PSpice for Digital Communications Engineering

1 15, 200721:30 PSpice for DigitalCommunications 15, 200721:30 Copyright 2007 by Morgan & ClaypoolAll rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted inany form or by any means electronic, mechanical, photocopy, recording, or any other except for brief quotationsin printed reviews, without the prior permission of the for Digital Communications EngineeringPaul : 1598291629paperbackISBN: 9781598291629 paperbackISBN: 1598291637ebookISBN: 9781598291636 ebookDOI Publication in the Morgan & Claypool Publishers seriesSYNTHESIS LECTURES ON Digital CIRCUITS AND SYSTEMS #10 Lecture #10 Series Editor: Mitchell A. Thornton, Southern Methodist UniversityLibrary of Congress Cataloging-in-Publication DataSeries ISSN: 1932-3166 printSeries ISSN: 1932-3174 electronicFirst 15, 200721:30 PSpice for DigitalCommunications EngineeringPaul TobinSchool of Electronic and Communications EngineeringDublin Institute of TechnologyIrelandSYNTHESIS LECTURES ON Digital CIRCUITS AND SYSTEMS #10M&CMorgan&Claypool 15, 200721:30ivABSTRACTPS pice for Digital Communications Engineering shows how to simulate Digital communicationsystems and modulation methods using the very powerful Cadence Orcad PSpice version of software programs.

2 Fourier series and Fourier transform are applied to signals to setthe ground work for the modulation techniques introduced in later chapters. Various basebandsignals, including duo-binary baseband signaling, are generated and the spectra are examinedto detail the unsuitability of these signals for accessing the public switched network. Pulsecode modulation and time-division multiplexing circuits are examined and simulated wheresampling and quantization noise topics are discussed. We construct a single-channel PCMsystem from transmission to receiver end-to-end, and import real speech signals to examinethe problems associated with aliasing, sample and is addressed here and we look at the A and mu law characteristics forachieving better signal to quantization noise ratios. Several types of delta modulators areexamined and also the concept of time division multiplexing is considered. Multi-level signalingtechniques such as QPSK and QAM are analyzed and simulated and home-made meters , suchas scatter and eye meters, are used to assess the performance of these modulation systems inthe presence of noise.

3 The raised-cosine family of filters for shaping data before transmissionis examined in depth where bandwidth efficiency and channel capacity is discussed. We plotseveral graphs in Probe to compare the efficiency of these systems. Direct spread spectrum isthe last topic to be examined and simulated to show the advantages of spreading the signal overa wide bandwidth and giving good signal security at the same series and Fourier transforms, baseband and passband modulation, pulse code mod-ulation, time-division multiplexing, quantization noise, M-ary signaling, QPSK, QAM, eye-meter, scatter diagrams, spread spectrum, raised cosine 15, 200721:30I would like to dedicate this book to my wife and friend,Marie and sons Lee, Roy, Scott and Keith and myparents (Eddie and Roseanne), sisters, Sylvia,Madeleine, Jean, and brother, 15, 200721 15, 200721 ,Signals, .. to Zero (NRZ) Coding .. (Biphase)Decoding .. Manchester 15, 200721:30viiiPSPICE FOR Digital Communications Pulse Code Modulation.

4 And Key Antialiasing Active Filter .. Code Modulation .. Universal Shift 4-Bit PCM Transmitter .. (DPSK).. Signaling and Bandwidth Efficiency .. Capacity .. Error Rate .. 15, 200721:30 PSpice FOR Digital Communications Quadrature Phase Shift Keying .. Amplitude Modulation .. Performance and Test Instruments .. 16-QAM Scatter , Noise, and Matched Filters .. 15, 200721:30xPSPICE FOR Digital Communications Error Rate (BER).. Channel Channel Capacity for DifferentM-aryLevels .. BER Performance for a Range of .. Generator .. Generator Part .. :References .. 189 AppendixB:Tables .. 15, 200721:30xiPrefaceBefore each simulation session, it is necessary to create a project file as shown in Figure 1. Selectthe small folded white sheet icon at the top left hand corner of the 1:Creating new project a suitable name in theNamebox and selectAnalog or Mixed A/Dand specify aLocationfor the file.

