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In telecommunication, a wireless phone,
handy, cellular mobile or cell phone (in the United States), also called a mobile phone in other English speaking countries, is a mobile communications system that uses a combination of radio
wave transmission and conventional telephone switching to permit telephone communication to and from
mobile users within a specified area.
The term does not comprise the so-called portable phone or cordless phone, which is associated with a fixed
telephone landline and can only be operated close to (less than 100 metres of) its base station, such as in and around the house
(see telephone for more). The term cell phone applies specifically to
mobile phones which use a cellular network; satellite phones are also mobile phones, but not cellular (see
the Iridium satellite system).
History
Mobile phones have existed at least since the 1950s, though the distinction becomes
blurry when special systems are used to "patch" conventional Radiotelephones (2-way radio) into a phone network with the
assistance of human operators. What was possibly the first real mobile phone, in the sense that it was connected to the telephone
network, was tested by the Swedish police in 1946. A half dozen calls could be made before
the (car's) battery ran out.
Modern mobile phones can make and receive calls automatically, operating as would a normal phone (though most have a superset
of the ability of fixed-line phones).
Mobile phones began to proliferate through the 1980s with the introduction of
"cellular" phones based on cellular networks with multiple base
stations located relatively close to each other, and protocols for the automated "hand-off" between two cells when a phone moved
from one cell to the other. In this era, mobile phones were somewhat larger than current ones, and many were designed for
permanent installation in cars, or as "transportable" phones the size of a briefcase.
As technology improved through the 1990s, the larger "bricks" disappeared and tiny
hand-held phones became the norm.
In most of Europe, wealthy parts of Asia, and
Australasia, mobile phones are now virtually universal, with the majority of
the adult, teenage, and even child population owning one. They are less common in the United States — while widely available, market penetration is lower than elsewhere in the developed
world (around 66 percent of the U.S. population as of 2003). Reasons advanced for this include incomplete coverage, relatively
high minimum monthly service charges (around $20), and the availability of relatively low-cost fixed-line networks (around $15
for unlimited local calling).
Due to their low establishment costs and rapid deployment, mobile phone networks are rapidly spreading throughout the
developing world, outstripping the growth of fixed telephony. Such
networks can often be economic, even with a small customer base, as mobile network costs are mostly call volume related, while
fixed-line telephony has a much higher subscriber related cost component.
Cellular telephony
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 3-15
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 from one cell area to another, the exchange automatically commands the handset and a cell site
with a stronger signal (from the handset) to go to a new radio channels. When the handset responds through the new cell-site, the
exchange switches the connection to the new cell-site.
With CDMA technology, the process is slightly different. CDMA handsets are not assigned
a specific "channel"; they instead send each bit using a pseudo-random code sequence specific to each phone. As the user moves
from one cell to another, the handset actually connects to both sites simultaneously. This is known as a "soft handoff" because,
unlike with traditional cellular technology, there is no one defined point where the phone switches to the new cell.
Modern mobile phones use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change
frequency under computer control and use low power transmitters so that a limited number of radio frequencies can be reused by
many callers with less interference. CDMA handsets, in particular, must have strict power controls to avoid interference with
each other. An incidental benefit is that the batteries in the handsets need less power.
The term "cell phone" is uncommon outside of the US. 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. The first digital cellular phone call was made in the United States in 1990.
There are a number of different digital cellular technologies; these include: GSM,
CDMA (Code Division Multiple Access), DECT, IS-136, and iDEN.
Mobile phone technology is often divided into generations: 1G, 2G, 2.5G, and 3G:
PCS is often mistakenly referred to as a different 2G
technology. It is not. PCS is an acronym for Personal Communications Service, which merely represents the 1900 MHz spectrum set aside by
the FCC in America for additional wireless phone capacity. GSM-1900, IS-95, IS-136, and
CDMA2000 operate on the 1900 MHz PCS band
today.
The other spectrum used in North America (850 MHz) was the original
spectrum licensed by the FCC in
the 1980s, commonly referred to as Cellular
spectrum. Today, AMPS, IS-95, CDMA2000, IS-136, and more recently GSM-850 all operate on the Cellular spectrum.
