Motorola E685, Service Manual, Page: 9 / 97

9
Overall Concept
Cellular systems are used to provide radiotelephone service in the frequency range
of 826 – 891 MHz.
A cellular system provides higher call handling capacity and system availability
than would be possible with conventional radiotelephone systems that require total
system area coverage on every operating channel. The cellular system divides the
system coverage area into several adjoining sub-areas, or cells.
Each cell contains a base station (cell site) which provides transmitting and
receiving facilities. CDMA is a “spread spectrum”technology, which means that it
spreads the information contained in a particular signal of interest over a greater
bandwidth than the original signal.
With CDMA, unique digital codes, rather than separate RF frequencies or channels
are used to differentiate subscribers, The codes are shared by both the mobile
station and base station and are called “pseudo-random code sequences”. Since
CDMA is a spread spectrum technology, all users share a range of the radio
spectrum.
CDMA cell coverage is dependent upon the way the network is designed. For each
system 3 characteristics must be considered, coverage, quality, and capacity.
There 3 must be balanced for desired lever of performance.