This document provides an introduction to digital modulation techniques. It discusses the reasons for choosing encoding techniques and defines modulation as adding information to a carrier signal. It describes the key signal characteristics that can be modified - amplitude, frequency, and phase. It also summarizes three common digital modulation techniques: ASK uses two amplitude levels to encode bits, FSK uses two frequencies, and PSK uses two phase shifts. References for further reading are also provided.

1. EC6651 Communication Engineering
Introduction to
Digital modulation techniques
Prepared by,
Mr.R.Deiva Nayagam, AP/ECE
Ramco Institute of Technology

2. Modulations systems

3. Reasons for choosing encoding
techniques

4. What is modulation ?
• Modulation = Adding information to a carrier signal
• The sine wave on which the characteristics of the
information signal are modulated is called a carrier signal

5. Analog modulation

6. Digital modulation and
demodulation

7. Signal characteristics that can be
modified
signal x(t) = A cos(2πft + Φ)
• A – amplitude
• f – frequency
• Φ – phase (initial angle of the sinusoidal function at its
origin

8. Modulation

9. Modulation (1)

10. Digital modulation techniques

11. ASK
• ASK On-off keying (Amplitude Shift Keying) –
frequency is kept constant, amplitude has 2 levels (for bit
1 and for bit 0)
The binary sequence 0010110010

12. FSK (Frequency shift keyring)

13. PSK (Phase shift keyring)

14. References
Taub & Schiling “Principles of Communication
Systems” Tata McGraw Hill 2007.
J.Das “Principles of Digital Communication” New Age
International, 1986.