Simulink Tutorial on Digital Modulation Methods - Cengage Learning

596 CHAPTER 13. SIMULINK TUTORIAL ON DIGITAL MODULATION
SOLUTION
1. The envelope is constant.
Figure 13.27: Source signal a(t).
Figure 13.28: Transmitted signal u(t).
Figure 13.29: Signal x(t) at matched filter input
2. The received signal is corrupted by additive noise (AWGN channel).
3. After demodulation the signal x(t) contains also a component at 2f c:
x(t) = s(t)cos(2πfct) · 2cos(2πfct)
= s(t)(1 + cos(4πfct)) plus noise
Now, look at the eye patterns and signal-space plots (see Figures 13.30 to 13.34).
The green trajectory describes the baseband signal after pulse shaping in the signalspace
(see Figure 13.30). The blue signal-space points in the scatter plot (see Figure
13.31) are obtained by sampling the green trajectory at the symbol rate at the optimum
sampling time, i.e., at maximum vertical eye opening. In the case of zero ISI we obtain
exactly the signal-space constellation points. The trajectory describes the transitions
between the constellation points.
First, look at the transmitter plots.
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