Sep 30, 2005CS477: Analog and Digital Communications1 SSB and Demodulation Analog and Digital Communications Autumn

Sep 30, 2005CS477: Analog and Digital Communications2 SSB-AM USB LSB First consider DSB-SC Pass it through an “SSB filter” Islands are not symmetric around

Sep 30, 2005CS477: Analog and Digital Communications3 SSB and DSB Comparison For DSB: For SSB: (Transmission BW is twice the signal BW)

Sep 30, 2005CS477: Analog and Digital Communications4 Tone Modulation: SSB & DSB Information signal is For DSB-SC or DSB: For USSB: For LSSB:

Sep 30, 2005CS477: Analog and Digital Communications5 Tone Modulation For DSB-SC or DSB: For USSB: Will Envelope detection work for SSB with tone modulation? NO, because envelope is a constant proportional to

Sep 30, 2005CS477: Analog and Digital Communications6 SSB With Arbitrary Input SSB Filter DSB InputSSB Output Assume SSB filter as a bandpass system with DSB as the input signal Then, apply equivalent lowpass analysis

Sep 30, 2005CS477: Analog and Digital Communications7 SSB With Arbitrary Input What is ? (Start from a DSB signal)

Sep 30, 2005CS477: Analog and Digital Communications8 SSB With Arbitrary Input For USSB Filtering: (we are filtering the DSB input signal) (For USSB)

Sep 30, 2005CS477: Analog and Digital Communications9 SSB With Arbitrary Input (For LSSB) Similarly, For LSSB: In general, for LSSB and USSB: Thus we can find the lowpass output

Sep 30, 2005CS477: Analog and Digital Communications10 SSB With Arbitrary Input Using the transform pair: Thus, lowpass output in time domain is: What is the SSB output from SSB filter?

Sep 30, 2005CS477: Analog and Digital Communications11 SSB With Arbitrary Input What are the in-phase and quadrature components? SSB output is a bandpass signal What is SSB envelope?

Sep 30, 2005CS477: Analog and Digital Communications12 SSB Generation Perfect SSB filters Hard to realize Rely on the absence of spectral components at low frequencies Use of phase shift methods SSB Filter DSB InputSSB Output

Sep 30, 2005CS477: Analog and Digital Communications13 VSB Signals Used in commercial TV broadcast Include a low power carrier in transmission One sideband is passed completely and the other is passed partially Generated by using a VSB filter Anti-symmetric around the carrier frequency Has amplitude 0.5 at the carrier frequency

Sep 30, 2005CS477: Analog and Digital Communications14 Demodulation Frequency conversion Synchronous detection Requires tight synchronization at the receiver Envelope detection Can be used with modulations where envelope truly reflects the information signal Can not be used if envelope is distorted