However, this was accomplished by making a slight modification into the WCDMA
standard by inserting a guard interval or cyclic prefix. Nevertheless this continues to prove to be a
viable alternative solution to the time-domain approaches.
6.4 SYMBOL TIMING RECOVERY
This next section addresses the need for time synchronization. This occurs when there is a difference
in the sampling clock frequencies between the received signal and locally generated signal. Also time
synchronization is required when the receiver clock sampling is not synchronized with the received
data symbols [4][26??“33].
We will base our discussion on the following block diagram and assume the sampling clock to
operate at twice the symbol rate (see Fig. 6.23). The complex samples are defined in terms of the even
and odd sampling, re(k) and ro(k), respectively.
(6.95)
(6.96) ro(k) r(t) ZttnT
T
2
re(k) r(t) ZttnT
RECEIVER DIGITAL SIGNAL PROCESSING 319
Memory ADC
~
r(t)
LPF
Sampling
Clock, fs
Timing Error
Estimator
LPF Interpolation
re(k)
ro(k)
Digital Domain
Timing Control
Signal
FIGURE 6.23 Timing recovery functional block diagram.
The complex, oversampled samples are temporarily stored in memory so the timing error estimator
can estimate the sampling phase offset between the received signal and the locally generated timing.
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