Since a particular chip now arrives at distinctly different
times, a time diversity gain can be observed.
Let us take a step to the side to try to describe the transmit and receive operations required in the
CDMA system. In Fig. 7.7, we show the baseband signal is spread to a larger BW to be transmitted.
This signal, along with other spread users, and narrowband interference are summed in the Mobile
Station (MS) antenna. At this point, the desired signal is extracted by performing the despreading
operation to create the narrowband signal at the receiver output.
What is interesting in Fig. 7.7 is that any narrowband interference present in the received signal
becomes spread in the despreading operation in the receiver. The desired signal is extracted or
despread because the correct PN code and timing offset was used during the despreading operations.
Lastly, other CDMA users entering the receiver remain spread because they have different
PN codes. Hence the receiver relies on autocorrelation and cross-correlation properties of the PN
sequence for this CDMA system to operate properly. The despreader output not only has the
desired signal, but also has other wideband interference and noise. In the block diagram of Fig.
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