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# L4 - NOISE Random disturbances usually additive Thermal...

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NOISE : Random disturbances, usually additive Thermal noise Burst-type noises Impulse noise Atmospheric noise THERMAL NOISE Due to random electron motion Proportional to absolute temperature Proportional to bandwidth

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Spectral density concept : S(f) measures how power of a random noise or signal is distributed in frequency. Thermal noise has a constant spectral density over all frequencies used in communication.
Maximum data rate of a channel Crudely, if we send the ideal 2W (2H in text notation) samples/second and can distinguish V = 2 levels, we could send k 2 2Hk = 2H*log V bits per second. This leaves unanswered how many levels V we could hope to distinguish. This is mainly limited by random noise fluctuations. Shannon developed an equation for the maximum data rate, as a function of: noise signal received power bandwidth.

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Assume pure thermal noise. 0 The noise power in a band of H herz is N H. S is the signal power. 0 S/N = S/N H is called the signal-to-noise power ratio.
0 S/N = S/N H Shannon proved it is not possible to send

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L4 - NOISE Random disturbances usually additive Thermal...

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