A cell phone is a portable telephone which receives or sends messages through a Cell site, or transmitting tower. Radio waves are used to transfer signals to and from the cell phone. Each cell site has a range of 3-5 miles and overlaps other cell sites. All of the cell sites are connected to one or more cellular switching exchanges which can detect the strength of the signal received from the telephone. As the telephone user moves or roams from one cell area to another, the exchange automatically switches the call to the cell site with the strongest signal.
The term “cell phone” is uncommon outside of the US and Japan. However, almost all mobile phones use cellular technology, including GSM, CDMA and the old analog mobile phone systems. Hence, many people use the term “cell phone” to mean any mobile telephone system. The exception to mobile phones using cellular technology are satellite phones.
The Iridium phone system is very like a cell phone system except the cell sites are in orbit. The marine radio telephone satellites administered by INMARSAT have a completely different system (see below).
Old systems pre-dating the cellular principle may still be in use in places. The most notable real hold-out is that many amateur radio operators maintain phone patches in their clubs’ VHF repeaters.
Early mobiles were analog; newer ones are digital.
There are a number of different digital cellular technologies; these include: GSM, CDMA, DECT.
Mobile phone technology is often divided into generations: 1G, 2G, 2.5G,2.7G, 3G, 4G:
1G: AMPS, TACS
2G: TDMA, CDMA, GSM, PCS, iDEN
All of these technologies were based on cellular technology. However, satellite based phones are called mobile phones too.
Major mobile phone manufacturers include Nokia, Sony Ericsson and Motorola.
Many mobile phones support ‘auto-roaming’, which permits the same phone to be used in multiple countries. However, both countries must use the same mobile system and the same frequencies, and there must be an agreement between the two countries’ telephone operators.
In the UK and Australia, mobile phones are often called simply mobiles. In Germany, they are called Handys. In Sweden they are sometimes called nalle, or “teddy bear”, referring to the fact that many people always carry them around and feel insecure if they misplace them.
Mobile phones must be distinguished from portable phones (called cordless phones in the US); with a portable phone the user purchases their own base station, which they connect to a landline, the range of the phone is generally restricted to under 50 m, and the phones operate on a different frequency and protocol (e.g. DCTS in North America; DECT in Europe).
Mobile phones do not only support voice calls; they can also send and receive data and faxes (if a computer is attached), sending short messages (or “text messages”; see Short Message Service), access WAP services, and provide full Internet access using technologies such as GPRS. Mobile phones often have a clock and a calculator and often one can play some games on them.
Newer models also allow for sending pictures and have a built-in digital camera. This gives rise to some concern about privacy, in view of possible voyeurism, for example in swimming pools. For this reason, Saudi Arabia has banned camera phones entirely; South Korea has ordered manufacturers to ensure that all new handsets emit a beep whenever a picture is taken. On the other hand, cameras can be used by crime victims or witnesses to help identify the criminals.
GPS receivers are starting to appear in cell phones, primarily to aid in dispatching emergency responders.
Newer models have included many features aimed towards personalisation, such as user defined ring tones and operator logos, and interchangeable covers, which have helped in the uptake by the teenage market.
Usually one can choose between a ring tone and a vibrating alert.
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