How do cell towers keep so many thousands of people connected at once? How does the message they send to my phone not interfere with the message sent at the same time to the person standing next to me?
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There are several techniques to do this, and different cellular standards (3G, 4G, 5G etc) use different combinations.
Most of them are analogous to the problem of having a bunch of people in a room trying to talk.
Time division: everyone takes turns talking. Note that for mobile phones, we can send a large amount of data in a very short turn, like one 1ms.
Frequency division: different people speak at different pitches. The tower has multiple listeners who only hear one voice pitch.
Beam-forming: Like putting your hands around your mouth or ears to speak or listen in one particular direction, to better hear just one person in a crowded room.
Code division: It’s a bit like different people speaking different languages. However the languages are specifically designed, mathematically, to be distinguishable when spoken over top of one another (unlike real natural languages).
These techniques can be combined to allow towers to serve many devices simultaneously. The other thing to note is that in dense urban areas, they deploy a lot of towers and everyone speaks at a lower volume to a closer tower.
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