This document discusses digital modulation schemes 8-QAM and 16-QAM. It covers: - The key aspects of 8-QAM and 16-QAM including how digital information is encoded in both amplitude and phase, their constellation diagrams, and bandwidth requirements. - The transmitters and receivers for 8-QAM and 16-QAM, including their modulator truth tables and functionality of components like product detectors and converters. - Calculations for 8-QAM including its baud rate, fundamental frequency, and minimum bandwidth based on its bit rate. Similar calculations are covered for 16-QAM.

1. Digital Communication
Presentation by:
KARTHIKA S.
AP,ECE
SSN College of Engineering

2. Learning Objectives
On completion of this lesson you will be able to:
• Know 8-QAM, 16-QAM digital modulation schemes
Understand Bit rate, baud, BW requirement, transmitters
and receivers for the modulation schemes
• Plot the constellation diagram

3. Quardrature Amplitude Modulation
• Digital information is contained both in amplitude
and phase of the transmission carrier
• 8-QAM and 16 QAM are M-ary encoding techniques
• In 8-QAM, M=8 and N=3
• For 16-QAM, M=16 and N=4

4. 8-QAM
8-QAM Transmitter
• Same as 8-PSK except that c bit is not inverted in Q channel

5. 8-QAM cont…
• 8-QAM modulator truth table, phasor and constellation diagram

6. 8-QAM cont…
• For 8-QAM,
baud = (1/3)bit rate
• Fundamental frequency,
fa = fb / 6

7. 8-QAM cont…
• Bandwidth requirement
mathematically output of BM is,
= Xsin(ωat) x sin(ωct)
=X/2[cos(ωc-ωa)t-cos(ωc+ωa)t]
Minimun double side Nyquist bandwidth (FN )is,
B= fb /3

8. 8-QAM cont…
8-QAM Receiver
• Similar to 8-PAK receiver, difference are the PAM levels at
output of product detectors and binary signal at analog-to-
digital converter
• Output of I channel 4-to-2 level converter are I and C bits
• Output of Q channel 4-to-2 level converter are Q and C bits

9. 8-QAM cont…

10. 8-QAM cont…
8-QAM Receiver

11. 16-QAM
16-QAM Transmitter

12. 16-QAM cont…
• For 16-QAM,
baud = (1/4)bit rate
• Fundamental frequency,
fa = fb / 8

13. • Bandwidth requirement
mathematically output of BM is,
= Xsin(ωat) x sin(ωct)
=X/2[cos(ωc-ωa)t-cos(ωc+ωa)t]
Minimun double side Nyquist bandwidth (FN )is,
B= fb /4

14. Assessment
• Define 8-QAM
• What is the bit rate and baud for 8-QAM
• Draw the phasor and constellation diagram for 8-QAM

15. Summary
On completion of this lesson you have learned:
• Definitions of 8-QAM, 16-AM digital modulation schemes
and its BW requirement, transmitter and receivers.
• To calculate bit rate and baud, plot the constellation diagram