The document discusses various digital transmission methods, including encoding techniques for converting digital data into signals. It covers line coding types such as unipolar, polar, return-to-zero, and Manchester encoding, as well as modulation techniques like amplitude, frequency, and phase modulation. Additionally, it addresses transmission modes such as asynchronous and synchronous transmission.

1. Data Communication
and Computer Networks
[EEE 314]
Mubashir Husain RehmaniMubashir Husain Rehmani
Assistant Professor
Department of Electrical Engineering
COMSATS Institute of Information Technology,
Wah Cantt, Pakistan

2. Digital
Transmission

3. Conversion Methods

4. Digital
to
DigitalDigital
Encoding

5. LineLine coding is the process ofcoding is the process of
converting digital data to digitalconverting digital data to digital
signalssignalssignalssignals

6. Line Coding

7. Signal Level vs Data Level

8. Lack of Synchronization

9. Line Coding

10. Unipolar encoding uses only one
voltage level.
In a unipolar scheme, all the
signal levels are on one side of
the time axis, either above
or below.

11. UniPolar Encoding

12. Polar encoding uses two voltagePolar encoding uses two voltage
levels (positive and negative).levels (positive and negative).

13. Types of Polar Encoding

14. NRZ Non Return to Zero
NRZ-L Non Return to Zero - Level
NRZ-I Non Return to Zero – Inverted

15. In NRZIn NRZ--L the level of the signal isL the level of the signal is
dependent upon the state of thedependent upon the state of the
bit.bit.bit.bit.

16. In NRZIn NRZ--I the signal is inverted if aI the signal is inverted if a
1 is encountered.1 is encountered.

17. NRZ-L and NRZ-I

18. RZ Encoding
Return-to-zero (RZ) scheme uses three values: positive,
negative, and zero. In RZ, the signal changes not
between bits but during the bit. The signal goes to 0 in the
middle of each bit. It remains there until the beginning of
the next bit.

19. Manchester Encoding
In Manchester encoding, the duration of the bit is divided into
two halves. The voltage remains at one level during the first
half and moves to the other level in the second half.

20. In Manchester encoding, theIn Manchester encoding, the
transition at the middle of the bittransition at the middle of the bit
is used for both synchronizationis used for both synchronizationis used for both synchronizationis used for both synchronization
and bit representation.and bit representation.

21. Differential Manchester
Encoding

22. In differential ManchesterIn differential Manchester
encoding, the transition at theencoding, the transition at the
middle of the bit is used only formiddle of the bit is used only for
synchronization.synchronization.synchronization.synchronization.
The bit representation is definedThe bit representation is defined
by the inversion orby the inversion or noninversionnoninversion
at the beginning of the bit.at the beginning of the bit.

23. In bipolar encoding, we use threeIn bipolar encoding, we use three
levels: positive, zero,levels: positive, zero,
and negative.and negative.and negative.and negative.

24. Types of Bipolar Encoding

25. BiPolar AMI Encoding

26. B8ZS Encoding

27. Analog
to
DigitalDigital
Encoding

28. Analog to Digital Encoding

29. Pulse Code Modulation (PCM)
The Analog signal is Sampled
The Sampled signal is Quantized
The Quantized values are encoded as stream
of bitsof bits

30. Sampling: PAM

31. Quantized PAM Signal

32. Digital
to
AnalogAnalog
Encoding

33. Digital to Analog Encoding

35. Bit rate is the number of bits per
second. Baud rate is the number of
signal units per second. Baud rate issignal units per second. Baud rate is
less than or equal to the bit rate.

38. ASK
In amplitude shift keying, the amplitude of the carrier signal is
varied to create signal elements. Both frequency and phase
remain constant while the amplitude changes.

39. FSK
In frequency shift keying, the frequency of the carrier
signal is varied to represent data.

40. PSK
In phase shift keying, the phase of the carrier is varied to
represent two or more different signal elements. Both peak
amplitude and frequency remain constant as the phase
changes.

41. PSK Consetllation
A constellation diagram can help us define the amplitude
and phase of a signal element

42. 4-PSK Method

43. 4-PSK Constellation

44. 8-PSK

45. QAM
Quadrature amplitude modulation is a
combination of ASK and PSK so that a
maximum contrast between each signalmaximum contrast between each signal
unit (bit, dibit, tribit, and so on) is
achieved.

46. Table 5.1 Bit and baud rate comparison
ModulationModulation UnitsUnits Bits/BaudBits/Baud Baud rateBaud rate Bit Rate
ASK, FSK, 2ASK, FSK, 2--PSKPSK Bit 1 N N
44--PSK, 4PSK, 4--QAMQAM Dibit 2 N 2N
88--PSK, 8PSK, 8--QAMQAM Tribit 3 N 3N
1616--QAMQAM Quadbit 4 N 4N
3232--QAMQAM Pentabit 5 N 5N
6464--QAMQAM Hexabit 6 N 6N
128128--QAMQAM Septabit 7 N 7N
256256--QAMQAM Octabit 8 N 8N

47. Transmission Mode

48. Parallel Transmission

49. Serial Transmission

50. In asynchronous transmission,In asynchronous transmission,
we send 1 start bit (0) at thewe send 1 start bit (0) at the
beginning and 1 or more stopbeginning and 1 or more stopbeginning and 1 or more stopbeginning and 1 or more stop
bits (1s) at the end of each byte.bits (1s) at the end of each byte.
There may be a gap betweenThere may be a gap between
each byte.each byte.

51. Asynchronous here meansAsynchronous here means
“asynchronous at the byte level,”“asynchronous at the byte level,”
but the bits are stillbut the bits are stillbut the bits are stillbut the bits are still
synchronized; their durations aresynchronized; their durations are
the same.the same.

52. Asynchronous Tranmission

53. In synchronous transmission,In synchronous transmission,
we send bits one after anotherwe send bits one after another
without start/stop bits or gaps.without start/stop bits or gaps.without start/stop bits or gaps.without start/stop bits or gaps.
It is the responsibility of theIt is the responsibility of the
receiver to group the bits.receiver to group the bits.

54. Synchronous Tranmission

55. Modulation of Analog Signals
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)

56. Analog to Analog Modulation

57. Types of Analog Modulation

58. AM

59. FM