Simulink Tutorial on Digital Modulation Methods - Cengage Learning

13.9. 16-ARY QUADRATURE AMPLITUDE-SHIFT KEYING (16-QAM) 629
Figure 13.124: Eye pattern in inphase
component at the transmitter for
16-QAM with square-root raised-cosine
pulses
SOLUTION
Figure 13.125: Eye pattern in in-phase
component at the receiver for 16-QAM
with square-root raised-cosine pulses
16-QAM is more sensitive to additive noise since for the same per symbol energy the
minimum Euclidean distance of the constellation points is smaller. We observe four
nodes in the eye patterns, which results in a smaller vertical eye opening and higher
sensitivity to additive noise.
13.9.2 16-QAM with Raised-Cosine Pulses
We now replace the square-root raised-cosine pulses by raised-cosine pulses:
16-QAM > Raised-Cosine
The relevant diagrams are depicted in Figures 13.126 to 13.129.
TUTORIAL PROBLEM
Problem 13.24 [16-QAM with Raised-Cosine Pulses (α = 0.5)] Do errors occur if
no noise is present? Explain, using the eye patterns and scatter plot at the receiver.
SOLUTION
Using a raised-cosine transmit filter and a matched filter at the receiver results in ISI.
Due to the small minimum Euclidean distance of the signal-space constellation points,
the ISI imposed by wrong filter design causes errors even if no noise is present. In the
eye patterns it can be observed that error-free detection is not possible.
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