1. Welcome

2. Analog Communication System
Chapter- 2
Analog Communication System

3. Data Communication & Computer Network-1

4. What is communication?

5. Communication :
Communication is about sending and receiving information or the transmission of information and meaning from one party to another through using shared symbols or messages.

6. Communication process model
Sender
Message
Channel
Medium
Receiver
Feedback
© PhotoDisc

7. Elements of a Communication System
Communication involves the transfer of information or intelligence from a source to a recipient via a channel or medium.
Basic block diagram of a communication system:
Channel
Source
Transmitter
Receiver
Recipient

8. Brief Description Source: analogue or digital
Transmitter: transducer, amplifier, modulator, oscillator, power amp., antenna
Channel: e.g. cable, optical fibre, free space
Receiver: antenna, amplifier, demodulator, oscillator, power amplifier, transducer
Recipient: e.g. person, speaker, computer

9. Elements of a Communication System
Output message
Input message
Input Transducer
Transmitter
Channel
Receiver
Output Transducer

10. Input Transducer: The message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system.
Example: In electrical communications, speech waves are converted by a microphone to voltage variation.

11. Transmitter: The transmitter processes the input signal to produce a signal suits to the characteristics of the transmission channel.
Signal processing for transmission almost always involves modulation and may also include coding. In addition to modulation, other functions performed by the transmitter are amplification, filtering and coupling the modulated signal to the channel.

12. Channel: The channel can have different forms: The atmosphere (or free space), coaxial cable, fiber optic, waveguide, etc.
The signal undergoes some amount of degradation from noise, interference and distortion
Receiver: The receiver’s function is to extract the desired signal from the received signal at the channel output and to convert it to a form suitable for the output transducer.
Other functions performed by the receiver: amplification (the received signal may be extremely weak), demodulation and filtering.
Output Transducer: Converts the electric signal at its input into the form desired by the system user.
Example: Loudspeaker, personal computer (PC), tape recorders.

13. Digital data have discrete states and take discrete values.
Data can be analog or digital. Analog data are continuous and take continuous values.
Digital data have discrete states and take discrete values.

14. Signals can be analog or digital
Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values.

15. Figure Comparison of analog and digital signals

16. Figure Two signals with the same phase and frequency, but different amplitudes

17. Frequency and period are the inverse of each other.

18. Figure Two signals with the same amplitude and phase, but different frequencies

19. Frequency is the rate of change with respect to time
Frequency is the rate of change with respect to time. Change in a short span of time
means high frequency. Change over a long span of time means low frequency.

20. Phase describes the position of the waveform relative to time 0.

21. Figure Three sine waves with the same amplitude and frequency, but different phases

22. Bandwidth Width of the spectrum of frequencies that can be transmitted
if spectrum=300 to 3400Hz, bandwidth=3100Hz
Greater bandwidth leads to greater costs
Limited bandwidth leads to distortion

23. Figure 1.1 Components of a data communication system
1.#

24. Data flow (simplex, half-duplex, and full-duplex)
1.#

25. Asynchronous Transmission
Used in serial communication
Data transmitted 1 character at a time
Character format is usually 1 start & 1+ stop bits, plus data of 5-8 bits
Character may include parity bit
Timing needed only within each character
Resynchronization is accomplished with each start bit
Uses simple, cheap technology
Wastes 20-30% of bandwidth 3

26. Asynchronous Character Transmission26

27. Asynchronous Transmission

28. Synchronous Transmission
Used in parallel communication
Large blocks of bits transmitted without start/stop codes
Synchronized by a clock signal or clocking data
Data framed by preamble (opening)/ postamble (closing) bit patterns
More efficient than asynchronous
Overhead typically below 5%
Used at higher speeds than asynchronous 4

29. Synchronous Transmission29

30. Bytes, Blocks, and Frames30

31. Analog Communication System
Chapter- 2
Analog Communication System

32. Amplitude Modulation
Amplitude Modulation is a process where the amplitude of a carrier signal is altered according to information in a message signal.
The frequency of the carrier signal is usually much greater than the highest frequency of the input message signal.

33. Figure 5.16 Amplitude modulation

34. Frequency Modulation
The modulating signal changes the freq. fc of the carrier signal
The bandwidth for FM is high
It is approx. 10x the signal frequency

35. Figure Frequency modulation

36. Phase Modulation (PM)
The modulating signal only changes the phase of the carrier signal.
The phase change manifests itself as a frequency change but the instantaneous frequency change is proportional to the derivative of the amplitude.
The bandwidth is higher than for AM.

37. Figure Phase modulation

38. Digital Communication System
Chapter- 3
Digital Communication System

41. DIGITAL-TO-DIGITAL CONVERSION
How we can represent digital data by using digital signals. The conversion involves three techniques: line coding, block coding, and scrambling. Line coding is always needed; block coding and scrambling may or may not be needed.

