LabVIEW Digital Signal Processing This page intentionally left blank. LabVIEW Digital Signal Processing and Digital Communications Cory L. Clark Motorola McGraw-Hill New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Manufactured in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. 0-07-146966-4 The material in this eBook also appears in the print version of this title: 0-07-144492-0. All trademarks are trademarks of their respective owners. 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If you’d like more information about this book, its author, or related books and websites, please click here. To Z, who always shows me what’s important; to my parents, who started me out right; and to my sister Holly, who taught me to read This page intentionally left blank. For more information about this title, click here Contents Preface xi Part 1. Getting Started Chapter 1. Digital Communications and LabVIEW 3 1.1 Conventional Digital Receiver 5 1.2 Subsampling Receiver 6 Summary 11 References 12 Chapter 2. Getting a Signal into LabVIEW 13 2.1 Conventional Digital Receiver 13 2.2 Subsampling Digital Receiver 19 2.2.1 Choosing a sample rate 21 2.2.2 Subsampling SNR 23 2.2.3 Subsampling signal placement 29 2.3 Other Sampling Methods 30 2.3.1 Digital oscilloscope 30 2.3.2 RF spectrum analyzer 31 2.3.3 Analog sampling card 31 2.3.4 Soundcard 35 Summary 35 References 36 Part 2. Building Blocks Chapter3. Spectral Analysis 39 3.1 Low-Level Frequency Domain Functions 39 3.1.1 Simple FFT 41 3.1.2 Improved FFT 43 3.2 Analyzing the DFT Results 44 3.2.1 Spectral leakage 46 3.2.2 Sampling window shape 46 3.3 High-Level Spectral Functions 50 vii viii Contents 3.4 Adding C Routines to LabVIEW 53 3.5 Spectral Measurements Toolset 56 Summary 59 References 59 Chapter4. Digital Filters 61 4.1 Filter Types 61 4.2 FIR Filters 63 4.2.1 FIR filter design by windowing 63 4.2.2 Equiripple FIR filters 69 4.3 IIR Filters 73 4.4 Comparing IIR and FIR Filters 74 4.4.1 IIR versus FIR magnitude 76 4.4.2 Effects of filter-phase response 76 4.5 Pulse-Shaping Filter 78 Summary 82 References 82 Chapter 5. Multirate Signal Processing in LabVIEW 83 5.1 Upsampling 83 5.2 Downsampling 85 5.3 Resampling Filters 85 5.3.1 Halfband filters 88 5.3.2 Polyphase filters 90 Summary 93 References 93 Chapter 6. Generating Signals with LabVIEW 95 6.1 Basic Functions 95 6.2 Sinusoids 97 6.2.1 Complex mixer 98 6.2.2 Sinc function 101 6.2.3 Chirp sequence 103 6.3 Generating Channel Models 103 6.3.1 Rayleigh fading 103 6.3.2 White gaussian noise 107 6.4 Generating Symbols 107 Summary 112 References 112 Part 3. Building a Communication System Chapter 7. Assembling the Pieces 115 7.1 Modulator 115 7.2 Demodulator 118 7.3 Channel Impairments 122 7.4 Signal Detection and Recovery 127 7.4.1 Matched filter detection 129 7.4.2 Threshold decisions 129