As the title of this blog is “Mobile Devices,” I thought I would get back to that topic for a while.
As an employee of a large cellular service provider, I get asked how cell phones work on a fairly regular basis. Many people I speak with assume that cell phones use satellites orbiting the Earth to make and receive calls. While there are phones that do use satellites, these are expensive to operate and usually only used by the military or companies that are regularly in areas without cell phone coverage. The cell phone that you probably have sitting on your desk as you read this uses radio signals. Essentially, it operates like a walkie talkie, but with a much bigger range.
Mobile phones use radio signals, just like your car stereo uses, only at a higher frequency, to send and receive calls, text/picture messages, web, TV and downloads.When you hit the “send” button a radio frequency or “RF” is sent to the nearest base station or “cell site” as they are known in the industry. These cell sites dot the country and the world. You have almost certainly seen them when outside, they are tall metal antennas that generally look like this, though recently service providers have begun to disguise them as natural objects like this. They have also begun to hide the towers in structures like billboards, business signs and even the crosses on churches.
Your call then goes to a central facility, called a switch, that identifies the destination for your call and forwards it via the public telephone network, the same infrastructure land line calls use. Your call will go directly to a land line phone or if it’s headed to another mobile phone, it will travel to another switch, a cell site, and then be delivered via radio signal.
Cell sites, ideally, are spaced so their coverage overlaps which provides, in theory, a continuous, uninterrupted signal as you walk or drive around. Mobile phones use the minimum amount of power needed to connect to a cell site and continuously adjusts itself as the distance varies. Therefore, when you are closer to a cell site, your phone uses less power. As you get further away, the phone adjusts the power to the strength needed to connect.
Each cell site can handle a limited number of connections at a time. This is the reason, during peak hours, that you sometimes get an error message “Network unavailable,” a fast busy signal or similar issue. To combat these issues, providers have what my company calls “COW”s or Cell on wheels. These are portable cell sites that are deployed when needed to give an area more connection capabilities. They are also used to give customers service during or after natural disasters, such was the case during hurricane Katrina.
I have intentionally made this explanation as straight forward and stayed away from any “techie speak” so anyone can understand how a cell phone sends and receives calls. If you want a more technical explanation, you can find one easily by searching the internet.