42. Line Coding The process of converting digital data to digital signals
Digital data – sequences of bits

43. Line coding and decoding

44. Characteristics of Line Coding
Signal element vs. data element
A signal element is the shortest time unit of a digital signal.
Data elements are what to need to send as information.
Data rate vs. signal rate
Data rate (bit rate) – the number of data elements in a unit time (bps).
Signal rate (pulse, modulation rate, baud rate) – the number of signal element in a unit time (baud).
The goal is two-fold of “high data rate” and “low signal rate”.
Bandwidth
Although the actual bandwidth of a digital signal is infinite, the effective bandwidth is finite.
Baseline wandering
DC components – unable to pass a low-pass filter
Self-synchronization
Built-in error detection
Immunity to noise and interferences
Complexity

45. Figure Signal element versus data element

46. Figure Effect of lack of synchronization

47. Figure Line coding schemes

48. Unipolar
All signal levels are on one side of the time axis - either above or below
NRZ - Non Return to Zero scheme is an example of this code. The signal level does not return to zero during a symbol transmission.
Scheme is prone to baseline wandering and DC components. It has no synchronization or any error detection. It is simple but costly in power consumption.

49. Figure Unipolar NRZ scheme

50. Polar - NRZ The voltages are on both sides of the time axis.
Polar NRZ scheme can be implemented with two voltages. E.g. +V for 1 and -V for 0.
There are two versions:
NZR - Level (NRZ-L) - positive voltage for one symbol and negative for the other
NRZ - Inversion (NRZ-I) - the change or lack of change in polarity determines the value of a symbol. E.g. a “1” symbol inverts the polarity a “0” does not.

51. Figure Polar NRZ-L and NRZ-I schemes

52. Polar - RZ
The Return to Zero (RZ) scheme uses three voltage values. +, 0, -.
Each symbol has a transition in the middle. Either from high to zero or from low to zero.
This scheme has more signal transitions (two per symbol) and therefore requires a wider bandwidth.
No DC components or baseline wandering.
Self synchronization - transition indicates symbol value.
More complex as it uses three voltage level. It has no error detection capability.

53. Figure Polar RZ scheme

54. Polar Bi-phase: Manchester and Differential Manchester
Manchester coding consists of combining the NRZ-L and RZ schemes.
Every symbol has a level transition in the middle: from high to low or low to high. Uses only two voltage levels.
Differential Manchester coding consists of combining the NRZ-I and RZ schemes.
Every symbol has a level transition in the middle. But the level at the beginning of the symbol is determined by the symbol value. One symbol causes a level change the other does not.

55. Figure Polar biphase: Manchester and differential Manchester schemes

56. Line Coding Schemes, con’t
Bipolar. Ex: AMI and Pseudoternary
use three levels: positive, zero, and negative.
Multilevel
mBnL
a pattern of m data elements is encoded as a pattern of n signal elements in which 2m ≤ Ln.
Ex)
2B1Q: 2 binary 1 quaternary (=2B4L)
8B6T: 8 binary 6 ternary. 28 data patterns, and 36 signal pattern
4D-PAM5 (4-D 5-level pulse amplitude mod.)
Multitransition
MLT-3 : multiline transmission, three level.

57. Figure Bipolar schemes: AMI and pseudoternary

58. Figure Multilevel: 2B1Q scheme

59. Table line coding schemes

60. Chapter 4
Transmission Media

61. Figure 4.1 Transmission medium and physical layer

62. Figure 4.2 Classes of transmission media

63. 4.1 Guided Media
Twisted-Pair Cable
Coaxial Cable
Fiber-Optic Cable

64. Figure Twisted-pair cable

65. Figure UTP and STP

66. Table Categories of unshielded twisted-pair cables
Category
Bandwidth
Data Rate
Digital/Analog
Use 1
very low
< 100 kbps
Analog
Telephone 2
< 2 MHz
2 Mbps
Analog/digital
T-1 lines 3
16 MHz
10 Mbps
Digital
LANs 4
20 MHz
20 Mbps 5
100 MHz
100 Mbps
6 (draft)
200 MHz
200 Mbps
7 (draft)
600 MHz
600 Mbps

67. Figure UTP connector

68. Figure Coaxial cable

69. Fiber-Optic Cable
Fiber-optic cable uses light to transmit data signals. The core of the fiber-optic cable is composed of one or more thin tubes of glass or plastic. Each tube is called the optical fiber and is as thin as the human hair. A light-emitting diode (LED) or a laser is used to send light through the fibers.

71. Figure Optical fiber

72. Figure Propagation modes

73. Figure Modes

74. Multimode, graded-index
Table Fiber types
Type
Core
Cladding
Mode
50/125 50
125
Multimode, graded-index
62.5/125
62.5
100/125
100
7/125 7
Single-mode

75. Figure Fiber construction

76. Figure Fiber-optic cable connectors

77. Note:
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

78. Note:
Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation.