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What is Global Positioning System and How Does It Work

An introduction to the Global Positioning System, better known as GPS, and how it has changed the world as we see it

A look at the science behind the GPS, how it works and how we have come to depend on it for myriad civilian and military purposes…

Apr 08, 2019    By Team YoungWonks *

What is GPS? It’s an often-asked question as GPS is a buzzword and not just in the tech worlds today. To understand this technology, let’s ask ourselves this question: When was the last time you / your friend/ parent needed to ask someone for directions? Or did you/ your friend/ parent just keep looking at the maps on your/ their phones to track self-movement and the road ahead? Indeed, with technology making greater strides, our phones are all we need to get to point B from point A, even if it’s our first time visiting point B. This then is now possible (and seamlessly so, might we add!) thanks to the GPS technology. In this blog, we shall take a look at what this technology is about, all that it entails and how exactly it has changed our worlds… 

 

What is GPS?

The Global Positioning System (GPS), originally called Navstar GPS, is a satellite-based radionavigation system owned by the United States government and run by the United States Air Force. It is a global navigation satellite system that provides geographical location and time information to a GPS receiver anywhere on or near earth where there is an unobstructed line of sight to four or more GPS satellites. However, obstacles such as mountains and buildings can block the relatively weak GPS signals. 

Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corporation, and Bradford Parkinson of the Applied Physics Laboratory are credited with the invention of the GPS technology. It is important to note here that GPS does not need the user to pass on any data, and it runs independently of any telephonic or internet reception, though these technologies can make the GPS positioning information more useful. 

Since the GPS can share geographical location and time, it has a crucial role to play when it comes to offering important positioning information to military, civil, and commercial users around the world. The United States government, which created the system, continues to maintain it, and has made it freely available to anyone with a GPS receiver. 

 

How GPS came about

The GPS project was launched in the US back in 1973 in order to get around the limitations of previous navigation systems. During Labor Day weekend that year, twelve military officers met at the Pentagon to discuss the creation of a Defense Navigation Satellite System (DNSS). The idea being to integrate ideas from several predecessors, including classified engineering design studies from the 1960s. Later that year, the DNSS program was named Navstar, or Navigation System Using Timing and Ranging.

And so it was the U.S. Department of Defense that developed the Navstar.  Not surprisingly, the system was originally developed and designed for use only by the United States military. But after a Korean Air Lines Flight 007, a Boeing 747 carrying 269 people, was shot down in 1983 after straying into the USSR’s prohibited airspace, American President Ronald Reagan issued a directive that made GPS, once it was sufficiently developed, freely available for civilian use as a common good. 

Initially, the system used only 24 satellites; the first Block II satellite was launched on February 14, 1989, and the 24th satellite was launched in 1994. The next year (1995) was when the system became fully operational. 

It may be pointed out here that even then initially, the highest-quality signal was reserved only for military use, and the signal available for civilian use was intentionally degraded as part of the Selective Availability policy. This policy was scrapped in the year 2000 when then US President Bill Clinton signed a directive to turn off Selective Availability and thus offer civilians the same accuracy that the military enjoyed. 

Modernization of the satellite system is an ongoing initiative of the US Department of Defense; since its deployment, the US government has carried out several improvements to the GPS service, including new signals for civil use and increased accuracy and integrity for all users. 

 

How does GPS work? 

The GPS concept relies on checking the time and the known position of GPS specialized satellites. These satellites carry very stable atomic clocks that are in sync with one another and with the ground clocks. It must be pointed out here that atomic clocks are clock devices that make use of a hyperfine transition frequency in the microwave, electron transition frequency in the optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for timekeeping. Known to be the most accurate time and frequency standards, atomic clocks are used as primary standards for international time distribution / tracking services, including in GPS. In the GPS context, an atomic clock basically measures the electromagnetic signal that electrons in atoms emit when they change energy levels. All digressions from true time as maintained on the ground are corrected on a daily basis. Similarly, the satellite locations are known with great precision. GPS receivers too have clocks, but they are typically less stable and less precise. 

