Navigation apps, ride-hailing services, food-delivery platforms… are arguably some of the most popular apps out there. And they all have one thing in common — they make use of GPS (or, for better clarity, satellite positioning). GPS receivers are everywhere. In smartphones (obviously), inside many vehicles, stand-alone GPS systems for hiking and adventure sports, and even in smartwatches…
What is GPS and how does it work?
First up, we should clarify that the Global Positioning System (GPS) is just one of a handful of satellite positioning systems – but being the oldest (and most widely used) system around, has almost become a generic term.
GPS tech is based on the principle of trilateration — satellites transmit location data, and receivers (such as the ones in your phone) calculate their exact position by crunching the data they get from three or more satellites. Think of the signals as spreading out in a circle – your phone’s GPS receiver finds out your position by seeing where the ‘circles’ created by different satellites intersect.
This also explains why GPS can sometimes be inaccurate, especially if you’re surrounded by tall buildings or trees — your phone can’t communicate with enough satellites to get an accurate fix (the GPS signal is not a very powerful one).
How accurate is GPS?
Till around two decades ago, GPS was divided into two versions – a higher-accuracy system for use by the US (and allies’) military, and a lower-accuracy one accessible to civilians. That’s no longer the case and anyone can get the highest accuracy by using the latest GPS equipment. So what’s the best case scenario? Smartphone users can get to around 5m accuracy, but get some pro gear, and the US government says you could get this down to “within a few centimetres”.
Newer devices support dual-band GPS (The Xiaomi Mi 8 is the first smartphone to do so), which should improve accuracy in places like cities and even forests — basically, places where a GPS signal can get blocked or reflected (which confused the receiver).
Can GPS be jammed or spoofed?
Yes! Civilian GPS might now be as accurate as its military counterpart, but the signals are not encrypted (military signals are). GPS signals are very weak, and can be blocked by jamming them (transmitting ‘noise’ at the same frequencies). You can also ‘spoof’ GPS by transmitting false data (remember that civilian GPS isn’t encrypted). Of course, this is illegal, and can even be life-threatening — emergency services, shipping, aviation — GPS is integral to the smooth functioning of many critical services.
Satellite navigation systems across the world
GPS is operated by the US Government. Other nations have also developed their own systems for reasons of strategic interest – the European Union has Galileo, China has BeiDou, and Russia has GLONASS. Many smartphones also support these alternative positioning systems. And guess what, even India’s building its own positioning system – known as NavIC (earlier called the Indian Regional Navigation Satellite System – IRNSS).
GPS and relativity
Here’s an interesting tidbit about GPS. GPS satellites use onboard atomic clocks to keep track of time as accurately as possible. That’s not surprising. But this is: GPS satellites also take into account Einstein’s theory of relativity. First, they’re travelling much faster than us here on planet earth, so time passes slower. On the other hand, the gravitational pull is less in orbit than on earth, which speeds up time. All this creates a difference of 38 microseconds a day.
What is A-GPS?
Your phone supports one more kind of positioning tech — Assisted (or Augmented) GPS. A-GPS uses the cell towers just like GPS uses satellites — calculating your position based on the signals it received from multiple sources. A-GPS is not as accurate as GPS, but it helps save power and can provide an interim ‘fix’ till the GPS fix is final.
What is an e-compass?
Most phones come with a built-in e-compass that helps you track direction – this is pretty useful as GPS only tracks your position (and velocity) and can’t tell what direction you’re facing till you start to move. E-compasses combine a magnetometer (senses the earth’s magnetic field), with an accelerometer (senses acceleration) to give you quick directional guidance.
Beyond GPS – other positioning technologies
GPS (which dates back to the 1970s) is being continually upgraded. But there are alternatives to satellite positioning on the way – especially for indoor and urban usage. These harness Wi-Fi and Bluetooth for short-range positioning. For example, Waze (owned by Google) is placing Bluetooth beacons in tunnels (where GPS signals can’t penetrate) in New York City. And did you know that your phone narrows down its location by tracking the Wi-Fi networks within range. Bluetooth 5.1 also includes direction-tracking capabilities, while researchers are using the characteristics of radio waves (all wireless tech depends on some sort of radio comms) to create alternatives to GPS.
Some useful and fun apps
Navigation and cab-hailing apps aren’t the only useful GPS apps around. Here’s a short selection of fun (and useful) apps you can install right away:
Pokemon Go: This massive hit combines Augmented Reality and GPS to create a real-world game.
Zombies, Run: This exercise app weaves in a story of a zombie epidemic to make your morning runs a lot more enjoyable.
Geocaching: Geocaching is the closest you’ll come to a real-life treasure hunt. But you don’t have to use this app — just join one of the many geocaching communities online.
Locus: Use maps from many sources, create hiking routes, save waypoints during an off-road trip — this app’s perfect for the outdoors enthusiast.
GPS Test: Make the most of your smartphone GPS — view what satellites are in range, how strong the signal is, download fresh A-GPS data…