Cellular telephone technology is also called cellular radio. The cellular radio network became fully operational in North America in 1978. This technology relies on the distribution of what are called cell sites over a wide geographical area. Each cell site consists of a radio transceiver and a controller that sends and receives signals from the mobile phones in the area to a telephone switch. The signals can be beamed to a central point called the mobile telecommunications switching office. This office places calls from land based telephones to mobile telephones, and allows mobile phones to operate across the globe as the phone signal is relayed from one switching office to another.
Mobile telephone service was severely limited in availability until 1984. Until that year, only urban areas had mobile service, primarily for city services. Each city had a single antenna to transmit signals to and from the antennae of car phones. The Federal Communications Commission (FCC) assigned only 12–4 frequencies to an urban area. As a result, only one or two-dozen car phone calls could take place in the entire city at one time. The system was frustrating. Users had to wait up to 30 minutes to get a dial tone, and potential mobile phone customers were put on five to 10-year waiting lists.
Cellular phone technology changed all this. In a cellular system, each metropolitan area is divided into broadcasting zones or "cells." Each 6–10-mi2 (15.5–25.9-km2) cell has its own broadcast antenna or tower. As a car phone moves through the city, a computer automatically passes its frequency from one cell to the next. A single frequency can be used for multiple, nonadjacent cells; and, as the number of users increases, cells can be subdivided into any number of smaller cells, so the cellular system is capable of far greater usage than the old mobile service.
Rudimentary cellular technology was known as early as 1947. By the 1960s and 1970s, mobile phone service was overcrowded, and the need for a more efficient system led to a re-examination and refinement of cellular technology. Bell Laboratories, a research division within the American Telephone and Telegraph Company (AT&T), took the lead in this development. A prototype network had been developed by 1971. In 1978 the first experimental cellular service, which was called the Advanced Mobile Phone Service (AMPS), was operational in the Chicago, Illinois, area. AT&T was declared a monopoly and was reorganized in 1978. This opened the cellular phone market to competitors. Seven new regional phone companies began to pursue the cellular phone market.
In 1981, the FCC issued cellular phone regulations. In October 1983, Ameritech Mobile Communications (a subsidiary resulting from the Bell breakup) introduced the first American commercial cellular system in Chicago. Cellular service was also available by then in a number of other countries. The FCC also allowed one non-Bell service in each metropolitan area. For example, Cellular One began transmitting in Washington, D.C., in December 1983.
As the number of cellular phone systems and subscribers increased, the costs for equipment and service decreased. As of 2002, pocket-size personal telephones based on cellular technology are available, as are machines that combine a cellular phone, facsimile machine, voice and e-mail systems, answering machine, and pager.
The cellular technology that relied on ground-based antennae is giving way to satellite technology. Communication satellites are being used increasingly by the cellular services to provide uniform service as the telephone and its user travel through a number of cells. A new form of satellite technology called Global Mobile Personal Communications by Satellite (GMPCS) allows telecommunication virtually anywhere in the world.
Earlier communication satellites traveled high above Earth and orbited at the same speed as Earth rotates. The satellites stayed in one position relative to the ground. This geosynchronous orbit caused delays and loss of quality in signal transmission. GMPCS satellites have much lower orbits and can be used in clusters called constellations to transfer signals rapidly and with greater clarity. Developing countries and remote areas have access to cellular service, and, during natural disasters, emergency relief can be mobilized and coordinated when land-line telephones have been disabled or the region is remote.
The telephone industry is making advances toward a single telephone number per person. This is called a Personal Communications Network or PCN. The PCN can be used for both land-line networks (telephone service by cable that has traditionally been provided to homes and businesses) and cellular systems. Basically, this service is a form of call-forwarding in which the signal is transferred through the land-line network until a transceiver detects that the cell phone is within range. The call is then sent as a cellular signal.
Further development is expected to lead to digital transmissions that convert conversations into computer code that can be transferred by advanced cellular technology. Also microcellular technology that uses smaller and more closely spaced transceivers instead of cellular towers or by satellite is on the horizon. Microcells will relieve the pressure to provide enough access telephone numbers, and the FCC is working on modifying communications regulations to suit the new technologies and to free frequencies with less demand for cellular use. Radio frequencies may be converted to phone service, and dedicated land-lines for telephone service may be outmoded by delivering phone signals via cable television.
Telecommunications experts predict that all telephones will be wireless by 2010.
The ease of use and life saving potential of cellular telephones has not come without negative aspects. Foremost is the use of cellular telephones in motor vehicles.
The use of a phone can divert the driver's attention from the road. The increase in motor vehicle accidents and in injuries and death has been attributed to the use of cellular telephones. Increasingly, legislation is requiring the use of "hands off" cellular technology in motor vehicles, where the phone is positioned somewhere on the dashboard and a speaker is activated to carry on the conversation.
See also Fiber optics; Synthesizer, voice.
Dodd, A.Z. The Essential Guide to Telecommunications. 3rd ed. Englewood Cliffs, NJ: Prentice-Hall, 2001.
Laino, J. The Telephony Book-Understanding Systems and Services. Gilroy, CA: CMP Books, 1999.
Noll, A.M. Introduction to Telephones and Telephone Systems Norwood. MA: Artech House, 1999.
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