Digital Signal Processing Reference
In-Depth Information
FIGURE 10.26.
MATLAB plots of an encoded voice signal (lower graph) and received
segment of
TheForce.wav
(upper graph).
10.11.3 Phase-Locked Loop
This project is a PLL receiver. In BPSK, the receiver must be able to lock onto the
phase of a received signal in order to distinguish between 1s and 0s. A sinusoid of
1 kHz, with varying phase, is used as the real-time input to the DSK. This input signal
has eight unique phase shifts. The real-time output signal is the phase of the received
signal. Two DSKs are required to implement this project.
To determine the phase of an incoming sinusoid, the maximum of the correla-
tion coefficient is calculated between the received sinusoid and a sinusoid offset by
a phase estimate. The correlation coefficient,
Y
, between two sinusoids is given by
2
p
Ú
(
)
◊
(
)
Y
=
sin
t
◊
wf
+
sin
t
◊
wf
+
carrier
est
0
The received sine wave has a phase of
f
carrier
, and an estimate of the phase is
f
est
.
The correlation coefficient has a maximum value when
f
carrier
and
f
est
are equal.
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