5 PressOKand a further menu will appear so tickCreate a blank projectas shown in Figure produces an empty schematic area calledPage 1where component are have to be added, (Add library) by selecting the little AND symbol in the righttoolbar icons. The easiest method is to select all the libraries. However, if you selectCreatebased upon an existing project, then all previously used libraries associated with that projectwill be loaded. Chapter 1 uses the Fourier series expansion and Fourier transform to showthe relationship between pulse width and pulse period by examining the spectra for differentpulse signals. In chapter 2 we generate baseband signals and again examine the spectra forthese signals. Chapter 3 examines another baseband modulation technique the importanttopic called pulse code modulation (PCM). In this chapter we examine sampling, 15, 200721:30xiiPSPICE FOR Digital Communications ENGINEERINGFIGURE 2:Create a blank 3:QPSK modulator hierarchical , quantization noise and sample and hold.

6 Also investigated in this chapter is time divisionmultiplexing and we construct a single channel PCM system from transmission to receiver Passband systems are considered in chapter 4 where systems such as frequencyshift keying (FSK), amplitude shift keying (ASK) and phase shift keying (PSK) and differentialforms are considered. Chapter 5 considers multi-level systems (M-ary) such as quadrature phaseshift keying (QPSK) and quadrature amplitude modulation (QAM). The hierarchical methodof construction is used in these systems because of the system complexity. Figure 3 shows aQPSK modulator system broken into manageable blocks. The main schematic is named Figure5-005 and the sub-circuits in different pages are named Figure 5-005a to Figure 6 looks at systems performance where we introduce home-made PSpice metersfor producing eye and scatter diagrams to assess the performance of the modulation techniquesin the presence of noise deliberately introduced.

7 The raised-cosine filter family, the integrate-and-dump filters, and zero forcing equalizers are also investigated in this chapter. The powerof the macro is introduced to plot statistical probability curves and a bit error rate (BER) 15, 200721:30 PREFACE xiiiis investigated. Chapter 7 looks at spread spectrum transmission methods showing how thistechnique excels in detecting and recovering wanted signals buried in would like to acknowledge certain people who helped me directly and indirectly in producingthis book. Many years ago two gentlemen, Tim O Brien and Paddy Murray introduced me tothe world of Communications Engineering . Much earlier than this though, when I was not quitea teenager, my dad Eddie Tobin (Wizard of the G-banjo), showed me how to build a crystalset and probably this, more than anything else, left me with a passion for this subject whichcontinues to this day. I would like to thank Dr Gerald Farrell, Head of School of Electronicsand Communications Engineering DIT, for his help and encouragement.

8 Last, but not least,I would like to thank Joel Claypool of Morgan and Claypool publishing for taking on my 15, 200721:30bookMobk066 March 15, 200721:181 CHAPTER 1 Fourier Analysis, Signals, SIGNALSData signals on a limited-bandwidth Communications channel are distorted, attenuated, phaseshifted, and the ever-present noise added at different stages in the transmission path. Thereare two basic communication channels: free space, where passband techniques transport thedata in an unguided fashion (microwave point-to-point systems are not really in this category),and guided transmission systems such as cables, optical fibers, coax, etc. For example, signalsreceived from an unguided free-space channel are a composite signal comprising signals reflectedfrom buildings, structures, , reflected multipath signals. We should be thankful for thisphenomenon because without it we might not receive signals on our mobile phones wherebuildings, walls, etc.

9 Would block line-of-sight to the , multipath signals also cause signal distortion and have to be removed in thereceiver. The channel also distorts the transmitted signal with energy from each transmittedpulse leaking into the next transmitted pulse making it difficult for correct pulse identificationin the receiver. This is a phenomenon called intersymbol interference (ISI) and the receivercannot make correct decisions whether a pulse is present or not. One technique for reducingISI and producing a maximum transmission symbol rate is to shape, or predistort, pulses beforetransmission. This removes high frequencies from the signal prior to transmission. Fig. the elements of a Digital transmission encoded data from the modulator is prefiltered before transmission using a root-raised cosine (RCC) filter and attempts to mimic the ideal brick-wall Nyquist filter. At theFIGURE :Transmission 15, 200721:182 PSpice FOR Digital Communications Engineering receiver is another RCC filter so that the overall path response has a raised cosine filterresponse.

10 These filters are implemented using Digital signal processors that can implementhigh-order cosine filters that approach the ideal filter response (8). However, transmissionpath characteristics are generally unknown and vary with time, so adaptive equalizers in thereceiver track these changes and subsequently change the filter characteristics as needed. Theequalizer flattens the channel response thus ensuring that the RCC filter works efficiently. Afterequalization, the received signal is root-raised cosine filtered and the demodulator can then makedecisions to determine if a pulse is present or not. It does this by sampling the received signalat the center of a pulse and uses logic circuits to ascertain the presence or absence of a analog Communications system, bandwidth is defined as the range of frequencies over which asignal may be transmitted and received with reasonable fidelity, or minimum errors, if the signalis Digital .