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Digital Communications
Volumes 1, 2, and 3
Courseware Sample
27695-F0
A
DIGITAL COMMUNICATIONS
VOLUMES 1, 2, AND 3
COURSEWARE SAMPLE
by
the Staff
of
Lab-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 permission
of Lab-Volt Ltd.
Printed in Canada
March 2009
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
III
IV
Introduction
The Lab-Volt Digital Communications Training System, Model 8085, is a complete,
operational, state of the art communications system. It incorporates the latest in IC
technology and most current types of signal demodulators enabling it to perform at
industry standards. At the same time, it has been designed from the ground up as
an educational system, so it includes all of the features required to effectively train
students.
The physical design of the digital communications modules emphasizes functionality
with block diagrams silk-screened on the module front panels. Major inputs and
outputs are readily accessible through BNC connectors on the front panels. Test
points 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 test
points and signal outputs are short-circuit protected.
The Digital System consists of 13 instructional modules supported by 10
instrumentation modules. These are used in conjunction with the Power Supply and
five instrument modules from the Analog Communications Training System,
Model 8080. The complete set-up non only forms a highly elaborate digital
communications system, but also allows students to make observations and
accurate measurements of important phenomena.
The equipment and courseware have been designed to reflect the standards
commonly used in digital communications today. Sampling rates, data rates, coding
methods, modem frequencies, compression laws, etc. are those used in real
systems.
The courseware for the Digital System consists of a 3-volume set of student manuals
which separate the subject matter into three main areas:
–
Volume one presents pulse modulation fundamentals centered around the study
of PAM / PWM / PPM signals.
–
Volume two presents pulse code modulation (PCM, DPCM, ∆M) and related
concepts such as compression laws and quantization noise.
–
Volume three presents modems and data transmission using ASK, FSK and
BPSK.
The Unit-Exercise structure of the digital courseware is similar to the one used in the
Analog Communications Training System. Each unit of instruction consists of several
exercises designed to present material in convenient instructional segments.
Principles and concepts are presented first an hands-on procedures complete the
learning process to involve and better acquaint the student with each module. At the
end of each exercise, there is a five-question review section requiring brief written
answers. Suggested answers for these questions, as well as those found in the
exercise procedures are included in the appendices of the manual. Each unit
terminates with a ten-question multiple choice test to verify the knowledge gained in
the unit.
V
VI
Courseware Outline
PULSE MODULATION AND SAMPLING
Unit 1
Pulses
Basic concepts associated with pulses as used in digital communications.
Techniques for measuring pulse characteristics and the signal-to-noise
ratio of a pulse signal.
Ex. 1-1 Time Characteristics of Pulses
Definition and measurement of basic pulse characteristics in the
time domain.
Ex. 1-2 Frequency Characteristics of Pulses
Pulse signal spectra. The relationship between frequency and
time characteristics.
Ex. 1-3 Band-Limiting
Comparison of ideal and practical band-limited systems. The
effect of band-limiting on the pulse spectrum using a low-pass
filter. 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 the
signal-to-noise ratio of a noisy pulse signal.
Unit 2
Pulse Amplitude Modulation (PAM)
The concepts associated with PAM signals. Time and frequency domain
observations. Aliasing.
Ex. 2-1 PAM Signals
Time domain observations of PAM signals. Sampling rate. Natural
and flat-top sampling.
Ex. 2-2 Spectral Characteristics of PAM Signals
Frequency domain observations of PAM signals. Comparison of
message signal, sampling signal, and PAM signal spectra. The
effect of natural and flat-top sampling on the PAM signal
spectrum.
Ex. 2-3 Aliasing and the Nyquist Rate
Time and frequency domain observations of aliasing in PAM
signals. The sampling theorem. The Nyquist rate.
VII
Courseware Outline
PULSE MODULATION AND SAMPLING
Ex. 2-4 Pre-filtering
The use of pre-alias filters to reduce aliasing. Practical
considerations in the choice of filter characteristics.
Unit 3
Demodulating PAM Signals
Demodulating PAM signals. The effects of aperture distortion, aliasing and
noise.
Ex. 3-1 PAM Signal Demodulation
Observation in the time and frequency domains of PAM signal
demodulation by low-pass filtering. Practical considerations of
filter characteristics. The effects of aperture distortion.
Ex. 3-2 Aliasing
The effects of aliasing on the recovered message signal. The
effects 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 signal
transmission and demodulation. Measurement of the
signal-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 PPM
signals.
Ex. 4-1 PWM and PPM Signals
The generation of PWM and PPM signals, and their
characteristics. Guard time and modulation constant. The spectra
of PWM and PPM signals.
