Digital CommunicationsVolumes 1, 2, and 3

Courseware Sample

27695-F0

A

DIGITAL COMMUNICATIONSVOLUMES 1, 2, AND 3

COURSEWARE SAMPLE

bythe Staff

ofLab-Volt Ltd.

Copyright 2009 Lab-Volt Ltd.

All rights reserved. No part of this publication may be reproduced,in any form or by any means, without the prior written permissionof Lab-Volt Ltd.

Printed in CanadaMarch 2009

III

Table of ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V

Courseware Outline

Pulse Modulation and Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII

Digital Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XI

Modems and Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XIV

Sample Exercise Extracted from Pulse Modulation and Sampling

Exercise 2-1 PAM Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Sample Exercise Extracted from Digital Modulation

Exercise 2-2 Characteristics of Quantization Noise . . . . . . . . . . . . . . 2-23

Sample Exercise Extracted from Modems and Data Transmission

Exercise 5-1 Generation and Demodulation of BPSK Signals . . . . . . . 5-3

Other sample extracted from Digital Modulation

Unit Test 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-59

Instructor Guide Sample Units Extracted from Digital Communications,Volumes 1, 2, and 3

Unit 2 Pulse Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Unit 3 Demodulation PAM Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

IV

VIntroduction

The Lab-Volt Digital Communications Training System, Model 8085, is a complete,operational, state of the art communications system. It incorporates the latest in ICtechnology and most current types of signal demodulators enabling it to perform atindustry standards. At the same time, it has been designed from the ground up asan educational system, so it includes all of the features required to effectively trainstudents.

The physical design of the digital communications modules emphasizes functionalitywith block diagrams silk-screened on the module front panels. Major inputs andoutputs are readily accessible through BNC connectors on the front panels. Testpoints form the instructional modules are also brought out to front panel connectors,and the front panel screening shows their location on the block diagram. All testpoints and signal outputs are short-circuit protected.

The Digital System consists of 13 instructional modules supported by 10instrumentation modules. These are used in conjunction with the Power Supply andfive instrument modules from the Analog Communications Training System,Model 8080. The complete set-up non only forms a highly elaborate digitalcommunications system, but also allows students to make observations andaccurate measurements of important phenomena.

The equipment and courseware have been designed to reflect the standardscommonly used in digital communications today. Sampling rates, data rates, codingmethods, modem frequencies, compression laws, etc. are those used in realsystems.

The courseware for the Digital System consists of a 3-volume set of student manualswhich separate the subject matter into three main areas:

Volume one presents pulse modulation fundamentals centered around the studyof PAM / PWM / PPM signals.

Volume two presents pulse code modulation (PCM, DPCM, M) and relatedconcepts such as compression laws and quantization noise.

Volume three presents modems and data transmission using ASK, FSK andBPSK.

The Unit-Exercise structure of the digital courseware is similar to the one used in theAnalog Communications Training System. Each unit of instruction consists of severalexercises designed to present material in convenient instructional segments.Principles and concepts are presented first an hands-on procedures complete thelearning process to involve and better acquaint the student with each module. At theend of each exercise, there is a five-question review section requiring brief writtenanswers. Suggested answers for these questions, as well as those found in theexercise procedures are included in the appendices of the manual. Each unitterminates with a ten-question multiple choice test to verify the knowledge gained inthe unit.

VI

PULSE MODULATION AND SAMPLING

Courseware Outline

VII

Unit 1 Pulses

Basic concepts associated with pulses as used in digital communications.Techniques for measuring pulse characteristics and the signal-to-noiseratio of a pulse signal.

Ex. 1-1 Time Characteristics of Pulses

Definition and measurement of basic pulse characteristics in thetime domain.

Ex. 1-2 Frequency Characteristics of Pulses

Pulse signal spectra. The relationship between frequency andtime characteristics.

Ex. 1-3 Band-Limiting

Comparison of ideal and practical band-limited systems. Theeffect of band-limiting on the pulse spectrum using a low-passfilter. The relationship between bandwidth and pulse rise time.

Ex. 1-4 Noise and Signal Power Measurement

The relationship between noise power and noise bandwidth.Pulse signal power measurement. Measurement of thesignal-to-noise ratio of a noisy pulse signal.

Unit 2 Pulse Amplitude Modulation (PAM)

The concepts associated with PAM signals. Time and frequency domainobservations. Aliasing.

Ex. 2-1 PAM Signals

Time domain observations of PAM signals. Sampling rate. Naturaland flat-top sampling.

Ex. 2-2 Spectral Characteristics of PAM Signals

Frequency domain observations of PAM signals. Comparison ofmessage signal, sampling signal, and PAM signal spectra. Theeffect of natural and flat-top sampling on the PAM signalspectrum.

