8_QAM__16_QAM.pdf

digital communication

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, transmit ters
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-aryencoding 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, phasorand constellati on diagram

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

7. 8-QAM cont… • Bandwidth requirement
mathematically output of BM is,
= Xsin(
ω
a
t) x sin(
ω
c
t)
=X/2[cos(
ω
c
-
ω
a
)t-cos(
ω
c
+
ω
a
)t]
Minimundouble side Nyquistbandwidth (F
N
)is,
B= f
b
/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 an alog-to-
digital converter
• Output of I channel 4-to-2 level converter are I a nd C bits
• Output of Q channel 4-to-2 level converter are Q a nd 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,
f
a
= f
b
/ 8

13. • Bandwidth requirement
mathematically output of BM is,
= Xsin(
ω
a
t) x sin(
ω
c
t)
=X/2[cos(
ω
c
-
ω
a
)t-cos(
ω
c
+
ω
a
)t]
Minimundouble side Nyquistbandwidth (F
N
)is,
B= f
b
/4

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

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