Cellular telephone is a small device that sends and receives voice calls and often other messages via wireless radio signals. The signals travel between the phone’s antenna and special towers called base stations. Each base station provides coverage to a surrounding area called a cell—giving the technology its name. Cellular telephones are also known as cell phones or mobile phones. Smartphones are cell phones that also work as small computers.
Before the 1990’s, cell phones sent signals as analog waves. Such signals are constantly varying waves representing sounds. Modern cell phones use digital signals. Such signals are encoded in numbers. Digital technology enables cell phones to transfer other signals besides voice calls. For example, cell phones can transmit text messages and internet data. Smartphones typically have built-in cameras. Smartphones can store digital photos, music, and videos. They also enable users to play video games and use other programs, often called apps.
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How cellular telephones work.
Each cell phone includes a transmitter and receiver. When a user makes a call or sends text messages or data, the phone sends the signal wirelessly to an antenna on a base station tower. Cables connect the base station to a mobile telephone switching office (MTSO). If the receiving cell phone is not in a cell connected to the MTSO, then the signal is retransmitted to another MTSO. The signal moves through the network until it can reach the receiving phone. MTSO’s also connect to local telephone companies and the internet.
Cells range from less than a mile to several dozen miles wide. If the caller moves from one cell region into another, the network automatically passes the call to the new base station without interruption. This transfer of a call from cell to cell is called handoff or handover. A process called roaming enables moving cell phones to maintain a constant connection with a network of base stations, even when outside the service provider’s area.
Features.
Almost all cell phones have rechargeable batteries. A cell phone typically stores a list of contacts and can automatically dial their phone numbers. Some phones can receive signals from the Global Positioning System (GPS) satellites. Such a phone uses GPS signals to determine its position and to help its user navigate. Certain advanced cell phones can transmit calls and other signals directly to orbiting satellites. This feature enables them to work in remote areas far from base stations.
Smartphones, like full-sized computers, are built around specialized operating systems (OS’s). An OS is a master computer program that controls the rest of the phone’s features. The OS also determines the kinds of apps that a user can install on the phone.
History.
The world’s first commercial cellular system went into operation in Japan in 1979. The first commercial cell phone in the United States was released by Motorola, Inc. (now called Motorola Solutions, Inc.) in 1983. By the early 1990’s, a “second generation” of cell phones using digital transmission was available. Third generation (3G) cell phone technology arrived in the United States in 2002. Modern cell phones use a combination of fourth generation (4G) and fifth generation (5G) systems. Each subsequent generation features more sophisticated phone and transmission system technology. Such countries as China, Germany, South Korea, and the United States have begun to implement nationwide 5G networks.
The Canadian firm Research in Motion released its first BlackBerry device with telephone capabilities in 2002, pioneering the development of smartphones. Apple’s iPhone, released in 2007, introduced a touch screen that could be manipulated using finger gestures. Google Inc. released a popular smartphone OS called Android in 2008.
In the early 2000’s, cell phones became more numerous than traditional landline phones throughout the world. In many less developed countries, landline phone systems were never built in the first place. Cell phones may thus be the only practical means of long-distance communication for many people in such countries.