Ex. 2-3 Aliasing and the Nyquist Rate

Time and frequency domain observations of aliasing in PAMsignals. The sampling theorem. The Nyquist rate.

PULSE MODULATION AND SAMPLING

Courseware Outline

VIII

Ex. 2-4 Pre-filtering

The use of pre-alias filters to reduce aliasing. Practicalconsiderations in the choice of filter characteristics.

Unit 3 Demodulating PAM Signals

Demodulating PAM signals. The effects of aperture distortion, aliasing andnoise.

Ex. 3-1 PAM Signal Demodulation

Observation in the time and frequency domains of PAM signaldemodulation by low-pass filtering. Practical considerations offilter characteristics. The effects of aperture distortion.

Ex. 3-2 Aliasing

The effects of aliasing on the recovered message signal. Theeffects of pre-filtering to reduce distortion due to aliasing.

Ex. 3-3 PAM Signal Transmission in the Presence of Noise

The effect of transmission channel noise on PAM signaltransmission and demodulation. Measurement of thesignal-to-noise ratio at the receiver output.

Unit 4 Pulse-Time Modulation (PWM / PPM)

The concepts associated with Pulse Width / Pulse Position Modulation(PWM / PPM). The effects of noise and band-limiting on PWM and PPMsignals.

Ex. 4-1 PWM and PPM Signals

The generation of PWM and PPM signals, and theircharacteristics. Guard time and modulation constant. The spectraof PWM and PPM signals.

Ex. 4-2 The Effects of Noise and Band-Limiting on Pulse-TimeModulated Signals

The effects of noise and band-limiting on the timing accuracy ofPWM and PPM signals.

PULSE MODULATION AND SAMPLING

Courseware Outline

IX

Unit 5 Demodulating PWM / PPM Signals

Receiving and demodulating PWM and PPM signals. The effects of noiseand band-limiting.

Ex. 5-1 PWM and PPM Signal Demodulation

The techniques used for receiving and demodulating PWM andPPM signals. Observation of the signals at different stages in thePWM / PPM Receiver. Timing recovery of PPM signals and PPMoffset error.

Ex. 5-2 The Effects of Noise and Band-Limiting on PWM / PPM SignalDemodulation

Observation of signals at different stages of the PWM / PPMReceiver. Measurement of the signal-to-noise ratio at the receiverinput and output. Plotting the improvement in the S/N ratio versustransmission channel bandwidth.

Unit 6 Troubleshooting PAM / PWM / PPM Systems

A methodical approach to troubleshooting PAM / PWM / PPMcommunications systems.

Ex. 6-1 Troubleshooting Techniques

Presentation and use of an effective technique for troubleshootingthe PAM / PWM / PPM communications modules. Application ofthis technique for diagnosing instructor-inserted faults in the PAMGenerator.

Ex. 6-2 Troubleshooting the PAM Receiver

Diagnosing instructor-inserted faults in the PAM section of thePAM ASK Receiver.

Ex. 6-3 Troubleshooting a PAM Communications System

Diagnosing instructor-inserted faults in a PAM communicationssystem.

Ex. 6-4 Troubleshooting the PWM / PPM Generator

Diagnosing instructor-inserted faults in the PWM / PPMGenerator.

Ex. 6-5 Troubleshooting the PWM / PPM Receiver

Diagnosing instructor-inserted faults in the PWM / PPM Receiver.

PULSE MODULATION AND SAMPLING

Courseware Outline

X

Ex. 6-6 Troubleshooting a PWM / PPM Communications System

Diagnosing instructor-inserted faults in a PWM / PPMcommunications system.

Appendices A The Spectrum of a Pulse SignalB Timing Uncertainty and Signal-to-Noise Ratio Improvement in

PWM / PPM SystemsC Common SymbolsD Module Front PanelsE Test Points and DiagramsF Answers to Procedure Step QuestionsG Answers to Review QuestionsH BibliographyI Index of New Terms and WordsJ Equipment Utilization Chart

DIGITAL MODULATION

Courseware Outline

XI

Unit 1 Analog-to-Digital and Digital-to-Analog Conversion

An introduction to binary and hexadecimal numbers. Using the LogicAnalyzer. Basic concepts associated with analog-to-digital anddigital-to-analog conversion.

Ex. 1-1 Binary and Hexadecimal Numbers

Binary and hexadecimal representation of decimal numbers andconversions between them. Use and knowledge of the operationof the Logic Analyzer.

Ex. 1-2 Analog-to-Digital Conversion

Fundamentals and principles of A/D conversion. Introduction tothe Binary Offset Code.

