Simulink Tutorial on Digital Modulation Methods - Cengage Learning
Simulink Tutorial on Digital Modulation Methods - Cengage Learning Simulink Tutorial on Digital Modulation Methods - Cengage Learning
614 CHAPTER 13. SIMULINK TUTORIAL ON DIGITAL MODULATION Figure 13.79: Eye pattern in in-phase component for QPSK with phase offset in cos component Figure 13.81: Cos carrier parameter window SOLUTION Figure 13.80: Eye pattern in quadrature component for QPSK with phase offset in cos component Figure 13.82: Sin carrier parameter window The received signal-space constellation rotates according to the frequency offset ∆f . Detection is not possible. This can also be concluded from the chaotic behavior of the trajectory and the eye patterns. 13.7 Offset-QPSK 13.7.1 Theory In Problem 13.13 we encountered the problem of envelope fades in QPSK-modulated signals. If two successive symbols are symmetric in the origin of the signal-space constellation, the trajectory performs a diagonal transition through the origin. This results © 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
13.7. OFFSET-QPSK 615 Figure 13.83: Receiver trajectory for QPSK with frequency offset Figure 13.85: Eye pattern in in-phase component for QPSK with frequency offset Figure 13.84: Receiver scatter plot for QPSK with frequency offset Figure 13.86: Eye pattern in quadrature component for QPSK with frequency offset in amplitude fading of the transmitted signal. Consequently, the transmitted signal becomes sensitive to nonlinear distortions during transition as imposed by amplifiers. Therefore, many applications require a close to constant envelope of the transmitted signal. A simple method to avoid deep fades is Offset-QPSK. In Offset-QPSK, the quadrature component of a QPSK signal is delayed by T/2 with respect to the in-phase component. Hence, the in-phase and the quadrature components cannot change simultaneously anymore, and diagonal transitions of the trajectory are avoided. © 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
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614 CHAPTER 13. SIMULINK TUTORIAL ON DIGITAL MODULATION<br />
Figure 13.79: Eye pattern in in-phase<br />
comp<strong>on</strong>ent for QPSK with phase offset<br />
in cos comp<strong>on</strong>ent<br />
Figure 13.81: Cos carrier parameter window<br />
SOLUTION<br />
Figure 13.80: Eye pattern in quadrature<br />
comp<strong>on</strong>ent for QPSK with phase offset<br />
in cos comp<strong>on</strong>ent<br />
Figure 13.82: Sin carrier parameter window<br />
The received signal-space c<strong>on</strong>stellati<strong>on</strong> rotates according to the frequency offset ∆f .<br />
Detecti<strong>on</strong> is not possible. This can also be c<strong>on</strong>cluded from the chaotic behavior of the<br />
trajectory and the eye patterns.<br />
13.7 Offset-QPSK<br />
13.7.1 Theory<br />
In Problem 13.13 we encountered the problem of envelope fades in QPSK-modulated<br />
signals. If two successive symbols are symmetric in the origin of the signal-space c<strong>on</strong>stellati<strong>on</strong>,<br />
the trajectory performs a diag<strong>on</strong>al transiti<strong>on</strong> through the origin. This results<br />
© 2013 <strong>Cengage</strong> <strong>Learning</strong>. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
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