Lecture-01 analog and digital communication.pptx

Radio Wave Propagation: Surface and space wave propagation, Sky wave through
Ionosphere. Pulse method for measuring height and electron concentration of
Ionospheric region; Chapman theory of layer formation, Ionospheric storm.
Modulation and Demodulation: Linear modulation - AM, SSB, DSB, and SSB
generation, PLL Circuit to generate linear modulated signals, low and high power
modulators, Exponential modulation- FM and PM, demodulation of AM, FM.
Broadcasting Transmitter: Transmitter classification, Elements of transmitter, AM and
FM transmitters, SSB transmitter, stabilized master oscillator, Frequency multipliers,
Mixer circuits, RF power amplifier, Pre-emphasis circuits, Transmitter performance-
carrier frequency requirements, audio frequency response, distortion, and signal to
distortion ratio.
Radio Receiver: Receiver classification, Elements of receiver, AM and FM receivers,
SSB receiver, Comparison of AM and FM receivers, Noise in receiver, AGC circuits, AFC
circuits, Noise limiters, Receiver sensitivity, Cross modulation, Spurious responses.
Representation of Random Signals and Noise in Communication System: Signal
Power and Spectral Representations, White noise, Thermal noise, PSDF of White
Signals. Input and Output Relationship for Random Signals and Noise Passed Through
a Linear Time Invariant System, Band Limited White Noise, ARC Filtering of White
Noise.
Course Contents

Elements of Digital Communication Systems: Elements of Digital Communication
Systems: Model of Digital Communication Systems, Digital Representation of Analog
Signal, Certain issues in Digital Transmission, Advantages of Digital Communication
Systems, Bandwidth-S/N tradeoff, Hartley Shannon Law.
Pulse Code Modulation: Pulse Code Modulation: PCM Generation and
Reconstruction, Quantization noise, Non uniform Quantization and Companding,
DPCM, Adaptive DPCM, DM and Adaptive DM. Noise in PCM and DM.
Digital Modulation Techniques: Digital Modulation Techniques: Introduction, ASK,
ASK Modulator, Coherent ASK Detector, Non-Coherent ASK Detector, FSK, Bandwidth
and Frequency Spectrum of FSK. Non coherent FSK Detector, Coherent FSK Detector,
FSK Detection Using PLL, BPSK, Coherent PSK Detection, QPSK, Differential PSK.
Line Coding: Techniques and Analysis.
Course Contents
Required Text Books:
B.P.Lathi, "Modern Digital & Analog Communication", Prison Books Pvt Ltd., 1989
Sanjay Sharma, "Communication Systems, Analog & Digital
Reference Books:
Simon Haykin, "Communication System", John Wiley & Sons, 4th Edition, 1991
K.Sam Shanmugam, "Digital & Analog Communication System", John Wiley & Sons

Course Objectives
To introduce with basic communication systems.
Various Amplitude modulation and demodulation systems
Various Angle modulation and demodulation systems
Basics of Noise theory and performance of various
receivers.
Design modulation and optimum demodulation and
detection methods for digital communications over an
AWGN channel.
Calculate the error rate performance for a number of
modulation schemes in AWGN environments

Course Outcomes
Understand basic elements of a communication system
Conduct analysis of baseband signals in time domain and in
frequency domain
Demonstrate understanding of various analog and digital
modulation and demodulation techniques.
Analyze the performance of modulation and demodulation
techniques in various transmission environments
Understand the importance of noise considerations in
communication systems.
Baseband and band-pass transmission techniques
 Detection & Estimation of signal

Communication Engineering concerned with the sending and receiving of signals
especially by means of electrical devices and electromagnetic waves.

