GPS & GSM: HOW YOUR PHONE KNOWS WHERE IT IS

Published August 23, 2016

Unless you’ve been living under a rock, you know that cell phones have come a long way. From the large brick-sized units that people used to carry around, they have become a necessary part of modern life and often pack the power of small computers and other extra features.

One of the many useful features of cell phones is the ability to tell you exactly where you are on the planet. If you’re within reach of cell towers, or have some open sky, or both, your phone will be able to pinpoint your location within a few feet. But how does it work? What’s the magic behind the screen?

Let’s take a look:

GPS – Locating People Since 1995

The idea for a modern GPS satellite network came about as early as 1973 and, after a long and expensive development, the first modern Bock-II satellite was launched in 1989. It was first widely used in 1990 and 1991 during the Gulf War. The military initially “degraded” the signal for civilian use, making the system far less accurate than what was actually available, but in 1996, US President, Bill Clinton signed a directive to allow civilians the same signal accuracy as the military. Since that time, the accuracy of the GPS satellite network and Earth-bound receivers has increased, making it a valuable tool all around the world.

Satellites are tracked with very high precision, and their locations are always known. Each satellite contains an extremely accurate clock that is synchronized with a control clock on Earth. GPS receivers, on the other hand, contain clocks that are not synchronized. While monitoring a minimum of four satellites at any time, a GPS receiver is able to determine the distance to the satellites based on the time it takes for a satellite signal to reach the GPS. This causes a discrepancy in the time code of the satellite and the receiver.

Between the known positions of the satellites and the amount of difference between the clocks, a GPS receiver can calculate your exact location anywhere.

GSM Localization

You might have also noticed that a phone can find its location even when the GPS receiver is turned off. This is part of the location based services known as GSM localization.

GSM localization works in similar ways than GPS but with cell towers instead of satellites.  The cell signal travels from your phone to a cell tower. Over distance, the signal degrades in predictable ways and the strength of the signal to multiple towers can be used to determine a phone’s location, whether moving or stationary. Although less accurate than GPS, this method of location can be used even without making a phone call. The phone simply needs to be transmitting a roaming signal. Now you know why you see people on the run in movies take the batteries out of their phones!

Technological Applications

Many companies have embraced the location services on cell phones. Map companies use them to help people find their way around the world, dating apps help people find love in their area, Uber helping you get a ride and even Tim Hortons helps you find the nearest location to get your morning coffee.

Services like Punchtime helps business with a mobile workforce collect time and location data from employees smartphones to facilitate project management and automate timesheets.