Why is a cell phone called a cell phone?

Cellular phone systems divide areas of coverage into "cells," hence the name. But how do they actually work? Listen in as Marshall Brain breaks down the nuts and bolts of cell phone systems in this episode.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how stuff Works dot com
where smart Happens. Hi Am Marshall Brain with today's question,
how does a cell phone work in your pocket? You
have an amazing device. It's a communicator that allows you

(00:21):
to talk instantly to almost anyone on the planet. Plus
it may also give you instant stock quotes, help you
read your email, and let you play games. Your cell
phone truly is an achievement. But how does it do it?
A little history can help here. Remember when you were
a kid and you played with a walkie talkie. A
walkie talkie is an incredibly simple toy that can send

(00:44):
your voice to a friend who's a quarter of a
mile away or so. It does this with about twenty
five cents worth of parts. The parts take your voice,
change it from sound waves to electric waves, and then
amidst those electronic waves with the antenna at the other end,
your friends walkie talkie receives the waves and converts them

(01:06):
to sound waves with the speaker your friend, here's your voice,
and vice versa. What if you want to transmit for
more than a quarter of a mile, you increase the
power A toy walkie talkie transmits at about a tenth
of a watch. A CB radio, which can transmit several miles,
uses four watts. Before there were cell phones, there were

(01:28):
car radios, which were essentially very very large walkie talkies
using twenty five watts or more. These things were huge.
But you can't stick at wat radio in your pocket.
It would need a gigantic battery. So how did engineers
solve the problem and create the tiny cell phones we
have today. The genius of the cell phone system is

(01:52):
the idea of a cell At the time it was conceived,
the idea was incredibly audacious. The idea for poses that
cell phone companies would put up cell phone towers, which
cost on the order of a million dollars each, on
a grid approximately four miles apart. A large city would
need dozens and dozens of these towers. But if you

(02:15):
put up all those towers, it means that the radio
and the cell phone only has to transmit at most
about two miles or so. The radio doesn't have to
be much more powerful than the radio in a walkie talkie,
which keeps it and its battery requirements small. There was
another part of the original cell phone idea that was

(02:35):
also audacious. A normal Wakie talkie can only transmit on
one frequency. Cell phones can transmit on hundreds of frequencies.
That means that one tower can handle dozens of simultaneous
calls without people interfering with each other. Each cell phone
uses a different frequency to talk to the tower, so

(02:57):
the different people can't hear each other, and each cell
phone actually uses too frequencies simultaneously for a call, so
you and your friend can talk simultaneously without the walkie
talkies push to talk button. And there is a third
radio in your phone that's always talking to the tower
even if you aren't on a call. This radio handles

(03:18):
the control channel. When a call comes in, the tower
talks to your phone on the control channel to set
the call up. The tower tells your phone what frequencies
do you use for the call, and also sends stuff
like the caller I D to the phone. The control
channel also handles one other important feature of cell phones.

(03:39):
Let's say that you're in your car driving down the
road while talking on the phone. Your phone is connected
to one tower, but it's driving away from it. As
you get closer to the next tower, the towers communicate
and arrange a handoff your phone gets a message on
the control channel telling it to change frequencies as your

(03:59):
driveing along. Your phone might switch between ten different towers
on a single call and you don't even know it.
The original cell phones were called analog cell phones. That
was the first generation. These were replaced by digital cell
phones because several digital calls can fit in the space
of one analog call. Digital cell phones were the second generation.

(04:23):
Now we're in the third generation, or three G, where
the towers and phones can handle calls as well as
high speed data connections. The data connection allows a phone
to browse web pages, get stock quotes, read email, watch videos,
and so on. When you think about it, it's truly
amazing that in your pocket you can have a mini

(04:44):
laptop computer that's always connected to the Internet, combined with
the ability to talk to anyone in the world. Be
sure to check out our new video podcast, Stuff from
the Future. Join how Stuff Work staff as we explore
the most promising and perplexing possibilities of tomorrow. The Houstufforks

(05:04):
iPhone app has arrived. Download it today on iTunes.