Ex. 4-2 The Effects of Noise and Band-Limiting on Pulse-Time
Modulated Signals
The effects of noise and band-limiting on the timing accuracy of
PWM and PPM signals.
VIII
Courseware Outline
PULSE MODULATION AND SAMPLING
Unit 5
Demodulating PWM / PPM Signals
Receiving and demodulating PWM and PPM signals. The effects of noise
and band-limiting.
Ex. 5-1 PWM and PPM Signal Demodulation
The techniques used for receiving and demodulating PWM and
PPM signals. Observation of the signals at different stages in the
PWM / PPM Receiver. Timing recovery of PPM signals and PPM
offset error.
Ex. 5-2 The Effects of Noise and Band-Limiting on PWM / PPM Signal
Demodulation
Observation of signals at different stages of the PWM / PPM
Receiver. Measurement of the signal-to-noise ratio at the receiver
input and output. Plotting the improvement in the S/N ratio versus
transmission channel bandwidth.
Unit 6
Troubleshooting PAM / PWM / PPM Systems
A methodical approach to troubleshooting PAM / PWM / PPM
communications systems.
Ex. 6-1 Troubleshooting Techniques
Presentation and use of an effective technique for troubleshooting
the PAM / PWM / PPM communications modules. Application of
this technique for diagnosing instructor-inserted faults in the PAM
Generator.
Ex. 6-2 Troubleshooting the PAM Receiver
Diagnosing instructor-inserted faults in the PAM section of the
PAM ASK Receiver.
Ex. 6-3 Troubleshooting a PAM Communications System
Diagnosing instructor-inserted faults in a PAM communications
system.
Ex. 6-4 Troubleshooting the PWM / PPM Generator
Diagnosing instructor-inserted faults in the PWM / PPM
Generator.
Ex. 6-5 Troubleshooting the PWM / PPM Receiver
Diagnosing instructor-inserted faults in the PWM / PPM Receiver.
IX
Courseware Outline
PULSE MODULATION AND SAMPLING
Ex. 6-6 Troubleshooting a PWM / PPM Communications System
Diagnosing instructor-inserted faults in a PWM / PPM
communications system.
Appendices A The Spectrum of a Pulse Signal
B Timing Uncertainty and Signal-to-Noise Ratio Improvement in
PWM / PPM Systems
C Common Symbols
D Module Front Panels
E Test Points and Diagrams
F Answers to Procedure Step Questions
G Answers to Review Questions
H Bibliography
I Index of New Terms and Words
J Equipment Utilization Chart
X
Courseware Outline
DIGITAL MODULATION
Unit 1
Analog-to-Digital and Digital-to-Analog Conversion
An introduction to binary and hexadecimal numbers. Using the Logic
Analyzer. Basic concepts associated with analog-to-digital and
digital-to-analog conversion.
Ex. 1-1 Binary and Hexadecimal Numbers
Binary and hexadecimal representation of decimal numbers and
conversions between them. Use and knowledge of the operation
of the Logic Analyzer.
Ex. 1-2 Analog-to-Digital Conversion
Fundamentals and principles of A/D conversion. Introduction to
the 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 and
aperture distortion in PCM Systems. Observation and measurement of
quantization noise.
Ex. 2-1 Distortion in PCM Systems
The sampling theorem and aliasing distortion. Frequency domain
observation of aliasing and aperture distortion.
Ex. 2-2 Characteristics of Quantization Noise
Characteristics of quantization noise in the time and frequency
domains.
Ex. 2-3 Quantization Noise Measurement
Measuring quantization noise using the method of sine wave
injection and filtering. The effects of resolution and message
signal amplitude on the signal-to-quantization noise ratio.
XI
Courseware Outline
DIGITAL MODULATION
Unit 3
Pulse Code Modulation (PCM)
Transmitting with a PCM system. The effects of band-limiting and noise on
PCM 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 to
companding and the characteristics of the A- and p.-compression
laws. Observation of the effect of compression on the message
signal.
Ex. 3-2 Resistance of PCM to Noise and Distortion
The effects of bandwidth, channel noise, and jitter on PCM
signals. The eye diagram and its use in determining a qualitative
indication of the performance of a PCM system. Observation of
the quantization noise-to-channel noise ratio threshold in a PCM
system.
Ex. 3-3 Effect of µ-Law Companding on the Performance of a PCM
System
Measurement of the signal-to-quantization noise ratio at the
output of the PCM decoder using ti-law companding. Comparison
with results obtained with no companding.
Ex. 3-4 Effect of A-Law Companding on the Performance of a PCM
System
Measurement of the signal-to-quantization noise ratio at the
output of the PCM decoder using A-law companding. Comparison
with results obtained with no companding.
Unit 4
Differential Pulse Code Modulation (DPCM)
Introduction to the codes used in the DPCM system. The principles and
operation 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 the
signed binary codes. Observation of the operation of the DPCM
system.
