Simulink Tutorial on Digital Modulation Methods - Cengage Learning

13.6. QUADRATURE PHASE-SHIFT KEYING (QPSK) 609
Figure 13.62: In-phase component u_c(t) of transmitted signal
Figure 13.63: Quadrature component u_s(t) of transmitted signal
SOLUTION
Figure 13.64: Transmitted signal u(t)
1. Since the zero ISI condition is not met at the transmitter, the trajectory shows no
nodes in the four QPSK signal-space constellation points.
2. The envelope fades if both quadrature components change simultaneously. In
this case the trajectory performs a diagonal transition through or close to the
origin. Due to the bandlimitation, the shift keying between constellation points
is not rectangular, which results in envelope fades. A simple method to reduce
amplitude fades is Offset-QPSK, which is covered in Section 13.7.
Double-click on the blue box Close transmitter and then Receiver to simulate the
receiver.
TUTORIAL PROBLEM
Problem 13.14 [QPSK with Square-Root Raised-Cosine Pulses: Receiver] What
do you observe in the eye patterns and in the signal-space plots?
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