THE CELLULAR CONCEPT
THE CELLULAR CONCEPT
The cellular concept was
developed and introduced by the Bell Laboratories in the early 1970s. One of
the most successful initial implementation of the cellular concept was the
advanced mobile phone system (AMPS), which has been available in the United States
since 1983. A cellular system is a high capacity land mobile system. The
available frequency spectrum is partitioned into discrete channels which are
assigned in groups to geographic cells. Each cell covers a Geographic Service
Area (GSA). The discrete channels are capable of being reused in different
cells within the service area. Thus the principle of cellular systems is to
divide a large geographic service area into cells with diameters from 2 to 50
km, each of which is allocated a number of radio frequency (RF) channels.
Transmitters in each adjacent cell operate on different frequencies to avoid
interference.
MULTIPLE ACCESS TECHNIQUES
Multiple Access is a
multiplexing technique in which the signals to be multiplexed originate at
different at different locations. The simplest multiple access scheme is the
one used by radio and television broadcasting stations. There are three types
of multiple access:
§Frequency Division Multiple Access (FDMA)
§Time Division Multiple Access (TDMA)
§Code Division Multiple Access (CDMA)
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