CSE3213_05_AnalogDigitalTransmissionW2012_Part_8 - Data...

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36 Example [ multilevel digital transmission ] 2-level encoding: C=2B [bps] one pulse – one bit 4-level encoding: C=2*2=4B [bps] one pulse – two bits Data Rate Limits: Nyquist Theorem 8-level encoding: C=2*3=6B [bps] one pulse – three bits 100110100011010010 100110100011010010
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Data Rate Limits: Shannon Theorem Shannon Law max transmission rate over a channel with bandwidth B, with Gaussian distributed noise , and with signal-to- noise ratio SNR=S/N , is theoretical limit – there are numerous impairments in every real channel besides those taken into account in Shannon's Law (e.g. attenuation, delay distortion, or impulse noise) no indication of levels – no matter how many levels we use , we cannot achieve a data rate higher than the capacity of the channel in practice we need to use both methods (Nyquist & Shannon) to find what data rate and signal levels are appropriate for each particular channel: The Shannon capacity gives us the upper limit! The Nyquist formula tells us how many levels we need!
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CSE3213_05_AnalogDigitalTransmissionW2012_Part_8 - Data...

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