The basic of spread communication system with the binarry information sequence as the input at the transformer end, as its output at the receiver.

The channel encoder and the modulator modulates the signal to be transmitted and the decoder and demodulator

detect the signal at the receiver.

in addition to these, two identical pseudo random pattern generators are used, one that interference with the modulator at the transmitter

side, and second that interferences with the demodulator at the receiver side. These generator generates a psedudo random binary valued sequence, which

is impressed on the transmitted signal at the modulator amd removed from the received signal at the demodilator.

The pn sequence spread the singal rnadomly over the wide frequence band in the transmitter side and despreads the modulated signal

at the receiver side.

synchronization of pn sequence generated at the receiver with the pn sequence containing in the incomming signal is required in order

to demodulate the received signal.

Actually the sychronization between the transmitter and thr receiver is achived by, prior to actual transmission, a fixed pseudo random bit

pattern that the receiver will organize in the presence of interference withn ahigh probability.

Interference is introdused in the transformation of the information beraring signal through the channel. the characteristics of the interferece

may be charactorized as the narrow band and the wide band .

In the case, two modulated techiniques are used such PSK and FSK. The PSK is used where the phase coherence signal over a long time

interval is required. The FSK moculation is used where such phase coherence in not required.



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