ADVANCED COMMUNICATION BLOCK DIAGRAM System

Advanced Communication system block diagram

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Dr. Mayank Pandey
Assistant Professor
Department of Physical Sciences (Electronics)
Kristu Jayanti College, Bangalore

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BLOCK DIAGRAMBLOCK DIAGRAM
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1.Digital source1.Digital source
a. Analog information source
b. Digital Information source
2. Source Encoder2. Source Encoder
3.Channel encoder3.Channel encoder
4.Modulator4.Modulator
5.Channel5.Channel
6.Detector6.Detector
7.Channel Decoder7.Channel Decoder
8.Source Decoder8.Source Decoder
9.Destination9.Destination

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Advantages and disadvantagesAdvantages and disadvantages
1. More immune to noise
2. provides better security
3. Receiving signals simpler
4. Less expensive- repeaters are required after 5-6km
5. Compatibility with other digital systems
6. More reliable
7. Easy to manipulate
8. Flexible
9. Only digitized information can be transported through a noisy
channel without degradation
AdvantagesAdvantages
Dis-advantagesDis-advantages
1. Sampling Error
2. Requires more bandwidth
3. Detection of digital signals requires the communications
system to be synchronized,

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Many signals in modern communication systems are digital
Additionally, analog signals are transmitted digitally
A digital signal is superior to an analog signal because it is
more immune to noise and can easily be recovered,
corrected and amplified.
For this reason, the tendency today is to change an
analog signal to digital data.
The process of transmitting signals in the form of pulses
(discontinuous signals) is by using special techniques.
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PULSE MODULATIONPULSE MODULATION
Analog Pulse Modulation Digital Pulse Modulation
Pulse Amplitude (PAM)
Pulse Width (PWM)
Pulse Position (PPM)
Pulse Code (PCM)
Differential Pulse Code
(DPCM)
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In pulse modulation, the carrier signal is a discrete pulse train
(rectangular pulse) instead of a sine wave.
The modulating signal will vary any one of the parameter of the
rectangular pulses(carrier) with respect to the modulation signal by keeping
the other parameters constant. This is known as pulse modulation
PULSE MODULATIONPULSE MODULATION
Delta Modulation(DM)

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Pulse Amplitude Modulation(PAM)Pulse Amplitude Modulation(PAM)
It is a type of
modulation technique
in which amplitude of
the carrier pulses is
varied in accordance
with the modulating
signal, by keeping
width and position
constant.
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Pulse Amplitude Modulation

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Depending upon the shape and polarity of
the sampled pulses, PAM is of two types,
•Double polarity PAM
•Single polarity PAM
Pulse Amplitude Modulation

9. Generation & Detection of PAMGeneration & Detection of PAM
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Generation:
The signal that contains the intelligence(modulating signal) to be
transmitted is applied to one of the multiplier inputs, and the train of pulses
(carrier signal) is applied to the other multiplier input.
The multiplier output will consist of a train of pulses, each having an amplitude
equal to the signal amplitude at the time of sampling.
Detection:
The PAM signal can be detected by passing it through a low pass filter.
Pulse Amplitude Modulation

10. Advantages
Generation and demodulation is easy
No complex circuitry is required for both transmission and reception
PAM can generate other pulse modulation signals
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Disadvantages
Less immune to noise
Power transmitted is not constant
Power required to transmit pulse is more
Bandwidth required is more
Variation in frequency according to the modulating
signal results is interferences.
Pulse Amplitude Modulation

11. Applications
It is mainly used in Ethernet
It is also used for photo biology
Used as electronic driver for LED lighting.
Used in many micro controllers for generating the control signals etc.
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Pulse Amplitude Modulation

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Pulse Width Modulation (PWM)Pulse Width Modulation (PWM)
It is a type of modulation
technique in which width of
the carrier pulses is varied
in accordance with the
modulating signal, by
keeping amplitude and
position constant.
In pulse width modulation (PWM), the width of each pulse is made directly
proportional to the amplitude of the information signal.
It is also known as PDM (Pulse Duration Modulation), PLM(Pulse Length
Modulation)

