LG LG511C, Service Manual

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LG Electronics Inc.
LN510
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Chapter1. System Introduction
Chapter1. System Introduction
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 correlators 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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