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cellular radio,telecommunications system in which a portable or mobile radio transmitter and receiver, or "cellphone," is linked via microwavemicrowave,
electromagnetic wave having a frequency range from 1,000 megahertz (MHz) to 300,000 MHz, corresponding to a wavelength range from 300 mm (about 12 in.) to 1 mm (about 0.04 in.). Like light waves, microwaves travel essentially in straight lines.
..... Click the link for more information. radio frequencies to base transmitter and receiver stations that connect the user to a conventional telephone network. The geographic region served by a cellular system is subdivided into areas called cells. Each cell has a central base station and two sets of assigned transmission frequencies; one set is used by the base station, and the other by cellphones. To prevent radio interference, each cell uses frequencies different from those used by its surrounding cells, but cells sufficiently distant from each other can use the same frequencies. When a cellphone leaves one cell and enters another, the telephone call is transferred from one base station and set of transmission frequencies to the next using a computerized switching system. Over the years, cellular telecommunications systems have undergone a series of generational improvements that have increased the ability of the system to support more sophisticated telephones that utilitze increasing data transmission rates and ever more versatile software.
The camera phone, an innovation that dates commercially to 2000, is a cellular phone that also has picture taking and often video recording capabilities; the pictures and videos may be sent to another cellular phone or to a computer. Nearly all cellphones are now so equipped, and also have the ability to send text messages. Advances in digital technology and microelectronics also led to the development of so-called smartphones, which date to the early 1990s but only became significant in the mid-2000s, now dominate the market and typically also include e-mail programs, Internet browsers, personal information managers, music and video players, alarm clocks, calculators, games, voice memo recorders, e-book readers, payment services, and many other specialized software applications, or apps. Such phones typically have touch screens for accessing data and content, and are usually capable of accessing the Internet through a wireless network connection as well as through the cellular telephone system. These features have allowed smartphones to replace personal digital assistants, portable music players, and other portable electronic devices, and also supplant portable computers in many uses. The increasing size of smartphone screens has blurred most of the distinctions between the largest smartphones and smallest computer tablets, though the largest smartphones can be awkward when used for making telephone calls. The software needed for smartphone programs can make the devices vulnerable to software viruses.
The first cellular telephone system began operation in Tokyo in 1979, and the first U.S. system began operation in 1983 in Chicago. In many countries with inadequate wire-based telephone networks, cellular telephone systems have provided a means of more quickly establishing a national telecommunications network.
Cellphones emit nonionizing radiation, and there have been concerns expressed about whether they might cause cancer. Studies on the subject that have found evidence of increased cancer rates have been criticized for having methodological flaws. Although a World Health Organization panel concluded in 2011 that cellular phones were "possibly carcinogenic," that finding was criticized by the American Cancer Society and the National Cancer Institute and undermined by a large Danish study published in 2011.
cellphone(CELLular telePHONE) The first ubiquitous wireless telephone. Originally analog, all cellular systems today are digital, which has enabled the cellphone to turn into a handheld personal computer (see smartphone and cellphones vs. smartphones). A cellphone is also called a "mobile," "mobile phone," "handset" or "cell." In the U.S., there are more than 20 companies offering cellphone service (see cellphone services).
In 1983, the Motorola DynaTAC was the first cellphone, which sold for USD $3,995 (see image below). In the 1990s, cellphone sales were exploding worldwide, and three billion units were in use by 2008. The cellphone became an addiction for many people, who would never leave their house without it (see nomophobia). By 2012, there were more than 300 million cellphone subscriptions (including smartphones) in the U.S. Although third-world countries adopted cellphones without ever having landlines, by 2016, half the homes in the U.S. relied only on cellular technology.
In the U.S., the major cellular carriers are Verizon Wireless (formerly Bell Atlantic Mobile and Alltel), AT&T Mobility (formerly Cingular) and T-Mobile. T-Mobile absorbed Sprint in 2020, which was a merger of Sprint and Nextel in 2005. Outside the U.S., the largest companies are China Mobile, UK-based Vodafone and Nippon Telegraph & Telephone (NTT).
Geographic areas are divided into a number of slightly overlapping circular "cells." Each cell contains a base station, which is identifiable by its transmitting and receiving antenna located on a tower at the top of a hill or building. The base stations connect to the landline telephone system of the country and to the Internet.
The multiple cells combined with low power transmitters allow the same frequencies to be reused with different conversations in different cells within the same city or locale. The primary digital cellphone technologies are LTE, GSM, CDMA and TDMA. See 3G, PCS, AMPS, LTE, GSM, CDMA, TDMA, WAP, feature phone, cellspace, cellular network extender, screaming cellphone and cordless phone.
|The cellular system uses multiple base stations to cover a geographic area. As the mobile phone user travels from cell to cell, the call is automatically "handed off" to the next station. The more cells, the greater number of customers can be handled at the same time, because the same frequencies are reused within each cell.|
|First Cellphone in U.S.|
|Introduced in 1983, this Motorola DynaTAC 8000X cost USD $3,995 and weighed two pounds. (Image courtesy of Motorola, Inc.)|
|Could They Have Imagined?|
|As Europeans began to use their new-fangled Ericsson phones in the late 1800s, could they have imagined today's smartphones? Photo taken at Antoni Gaudi's famous "La Pedrera" apartment house in Barcelona.|
|A Cellphone to Die For|
|This is an example of a "fantasy coffin" in the National Museum of African Art in Washington, D.C. Popularized in the mid-1950s by Ghanaian artist Kane Kwei, each custom-crafted coffin was built to illustrate an important aspect of the deceased's life.|