What is communication? Information Transfer Modulation Communication System Input/output Device Transmitter Channel Noise Receiver Simplex and duplex communication

1. EE334: Communication Systems

2. Review: Lecture 1
2
What is communication?
Information Transfer Modulation
Communication System
Input/output Device Transmitter
Channel
Noise Receiver
Simplex and duplex communication

3. 3
● SIGNAL TO NOISE RATIO
● CHANNEL BANDWIDTH
● RATE OF COMMUNICATION
● RANDOMNESS
● REDUNDANCY
● CODING
● Q1: WHY DIGITAL IS PREFERRED OVER
ANALOG?
● Q2: WHY WE MODULATE OUR SIGNAL?

4. 4

5. 5

6. Outline
6
Signals
Complex Waves and Harmonics
Sine Wave
Square Wave
Saw tooth Wave
Conversion/Signal Formatting
Character Coding
Sampling
Quantization
PCM

7. Signal
7
Flow of information: generally convey information about the
state or behavior of a physical system.
 measured quantity that varies with time (or position)
 electrical signal received from a transducer (microphone,
thermometer, accelerometer, antenna, etc.)
 electrical signal that controls a process
Continuous-time signal: Also know as analog signal.
voltage, current, temperature, speed, speech signal, etc.
Discrete-time signal: daily stock market price, daily average
temperature, sampled continuous signals.

8. Some Examples
8
Dimensionality
speech signal: represented as a function over time. -- 1D
signal
 image signal: represented as a brightness function of two
spatial variables. -- 2D signal
 ultra sound data or image sequence – 3D signal
Electronics can only deal easily with time-dependent signals,
therefore spatial signals, such as images, are typically first
converted into a time signal.

9. Signal And Direction
● Simplex communication is permanent unidirectional communication. Some
of the very first serial connections between computers were simplex
connections. For example, mainframes sent data to a printer and never checked
to see if the printer was available or if the document printed properly since that
was a human job.
● Simplex links are built so that the transmitter (the one talking) sends a signal
and it's up to the receiving device (the listener) to figure out what was sent and
to correctly do what it was told. No traffic is possible in the other direction
across the same connection.

10. Half Duplex
A half duplex link can communicate in only one direction, at a time. Two way
communication is possible, but not simultaneously. Walkie-talkies and radios
sort of mimic this behavior in that you cannot hear the other person if you are
talking. Half-duplex connections are more common over electrical links. Since
electricity won't flow unless you have a complete loop of wire, you need two
pieces of wire between the two systems to form the loop. The first wire is used
to transmit, the second wire is referred to as a common ground. Thus, the flow
of electricity can be reversed over the transmitting wire, thereby reversing the
path of communication. Electricity cannot flow in both directions
simultaneously, so the link is half-duplex.

11. Full Duplex
Full duplex communication is two-way communication achieved over a
physical link that has the ability to communicate in both directions
simultaneously. With most electrical, fiber optic, two-way radio and satellite
links, this is usually achieved with more than one physical connection. Your
telephone line contains two wires, one for transmit, the other for receive. This
means you and your friend can both talk and listen at the same time.

13. 13
How to check the frequency component of a signal?
Which one is the fundamental waveform? And why?
Fourier series is used for ?
Fourier transform is used for ?

14. 14
● Fourier Series
● Fourier Transform

15. Complex Waves
15
Complex waveform: components of sine wave
1.
2.
3.
Sine Wave
Square Wave
Saw tooth Wave
Harmonics: A harmonic of a wave is a component frequency of the
signal that is an integer multiple of the fundamental frequency, i.e. if
the fundamental frequency is f, the harmonics have frequencies 2f, 3f,
4f, . . . etc.
The harmonics have the property that they are all periodic at the
fundamental frequency, therefore the sum of harmonics is also
periodic at that frequency. Harmonic frequencies are equally spaced
by the width of the fundamental frequency and can be found by
repeatedly adding that frequency. For example, if the fundamental
frequency is 25 Hz, the frequencies of the harmonics are: 50 Hz, 75
Hz, 100 Hz etc

16. Understanding Harmonics
16

17. Contd.
17
Harmonic Functi
0.5
1.5
1
-1
-1.5
-0.5
0
1 65 129 193 257 321 385 449 513 577 641 705 769 833 897 961
independent variabl
n = 1
n = 2
n = 3
n = 4
n = 5
n = 6

18. 18
Phase Relations
0.5
2.5
2
1.5
1
-1
-1.5
-2
-2.5
0
0
-0.5
200 400 600 800 1000
independent variable, x
phase = 0
phase = š/4
sum

19. Contd.
19
Aperiodic S
-1
-1.5
-2
-2.5
2.5
2
1.5
1
0.5
0
-0.51 65 129 193 257 321 385 449 513 577 641 705 769 833 897 961
independent variab
n = 5
n = 6
sum

20. Fourier Explanation
20
A periodic function f(t) can be represented by an
infinite sum of sine and/or cosine functions that are
harmonically related. That is, the frequency of any
trigonometric term in the infinite series is an integral
multiple, or harmonic, of the fundamental frequency of the
periodic function.
Thus, given f(t) is periodic (e.g. square wave, triangular
wave, half rectified wave, etc.), then f(t) can be represented
as follows:

21. 21

22. 22

23. 23

24. First Step: Formatting
24

25. Formatting
25
● Character coding
● Sampling
● Quantization
● Pulse Code Modulation(PCM)

26. Formatting and Transmission of baseband signal
26

27. Input Signal
27
1. Textual
2. Digital
3. Analog

28. Textual Signal
28

29. Message, Characters and Symbols
29

30. Input Data
30
1. Textual
2. Digital
3. Analog

31. Different Conversion Scheme

32. 1. Digital to Digital conversion

33. Line Coding
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● Pulse modulation applied to binary symbols, resulting
binary wave is called PCM. Process of converting
multilevel voltage to binary pulses.
● Several type of PCM waveforms also known as Line
Codes.
1. ON-OFF
2. Polar Coding
3. Bipolar coding
4. Duo binary
5. Split Phase Manchester
6. HDB, high density bipolar

34. 34

35. 1. On-Off Coding
35
DC levels
Logic levels
5 V: 1
0 V: 0
Ex. 101001

36. 2. Polar Coding
36
DC levels
Logic levels
+5 V: 1
-5 V: 0
Ex. 101001

37. 3.Bipolar Coding
37
DC levels
Logic levels
+5 V, -5: 1
0 V : 0
Ex. 101001

38. 4. Duo binary
38
DC levels
Logic levels
+5 , -5 V: 1
0 V: 0
If even number of 0’s then same polarity
Else(odd number of 0’s change polarity)
Ex. 101001

39. 5. Split Phase Manchester
39
DC levels
Logic levels
5 V, -5: 1
-5, 5 V: 0
Ex. 101001

40. 6. HDB, high density bipolar
40
Long string of zeros cause error, change direction
after respective number of zeros.
(HDB)2, (HDB)4,
Ex. 10000111
Generally, (HDB)n where n=1,2,3,…

41. Various PCM Waveforms
41