Introduction
“Communication is the process of establishing connection or link between
two points for information exchange”
The examples of communication:
1. Ancient communication
2. Telegraph
3. Line telephony
4. Radio telephony
5. Radio telegraph
6. Point to point communication
7. Mobile communication
8. Computer communication
9. Radar communication
10. Television broadcasting
11. Radio telemetry
12. Radio aids to navigation
13. Radio aids to aircraft landing

Ancient Communications
Harkara Pigeons Fire and Smoke

Telegraph (1836)
Invention Of Telegraph: First Wireless Communication

Telephone (1876)
Invention Of Telephone ByAlexander Graham Bell: The Beginning of Electricity
Based Analog Communication

Mobile Phones (1983)
Mobile phone was first available
commercially in 1983. This indicated the
beginning of the large commercialization
of communication systems.

Contribution of Electronics in
Communication Devices

Lecture-01 analog and digital communication.pptx

Modern Communication System
Message: sounds (voice,
music), pictures, words,
codes, light, temperature,
pressure, etc.
Microphone, camera,
scanner, etc.
Information in
electrical signal/
modulating signal
Modulated signal
in RF range
(transmitted
through channel)
Modulator (Analog:
AM,FM.PM. Digital:
ASK, FSK, PSK, DM)
Information
source
Input
transducer
Transmitter
(Modulator)
Channel Receiver
Output
transducer
Noise
Reconstructed
electrical signal/
modulating signal
Modulated signal
in RF range
(received from
the channel)
Information in
the original form
Figure: Block diagram of a communication system
Information source:
• The message produced by the information source is not an electrical in
nature.
•Such as voice, music pictures, words, codes, lights, temperature etc.
•So we need transducer to convert from physical message to electrical signal.
Input transducer:
• It converts one form of energy into another form.
•It is used to convert physical message signal into time varying electrical signal.
Transmitter:
• Here, restriction of range of audio frequencies, amplification, and modulation
are achieved.
•Modulation is the superimposed of audio signal upon the high-frequency
carrier signal.

Modern Communication System
The channel and the Noise:
• It is the path through which the signal propagates from transmitter to
receiver.
•It may be a pair of wires, a coaxial cable, microwave links or radio waves or
space.
•In the channel, the signal gets distorted due to noise introduced in the
system.
•Noise signals are always random in character.
Receiver:
• It receives information from the modulated signal available at the transmission
channel.
•The main function of the receiver is to extract the original message signal from
the degraded version of the transmitted signal.
•Example: TV sets and Radio set are example for receivers
Destination:
• Destination is the final stage where electrical message signal is converted into
its original form, such as voice, message, etc.
•For example, in radio broadcasting, loudspeaker which works as a transducer.

Noise
Noise in a communication system is basically undesirable or unwanted
signals that get randomly added to the actual information carrying signal

Bandwidth
The bandwidth is the frequency range over which an information signal is
transmitted
We may also say that bandwidth is the difference between the upper and
lower frequency limits of the signal.
Bandwidth
BW
0 Frequency, f
f1 =20 Hz f2 =15kHz
For example, the range of music signal is 20 Hz to 15 kHz, therefore, as
shown in the above figure, the bandwidth is
BW= f2-f1
BW=15000-20=14980 Hz.

Signal
A signal may be defined as the single valued function of time.
Speech: The band of frequencies required for the speech communication is 300 Hz
to 3100 Hz. This band is utilized for the commercial telephonic communication.
Music: Music signal is a bipolar signal and it requires a bandwidth of about 15 kHz.
Video: The bandwidth required for this video signal is 0 to 5 MHz.
Computer Data: The text transmitted by a computer is encoded using American
Standard Code for Information Interchange (ASCII)

Communication Channels
Some important characteristics of a channel are:
Power required to achieve the desired S/N ratio.
Bandwidth of the channel.
Amplitude and phase response of channel.
Type of channel (linear or non-linear).
Effects of external interference on the channels.

Telephone channels:
It is designed for providing service to voice signals such as telephones
Bandpass characteristics over 300 to 3400 Hz.
High signal to noise ratio of about 30 dB.
Approximately linear response.
Example of telephone channels: A common examples is twisted pair cable.
Advantages: It is quite cheaper.