Ex. 1-3 Digital-to-Analog Conversion

Fundamentals and principles of A/D conversion.

Unit 2 Distortion and Quantization Noise

The sampling theorem in PCM. Frequency characteristics of aliasing andaperture distortion in PCM Systems. Observation and measurement ofquantization noise.

Ex. 2-1 Distortion in PCM Systems

The sampling theorem and aliasing distortion. Frequency domainobservation of aliasing and aperture distortion.

Ex. 2-2 Characteristics of Quantization Noise

Characteristics of quantization noise in the time and frequencydomains.

Ex. 2-3 Quantization Noise Measurement

Measuring quantization noise using the method of sine waveinjection and filtering. The effects of resolution and messagesignal amplitude on the signal-to-quantization noise ratio.

DIGITAL MODULATION

Courseware Outline

XII

Unit 3 Pulse Code Modulation (PCM)

Transmitting with a PCM system. The effects of band-limiting and noise onPCM signals. A-law and ti-law companding.

Ex. 3-1 Information Transmission with a PCM System

Parallel-to-serial and serial-to-parallel converters. Introduction tocompanding and the characteristics of the A- and p.-compressionlaws. Observation of the effect of compression on the messagesignal.

Ex. 3-2 Resistance of PCM to Noise and Distortion

The effects of bandwidth, channel noise, and jitter on PCMsignals. The eye diagram and its use in determining a qualitativeindication of the performance of a PCM system. Observation ofthe quantization noise-to-channel noise ratio threshold in a PCMsystem.

Ex. 3-3 Effect of -Law Companding on the Performance of a PCMSystem

Measurement of the signal-to-quantization noise ratio at theoutput of the PCM decoder using ti-law companding. Comparisonwith results obtained with no companding.

Ex. 3-4 Effect of A-Law Companding on the Performance of a PCMSystem

Measurement of the signal-to-quantization noise ratio at theoutput of the PCM decoder using A-law companding. Comparisonwith results obtained with no companding.

Unit 4 Differential Pulse Code Modulation (DPCM)

Introduction to the codes used in the DPCM system. The principles andoperation of a DPCM system. Performance of a DPCM system.

Ex. 4-1 Principles of a DPCM System

Introduction to the two's complement (2's complement) and thesigned binary codes. Observation of the operation of the DPCMsystem.

Ex. 4-2 Dynamic Operation of a DPCM System

The DPCM difference signal. Transmitting information with aDPCM system. Effects of the sampling frequency and of thecharacteristics of the message signal on a DPCM system.

DIGITAL MODULATION

Courseware Outline

XIII

Unit 5 Delta Modulation (DM)

The principles and operation of a Linear Delta Modulation (LDM) systemand of an Adaptive Delta Modulation (ADM) system.

Ex. 5-1 A Linear Delta Modulation (LDM) System

The principles and operation of an LDM system. Granular noisein an LDM system.

Ex. 5-2 An Adaptive Delta Modulation (ADM) System

Slope overload distortion in LDM. Observation of the operation ofthe CVSD system.

Ex. 5-3 Signal-to-Noise Ratio in Delta Modulation

Measuring the signal-to-noise ratio at the output of both an LDMsystem and an ADM system.

Unit 6 Troubleshooting Digital Communications Systems

A methodical approach to troubleshooting PCM /DPCM / DMcommunications systems.

Ex. 6-1 Troubleshooting a PCM Communications Systems

Presentation and use of an effective technique for troubleshootingdigital communications systems. Application of this technique fordiagnosing instructor-inserted faults in the PCM communicationssystem.

Ex. 6-2 Troubleshooting a DPCM Communications Systems

Diagnosing instructor-inserted faults in a DPCM communicationssystem.

Ex. 6-3 Troubleshooting a DM Communications Systems

Diagnosing instructor-inserted faults in a DM communicationssystem.

Appendices A Common SymbolsB Module Front PanelsC Test Points, Test Busses, and DiagramsD Answers to Procedure Step QuestionsE Answers to Review QuestionsF BibliographyG Index of New Terms and WordsH Equipment Utilization Chart

MODEMS AND DATA TRANSMISSION

Courseware Outline

XIV

Unit 1 Baseband Data Transmission

The characteristics and use of pseudo-random binary sequences. Theeffect of noise on the detection of a pseudo-random sequence. Measuringthe bit error rate (BER).

Ex. 1-1 Pseudo-Random Binary Sequences

The characteristics of pseudo-random binary sequencesobserved in both the time- and frequency-domains. Generation ofpseudo-random sequences.

