1. CHAPTER Modulation

2. Chapter Objectives
Explain amplitude, frequency and phase shift modulation
Give an example of a modulation technique used in modems
Discuss modem standards
Communication, compression etc.
Continued

3. Continuation of Chapter Objectives
Differentiate between bps and Baud that are units used for measuring communication speed
Describe analog-to-digital modulation
Explain digital-to-digital interface
Summarize the different types of signal conversions
Digital-to-analog, analog-to-digital, analog-to-analog and digital-to-digital

4. Chapter Modules Amplitude modulation
Frequency and phase shift modulation
Modems and modulation
FM modulation in modems
Speed of modulated signals
Analog-to-digital modulation
Digital-to-digital interfacing

5. Overview Digital-to-analog modulation Analog-to-digital modulation
Computer-to-telephone interface
Analog-to-digital modulation
Digitization of audio
Digital-to-digital interface
Computer-to-ISDN interface

6. Modulation
Amplitude Modulation

7. Overview of Modulation
Phone
Line
RJ-11
Serial link
RS -232
Modem
Computer
Digital
Analog

8. Amplitude Modulation (AM)1 1 A B
Amp. 2
Amp. 1

9. Characteristics of Amplitude Modulation
Amplitude of the analog signal is modulated
One amplitude represents a 0
Another amplitude represents a 1
Frequency remains unchanged in both cases
Signals that are modulated at one end are demodulated at the other end

10. Usage Amplitude is susceptible to interference
This technique in not normally used in modems
A variation of this technique is used in AM radio transmission
Analog-to-analog modulation takes place

11. AM and Radio Transmission
Voice
Carrier
Wave
Modulated Amplitude

12. End of Module

13. Module
Frequency Modulation

14. Frequency Modulation (FM)
1 = Frequency F1
0 = Frequency F2 1 1
Freq. 2
Freq. 1

15. Characteristics of Frequency Modulation
Frequency is modulated
Frequency f1
Represents 1
Frequency f2
Represents 0
The amplitude remains unaltered in both cases

16. Usage Variations in frequency are easy to detect
They are less susceptible to interference
FM and variations of this technique are used in modems
Easy to implement full duplex transmission under FM
A variation of the FM technique described here is used in FM radio transmission

17. Use of FM in Early Day Modems
Voice
Band-
Width F3 F4 1 F1 F2 1 B A
Full-duplex Communication

18. Modulation in Modern Day Modems
Modern day modems may not use the FM technique for modulation
They may be using a technique known as Phase Shift Modulation (or Phase Shift Keying)

19. End of Module

20. Phase Shift Keying (PSK) Modulation
Module
Phase Shift Keying (PSK) Modulation

21. Phase of an Analog SignalY
Strength 90
180
270
360 X
Time Frame

22. The Concept of Phase Shift
90 degrees phase shift 90
180 degrees phase shift
180

23. Phase Modulation Technique1
90 Degrees
phase shift
0 Degree
phase shift
This is also known as phase shift keying.

24. Characteristics of Phase Shift Modulation
Phase is modulated
Phase shift of 0 represents a 0
Phase shift of 90 degrees represents a 1
Both amplitude and frequency remain unaltered is both cases
Also known as Phase Shift Keying, it is used in a number of modern modems as well

25. End of Module

26. FM Modulation in Modems
Module
FM Modulation in Modems

27. Module Objectives Explain the basic concept of modem communication
Provide an example of frequency modulation used in modems
Discuss the importance of call mode setting
Call mode and receive mode settings

28. Basic Concepts of Modem Communication
Voice
Band-
Width F3 F4 1 F1 F2 1 B A
Full-duplex Communication

29. FM Details Different frequencies are used for transmission At node A
F1 for 0
F2 for 1
At node B
F3 for 0
F4 for 1

30. Call and Receive Modes Setting for communication
Set one side on call mode
Set the other side on receive mode
The above would ensures proper assignment of frequencies

31. Mode Setting Rule Calling mainframes or on-line services In general
Set the calling computer on call mode
In general
Set the home computer on the call mode
Fortunately, in a number of cases, the modems poll and set themselves dynamically for communication between the receiver and the sender

32. End of Module

33. Terms Used in Measuring the Communication speed
Module
Terms Used in Measuring the Communication speed

34. Overview
In general, the terms used for measuring speed are bps and Baud
The former is being used more widely than the latter
bps is the accurate measure of the speed of communication
In the past, Baud was being used interchangeable with bps
Both are not interchangeable
Only in certain circumstances they amount to the same

