Pulse modulation related topics

1. One gains ¼ of the knowledge from the Acharya (the teacher), ¼ from
his own self-study and intellect, ¼ from his classmates and the
remaining ¼ is gained as a person becomes matured as time passes.

2. COMMUNICATION ENGINEERING
Mr.R.VIJAY ANANDH

3. Learn how to think from your Gurus, not what to think
Just as your teachers cannot eat for you,
dont let others think for you
---go your own path
---create something new!!

4. Instructions to all Participants
➢ Kindly mute Audio & turnoff Video while entering and till the
session end. Don’t try to record Video.
➢ Get your pen, notebook and calculator along with you.
➢ https://www.slideshare.net/rmkrva/communication-engineering-class-1
➢ https://www.slideshare.net/rmkrva/communication-engineering-class-2
➢ https://www.slideshare.net/rmkrva/communication-engineering-class3
➢ https://www.slideshare.net/rmkrva/communication-engineering-class-4
➢ https://www.slideshare.net/rmkrva/communication-engineering-class5
➢ Subject clarifications will be given wherever necessary and
during Q&A sessions also.

6. 5
• MULTIPLEXING
• TDM & FDM
• LINE CODES
• CHANNEL VOCODERS
• Summary
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SESSION TOPICS

7. MULTIPLEXING
➢Multiplexing is the process of simultaneously transmitting
two or more individual signals over a single communication
channel.
➢Due to multiplexing it is possible to increase the number of
communication channels so that more information can be
transmitted.
➢The typical application of multiplexing are telemetry or
telephone, satellite comm etc.

8. What will happen when you do
Mixing of signals ??? (Any Guesses)
➢ Chances of mixing or overlapping of different
signals will happen (i.e.) Interference

9. TYPES
➢To avoid interference of signals, we are going to employ
different types of Multiplexing

10. DEMONSTRATIONSFDM

11. DISCUSSIONS
In FDM, many signal are transmitted simultaneously where each signal
occupies a different frequency slot within a common BW..
➢ The operation of FDM is based on sharing the available BW of a
communication channel among the signals to be transmitted.
➢ Each signal to be transmitted modulates a different carrier, the
modulation can be AM, SSB, FM or PM.
➢ The modulated signals are then added to form a composite signal
which is transmitted over a single channel.
➢ Generally, FDM systems are used for multiplexing the analog signals.

12. Block diagram of FDM transmitter
• Each signal modulates a separate carrier which contains the sidebands of the signal.
The modulator o/p are then added in linear mixer or adder.
• The composite signal at the o/p of the mixer is transmitted over the single
communication channel.

13. ➢ The information of composite FDM signal is shown below:

14. Block diagram of FDM Receiver
• The composite signal is applied to a group of BPF.
• Each BPF has a center frequency corresponding to one of the carriers.
• The BPF have an adequate BW to pass all the channel information without any distortion.
• Each filter will pass only its channel and reject all the other channels.
• The channel/demodulator then removes the carrier and recovers the original signal back.

15. The Figure shows FDM technique applied to the commercial
AM broadcast station for transmission on a common medium.

16. DEMONSTRATIONSTDM

17. Synchronous TDM

19. Pre Alias filter
Rotating Switch
Reconstruction Filter
BLOCK DIAGRAM

20. ➢The commutator circuit, acts as SWITCH in each one of its rotation and
extracts or samples, one sample from each message input .
➢Thus, at the output of commutator, we get PAM waveform which contain
the samples of messages input which are periodically inter placed in time.
➢These multiplexed message samples are transmitted over the
communication channel.
Transmission side:

21. Decommutator distributes the pulses to different receiver. It is used to separate
various received samples and to distribute them to an assembly of LPFs.
The LPF then re construct the individual messages, at the output.
Here it is necessary that rate of switching of commutator and decommutator
must be same and they must be synchronized to each other, this synchronization
is achieved by sending a synchronization pulse.
Receiver side:

22. LINE CODING

23. Observe the Picture: understand it….
• Blue Color represents—
• Red Color represents—
• Shaping Pulses
• Analog waveforms

24. Line coding schemes
➢ The conversion of the digital data (‘1’ & ‘0’) into the digital signal is known as
Line Coding.
➢ It represents the digital signal that needs to be transmitted.
➢ Line Coding is to represent each binary codeword by a sequence of pulses;
➢ For example, symbol 1 is represented by the presence of a pulse and symbol 0
is represented by absence of the pulse.
➢ The common types of line encoding are unipolar, polar, bipolar, and
Manchester encoding.