Ex. 1-2 Detection of NRZ Signals in Noise

How errors occur when detecting NRZ signals in the presence ofnoise. The error probability function of NRZ signals. Measurementof the error rate for unipolar NRZ signals in the presence of noise.Plotting the error rate versus the signal-to-noise ratio.

Unit 2 Amplitude-Shift Keying (ASK)

Time- and frequency-domain characteristics of ASK signals. Measurementof ASK modem performance in the presence of noise. Bandwithrequirements of ASK signals.

Ex. 2-1 Generation and Reception of ASK Signals

Generation and demodulation of ASK signals. Time- andfrequency-domain observations.

Ex. 2-2 ASK Performance in Noise

How errors occur when demodulating ASK signals in thepresence of noise. The error probability function of ASK signals.Measurement of the error rate for ASK signals in the presence ofnoise. Plotting the error rate versus the signal-to-noise ratio.

Unit 3 Frequency-Shift Keying (FSK)

Time- and frequency-domain characteristics of FSK signals. Measurementof FSK modem performance in the presence of noise. Comparison withASK signal performance.

Ex. 3-1 FSK Principles

FSK modulation and demodulation. Time- and frequency-domaincharacteristics of FSK.

MODEMS AND DATA TRANSMISSION

Courseware Outline

XV

Ex. 3-2 FSK Performance in Noise

How errors occur when demodulating FSK signals in thepresence of noise. The error probability function of FSK signals.Measurement of the error rate for FSK signals in the presence ofnoise. Plotting the error rate versus the signal-to-noise ratio.Comparison with ASK signal performance.

Unit 4 FSK Communications Standards

An overview of the characteristics and particularities of the most currentlyused FSK standards. Concepts behind full-duplex and half-duplextransmission. Operation and use of FSK modems.

Ex. 4-1 CCITT V.21 and Bell 103 Modems (300 baud)

Signalling frequencies used by the CCITT V.21 and the Bell 103modems. Full-duplex transmission. Originate and answer modes.Modem control signals.

Ex. 4-2 CCITT V.23 Mode 2 Modem (1200 baud)

Signalling frequencies used by the CCITT V.23 Mode 2 modemHalf-duplex transmission. Use and operation of the back channel.Back-channel control signals. Frequency-domain observations.

Ex. 4-3 Bell 202 Modem (1200 baud)

Signalling frequencies used by the Bell 202 modem. Half-duplextransmission. Use and operation of the back channel.Back-channel control signals. Frequency-domain observations.

Unit 5 Binary Phase-Shift Keying (BPSK)

Time- and frequency-domain characteristics of BPSK signals.Measurement of BPSK modem performance in the presence of noise.Comparison with ASK and FSK signal performance.

Ex. 5-1 Generation and Demodulation of BPSK Signals

BPSK modulation. Carrier recovery and demodulation of BPSKsignals using a Costas Loop. Phase ambiguity associated with thedemodulation of BPSK signals. Time- and frequency-domainobservations of BPSK signals.

MODEMS AND DATA TRANSMISSION

Courseware Outline

XVI

Ex. 5-2 BPSK Performance in Noise

How errors occur when demodulating BPSK signals in thepresence of noise. The error probability function of BPSK signals.Measurements of the error rate for BPSK signals in the presenceof noise. Plotting the error rate versus the signal-to-noise ratio.Comparison with ASK and FSK signal performance.

Unit 6 Troubleshooting Digital Communications Systems

A methodical approach to troubleshooting ASK, FSK, and BPSKcommunications systems.

Ex. 6-1 Troubleshooting an ASK Communications System

Presentation and use of an effective technique for troubleshootingdata transmission systems. Application of this technique todiagnosing instructor-inserted faults in the ASK communicationssystem.

Ex. 6-2 Troubleshooting an FSK Modem

A technique that reduces the number of test signals needed totroubleshoot FSK modems. Diagnosing instructor-inserted faultsin an FSK modem.

Ex. 6-3 Troubleshooting a BPSK Communication System

A technique for troubleshooting systems with feedback loops.Diagnosing instructor-inserted faults in a BPSK communicationssystem.

Appendices A Common SymbolsB Module Front PanelsC Test Points and DiagramsD Answers to Procedure Step QuestionsE Answers to Review QuestionsF BibliographyG Index of New Terms and WordsH Equipment Utilization Chart

Sample Exercise

Extracted from

Pulse Modulation and Sampling

Sample Exercise

Extracted from

Digital Modulation

.

Sample Exercise

Extracted from

Modems and Data Transmission

.

Other Sample

Extracted from

Digital Modulation

Instructor Guide

Sample Units

Extracted from

Digital Communications,

Volumes 1, 2, and 3