Co-axial cables:
It was initially developed as the backbone of analog telephone networks
A single cable would be used to carry more than 10,000 voice channels.
Two types of cables having 75 Ω and 50 Ω impedance are available.
Because of shielding, this cable has noise immunity.
It has large bandwidth and low losses
This cable is suitable for both point to point or point to multipoint
applications.
It expensive than twisted pair cable however, cheaper than optical fiber.
Repeaters are used after every 1 km to achieve data rates 8.5 Mb/s to
274 Mb/s
Advantages: co-axial cables provide higher immunity to electromagnetic
interference and higher bandwidth compared with twisted pair cables.

Optical fiber cables:
An optical fiber is a very thin strand of plastic or glass that is used to
transmit messages via light.
It consist of an inner glass core. High bandwidth
Long distance
Immunity to electromagnetic interference required
It can transmit voice, video, and telemetry through LAN, computer
networks, or across long distances.
Advantages: Small size and light weight, easy availability and low cost, no
electrical or electromagnetic interference, large bandwidth.
Disadvantages: High initial cost, Maintenance and repairing cost, Jointing and test
procedures, Tensile stress, Fiber losses.

Terrestrial microwave channel:
Terrestrial microwave channel requires a line of sight path between a
sender and a receiver.
Unidirectional
Repeaters are needed for long distance communication.
No adverse effects such as cable breakage etc.
Very high frequency microwave cannot penetrate walls
Less maintenance compared with cables.
Microwave waves are used for cellular networks, satellite and wireless
networks.
Disadvantages: Signal strength at the receiving antenna reduces due to multipath
reception.
Advantages: No cables needed, multiple channel available, wide bandwidth.

Satellite channel:
A communication satellite is a microwave relay station.
Used to link two or more ground stations
It uses frequency range between 11 GHz and 14 GHz.
The message signal transmitted by the earth station to the satellite is
called as an uplink frequency.
It is amplified and down converted in frequency by the transponder.
The signal from satellite to earth is called downlink frequency.
It receives signal on one frequency (uplink=6 GHz) and transmits on
another frequency (downlink= 4 GHz).
Rotation match occurs at a height of 35,683 km at the equator.
Disadvantages: The cost of building and launching is very high.

Electronic communication systems
Classification: The electronic communication may be classified into three groups
based on
 whether the system is unidirectional or bidirectional.
Whether it uses an analog or digital information signal/modulating
signal.
Whether the system uses baseband transmission or use some kind of
modulation.
Fig. Classification of electronic communication system

Based on direction of communication
Based on the direction of communication, the communication systems are:
i. Simplex systems
ii. Half duplex systems
iii. Full duplex systems
Simplex systems: The information is communicated in only one direction such
as the radio and TV broadcasting.
Half duplex systems: The information is communicated in bi-direction but one
at a time such as walky-talky.
Full duplex systems: The information is communicated in both direction
simultaneously such as telephone.

Based on nature of information signal
Based on the nature of information signal the communication systems are:
Analog communication: The modulation systems or techniques in which one of
the characteristics (amplitude, phase or frequency) of the carrier is varied in
proportion with the instantaneous value of modulating signal is called as analog
modulation system.

Examples of analog modulation: Following are the examples of analog modulation
systems :
Amplitude modulation (AM)
Frequency modulation (FM)
Phase modulation (PM)
Pulse Amplitude Modulation (PAM)
Pulse Width Modulation (PWM)
Pulse Position Modulation (PPM)
Advantages of analog communication:
Transmitters and receivers are simple
Low bandwidth requirement
FDM (Frequency division multiplexing) can be used
Drawbacks of analog communication:
Noise affects the signal quality
It is not possible to separate noise and signal
Repeaters can not be used between transmitter and receiver
Coding is not possible
It is not suitable for the transmission of secret information
Applications:
Radio broadcasting (AM and FM)
TV broadcasting
Telephones

