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Radio Cellular |
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Cellular radio provides mobile telephone
service by employing a network of cell sites distributed over
a wide area. A cell site contains a radio transceiver and a
base station controller which manages, sends, and receives traffic
from the mobiles in its geographical area to a cellular telephone
switch. It also employs a tower and its antennas, and provides
a link to the distant cellular switch called a mobile telecommunications
switching office. This MTSO places calls from land based telephones
to wireless customers, switches calls between cells as mobiles
travel across cell boundaries, and authenticates wireless customers
before they make calls. |
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| Cellular uses a principle called
frequency reuse to greatly increase customers served. Low powered
mobiles and radio equipment at each cell site permit the same
radio frequencies to be reused in different cells, multiplying
calling capacity without creating interference. This spectrum
efficient method contrasts sharply with earlier mobile systems
that used a high powered, centrally located transmitter, to
communicate with high powered car mounted mobiles on a small
number of frequenices, channels which were then monopolized
and not re-used over a wide area. |
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| Complex signaling routines handle
call placements, call requests, handovers, or call transfers
from one cell to another, and roaming, moving from one carrier's
area to another. Different cellular radio systems use frequency
division multiplexing (analog), time division multiplexing (TDMA),
and spread spectrum (CDMA) techniques. Despite different operating
methods, AMPS, PCS, GSM, E-TACS, and NMT are all cellular radio.
That's because they all rely on a distributed network of cell
sites employing frequency re-use. Is your head spinning yet?
Let's ease into this cellular discussion by discussing some
history first. |
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