Communication Systems-II
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Transcript of 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