Digital communication
The modulation system or technique in which the transmitted signal is in the form of digital
pulses of constant amplitude, constant frequency and phase is called as digital modulation
system : The common applications are: Long distance, communication between earth and
space ships , Satellite communication, Military communication, Telephone systems, Data and
computer communications
Examples of digital modulation: Following are the examples of analog modulation systems :
Pulse code modulation (PCM)
delta modulation (DM)
Advantages of analog communication:
Reliable communication, less sensitivity to changes in environmental
conditions (such as temperature)
Easy multiplexing, easy signaling
Voice and data integration
Easy processing like encryption and compression
Integration of transmission and switching
FDM (Frequency division multiplexing) can be used
Drawbacks of Digital Communication:
The bit rates of digital systems are high . Therefore, they require a larger
channel bandwidth as compared to analog system .
Digital modulation needs synchronization in case of synchronous
modulation .

Classification based on technique of transmission
Baseband transmission systems: In baseband transmission systems, the baseband signals
(original information signals/modulating signal) are directly transmitted such as telephone
network
Limitations:
It cannot be used for free space communication because it gets suppressed after a
short distance.
Note: we can overcome this limitations using modulation
Based on the technique used for the signal transmission, we can categorize the
electronic communication system as under :
Baseband transmission system
Communication systems using modulation
Communication systems using modulation:
In the modulation process, two signals are used namely the modulating
signal and the carrier .
The modulating signal is nothing but the baseband signal or information
signal while the carrier is a high frequency sinusoidal signal .

What is modulation
Modulation is the process of varying one or more properties of a high frequency
periodic waveform, called the carrier signal, with a separate signal called
the modulation signal that typically contains information to be transmitted.
For example, the modulating signal might be an audio signal, a video signal etc.

Why do we need modulation
The modulation is necessary for the following reasons:
Reduction in the height of the antenna
Avoids mixing of signals
Increases the range of communication
Multiplexing is possible
Improve quality of reception
Reduction in the height of antenna : For the transmission of radio signals, the
antenna height must be a multiple of (λ/4). where λ is the wavelength (λ = c/f).
The minimum antenna height required to transmit a base-band signal of f = 10KHz
is calculated as follows:
Minimum antenna height = λ/4=C/4f=3×108 /(4×10×103)= 7500 m i.e. 7.5 km
The antenna of this height is practically impossible to install.
Now consider a modulated signal at f = 1MHz
The minimum height is given by=λ/4
=c/4f
=3×108 /(4×10×106)
= 75 m
This size antenna can be installed practically.

Different types of modulation systems

Amplitude modulation (AM)
The carrier is a sine wave frequency
The carrier frequency is much higher than the frequency of modulating signal.
Here, the information is contained in its amplitude variation.
The frequency of the carrier remains constant.
AM is used in radio and TV broadcasting applications.

Frequency modulation (FM)
The frequency of the carrier is changed in proportion with the amplitude of the
modulating signal.
The amplitude of the carrier remains constant.
FM is used for TV, sound, FM radio and police wireless transmission.

Phase modulation (PM)
The phase shift of the carrier is changed in proportion with the amplitude of the
modulating signal.
The amplitude of the carrier remains constant.
PM is used for generation of FM.
FM signal produced from PM signal is very stable.
The centre frequency called resting frequency is extremely stable.

Pulse analog modulation
The carrier is in the form of pulses instead of being a sinewave.
In PAM, the amplitude of the carrier is varied.
In PWM, the width of the carrier is varied.
In PPM, position of the pulses is varied with the amplitude of modulating signal.

Digital Communication System
A/D Converter: Analog to Digital Converter
D/A Converter: Digital to Analog Converter

Comparison of Analog and Digital Modulation

Limitation of communication systems
Physical limitations:
Bandwidth limitations
Measure of speed
The system ability to follow signal variations depends on the
transmission bandwidth
Available bandwidth determines the maximum signal speed.
Noise limitations
Unavoidable
The kinetic theory
Noise relative to information signal is measured in terms of
signal to noise ratio (SNR)
Compromise within:
Transmission time and power
SNR performance
Cost of equipments
Channel capacity
bandwidth

Lecture-01 analog and digital communication.pptx

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