Cellula Radio Telephone

Both cellular radio and PCS use high-frequency radio waves to transmit calls. High-frequency waves have short wavelengths that pass by a given point at a very high rate. High-frequency waves can provide better sound quality and more reliable short-distance transmission than lower-frequency waves (such as AM radio) as they are less susceptible to sound degradation caused by the noise generated by weather, such as lightning which causes static, and other noise generators such as motors. However, high-frequency signals cannot effectively travel as far as low-frequency signals can.

For cellular networks, the limited range of high-frequency waves is actually advantageous because it means the same frequencies can be reused at nearby locations. Cell phone calls connect with short-range antennas known as towers. If there were only one tower for a large area, more customers would be trying to use the same high-frequency waves, and these waves would tend to overlap and cause interference.

But because cell phone networks establish many towers covering small areas, a smaller number of customers access a given tower, and frequencies can be reused when a cell phone call is handed off from one tower to another as a mobile cell phone user travels. This ability to reuse frequencies is helpful because there are a limited number of radio frequencies available to cell phone companies. It also allows cellular network providers to accommodate a larger number of users.

The transceiver inside a cellular phone is a much more complex device than a conventional phone used over the wire-based network. A cellular telephone has circuitry that creates a unique identity code that is used to locate and track the telephone. This identity code is necessary for coordinating calls to and from the telephone, and for billing such calls.

Because a cellular telephone user may move quite a distance during the duration of a call, the cellular radio network must manage calls from different tower sites as the telephone moves out of the range of one tower and into the range of another tower.

Current cellular telephones offer such features as a memory database for storing frequently called numbers and a lock to deter theft. Most cell phones, whether old or new, also have a small liquid crystal screen to display the telephone number being called or the number from which an incoming call originated. Many newer cell phones can display a short text message, much like a pager displays this information.

Some cellular phones can also access the Internet and display text from Web sites, such as stock quotes and news stories. Internet-capable cell phones can also send and receive e-mail. Because mobile telephones use radio waves to send and receive calls, the device must include a power source. Rechargeable batteries provide the usual source of power, but most cell phones can also be attached to the cigarette lighter in a vehicle or to some other external power device.