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

2 Content Theory Transmitter Implementation Detector Implementation Power Analysis Summary

3 Single Side Band Suppressed Carrier From DSB-SC spectrum: Information  m is carried twice Bandwidth is is high  c -  m  c  c +  m Carrier USB LSB 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 SSB-SC - Implementation Frequency discrimination Multiplier Message m(t) Local oscillator c(t) = cos  c t Local oscillator c(t) = cos  c t DSB-SC Band pass filter  c +  c Band pass filter  c +  c Band pass filter  c -  c Band pass filter  c -  c Upper sideband Lower sideband

5 SSB-SC - Waveforms B = 2  m USB Bandwidth B =  m B =  m

6 SSB-SC - Implementation cont. Phase discrimination (Hartley modulator) X X SSB-SC signal X X E m sin  m t sin  c t sin  c t cos  c t Carrier 90 o phase shift 90 o phase shift Message m(t) 90 o phase shift 90 o phase shift   + - E m cos  m t cos  c t E m sin  m t E m cos  m t v(t) =E m cos  m t cos  c t + E m sin  m t sin  c t = E m cos (  m -  c )t LSB v(t) =E m cos  m t cos  c t + E m sin  m t sin  c t = E m cos (  m -  c )t LSB v(t) =E m cos  m t cos  c t - E m sin  m t sin  c t = E m cos (  m +  c )t USB v(t) =E m cos  m t cos  c t - E m sin  m t sin  c t = E m cos (  m +  c )t USB

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 - 90 o.

8 SSB-SC - Detection Synchronous detection Multiplier Low pass filter Low pass filter Message signal SSB-SC Local oscillator c(t) = cos  c t Local oscillator c(t) = cos  c t Condition: Local oscillator has the same frequency and phase as that of the carrier signal at the transmitter. mm 2c+m2c+m Low pass filter high frequency information

9 SSB-SC - Synch. Detection cont. Case 1 - Phase error Multiplier Low pass filter Low pass filter Message signal SSB-SC Local oscillator c(t) = cos (  c t+  ) Local oscillator c(t) = cos (  c t+  ) Condition: Local oscillator has the same frequency but different phase as that of the carrier signal at the transmitter. mm 2c+m2c+m Low pass filter high frequency information

10 SSB-SC - Synch. Detection cont. Case 1 - Frequency error Multiplier Low pass filter Low pass filter Message signal SSB-SC Local oscillator c(t) = cos (  c +  )t Condition: Local oscillator has the same phase but different frequency as that of the carrier signal at the transmitter.  m +  2  c +  m +  Low pass filter high frequency information

11 SSB-SC - Power The total power (or average power): The maximum and peak envelop power

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