LG VX8500 Service Manual page 7

VX8500
Chapter1. System Introduction
1.1 CDMA Abstract
The CDMA mobile communication system has a channel hand-off function that is used for collecting the
information on the locations and movements of mobile telephones from the cell site by automatically controlling
several cell site through the setup of data transmission routes, and then enabling one switching system to carry
out the automatic remote adjustment. This is to maintain continuously the call state through the automatic
location confirmation and automatic radio channel conversion when the busy subscriber moves from the service
area of one cell site to that of another by using automatic location confirmation and automatic radio channel
conversion functions. The call state can be maintained continuously by the information exchange between
switching systems when the busy subscriber moves from one Cellular system area to the other Cellular system
area.
In the Cellular system, the cell site is a small-sized low output type and utilizes a frequency allocation system
that considers mutual interference, in an effort to enable the re-use of corresponding frequency from a cell site
separated more than a certain distance.
Unlike the time division multiple access (TDMA) or frequency division multiple access (FDMA) used in the
band limited environment, the Code Division Multiple Access (CDMA) system which is one of digital Cellular
systems is a multi-access technology under the interference limited environment. It can process more number of
subscribers compared to other systems (TDMA system has the processing capacity three times greater than the
existing FDMA system whereas CDMA system, about 12~15 times of that of the existing system).
CDMA system can be explained as follows; TDMA or CDMA can be used to enable each person to talk
alternately or provide a separate room for each person when two persons desire to talk with each other at the
same time, whereas FDMA can be used to enable one person to talk in soprano, whereas the other in bass (one
of the two talkers can carry out synchronization for hearing in case there is a bandpass filter function in the area
of the hearer). Another available method is to make two persons to sing in different languages at the same time,
space, and frequency when wishing to let the audience hear the singing without being confused. This is the
characteristic of CDMA.
On the other hand, when employing the CDMA technology, each signal has a different pseudo-random binary
sequence used to spread the spectrum of carrier. A great number of CDMA signals share the same frequency
spectrum. In the perspective of frequency area or time area, several CDMA signals are overlapped. Among these
types of signals, only desired signal energy is selected and received through the use of pre-determined binary
sequence; desired signals can be separated, and then received with the correlator used for recovering the
spectrum into its original state. At this time, the spectrums of other signals that have different codes are not
recovered into its original state, and appears as the self-interference of the system.
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