How Cell Phones Work A cellular phone is actually a radio, an extremely sophisticated radio. The telephone was invented by Alexander Graham Bell in 1876, and wireless communications can trace its roots to the invention of the radio by Nikolai Tesla in the 1880’s. It was only natural that these two great technologies would eventually be combined. Before cell phones, people who really needed mobile-communications ability installed radio telephones in their cars. In the radio-telephone system, there was one central antenna tower per city, and very limited channels. With a single central antenna, the phone in your car needed a powerful transmitter. It also meant that not many people could use radio telephones there just weren’t enough channels. The ingenuity of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a city. This enables millions of people to use cell phones simultaneously. The cellular provider chops up the city into cells. Each cell is typically sized at about ten square miles. Modern digital cell phones can process millions of calculations per second in order to compress and decompress the voice data. The parts of a cell phone If you take a cell phone apart, you find that it contains: • • • • An circuit board containing the microprocessor An antenna A liquid crystal display A keyboard • • • A microphone A speaker A battery The guts of the cellular phone lie in the printed circuit board. The front of the circuit board The back of the circuit board The analog-to-digital and digital-to-analog conversion chips translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog. The digital signal processor is a highly customized processor designed to perform signal-manipulation calculations at high speed. The microprocessor The microprocessor handles all of the chores for the keyboard and display, deals with command and control signaling with the base station and also coordinates the rest of the functions on the board. The ROM and Flash memory chips provide storage for the phone's operating system and customizable features. Digital cell phones use the same radio technology as analog phones, but they use it in a different way. Analog systems do not fully utilize the signal between the phone and the cellular network. A nalog signals cannot be compressed and manipulated as easily as a true digital signal. Digital phones convert your voice into binary information and then compress it. This compression allows between three and ten digital cell-phone calls to occupy the space of a single analog call. A cell phone, like any other consumer electronic device, has its problems. Nonrepairable internal corrosion of parts results if you get the phone wet or use wet hands to push the buttons. Extreme heat in a car can damage the battery or the cell-phone electronics. Extreme cold may cause a momentary loss of the screen display. But with these manageable problems the cellular phone is here to stay.
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