Structure And Functions Of Tri-Band Cdma Mobile Phone - LG -TM250 Service Manual

LG-TM250

3. Structure and Functions of tri-band CDMA Mobile Phone

The hardware structure of CDMA mobile phone is made up of radio frequency (RF) part and logic part. The
RF part is composed of Receiver part (Rx), Transmitter part (Tx) and Local part (LO). For the purpose of
operating on tri-band, It is necessary dual Tx path, tri Rx path, dual PLL and switching system for band
selection. The mobile phone antenna is connected with the frequency seperater which divide antenna
input/output signals between cellular frequency band (824~894 Mhz) and PCS frequency band
(1850~1990Mhz). Each separated path is linked with the cellular duplexer and PCS duplexer. Duplexer carrys
out seperating Rx band and Tx band. The Rx signals from the antenna are converted into baseband frequency by
the frequency synthesizer and frequency down converter. And then, passive SAW filter which is a band pass
filter for removing Tx interferer frequency. The baseband signals is converted into digital signals via
Analog-to-Digital Converter (ADC). In front of the ADC, switching system is required to choose which band
path should be open. The digital signals send to 5 correlators in each CDMA de-modulator. Of these, one is
called a searcher whereas the remaining 4 are called data receivers (fingers). Digitalized IF signals include a
great number of call signals that have been sent out by the adjacent cells. These signals are detected with
pseudo-noise sequence (PN Sequence). Signal to interference ratio (C/I) on signals that match the desired PN
sequence are increased through this type of correlation detection process, but other signals obtain processing
gain by not increasing the ratio. The carrier wave of pilot channel from the cell site most adjacently located is
demodulated in order to obtain the sequence of encoded data symbols. During the operation with one cell site,
the searcher searches out multi-paths in accordance with terrain and building reflections. On three data receivers,
the most powerful 3 paths are allocated for the parallel tracing and receiving. Fading resistance can be improved
a great deal by obtaining the diversity combined output for de-modulation. Moreover, the searcher can be used
to determine the most powerful path from the cell sites even during the soft handoff between the two cell sites.
Moreover, 3 data receivers are allocated in order to carry out the de-modulation of these paths. Output data that
has been demodulated changes the data string in the combined data row as in the case of original
signals(deinterleaving), and then, are demodulated by the forward error correction decoder which uses the
Viterbi algorithm.
Mobile station user information send out from the mobile station to the cell site pass through the digital voice
encoder via a mike. Then, they are encoded and forward errors are corrected through the use of convolution
encoder. Then, the order of code rows is changed in accordance with a certain regulation in order to remove any
errors in the interleaver. Symbols made through the above process are spread after being loaded onto PN carrier
waves. At this time, PN sequence is selected by each address designated in each call.
Signals that have been code spread as above are digital modulated (QPSK) and then, power controlled at the
automatic gain control amplifier (AGC Amp). Then, they are converted into RF band by the frequency
synthesizer synchronizing these signals to proper output frequencies.
Transmit signals obtained pass through the duplexer filter and then, are sent out to the cell site via the antenna.
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