SSBC

1. 1
Single Side Band Suppressed Carrier
Professor Z Ghassemlooy
Electronics and IT Division
School of Engineering
Sheffield Hallam University
U.K.

2. 2
Content
• Theory
• Transmitter Implementation
• Detector Implementation
• Power Analysis
• Summary

3. 3
Single Side Band Suppressed Carrier
From DSB-SC spectrum:
• Information ωm is carried twice
• Bandwidth is is high
ωc - ωm ωc ωc + ωm
Carrier
USBLSB
Single frequency
Question: Why transmit both side bands?
Ans:
Question: Can one suppress one of the side bandcarrier?
Ans.: Yes, just transmit one side band (i.e SSB-SC)
System complexity at the receiver
But what is the penalty?

4. 4
SSB-SC - Implementation
• Frequency discrimination
MultiplierMultiplier
Message
m(t)
Local oscillator
c(t) = cos ωct
Local oscillator
c(t) = cos ωct
DSB-SC
t
ME
t
ME
ttEtc
mc
c
mc
c
cmm
)(cos
2
)(cos
2
coscos)(
ω−ω+ω+ω=
ωω=
Band pass
filter
ωc+ ωc
Band pass
filter
ωc+ ωc
Band pass
filter
ωc- ωc
Band pass
filter
ωc- ωc
t
ME
tc mc
c
)(cos
2
)( ω+ω=
t
ME
tc mc
c
)(cos
2
)( ω−ω=
Upper sideband
Lower sideband

5. 5
SSB-SC - Waveforms
B = 2ωm
USB
Bandwidth B = ωm
B = ωm

6. 6
SSB-SC - Implementation cont.
• Phase discrimination (Hartley modulator)
XX
SSB-SC
signal
XX
Em sin ωmt sin ωct
sin ωct
cos ωctCarrierCarrier
90o
phase shift
90o
phase shift
Message
m(t)
90o
phase shift
90o
phase shift
∑∑
+
-
Em cos ωmt cos ωct
Em sin ωmt
Em cos ωmt
v(t) =Em cos ωmt cos ωct + Em sin ωmt sin ωct
= Em cos (ωm - ωc)t LSB
v(t) =Em cos ωmt cos ωct + Em sin ωmt sin ωct
= Em cos (ωm - ωc)t LSB
v(t) =Em cos ωmt cos ωct - Em sin ωmt sin ωct
= Em cos (ωm + ωc)t USB
v(t) =Em cos ωmt cos ωct - Em sin ωmt sin ωct
= Em cos (ωm + ωc)t USB

7. 7
SSB-SC - Hartley Modulator
• Advantages:
– No need for bulky and expensive band pass filters
– Easy to switch from a LSB to an USB SSB output
• Disadvantage:
– Requires Hilbert transform of the message signal. Hilbert
transform changes the phase of each +ve frequency
component by exactly - 90o
.

8. 8
SSB-SC - Detection
• Synchronous detection
MultiplierMultiplier
Low
pass
filter
Low
pass
filter Message signal
SSB-SC
Local oscillator
c(t) = cos ωct
Local oscillator
c(t) = cos ωct
Condition:
•Local oscillator has the same
frequency and phase as that of the
carrier signal at the transmitter.
ωm 2ωc+ωm
Low pass filter
high frequencyinformation
tt
ME
ty cmc
c
ω∗ω+ω= cos)(cos
2
)(
t
ME
t
ME
ty mc
c
m
c
)2(cos
4
)(cos
4
)( ωωω ++−=
t
ME
tv m
c
ω= cos
4
)(

9. 9
SSB-SC - Synch. Detection cont.
• Case 1 - Phase error
MultiplierMultiplier
Low
pass
filter
Low
pass
filter Message signal
SSB-SC
Local oscillator
c(t) = cos (ωct+θ)
Local oscillator
c(t) = cos (ωct+θ)
Condition:
•Local oscillator has the same
frequency but different phase as
that of the carrier signal at the
transmitter.
ωm 2ωc+ωm
Low pass filter
high frequencyinformation
)(cos)(cos
2
)( θ+ω∗ω+ω= tt
ME
ty cmc
c
)2(cos
4
)(cos
4
)( θωωθω +++−= mc
c
m
c
t
ME
t
ME
ty
t
ME
tv m
c
)(cos
4
)( θ−ω=

10. 10
SSB-SC - Synch. Detection cont.
• Case 1 - Frequency error
MultiplierMultiplier
Low
pass
filter
Low
pass
filter Message signal
SSB-SC
Local oscillator
c(t) = cos
(ωc+∆ω)t
Condition:
•Local oscillator has the same
phase but different frequency as
that of the carrier signal at the
transmitter.
ωm +∆ω 2ωc+ωm +∆ω
Low pass filter
high frequencyinformation
tt
ME
ty cmc
c
)(cos)(cos
2
)( ω∆+ω∗ω+ω=
t
ME
t
ME
ty mc
c
m
c
)2(cos
4
)(cos
4
)( ωωωωω ∆+++∆−=
t
ME
tv m
c
)(cos
4
)( ω∆−ω=

11. 11
SSB-SC - Power
• The total power (or average power):
R
ME
ME
R
P
c
c
SCSSBT
8
)(
2
2/1
2
2
=






=−−
• The maximum and peak envelop power
2
4
)(
R
ME
P c
SCSSBP =−−

12. 12
SSB-SC - Summary
• Advantages:
– Lower power consumption
– Better management of the frequency spectrum
– Less prone to selective fading
– Lower noise
• Disadvantage:
- Complex detection
• Applications:
- Two way radio communications
- Frequency division multiplexing
- Up conversion in numerous telecommunication systems