13. Advantages
Noise added is less
Signal and noise separation is very easy
It does not require synchronization between transmitter and receiver
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Disadvantages
Large bandwidth is required
Pulse required is variable and large.
Pulse width Modulation

14. Applications
telecommunication systems.
used to control the amount of power delivered to a load
Audio effects and amplifications purposes
used to control the speed of the robot
used in robotics
Embedded applications
Analog and digital applications
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Pulse width Modulation

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Pulse position Modulation (PPM)Pulse position Modulation (PPM)
It is a type of modulation
technique in which position
of the carrier pulses is
varied in accordance with
the modulating signal, by
keeping amplitude and
width constant.
PPM is obtained by differentiating PWM

16. Advantages
Noise added is less
Signal and noise separation is very easy
Power transmitted is constant
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Disadvantages
Large bandwidth is required
Synchronization between transmitter and receiver is required.
Pulse position Modulation

17. Applications
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Pulse position Modulation
Environmental Monitoring
Water Treatment
Agriculture
Industrial Processes
Food and Beverage Industry
Health and Medicine
Gas Analysis
Semiconductor Industry

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SamplingSampling
The signal is sampled at regular
intervals such that each sample is
proportional to the amplitude of
signal at that instant. This
technique is called “sampling”.
Sampling is common in all pulse
modulation techniques.
Analog signal is sampled every T
S
secs.
T
s
is referred to as the sampling
interval.
f
s = 1/T
s is called the sampling rate
or sampling frequency.
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Sampling

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Types of SamplingTypes of Sampling

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There are 3 sampling methods:
Ideal - an impulse at each sampling
instant
Natural - a pulse of short width with
varying amplitude
Flat top - sample and hold, like
natural but with single amplitude
value
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Sampling

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Three different sampling methods Three different sampling methods
Sampling

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Sampling RateSampling Rate
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Sampling
•Nyquist criteria decides the minimum sampling rate.
•The Nyquist rate is the minimum sampling rate required to
represent complete information about analog signal in its
sampled form
•According to Nyquist sampling theorem
“The minimum sampling frequency required to represent the
analog signal into sample and reconstruct back the analog
signal from samples should be greater than twice the
highest frequency component of the analog signal”.
i.e. Fs(min) ≥ 2fmFs(min) ≥ 2fm
where fs is sampling frequency
•Sampling rates that are too low result in aliasing or
foldover

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Digital Pulse ModulationDigital Pulse Modulation
1.Digital signals are very easy to receive. The receiver has to
just detect whether the pulse is low or high.
2.AM & FM signals become corrupted over much short
distances as compared to digital signals. In digital signals,
the original signal can be reproduced accurately.
3.The signals lose power as they travel, which is called
attenuation. When AM and FM signals are amplified, the
noise also get amplified. But the digital signals can be
cleaned up to restore the quality and amplified by the
regenerators.
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Merits of Digital Communication:

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4.The noise may change the shape of the pulses but not
the pattern of the pulses.
5.AM and FM signals can be received by any one by
suitable receiver. But digital signals can be coded so
that only the person, who is intended for, can receive
them.
6.AM and FM transmitters are ‘real time systems’. i.e.
they can be received only at the time of transmission.
But digital signals can be stored at the receiving end.
7.The digital signals can be stored.
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Digital Pulse ModulationDigital Pulse Modulation
•Pulse Code Modulation
•Delta Modulation
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Pulse Code Modulation(PCM)Pulse Code Modulation(PCM)
Pulse-Code Modulation (PCM) is the most
commonly used digital modulation scheme
In PCM, the available range of signal
voltages is divided into levels and each is
assigned a binary number
Each sample is represented by a binary
number and transmitted serially
The number of levels available depends
upon the number of bits used to express
the sample value
The number of levels is given by: N = 2
m
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Pulse code Modulation