Ex. 4-2 Dynamic Operation of a DPCM System
The DPCM difference signal. Transmitting information with a
DPCM system. Effects of the sampling frequency and of the
characteristics of the message signal on a DPCM system.
XII
Courseware Outline
DIGITAL MODULATION
Unit 5
Delta Modulation (DM)
The principles and operation of a Linear Delta Modulation (LDM) system
and 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 noise
in an LDM system.
Ex. 5-2 An Adaptive Delta Modulation (ADM) System
Slope overload distortion in LDM. Observation of the operation of
the CVSD system.
Ex. 5-3 Signal-to-Noise Ratio in Delta Modulation
Measuring the signal-to-noise ratio at the output of both an LDM
system and an ADM system.
Unit 6
Troubleshooting Digital Communications Systems
A methodical approach to troubleshooting PCM /DPCM / DM
communications systems.
Ex. 6-1 Troubleshooting a PCM Communications Systems
Presentation and use of an effective technique for troubleshooting
digital communications systems. Application of this technique for
diagnosing instructor-inserted faults in the PCM communications
system.
Ex. 6-2 Troubleshooting a DPCM Communications Systems
Diagnosing instructor-inserted faults in a DPCM communications
system.
Ex. 6-3 Troubleshooting a DM Communications Systems
Diagnosing instructor-inserted faults in a DM communications
system.
Appendices A
B
C
D
E
F
G
H
Common Symbols
Module Front Panels
Test Points, Test Busses, and Diagrams
Answers to Procedure Step Questions
Answers to Review Questions
Bibliography
Index of New Terms and Words
Equipment Utilization Chart
XIII
Courseware Outline
MODEMS AND DATA TRANSMISSION
Unit 1
Baseband Data Transmission
The characteristics and use of pseudo-random binary sequences. The
effect of noise on the detection of a pseudo-random sequence. Measuring
the bit error rate (BER).
Ex. 1-1 Pseudo-Random Binary Sequences
The characteristics of pseudo-random binary sequences
observed in both the time- and frequency-domains. Generation of
pseudo-random sequences.
Ex. 1-2 Detection of NRZ Signals in Noise
How errors occur when detecting NRZ signals in the presence of
noise. The error probability function of NRZ signals. Measurement
of 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. Measurement
of ASK modem performance in the presence of noise. Bandwith
requirements of ASK signals.
Ex. 2-1 Generation and Reception of ASK Signals
Generation and demodulation of ASK signals. Time- and
frequency-domain observations.
Ex. 2-2 ASK Performance in Noise
How errors occur when demodulating ASK signals in the
presence of noise. The error probability function of ASK signals.
Measurement of the error rate for ASK signals in the presence of
noise. Plotting the error rate versus the signal-to-noise ratio.
Unit 3
Frequency-Shift Keying (FSK)
Time- and frequency-domain characteristics of FSK signals. Measurement
of FSK modem performance in the presence of noise. Comparison with
ASK signal performance.
Ex. 3-1 FSK Principles
FSK modulation and demodulation. Time- and frequency-domain
characteristics of FSK.
XIV
Courseware Outline
MODEMS AND DATA TRANSMISSION
Ex. 3-2 FSK Performance in Noise
How errors occur when demodulating FSK signals in the
presence of noise. The error probability function of FSK signals.
Measurement of the error rate for FSK signals in the presence of
noise. 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 currently
used FSK standards. Concepts behind full-duplex and half-duplex
transmission. 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 103
modems. 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 modem
Half-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-duplex
transmission. 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 BPSK
signals using a Costas Loop. Phase ambiguity associated with the
demodulation of BPSK signals. Time- and frequency-domain
observations of BPSK signals.
XV
Courseware Outline
MODEMS AND DATA TRANSMISSION
Ex. 5-2 BPSK Performance in Noise
How errors occur when demodulating BPSK signals in the
presence of noise. The error probability function of BPSK signals.
Measurements of the error rate for BPSK signals in the presence
of 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 BPSK
communications systems.
Ex. 6-1 Troubleshooting an ASK Communications System
Presentation and use of an effective technique for troubleshooting
data transmission systems. Application of this technique to
diagnosing instructor-inserted faults in the ASK communications
system.
Ex. 6-2 Troubleshooting an FSK Modem
A technique that reduces the number of test signals needed to
troubleshoot FSK modems. Diagnosing instructor-inserted faults
in 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 communications
system.
Appendices A
B
C
D
E
F
G
H
XVI
Common Symbols
Module Front Panels
Test Points and Diagrams
Answers to Procedure Step Questions
Answers to Review Questions
Bibliography
Index of New Terms and Words
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