communication systems-ii

7/30/2019 Communication Systems-II

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ECE304COMMUNICATION SYSTEMS-II

By -Mr. Koushik Barman

Asst. Professor, SECE


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Text Book

Symon Haykin- Communication Systems-4thEdition(JohnWiley & Sons, Inc.)

Reference Books

Taub and Schilling- Principles of CommunicationSystem-2nd Edition (Mc graw Hill)

Wayne Tomasi- Electronic Communication System-5th Edition (pearson)


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Why Digital Communication?

Immunity to transmission noise and interference.

Regeneration of the coded signal along the transmission path

is possible. Repeaters can be used.

Communication can be kept private and secured throughthe use of encryption.

The possibility of uniform format for different kinds of

baseband signals.

It is possible to store the signal and process it further Techniques such as data compression and image

enhancement can be used.

Lecture1


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Analog to digital conversion

Sampling

Quantizing

Encoding

Lecture1


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Block diagram of digital

communication System

Source of

Information

Channel

Modulator

Channel Encoder

Source Encoder

Demodulator

Channel Decoder

Source Decoder User of

Information

Transmitte

rReceiver

Lecture1


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Analog vs. Digital ModulationTransmitted modulated signal is analog in

nature

Transmitted signal is digital i.e. train of

digital pulses.

Amplitude, frequency or phase variations

in the transmitted signal represent the

information or message

Amplitude, width or position of the

transmitted pulses is constant. The

message is transmitted in the form of

code words

Noise immunity is poor for AM but

improved for FM and PM

Noise immunity is excellent

It is not possible to separate out noise and

signal. Therefore repeaters can not be

used

It is possible to Separate signal from noise.

So repeaters can be used

Coding is not possible Coding techniques can be used to detect

and correct the errorsBandwidth requirement is lower than

that for the digital modulation

Due to higher bit rates, higher channel

bandwidths is needed

FDM is used for multiplexing TDM is used for multiplexing

Analog modulation systems are

AM,FM,PM,PAM,PWM

Digital modulation Systems are

PCM,DM,ADM,DPCM, ASK,FSK,PSK etcLecture1


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Pulse modulation

It may be defined as a modulation system in which some

parameter of a train of pulse is varied in accordance with the

instantaneous value of the modulating signal.

The parameters of the pulses which may be varied are :

amplitude, width (or duration) and position.

Accordingly we have- PAM,PDM or PWD and PPM

Lecture2


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Pulse Amplitude modulation(PAM)

Proof:

Lecture2


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Lecture2


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PDM /PWM and PPM

Lecture2


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Types of Pulse modulation

Lecture2


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Sampling


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Quantization

Amplitude quantization is defined as the process of

transforming the sample amplitude m(nTs ) of a message

signal m(t) at time t=nTs into a discrete amplitude v(nTs )

taken from a finite set of possible amplitudes.

We assume that the quantization process is memory less and

instantaneous, which means that the transformation at tine t=

nTs is not affected by earlier or later samples of the message

signal


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Midtread and Midrise Quantization


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law

A law

Non uniform quantization


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Non uniform quantization

Figure (a) law and (b) A law


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Block diagram of PCM


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Block diagram of Repeaters


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Encoding


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Fig a)Unipolar NRZ b)Polar NRZ c) Unipolar RZ d) Bipolar RZ e) Split phase or Manchester

Line coding

techniques

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