1. CHAPTER - 5 Introduction to Communication Systems (222 CNET - 3)
DIGITAL MODULATION TECHNIQUES

2. Chapter Contents Digital Modulation Techniques 5.1 Introduction
5.2 Modulation Schemes : ASK , FSK and PSK
5.3 M-ARY Schemes : FSK and PSK

3. Objectives of this chapter
Upon completion of this chapter student able to
Define ASK,FSK,PSK.
Describe generation and demodulation of ASK,FSK and PSK.
Define M-ary FSK and M-ary PSK .

4. Introduction Need for Digital Modulation:
AM,FM,PM will help to translating the analog message from low frequency or baseband range to high frequency or passband range.
The Pulse modulation techniques deal with representing the message at discrete instants of time.
Discrete transmission of such message over long distance via high frequency channels is not possible.
As in such case analog and digital message needs to be translated to the high frequency range .

5. Types of Modulation Schemes
The digital modulation techniques are based on the analog modulation techniques.
Basic Digital Modulation Techniques:
Amplitude Shift Keying
Frequency Shift Keying
Phase Shift Keying
The variants of basic modulation techniques termed as M-ARY include
M-ary PSK
M-ary FSK

6. Applications & Advantages
Digital modulation can easily detect and correct the noise.
Security is more in digital modulation.
Digital modulation signal can travels a long
distance.

7. Categories

8. Definitions
The digitized message with sequence of 0’s and 1’s called as digital or binary message.
ASK is a digital modulation technique defined as the process of shifting the amplitude of the carrier signal between two levels, depending on whether 1 or 0 is to be transmitted.
FSK is a digital modulation technique defined as the process of shifting the frequency of the carrier signal between two levels, depending on whether 1 or 0 is to be transmitted.
PSK is a digital modulation technique defined as the process of shifting the phase of the carrier signal between two levels, depending on whether 1 or 0 is to be transmitted.

9. Generation of ASK signal

10. Waveforms
ASK waveforms

11. Generation of FSK

12. FSK waveforms

13. Phase Shift Keying
Vc1 = VC COS ωCt and Vc2 = -VC COS ωCt

14. Definition of M-ARY Scheme
This is the type of digital modulation technique used for data transmission in which two or more bits are transmitted at a time.
The channel bandwidth is reduced because more number of bits can be transmitted on a single signal.
M – is denoted as Multiple bits or number of conditions/levels.
Types of M-ARY Schemes:
1. M-ARY PSK
2. M-ARY FSK
M-ARY PSK :
This is called as M-ary Phase Shift Keying (M-ary PSK).
The phase of the carrier signal, takes on M different levels.

15. Generation of M-ARY PSK

16. M-ARY PSK

17. Generation of M-ARY FSK
This is called as M-ary Frequency Shift Keying (M-ary FSK).
The frequency of the carrier signal, takes on M different levels.

18. M-ARY FSK WAVE FORM

19. M-ARY Equation N is the number of bits necessary/no of messages
M is the number of conditions(Carrier), levels, or combinations possible with N bits.
2N= M
For example, with two bits, 22 = 4 conditions are possible.

20. Problems

21. Problems

22. Thank You