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, Motorola, and Samsung.
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 (this is an
important issue for GSM users traveling between North America and the rest of the world), and
there must be an agreement between the two countries' telephone operators.
In the UK, Australia and New Zealand, mobile phones are often called simply mobiles. In Germany, they are called Handys, in Switzerland Natel. 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. Many swimming pools have banned camera mobile phones in
their pools and changing rooms. 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 personalization, 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.
Satellite telephony (INMARSAT)
Inmarsats use a completely different system. Basically, the satellite simply retransmits whatever signals it receives. The
mobile stations actually log into a ground station. More information is available at INMARSAT.
Note: In cellular mobile systems, large geographical areas are segmented into many smaller areas, i.e.,
cells, each of which has its own radio transmitters and receivers and a single controller interconnected with the public switched telephone network. Synonyms cellular phone,
mobile phone, cellular radio, cellular telephone.
Using Mobile phones on aircraft
The use of mobile phones is generally disallowed on aircraft during flight. The reason given for this is that the mobile phone
could interfere with the sensitive equipment on the aircraft. This could be restated as "during development these aircraft were
not designed to accept signals from mobile phones and there has not been sufficient testing to be sure that they could" as can be
seen from plans to improve certification [1] . It is clear, however, that there is
some level interference possible from active radio transmitters such as mobile phones on aircraft. Exactly how much and in what
way is dependent on the particular phone system in use and which component of the plane we are discussing. Whether that level of
interference should have any infuence on electronic systems which should be designed to fly through lightning storms without
falling out of the sky is an entirely different question.
One area in which interference is likely is in the radio based audio equipment used for communicating from the aeroplane to
the ground. The mobile phone transmitter will be much closer to the reciever on the aircraft; this means that any cross talk from
the mobile phone will have a strong effect.
Some mobile phone systems such as GSM may cause an irritating buzz (explained in the
TDMA article) which would certainly disrupt communications from the pilot to ground.
Unfortunately, the conditions on an aeroplane are exactly those which might cause this. The maximum speed of travel in a mobile
phone system is limited by several factors, frequency changes, rate of change of timing offset etc. The speed of an aeroplane
often exceeds these (typically phones are designed for use in a fast car) which means the mobile will fail to register to the
network and retry registration repeatedly.
Older analogue systems simply broadcast at a high power of up to several watts. This will cause more general interference, and
since the voice signal is not encoded there may be direct cross talk into the communication systems of the phone.
Another factor is that from an altitude, distant cells are visible to the mobile with no attenuation from intervening
obstacles. This means that the phone could try to establish contact with a far away cell where the signal will not be recognised,
this transmission will probably be at maximum power due to the lack of prior response. Once more, this repeated sending of
maximum power messages increases the risk of interference with electronic equipment on the aircraft.
Having said all the above, according to the BBC "most of the evidence is circumstantial and anecdotal. There is no absolute
proof mobile phones are hazardous." [2] Further, certain airline companies, such as Boeing,
have begun to introduce paid wireless services on their planes (e.g. WLAN) and radio based satellite phones are a standard
installation on aeroplanes. Clearly there is a direct airline industry advantage in having control over communication systems
from within an aeroplane, with no clear way for potential competitors to certify their systems as safe for use on board. Some
articles have even gone so far as to accuse the airline industry of pushing the ban on mobile phones in order to increase revenue
from on board telephones [3] .
Health controversy
As with many new technologies, concerns have arisen about the effects on health of using a mobile telephone. Part of the radio
waves emitted by a mobile telephone are absorbed by the human head; the microwaves emitted by a GSM-900 handset can have a power of up to 2
watts. According to the scientific consensus, the only effect on the human body is that the
temperature of the head increases with a harmless fraction of a degree during prolongued calling. However, some controversial
studies claim that there exist other undesired effects on the health as a direct result of the radiation.
Parts of this page are from Federal Standard 1037C:
Glossary of Telecommunication Terms
See also
External links
dk:Mobiltelefon
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