Ec8491 communication theory

EC8491-COMMUNICATION THEORY
(REGULATION-2017)
Dr.M.S.Gowtham
Assistant Professor/ECE Department,
Karpagam Institute of Technology, Coimbatore

OBJECTIVES:
 To introduce the concepts of various analog modulations
and their spectral characteristics.
 To understand the properties of random process.
 To know the effect of noise on communication systems.
 To study the limits set by Information Theory.
2
KARPAGAM INSTITUTE OF TECHNOLOGY, COIMBATORE

Fundamentals
 Communication is the process of exchanging information.
 Basic components:
 Transmitter
 Channel or medium
 Receiver
 Noise degrades or interferes with transmitted information.
3KARPAGAM INSTITUTE OF TECHNOLOGY, COIMBATORE

Transmitter
 The transmitter is a collection of electronic components and
circuits that converts the electrical signal into a signal suitable for
transmission over a given medium.
Receivers
 A receiver is a collection of electronic components and circuits that
accepts the transmitted message from the channel and converts it
back into a form understandable by humans.
Communication Channel
 The communication channel is the medium by which the electronic
signal is sent from one place to another.
Transceivers
 A transceiver is an electronic unit that incorporates circuits that
both send and receive signals.

UNIT I - AMPLITUDE MODULATION
 To introduce the concepts of various amplitude modulations
and their spectral characteristics for designing AM
communication systems
 Modulation is the process of superimposing a low frequency
signal on a high frequency carrier signal.
CONTENT:
 AMPLITUDE MODULATION
 AM TRANSMITTER
 SSB - SC
 VSB - SC
 DSB - SC
 HILBERT TRANSFORM
 SUPER HETERODYNE RECEIVER
 COMPARISION OF VARIOUS AM TECHNIQUES

UNIT II - ANGLE MODULATION
 Angle modulation is the process by which the angle (frequency or
Phase) of the carrier signal is changed in accordance with the
instantaneous amplitude of modulating or message signal also
known as “Exponential modulation"
 classified into two types such as
 Frequency modulation (FM)
 Phase modulation (PM)
CONTENT:
• FREQUENCY & PHASE MODULATION
• NARROW BAND FM
• WIDE BAND FM
• GENERATION OF WIDE BAND FM
• TRANSMISSION BANDWIDTH
• FM TRANSMITTER

UNIT III - RANDOM PROCESS
 In probability theory, a stochastic process, or sometimes random process is a collection
of random variables, representing the evolution of some system of random values over
time. This is the probabilistic counterpart to a deterministic process. A random process,
or stochastic process, X(t), is an ensemble of number of sample functions {X1(t),X2(t), .
. . ,X_(t)} together with a probability rule which assigns a probability to any meaningful
event associated with the observation of these functions. Suppose the sample function
Xi(t) corresponds to the sample point si in the sample space S and occurs with
probability Pi.
 may be finite or infinite.
 Sample functions may be defined at discrete or continuous time instants. Random
process associated with the Poisson model, and more generally, renewal theory include
 The sequence of inter arrival times.
 The sequence of arrival times.
 The counting process.

CONTENT:
 RANDOM VARIABLES
 CENTRAL LIMIT THEOREM
 STATIONARY PEROCESS
 CORRELATION
 COVARIANCE FUNCTION
 ERGODIC PROCESS
 GAUSSIAN PROCES
 FLITERING THROUGH RANDOM PROCESS

UNIT IV -NOISE CHARACTERIZATION
 Noise is a general term which is used to describe an unwanted signal which
affects a wanted signal. These unwanted signals arise from a variety of
sources which may be considered in one of two main categories:-
• Interference, usually from a human source (man made)
• Naturally occurring random noise
 Noise is an inevitable consequence of the working of minerals and is an
important health and safety consideration for those working on the site.
Whether it becomes "environmental noise" depends on whether it disrupts
or disturbs people outside the site boundary.

CONTENT:
 NOISE IN COMMUNCATION SYSTEM
 CLASSIFICATION OF NOISE
 NOISE FIGURE & TEMPERATURE
 NOISE IN CASCADE SYSTEMS
 REPRESENTATION OF NARROW BAND NOISE
 NOISE PERFORMANCE
 PREEMPHESIS & DE EMPHESIS
 CAPTURE AND THERSHOLD EFFECT

UNIT V SAMPLING AND QUANTIZATION
An analog-to-digital converter (ADC) can be modeled as two
processes: sampling and quantization. Sampling converts a time-varying
voltage signal into a discrete-time signal, a sequence of real
numbers. Quantization replaces each real number with an approximation
from a finite set of discrete values.
 Analog signal is sampled every TS secs.
 Ts is referred to as the sampling interval.
 fs = 1/Ts is called the sampling rate or sampling frequency.
 There are 3 sampling methods:
 Ideal - an impulse at each sampling instant
 Natural - a pulse of short width with varying amplitude
 Flattop - sample and hold, like natural but with single amplitude value
 The process is referred to as pulse amplitude modulation PAM and the
outcome is a signal with analog (non integer) values

CONTENT:
 Low pass sampling
 Aliasing
 Quantization
 Quantization noise
 Logarithmic companding
 PCM-TDM,FDM

References
1. J.G.Proakis, M.Salehi, ―Fundamentals of Communication
Systems, Pearson Education 2014.
2. Simon Haykin, ―Communication Systems‖, 4th Edition,
Wiley, 2014.
3. B.P.Lathi, ―Modern Digital and Analog Communication
Systems‖, 3rd Edition, Oxford University Press, 2007.
4. D.Roody, J.Coolen, ―Electronic Communications, 4th
edition PHI 2006
5. B.Sklar, ―Digital Communications Fundamentals and
Applications‖, 2nd Edition Pearson Education 2007
6. Couch.L., "Modern Communication Systems", Pearson,
2001.

Thank You

Ec8491 communication theory

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Ec8491 communication theory