1. Electrical Communications Systems ECE.09.433
QAM Systems
Dr. Shreek Mandayam
Electrical & Computer Engineering
Rowan University

2. Plan Digital Bandpass Communications
Quadrature Phase Shift Keying (QPSK)
M-ary PSK and M-ary QAM
Different ways of looking at a digitally modulated signal
Constellation diagrams
Eye diagrams

3. ECOMMS: Topics

4. Digital Communications Transceiver
Anti-
aliasing
Filter
Data
Encryption
Encoder
Error
Control
Encoder
Sampling
Channel/
Line
Encoder
Quantization
Source
Encoder
MUX
Modulator
ADC
Analog i/p
CODEC
MODEM
Multiple access channel
Analog o/p
Data
Encryption
Decoder
Error
Control
Decoder
Audio
Amp
Reconstruction/
DAC
Source
Decoder
Equalization /
Decision
Circuits
DEMUX
Demod-ulator

5. Digital Modulation Carrier signal: Ac cos (2pfct + f) Modulation: m(t)
Modulated signal: Ac (t) cos (2pfc(t) t + f(t))
 m(t); discrete
Vary Vary Vary
amplitude frequency phase
Variations are discrete!!!!!

6. Recall: Dig Comm Principle
Digital message
………
Digital
code
Analog
message
modulate AM
Sinusoidal carrier FM PM
AM & PM

7. Quadrature Phase Shift Keying (QPSK)IQ
Diagram
s(t) = Ac cos(2pfct + f(t)) Q
3p/4 01 11 10
f(t)
p/4 00
p/4 t I 10
-p/4 11 01 00
-3p/4

8. M-ary Phase Shift Keying (M-ary PSK)Q I
Octophase
I-Q
Constellation

9. M-ary Quadrature Amplitude Modulation (M-ary-QAM)
I-Q
Constellation

10. Different ways of looking at a digitally modulated signal

11. Time & Frequency Domain View
Reproduced from:

12. Frequency & Power View
Reproduced from:

13. I-Q Constellation Diagram
Matlab Demo:
qam16.m
Reproduced from:

14. Eye Diagram Matlab Demo: eyeqpsk.m
Reproduced from:

15. Summary