25. WHY LINE CODING?
• Spectrum Shaping and Relocation without modulation or
filtering.
• DC component can be eliminated;
• Error detection capabilities.
• Bandwidth usage
• Bit clock recovery can be simplified.

26. TWO MAJOR CATEGORIES OF LINE CODING
• There are 2 major categories:
• Return–to–Zero (RZ) and Non-Return–to–Zero (NRZ).
• With NRZ coding, the waveform will occupy full duration of the
bit .
• With RZ coding, the waveform returns to a zero–volt level for a
portion (usually one–half) of the bit interval.

27. NRZ (NON-RETURN TO ZERO)

28. Unipolar Line Coding
• In Unipolar, we are simply representing a signal in a graphical form
where positive voltage represents logical or binary 1 and zero voltage
represents logical zero.

29. Unipolar NRZ signalling
Polar NRZ signalling
• Binary 1’s and 0’s are represented by equal positive and
negative levels.
• In positive–logic unipolar signaling, the binary 1 is represented
by a high level (+A volts) and a binary 0 by a zero level. This
type of signaling is also called on–off keying (OOK).

30. Unipolar NRZ signalling
Draw Polar NRZ signalling
V
-V
0
Are you able to
identify shortcut
???

31. Polar Non-Return to Zero (Polar NRZ)
NRZ scheme has two variants: NRZ-L and NRZ-I.
➢NRZ-L changes voltage level at when a different bit is
encountered .
➢NRZ-I changes voltage when a is ‘1’ and remain same when a
‘0’ is encountered .

32. 1.Example --- Understand this example
NRZ-L :-
Low voltage level for ‘0’ and
High voltage level for ‘1’.
NRZ-I :- Changes voltage when a is
‘1’ and remain same when a ‘0’ is
encountered .

33. Case 1 Case 2
In general, NRZ-L is
denoted as NRZ and
used commonly.

34. RZ (RETURN TO ZERO)

35. (c) Unipolar RZ signalling
(d) Bi-polar RZ signalling
‘0’ - No pulse (amplitude) and
‘1’ - High voltage level for the first
duration of Half-Symbol width
‘0’ - No pulse (amplitude) and
‘1’ - Positive and Negative pulses
of equal amplitude (+A and –A) are
used alternatively with each pulse
having a Half-Symbol width.

36. (d) Split-Phase or Manchester
•Transition from low to high in middle of interval for ‘0’ and
•Transition from high to low in middle of interval for ‘1’
=SHORT CUT: for ‘0’
=SHORT CUT: for ‘1’
For Easy understanding

37. (a) Unipolar NRZ signalling (b) Polar NRZ signalling
(c) Unipolar RZ signalling (d) Bi-polar RZ signalling
(d) Split-Phase or Manchester

38. Unipolar NRZ signalling
Polar NRZ signalling
Unipolar RZ signalling
Bipolar RZ signalling
Split-Phase or Manchester

39. TEST-2 : - In the given diagram,Match the following:
(2) Unipolar NRZ signalling
(3) Polar NRZ signalling
(4) Unipolar RZ signalling
(5) Bipolar RZ signalling
(1) Split-Phase or ManchesterA
B
C
D
E

40. TEST ANSWER-2

41. Channel Vocoder

42. Demo 1 Demo 2

43. Channel Vocoder
Interesting Facts:
➢ A vocoder is a category of voice encoder-decoder (CODEC) that
analyzes and synthesizes the voice signal for audio data
compression, multiplexing, voice encryption or voice
transformation.
➢ The vocoder was developed in 1928 by Bell Labs, and first demonstrated
in 1939.
➢ Its intended use was to reduce the bandwidth of voice information,
allowing it to be transferred across further distances.
➢ However, the voice reproduction of these early systems were not great
and they were never used for this purpose.
➢ However, they were used to send encoded messages during the second
world war.

44. Channel Vocoder
Applications:
➢ Vocoders were never used for civilian telecommunication because it
sounds inhuman and robotic.
➢ However, this can be a desired effect for creative usage.
➢ For musical use, a synthesizer that allows it to be pitched to specific
notes.

45. BLOCK DIAGRAM

46. ANALYSER & SYNTHESIZER
Channel vocoder models the vocal tract as bank of band-pass filters.

47. ANALYSER
NOTE: Filter bank work: To separate out the different frequency
components ( waveform).
Rectifier Work:The waveform is “rectified" to its absolute value.The
filter bank derives power levels for each frequency range.
HOW IT WORKS

48. SYNTHESIZERHOW IT WORKS