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The
DSSS is one of the spread spectrum system techniques,
which is known because of its uniqueness. That uniqueness
is laid in its modulation. It modulates the data signal
with the spreading code directly. In this system the users
are distinguished by the spreading code. So, it is clear
that the spreading code is unique for each user. In that
reason, this system can use the same band of frequency for
all users in the same system.
At
the receiver, the received signal must be synchronized
first by the locally generated spreading code. It is
accomplished in order to get the information signal
correctly. The synchronization in the spread spectrum
system can be divided into two subsections that are the
first acquisition and second the tracking code. The
acquisition is done to get the initial synchronization.
The tracking code in the other hand is used to maintain
the stability of synchronization.
One of the methods for tracking code is delay lock
tracking loop (DLL). The phase discriminator is built from
two independent correlators. These two correlators
correlate the received signal with the spreading code. The
output of the phase discriminator determines a decision
whether the received signal has been synchronized or not. |