1. Electrical Communications Systems ECE.09.331 Spring 2010
Lecture 7a March 2, 2010
Shreekanth Mandayam
ECE Department
Rowan University

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

3. ECOMMS: Topics

4. 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

5. Spectrum of a Bandpass Signal

6. 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

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

8. 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

9. 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

10. Single Sideband (SSB) Modulation
Recall: DSB-SC Spectrum
USSB - Signal with zero-valued spectrum for |f| < fc
LSSB - Signal with zero-valued spectrum for |f| > fc
-fc-B -fc fc+B fc-B fc fc+B
|S(f)| f

11. The Hilbert Transform time, t in sec -1 -0.5 0.5 1 1.5 2 3 4 5 6 7
0.5 1
1.5 2 3 4 5 6 7
time, t in sec
» t=0:0.1:2*pi;
» w=sin(t);
» plot(t,w)
» hold
Current plot held
» H=hilbert(w);
» plot(t,imag(H),'r');
» xlabel('time, t in sec')

12. SSB Generation S Phasing Method Filter Method m(t) s(t) m(t) s(t)
Product
Modulator
Carrier
-90o
Phase Shift
m(t) S
s(t)
Filter Method
Sideband
Filter
Carrier
Product
Modulator
m(t)
s(t)

13. SSB Generation: Weaver’s Method

14. Summary