Service Manual

LGP-2300/2310W
LG Information & Communications, Ltd.
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3. Structure and Functions of CDMA Mobile Phone
The mobile station of the CDMA system is made up of a radio frequency part and a logic/control (digital) part.
The mobile station antenna is connected with the transmitter/receiver via a duplexer filter so that it can carry out
the transmit/receive function at the same time.
The transmit frequency is the 60MHz band of 1850~1910MHz , whereas the receive frequency is the 60MHz
band of 1930~1990MHz. The transmit/receive frequency is separated by 20MHz. The RF signal from the
antenna is converted into intermediate frequency(IF) band by the frequency synthesizer and frequency down
converter and then, passes the bandpass SAW filter having the 1.25MHz bandwidth. The IF output signals that
have been filtered from spurious signals are converted into digital signals via an analog-to-digital
converters(ADC) and then, sent out respectively 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. Then, 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. Data output that
has been demodulated change the data string in the combined data row as in the case of original
signals(deinterleaving), and then, are de-modulated by the forward error correction decoder which uses the
Viterbi algorithm.
On the other hand, mobile station user information sent 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.