20 March 2009

Cell phone




The invention: 

Mobile telephone system controlled by computers
to use a region’s radio frequencies, or channels, repeatedly,
thereby accommodating large numbers of users.

The people behind the invention:

William Oliver Baker (1915- ), the president of Bell
Laboratories
Richard H. Fefrenkiel, the head of the mobile systems
engineering department at Bell





The First Radio Telephones

The first recorded attempt to use radio technology to provide direct
access to a telephone system took place in 1920. It was not until
1946, however, that Bell Telephone established the first such commercial
system in St. Louis. The system had a number of disadvantages;
users had to contact an operator who did the dialing and the
connecting, and the use of a single radio frequency prevented simultaneous
talking and listening. In 1949, a system was developed
that used two radio frequencies (a “duplex pair”), permitting both
the mobile unit and the base station to transmit and receive simultaneously
and making a more normal sort of telephone conversation
possible. This type of service, known as Mobile Telephone Service
(MTS), was the norm in the field for many years.
The history of MTS is one of continuously increasing business usage.
The development of the transistor made possible the design and
manufacture of reasonably light, compact, and reliable equipment,
but the expansion of MTS was slowed by the limited number of radio
frequencies; there is nowhere near enough space on the radio spectrum
for each user to have a separate frequency. In New York City, for
example, New York Telephone Company was limited to just twelve
channels for its more than seven hundred mobile subscribers, meaning
that only twelve conversations could be carried on at once. In addition,
because of possible interference, none of those channels could
be reused in nearby cities; only fifty-four channels were available na-
tionwide. By the late 1970’s, most of the systems in major cities were considered full,
and new subscribers were placed on a waiting list; some people had been waiting
for as long as ten years to become subscribers.
Mobile phone users commonly experienced long delays in getting poor-quality
channels.

The Cellular Breakthrough

In 1968, the Federal CommunicationsCommission (FCC) requested proposals for the
creation of high-capacity, spectrum- efficient mobile systems.
Bell Telephone had already been lobbying for the creation of such a system for some years.
In the early 1970’s, both Motorola and Bell Telephone proposed the use of cellular
technology to solve the problems posed by mobile telephone service.
Cellular systems involve the use of a computer to make it possible to use an area’s
frequencies, or channels, repeatedly, allowing such systems to accommodate many
more users.
A two-thousand-customer, 2100-square-mile cellular telephone
system called the Advanced Mobile Phone Service, built by the
AMPS Corporation, an AT&T subsidiary, became operational in
Chicago in 1978. The Illinois Bell Telephone Company was allowed
to make a limited commercial offering and obtained about fourteen
hundred subscribers. American Radio Telephone Service was allowed
to conduct a similar test in the Baltimore/Washington area.
These first systems showed the technological feasibility and affordability
of cellular service.
In 1979, Bell Labs of Murray Hill, New Jersey, received a patent for such a system.
The inventor was Richard H. Fefrenkiel, head of the mobile systems engineering
department under the leadership of Labs president William Baker.
The patented method divides a city into small coverage areas called “cells,” each served
by lowpower transmitter-receivers. When a vehicle leaves the coverage of one cell,
 calls are switched to the antenna and channels of an adjacent
cell; a conversation underway is automatically transferred
and continues without interruption. Achannel used in one cell can
be reused a few cells away for a different conversation. In this way,
a few hundred channels can serve hundreds of thousands of users.
Computers control the call-transfer process, effectively reducing
the amount of radio spectrum required. Cellular systems thus actually
use radio frequencies to transmit conversations, but because
the equipment is so telephone-like, “cellular telephone” (or “cell
phone”) became the accepted term for the new technology.
Each AMPS cell station is connected by wire to a central switching
office, which determines when a mobile phone should be transferred
to another cell as the transmitter moves out of range during a
conversation. It does this by monitoring the strength of signals received
from the mobile unit by adjacent cells, “handing off” the call
when a new cell receives a stronger signal; this change is imperceptible
to the user.

Impact

In 1982, the FCC began accepting applications for cellular system
licenses in the thirty largest U.S. cities. By the end of 1984, there
were about forty thousand cellular customers in nearly two dozen
cities. Cellular telephone ownership boomed to 9 million by 1992.
As cellular telephones became more common, they also became
cheaper and more convenient to buy and to use. New systems
developed in the 1990’s continued to make smaller, lighter, and
cheaper cellular phones even more accessible. Since the cellular telephone
was made possible by the marriage of communications and
computers, advances in both these fields have continued to change
the industry at a rapid rate.
Cellular phones have proven ideal for many people who need or
want to keep in touch with others at all times. They also provide
convenient emergency communication devices for travelers and
field-workers. On the other hand, ownership of a cellular phone can
also have its drawbacks; many users have found that they can never
be out of touch—even when they would rather be.

William Oliver Baker

For great discoveries and inventions to be possible in the
world of high technology, inventors need great facilities—laboratories
and workshops—with brilliant colleagues. These must
be managed by imaginative administrators.
One of the best wasWilliam Oliver Baker (b. 1915), who rose
to become president of the legendary Bell Labs. Baker started out
as one of the most promising scientists of his generation. After
earning a Ph.D. in chemistry at Princeton University, he joined
the research section at Bell Telephone Laboratories in 1939. He
studied the physics and chemistry of polymers, especially for use
in electronics and telecommunications. During his research career
he helped develop synthetic rubber and radar, found uses
for polymers in communications and power cables, and participated
in the discovery of microgels. In 1954 he ranked among the
top-ten scientists in American industry and asked to chair a National
Research Council committee studying heat shields for
missiles and satellites.
Administration suited him. The following year he took over
as leader of research at Bell Labs and served as president from
1973 until 1979. Under his direction, basic discoveries and inventions
poured out of the lab that later transformed the way
people live and work: satellite communications, principles for
programming high-speed computers, the technology for modern
electronic communications, the superconducting solenoid,
the maser, and the laser. His scientists won Nobel Prizes and legions
of other honors, as did Baker himself, who received dozens
of medals, awards, and honorary degrees. Moreover, he
was an original member of the President’s Science Advisory
Board, became the first chair of the National Science Information
Council, and served on the National Science Board. His
influence on American science and technology was deep and
lasting.

See also : Internet; Long-distance telephone; Rotary dial telephone;
Telephone switching; Touch-tone telephone.


2 comments:

Anonymous said...

Ϝаntastic goօds from you, man. I hav understand your stuff previous to and you're juust extremely excellent.
I really lіke what yoսu have acquired here, really lіkme what yyou
are sayiոg and the way іnn which you sаy it. You make it eոjoyable and you still care for to keep it sensible.
I cant wait to read much more fгom you. This is really a terrific site.


Ӎy web-site: zumba certification london

Anonymous said...

Harga HP Nokia Terbaru
HP Nokia
Harga Hp Oppo Terbaru
Hp Oppo
Harga Hp Smartfren Terbaru
Hp Smartfren
Harga Hp Smartfren
Hp
Harga Hp Oppo