Each GPS satellite, armed with its own internal atomic clock, continuously sends out on a specific frequency a time-coded radio signal that shares the current time and data about its position. Since the speed of radio waves is constant and doesn’t vary with any change in the satellite speed, the time delay between when the satellite sends a signal and the receiver collects it is proportional to the distance from the satellite to the receiver. A GPS receiver monitors multiple satellites and solves equations to determine the exact position of the receiver and its deviation from true time. In other words, the GPS receiver (including the one in your phone) figures out which satellites are visible and unobstructed and starts gathering data from the satellites with the strongest signals. Then it triangulates from this data your location and time. Keep in mind that while the geolocation is determined with the help of three signals, the fourth signal is used to calculate altitude. Thus, at any given time, at least four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and one clock deviation from the satellite time). 

GPS data is slow on purpose — satellites run on rechargeable batteries and sending a fast signal hundreds of thousands of miles would need lots more power — so it’ll take up to a minute to get your geolocation. Also, GPS receivers use a lot of power. 

As of early 2015, high-quality, FAA grade, Standard Positioning Service (SPS) GPS receivers provided horizontal accuracy of better than 3.5 meters (11 ft), though many factors such as receiver quality and atmospheric issues can impact this accuracy. 

 

GPS Applications 

Now let’s look at some of the advantages/ applications of the GPS technology, in addition to its originally intended use (military purposes, evacuation, disaster relief, etc). 

1. It’s free: One of the biggest advantages of GPS technology is the fact that it is free; it is entirely free of cost with no subscription or licence fees. Also, it does not need the  user to send data from his or her device. 

2. Independent of telecom infrastructure: In fact, GPS devices usually do not use wireless communication data; they work independently from telecommunication infrastructures. That said, telecommunication systems can help the device provide more accurate GPS information. 

3. Comprehensive coverage: Today, the earth’s orbit has 24 to 32 satellites that offer GPS services across the globe. These satellites orbit the globe to provide a comprehensive coverage of different areas. And having different satellites orbiting at different tracks and at different times has helped enhance the precision of geolocation information. 

4. Non-military uses: GPS technology is easily accessible anywhere in the world today as long as one has a GPS-enabled device. This accessibility has made GPS a dual-use technology that benefits not just the U.S. military but also non-military / civilian stakeholders from across the globe. 

For instance, let’s look at some of the commercial and scientific uses/ applications of GPS technology. Several industries and sectors have used GPS in order to track their resources’ geolocation, supervised their employees to increase productivity, and improve customer service. In scientific fields, the technology has been used to achieve specific goals and objectives, such as weather surveillance (since a GPS-enabled device can also come with features such as barometric altimeters). It has also been used in traffic monitoring, geological surveillance or tectonics, and in disaster and emergency response.

5. Other civilian and personal applications: The civilian applications of GPS include navigation, clock synchronization, and running different tracking applications. The technology is also supporting the development of other technologies such as automated or self-driving vehicles and improved the features of computers and smartphones. Several consumer-grade applications dwell mainly on the advantages of global positioning system. For example, apart from creating fitness devices with tracking capabilities, GPS technology has been applied and integrated into self-navigating robots and vehicles, social media and so on.

 

Disadvantages of GPS

Like all game-changing technologies today, GPS too can be a double-sided sword. Here we look at the some of the prominent disadvantages of the technology:

1. Inaccuracy: GPS devices operate by receiving signals from at least four satellites. This means that if they connect with only three, the positioning is not accurate. Problems can crop up if and when obstacles, such as walls, buildings, skyscrapers and trees block a signal. GPS technology is not immune to extreme atmospheric conditions, such as geomagnetic storms. Also, the mapping technology used along with the GPS may not be up to date, thereby creating navigational errors. 

