Wireless telephone systems

The system described above requires wires to carry electrical signals
from one telephone to another. As telephone usage became popular
in the early part of the twentieth century, the air above urban areas became
clogged with mazes of telephone wire systems. Eventually, many
of these systems were brought together into large cables and buried underground.
The 1970s saw the first widespread use of wireless telephone systems
in the United States. A wireless telephone system is one in which
the electrical signals produced by a telephone transmitter are attached to
a radio signal, similar to the one used to transmit radio broadcasts. Those
radio signals can then be transmitted from one tower to another, without
the need for wires. Cordless, mobile, and cellular telephones perform all
the same functions as conventional telephones but use radio waves instead
of wires.
The convenience and efficiency of wireless telephone communication
is the reason behind the impressive growth of this service. In 1984,
there were approximately 90,000 cellular telephone subscribers in the
United States. By 1990, the number of subscribers had reached 4.4 million.
And by the beginning of the twenty-first century, that number had
ballooned to more than 13 million. The inevitable future expansion of cellular
telephone communication on a global scale will be based on employing
low-altitude, low-weight satellites.
At present, voice communication and data communication exist
separately. As technologies become more advanced, the best of both
worlds will be integrated into a multimedia telecommunications network.
Multimedia will enable people to combine any media they need
to send, receive, or share information in the form of speech, music, messages,
text, data, images, video, animation, or even varieties of virtual reality.
The emerging capabilities offered by a unified, intelligent telecommunications
network will gradually transform the way people interact,
work, and learn