Cell Phones 101

4 Pages 1032 Words

Each day about 30,000 people in the United States sign up for and start using a cellular phone. Therefore it is likely that you or someone you know has a cell phone and uses it on a regular basis. They are such great gadgets - with a cell phone you can talk to almost anyone from just about anywhere, because about 80% of the U.S. has coverage (Dang). But have you ever wondered how a cell phone works?
One of the most interesting things about a cell phone is that it is really a radio- an extremely sophisticated radio, but a radio nonetheless. A good way to understand the sophistication of a cell phone is to compare it to a CB radio or a walkie-talkie. A CB radio is a simplex device. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cell phone is a duplex device, so it uses one frequency for talking, and a second separate frequency for listening (Dang). A CB radio has 40 channels. A cell phone can communicate on 1,664 channels. Cell phones also operate within cells and they can switch cells as they move around. Cells give cell phones incredible range. A walkie-talkie can transmit perhaps a mile. A CB radio, because it has much higher power, can transmit perhaps 5 miles. Someone using a cell phone, on the other hand, can drive clear across a city and maintain a conversation the entire time. Cells are what give a cell phone its incredible
range (Anonymous #2).
The genius of the cellular system is the realization that a city can be chopped up into small cells, and that the cells allow extensive frequency reuse across a city. Frequency reuse is what lets millions of people own cell phones without problems. It works because the carrier chops up an area to about 10 square miles (Dang).
In the dark ages before cell phones, people used radiotelephones in their cars. In the radiotelephone system there was one central antenna tower per city and perhaps 25 channels available ...