dealing with spheres, we could look at circles. When a satellite sends a signal, it creates a circle with the radius being the distance of the GPS device from the satellite.
When we add a second satellite, it creates a second circle and the location is narrowed down to two points — the two points where the circle intersects. A third satellite is used to determine the location of the device. The device is at the intersection of all three circles produced by the distance of the device from a given satellite.
In reality 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 — the point nearest Earth is chosen.
While we only need three satellites to produce a location on earth’s surface, a fourth satellite is often used to validate location. A fourth satellite is also required to move us into the third-dimension and calculate the altitude of a device.
As a device moves, the radius (distance to the satellite) changes. As the radius changes, new spheres are being 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 time it will take.
A GPS is considered to be a global navigational satellite system (GNSS) — meaning it’s a satellite navigation system with global coverage. The term GNSS is used to refer to all satellite systems with global coverage. As of 2016, there are two fully operational global navigation satellite systems: NAVSTAR GPS and the Russian GLONASS. The NAVSTAR GPS consists of 32 satellites owned by the U.S. and is the best-known, widely-utilised satellite system. The GLONASS is comprised of 28 satellites.
Illustration of GLONASS, GPS and Galileo Satellites
Other countries are working to build their own satellite systems. The EU has been working on Galileo, which is expected to reach full operation capacity by 2019. China is building BEIDOU, with 35 satellites planned. India is building IRNSS, with 7 satellites planned.
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 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. 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 allows the device to calculate location with greater precision. For example, when driving through central Seattle where high-buildings, greater signal reflections, and frequency noise exists, GNSS is more accurate than a GPS device. More satellites give a device a better chance of getting a positional fix when the receiver has calculated the location of the user.
Of course, a GNSS receiver isn’t without its drawbacks. The cost of GNSS chips are higher than those of GPS devices. Plus, GNSS uses a wider bandwidth (1559-1610 MHz) than GPS (1559-1591 MHz), which means standard GPS RF components (antennas, filters, amplifiers) cannot be used for GNSS receivers resulting in a cost impact. Lastly, power consumption would be slightly higher than with GPS receivers as it connects to more satellites and runs the calculations to determine location.
The accuracy of a GPS device is dependent on many variables; the number of satellites available, the ionosphere, and the urban environment. For example, accuracy tends to be higher in open areas with no adjacent tall buildings, known as urban canyons. When a device is surrounded by large buildings, like in Downtown Manhattan or Toronto, the satellite signal is blocked by the buildings and then bounced off the building where it’s finally read by the device. This could lead to miscalculations of the satellite distance.
In general, high-quality receivers provide better than 2.2 meter horizontal accuracy in 95% of cases, and better than 3 meter accuracy at a 99% confidence level. Some of the factors that will cause inaccuracy in a GPS device are:
Fortunately, many of the critical issues facing GPS technology have been identified and are on their way to resolution. As these issues begin to be resolved, it becomes reasonably clear what can be expected in the next decade.
Although GPS has performed extremely well and has generally exceeded expectations, it’s clear some significant improvements are needed. As we continue to investigate the system's needs and deficiencies over the past decade we are better able to determine what capabilities and features should be incorporated into a future GPS to satisfy both military and civil users.
Efforts worldwide are being made to improve not only the accuracy but the cost and reliability, including:
GNSS receivers are expected to become smaller, more accurate and efficient, and GNSS technology is set to penetrate even the most cost-sensitive GPS applications.
The trend for the next generation of GPS satellites currently being developed is to include protection for the signals making them even more useful for worldwide users, and less susceptible to signal jamming. The future of GPS tracking is determined to be more accurate and effective for both personal and business use.
To learn more about GPS tracking for vehicles and fleets visit our solutions page.
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