1. Electrical Communications Systems ECE.09.433 Spring 2019
Lecture 4a February 12, 2019
Shreekanth Mandayam
ECE Department
Rowan University

2. Plan DSB-SC Modulation Costas Loop QAM Complex Envelope Representation
Spectrum of a bandpass signal
Signals Systems
Time Domain
Complex Envelope
Spectrum
Power
Performance
Transmitters
Receivers
Standards
Modulation
Index
Efficiency
Bandwidth
Noise

3. ECOMMS: Topics

4. DSB-SC Modulation Signals Systems Message Spectrum Matlab Demo
Time Domain
Complex Envelope
Spectrum
Power
Performance
Transmitters
Receivers
Standards
Modulation
Index
Efficiency
Bandwidth
Noise
Message Spectrum
-B B
|M(f)|
Matlab Demo f
DSB-SC Spectrum
|S(f)|
-fc-B -fc fc+B fc-B fc fc+B f

5. DSB-SC: Balanced ModulatorAM
Accos2pfct
m(t) S AM
-Accos2pfct
-m(t)

6. DSB-SC: Coherent Detector
Product
Modulator
Baseband
LPF
v(t)
s(t)
Aocos2pfct
Local
Oscillator

7. Synchronous Coherent Detection: Costas PLL
I-Channel
s(t)
v1(t)
Product
Modulator
Baseband
LPF
VCO
-90o
Phase Shift X
v2(t)
v3(t)
v4(t)
Phase
Discriminator
Q-Channel

8. Quadrature Amplitude Modulation (QAM)Tx Rx
I-Channel
Product
Modulator
Local
Oscillator
-90o
Phase Shift
m1(t)
m2(t) S
s(t)
Product
Modulator
Local
Oscillator
-90o
Phase Shift
LPF
Q-Channel

9. Complex Envelope Representation
Modulator
message: m(t)
carrier: c(t)
s(t): radio signal
We want a common mathematical representation for
information transfer from baseband to bandpass
any bandpass signal
any time of modulation
signal/noise and signal+noise

10. Spectrum of a Bandpass Signal

11. Summary