This chapter discusses various modulation techniques used in communication systems. It explains concepts like amplitude, frequency and phase modulation. It provides examples of modulation used in modems and discusses modem standards for communication and data compression. Finally, it describes analog-to-digital modulation techniques like PAM, PCM and PDM used to represent analog signals digitally for computer processing.
This presentation will explain about the need for modulation in communication system. We made this presentation as our group assignment in Analog and Digital Communication System course in MIIT.
This presentation will explain about the need for modulation in communication system. We made this presentation as our group assignment in Analog and Digital Communication System course in MIIT.
Frequency Modulation In Data TransmissionBise Mond
This presentation includes concepts of FM, generation of FM, transmission, reception, with the concepts of stereo FM and some basic circuitry of receiver and transmitter system.
Modulation
In the modulation process, some characteristic of a high-frequency carrier signal (bandpass), is changed according to the instantaneous amplitude of the information (baseband) signal.
the modulation of a wave by varying its amplitude, used especially as a means of broadcasting an audio signal by combining it with a radio carrier wave.
the modulation of a wave by varying its amplitude, used especially as a means of broadcasting an audio signal by combining it with a radio carrier wave.
Frequency Modulation In Data TransmissionBise Mond
This presentation includes concepts of FM, generation of FM, transmission, reception, with the concepts of stereo FM and some basic circuitry of receiver and transmitter system.
Modulation
In the modulation process, some characteristic of a high-frequency carrier signal (bandpass), is changed according to the instantaneous amplitude of the information (baseband) signal.
the modulation of a wave by varying its amplitude, used especially as a means of broadcasting an audio signal by combining it with a radio carrier wave.
the modulation of a wave by varying its amplitude, used especially as a means of broadcasting an audio signal by combining it with a radio carrier wave.
ADC - Analog to Digital Conversion on AVR microcontroller Atmega16Robo India
Robo India in this PPT is explaining on the most crucial and important aspect of Embedded system, robotics, automation and physical computing.
Analog to digital conversion is required in almost every project of above mentioned domain. One advantage to use a AVR micro controller is that it has inbuilt ADC thus we donot need to use external system for ADC.
Here Robo India is teaching how to use ADC in AVR series microcontrollers.
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mail- info@roboindia.com
A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device.
The word modem is an acronym for modulator-demodulator. Basically, a modem is used for transmitting and receiving data over a communication channel, such as twisted-pair telephone lines, coaxial cables, and optical fibers. Currently the purpose of a modem is to convert a computer’s data stream to analog format so that it can be transmitted over the analog telephone line.
At the source, modulation techniques are used to convert digital
Data (0’s and 1’s) into analog form for transmission across the channel. At the destination, the received analog signal is converted to digital data via demodulation. This is a simplified explanation of how a modem works, and there are other issues that require attention; such as channel impairments, encryption, error detection/correction, data compression, modulation, handshake negotiation, and echo cancellation. These features will be discussed a bit later.
It is used in cases where the amount of data being sent is relatively small. It ensures that data integrity is maintained as it transmits the data bits in a specific order, one after another
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
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
Modulated Amplitude
Voice
Carrier
Wave
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
F1
0
F2
1
F3
0
F4
1
Voice
Band-
Width
A B
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)
21. Phase of an Analog Signal
Y
Strength
X
0 90 180 270 360
Time Frame
22. The Concept of Phase Shift
90 degrees phase shift
180 degrees phase shift
0 90
0 180
23. Phase Modulation Technique
1
0
90 Degrees
0 Degree phase shift
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
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
F1
0
F2
1
F3
0
F4
1
Voice
Band-
Width
A B
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
– 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
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 Same
1
0
F1 F2
1 Second
bps = 1
Baud = 1
37. Example Where bps and Baud are
Different
00 01 10 11
bps = 2
Baud = 1
1 second
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
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
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
Analog Signals
PAM or PDM
PCM
* See earlier slides for
details on PAM and PCM
Computer
Processing
Digitize
Encode
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
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
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