35. Definition of bps and Baud
bps represents the number of bits transmitted per second
Baud represents the number of times the signal changes its state during a given period of time

36. Example Where bps and Baud Represent the Same1
bps = 1
Baud = 1 F2 F1
1 Second

37. Example Where bps and Baud are Different
1 second 11 10 00 01
bps = 2
Baud = 1

38. Frequency Representation
Bits
Frequency
00 1
01 2
10 3
11 4

39. In Summary
bps measures the speed of communication correctly in bits per second
Baud indicates he number of times the state of a signal changes in one second

40. End of Module

41. Module
Modem Standards

42. Modem Standardization
The International body that standardizes the modulation technique is known as the ITU
ITU is also responsible for setting standards pertaining to:
Error correction
Data compression

43. Sample ITU Specifications
Modulation
ITU V.34
Error correction
ITU V.42
MNP 5
Data compression
ITU V.42 bis
MNP 2 to 4

44. Bell Standard and its Implications
At 1200 bps and below there were two standards
CCITT (ITU at present)
Bell
A Bell modem cannot communicate with a CCITT modem
Bell standard at that time was used predominantly in the US
Today, all modems fall under the ITU specifications

45. Sample Protocols and Speed
V.92 for 56,000 bps
V.90 for 56,000 bps
V.34 for 28,800 bps
V.32 bis for 14,400 bps
V.32 for 9,600 bps
A high speed modem could also operate at the lower speed
High speed modems can thus communicate with a low speed modems

46. A Note on the Protocol Used in the Faster 56K Modems
When the 56K modems were first introduced there were two competing standards
One was the X2 standard proposed by US Robotics that is now part of 3Com
The competing protocol was knows as the Kflex56 standard
A joint effort between Lucent and Rockwell

47. ITU Standard for 56K Modems
Both standards have now been superceded by the ITU V.90 standard
The vendors now produce modems that operate under the ITU V.90 protocol
The vendors also offer upgrades to the older X2 and Kflex modems so that they could operate under V.90

48. In Summary
ITU specified protocols with respect to modems exist for the following.
Modulation
Error correction
Data compression
Different protocols apply to different speeds of communication
A high speed modem can communicate with a low speed modem

49. End of Module

50. Analog-to-Digital Mapping
Module
Analog-to-Digital Mapping

51. An Overview of Analog-to-Digital Modulation
Representation of analog signals by digital signals is known as analog-to-digital modulation
Often the digitized information is further coded into binary form for computer processing
Sample applications include the encoding of audio for computer processing

52. Steps Involved in the Representation of Analog Signals by Digital Signals
* See earlier slides for
details on PAM and PCM
PAM or PDM
Digitize
Computer
Processing
PCM
Encode

53. Modulation Techniques
Pulse Amplitude Modulation (PAM)
Pulse Code Modulation (PCM)
Pulse Duration Modulation (PDM)

54. Pulse Duration Modulation
110
001
101 6 1 5
Note: pulse duration is proportional to
The height of the analog wave

55. Salient Points of Pulse Duration Modulation
Sample the analog signal at predetermined time intervals
Sampling rate
Generate digital pulses of duration proportional to the amplitude of the analog signal at the sampling point
Encode the information into binary form

56. Reference
More information on Asynchronous Transmission

57. End of Module

58. Digital-to-Digital Interfacing
Module
Digital-to-Digital Interfacing

59. Module Objectives
Explain the difference between signal modulation (conversion) and digital-to-digital signal transformation
Explain the concept of digital-to-digital interfacing using ISDN as an example
Provide a summary of the different modulation processes

60. Overview Analog-to-Digital signal conversion requires modulation
Digital-to-Digital interfacing
Requires conversion and not modulation
In this case, digital signals are converted from one digital format to another digital format
Hence, the need for an interface unit even though the signals at both ends are represented in digital form
An example is the Computer-to-ISDN link

61. Digital-to-Digital Interfacing
RS232C
Digital
ISDN
Phone
Line
Computer
ISDN
Adapter
Adapter Converts
From Computer To
ISDN Format

62. Summary of Modulation Digital-to-analog FM used in modems
Analog-to-digital
PAM and PCM used in the digitization of audio
Analog-to-analog
AM used in radio transmission
Digital-to-digital
This is not a modulation process
Used by the ISDN interface to the computer
Used in DSL communication

63. End of Modulation

64. END OF CHAPTER