Reported March 2010

WHAT IS THE "CELL" IN CELLULAR COMMUNICATION? Cellular technology makes it possible for millions of people to use their mobile phones every day. The name comes from the way individual cells are organized into a grid. Each cell is about 10 square miles, and has a base station consisting of a tower and a small building housing the radio equipment. Cell phones and base stations use low-power transmitters with limited ranges, so that the same frequencies can be reused outside the range. All cell phones have individual codes used to identify the phone, its owner and the service provider. Whenever you turn on your cell phone, it listens for a system identification code on the control channel -- a special frequency that the phone and base stations use to communicate with each other -- to locate the base station in the cell in which you are standing. If it can't find any such code, it is out of range. This is what happens when you get a "no service" message. Your service provider's central switching office keeps track of your phone in a database so that it always knows which cell is nearest to you, and hence your approximate location. When the office receives a call, it locates which cell you are in, picks a frequency pair for your phone to use to take the call, and communicates the frequency over the control channel. Your phone and the transmission tower switch on those frequencies simultaneously, allowing you to receive the call.

ABOUT THE EAR: There are three main parts to the human ear: the outer, middle and inner ear. The outer ear is the part you can see and opens into the ear canal leading to the middle ear. The middle ear is a closed, air-filled chamber, separated from the outer ear by the ear drum, and ventilated by the Eustachian tube. Sometimes the pressure in the middle ear becomes higher or lower than that in the outer ear, causing hearing loss, severe pain and the accumulation of fluid in the middle ear. The inner ear contains the hearing nerve that leads to the brain. It detects sound vibrations and turns them into electrical nerve impulses, which the brain then interprets as sound.

If you would like more information, please contact:

Rahul Sarpeshkar
(617) 258-6599
rahuls@mit.edu

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