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PCM consists of three steps to digitize
an analog signal:
1.Sampling
2.Quantization
3.Binary encoding
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Pulse code Modulation

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Pulse code Modulation

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Sampling: The process of generating pulses of
zero width and of amplitude equal to the
instantaneous amplitude of the analog signal.
The no. of pulses per second is called “sampling
rate”.
Quantization: The process of dividing the
maximum value of the analog signal into a fixed
no. of levels in order to convert the PAM into a
Binary Code.
The levels obtained are called “quantization
levels”.

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Pulse code Modulation
Analog to digital converter employs two techniques

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Time
V
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7
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1
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111
110
101
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011
010
001
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B
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C
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Time
Time
V
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0 1 0 1 0 1 1 1 0 1 1 1 1 1 0 1 0 1 0 1 0
Sampling,
Quantization and
Coding
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Pulse code Modulation

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Quantization ErrorQuantization Error
When a signal is quantized, we introduce an
error - the coded signal is an approximation
of the actual amplitude value.
The difference between actual and coded
value (midpoint) is referred to as the
quantization error.
The more zones, the smaller  which results
in smaller errors.
BUT, the more zones the more bits required
to encode the samples -> higher bit rate
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Pulse code Modulation

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DPCMDPCM
In DPCM, only the difference between
the sampled values is transmitted.
Amount of bits transmitted will reduce.
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Delta Modulation

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Delta ModulationDelta Modulation
In Delta Modulation, only one bit is
transmitted per sample

That bit is a one if the current sample is
more positive than the previous sample,
and a zero if it is more negative
Since so little information is transmitted,
delta modulation requires higher sampling
rates than PCM for equal quality of
reproduction
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Delta Modulation

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This scheme sends only the difference between
pulses, if the pulse at time t
n+1 is higher in amplitude
value than the pulse at time t
n, then a single bit, say
a “1”, is used to indicate the positive value.
If the pulse is lower in value, resulting in a negative
value, a “0” is used.
This scheme works well for small changes in signal
values between samples.
If changes in amplitude are large, this will result in
large errors.
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Delta Modulation

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Components of Delta Modulation
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Delta Modulation

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The process of delta modulation
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Delta Modulation

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Distortions in DM system
1.If the slope of analog signal is much higher
than that of approximated digital signal
over long duration, than this difference is
called Slope overload distortion.
2.The difference between quantized signal
and original signal is called as Granular
noise. It is similar to quantisation noise.
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Delta Modulation

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Conclusion
The main advantage of these pulse
modulation schemes are better noise
immunity and possibility of use of
repeaters which makes communication
more reliable and error free.
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Characteristics of data transmission circuitsCharacteristics of data transmission circuits
•SHANNON’S LAW
Shannon's law is any statement defining the theoretical
maximum rate at which error free digits can be transmitted
over a bandwidth limited channel
 in the presence of noise

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Shannon’s Theorem
(Shannon’s Limit for Information Capacity)

Claude Shannon at Bell Labs figured out how much
information a channel could theoretically carry:
I = BW log
2 (1 + S/N)
I = 2.32BW log
10 (1 + S/N)
Where I is Information Capacity in bits per second
(bps)
BW is the channel bandwidth in Hz
S/N is Signal-to-Noise ratio (SNR: unit less…don’t make
into decibel: dB)
Note that the log
is base 2!

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•Data Transmission speed
1.Bit rate or Data rate (rb)
2.Baud rate(rs)
rb = rs log
2 (M)

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•Cross talk
Remedies:
1.Twisted wire
2.Shielded cables
3.Balanced circuits

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•Noise
1.Gaussian White Noise
2.Impulse Noise

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•Echo Suppressors

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•Distortion
•Equalizers
1.Pre-set Equalizer
2.Adoptive Equalizer
Phase Delay distortion

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Line Coding techniques

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