In the year 2000 - when selective availability of GPS was lifted -- GPS had a five-meter (16 ft) accuracy. However, GPS receivers released in 2018 use the L5 band that has been deployed as part of latest stage of accuracy enhancement and are thus said to have much higher accuracy, pinpointing to within 30 centimetres or 11.8 inches. It must be pointed out that if the problem of inaccuracy is tackled successfully, it will be a boon to several industries, including the self-driving vehicle industry as GPS will then help in actively tracking the movements of such autonomous driving cars.  

2. Insufficient local knowledge: Thanks to the convenience offered by GPS technology, we have come to depend heavily on it. This, in turn, has led us to undermine the importance of local knowledge while traveling. Earlier, we would factor in local knowledge before/ during traveling but now that is exceedingly rare. We are thus missing out on information that could be useful for our journey. Take for example, GPS won’t tell us if a stretch of road is prone to flooding or other hazards, if it offers any scenic views, or if the road is closed at certain times of the day.

3. Battery / signal failure: Another disadvantage of relying just on GPS is that it can backfire in a big way upon a signal failure, or if your GPS device is battery-operated and runs out of power. Without a backup - either in the form of additional power or even good old traditional paper maps - you can be at a total loss about where you are / where you wish to go next. 

4. Dependence on US Department of Defense (DoD): The U.S. Department of Defense is mandated by law to maintain a Standard Positioning Service that will be available on a continuous, worldwide basis, and to develop measures so as to prevent hostile use of GPS and its augmentations without unduly disrupting civilian uses. And while this sounds very encouraging for civilians across the world, the fact remains that we are all very much at the mercy of the US DoD which can decide to pull off access to GPS at any time it chooses to. Also, while the service is free currently, there’s no way one can stop the US DoD from charging us for use, should they decide to do so. 

5. GPS can be a distraction: GPS devices can be quite distracting. Yes, they are supposed to relay you audio instructions and all we have to do is look at the map occasionally. But in reality, it is more demanding than that. More often than not, one ends up adjusting the destination, punching in data, or changing other settings while driving. Which makes it a big distraction during driving. 

6. Privacy invasion: GPS devices can be easily bought and used to stalk people without their knowing. For example, a tiny GPS device can be left behind in a car, leaving that person an easy target as his/ her movements can now be easily tracked. This information can in turn can be used for criminal purposes.

7. Commercial use and exploitation: Just like individuals, huge commercial organizations too can easily misuse GPS to track someone’s movements. This information can be exploited so as to gather data on a person’s eating, shopping habits, and thus target him/ her with advertising based on their geographical routine/ location.

 

 

GPS versus AGPS  

As mentioned earlier, GPS receivers tend to take up a lot of power and need an unobstructed view of multiple satellites to work. Obstructions include tall buildings, which means a lot of us living in / near tall buildings can have trouble getting the data needed to track GPS. This is where AGPS comes in.

A lot of us already have AGPS — Assisted Global Positioning System — in our phones. So what does AGPS do? It basically adds cellular location data to assist geolocation. Your phone carrier knows where you are since your phone “pings or bounces” off nearby cell towers. So when you are at a location, the three or more towers near you will help your phone company triangulate and figure out your current location. The precision of the location depends on the strength of the signal between your phone. 

So it’s the software on your phone that will feed the raw cellular location data to the GPS receiver which will periodically switch between GPS data and cellular location to get a close approximation (within 50 meters or so) in real time. AGPS does send data out of your phone, but it’s data that was already being sent when it checked for cell towers in range. So while you won’t be charged for this sending out of data, you will still need an active data plan to use AGPS. 

 

Between AGPS and GPS, the latter provides more accurate results and doesn’t need a data connection. The former, however, doesn’t take up as much power and works in real time (without the delay). 

 

*Contributors: Written by Vidya Prabhu; Lead image by: Leonel Cruz

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