Simulink Tutorial on Digital Modulation Methods - Cengage Learning
Simulink Tutorial on Digital Modulation Methods - Cengage Learning Simulink Tutorial on Digital Modulation Methods - Cengage Learning
582 CHAPTER 13. SIMULINK TUTORIAL ON DIGITAL MODULATION Figure 13.12: Matlab pathtool Figure 13.13:
13.4. PULSE SHAPING 583 13.4.1 Theory The impulse response gT (t) of the transmit filter determines the spectral characteristics of the transmitted signal. Impulses that are limited in the time domain are infinite in the frequency domain. On the other hand, bandlimited pulses are infinite in the time domain. Consequently, in order to avoid intersymbol interference (ISI) after sampling, the cascade of the transmit and receive filter g(t) = gT (t) ∗ gR(t) (13.4.1) needs to meet the first Nyquist condition, which was discussed in Section 6.5.1. TUTORIAL PROBLEM Problem 13.1 [Nyquist Condition (Zero-ISI Condition)] State the first Nyquist condition for zero ISI both for the impulse response g(t) and its Fourier transform G(f ). SOLUTION ∞� m=−∞ ⎧ ⎨1, g(nT) = ⎩0 n = 0 n ≠ 0 (13.4.2) � G f − m � = T = constant T (13.4.3) In the tutorial we use two types of pulses that meet the zero ISI condition: NRZ (nonreturn to zero) rectangular pulses and raised-cosine pulses (see Section 6.5.1). TUTORIAL PROBLEM Problem 13.2 [Eye Pattern] In Section 6.4 the eye pattern was introduced as a method to view the amount of ISI. Try to construct the eye diagram of a raised-cosine pulse with rolloff factor α = 0 for binary data. Take into account only the two neighboring interfering pulses. Which bit sequences have to be considered ? How does zero ISI show up in the eye diagram ? SOLUTION Raised-cosine pulse: g(t) = sin(πt/T ) πt/T · cos(απt/T ) 1 − 4α 2 (t/T ) 2 The following eight bit sequences have to be considered: +1 +1 +1 +1 +1 −1 +1 −1 +1 +1 −1 −1 −1 +1 +1 −1 +1 −1 −1 −1 +1 −1 −1 −1 © 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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582 CHAPTER 13. SIMULINK TUTORIAL ON DIGITAL MODULATION<br />
Figure 13.12: Matlab pathtool<br />
Figure 13.13: <str<strong>on</strong>g>Tutorial</str<strong>on</strong>g> main menu<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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