Signal Modulation in Communication Systems
Learn about message signals such as audio, video, text, and email, and how they require a carrier signal for long-distance transmission through modulation. Explore concepts like DSB, SSB generation, modulation efficiency, demodulation, FM, PM, and more in communication systems.
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Presentation Transcript
Message signals such as audio, video, text, email are weak power signals Message signals need a carrier signal to travel long distances The process of combining message and carrier signals is called modulation modulation
Time domain equation yAM(t) = Information or message x carrier = m(t) x A cos(wct) Frequency domain equation
Power in DSB signal DSB-C (with carrier) = Carrier Power + Carrier Power x Message power DSB-SC (suppressed carrier) = Carrier Power x Message power Bandwidth of DSB signal = 2 m
Balanced Modulator SSB generation ySSB(t)=0.5m(t)cos(wct) 0.5 sin(wct) SSB power and bandwidth SSB power = DSB power/2 SSB bandwidth = DSB bandwidth/2
Modulation index , -1 < < 1, Modulation efficiency
Demodulation message from the AM signal Demodulation is the process of extracting the
Frequency Modulation (FM) Phase Modulation (PM)
Power in FM/PM signal Bandwidth of FM/PM signal BFM/PM = 2B ( + ) Modulation index
FM is less susceptible to noise as compared to AM FM has better sound quality than AM; however, this also requires higher bandwidth than AM. Power requirement is less in FM as compared to AM FM has shorter range of transmission, requiring Line of Sight (LOS) propagation.
Channel interference is estimated by Signal to Noise ratio Signal to Noise ratio (SNR) SNR) SNR in AM is constant SNRAM = SNRbaseband SNR in FM can be improved by increasing the modulation index SNRFM = 1.5 2SNRbaseband
Filters can minimize noise in AM/FM systems Weiner Filter can adapt to signal power (Sx) and channel noise power (Sn) densities
