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Fundamentals of Digital Communication

Fundamentals of Digital Communication. Digital communication system. Input Signal Analog/ Digital. Low Pass Filter. Sampler. Quantizer. Source Encoder. Channel Encoder. Multiplexer. Carrier. Modulator. Pulse Shaping Filters. Line Encoder. To Channel. De- Modulator.

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Fundamentals of Digital Communication

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  1. Fundamentals of Digital Communication

  2. Digital communication system Input Signal Analog/ Digital Low Pass Filter Sampler Quantizer Source Encoder Channel Encoder Multiplexer Carrier Modulator Pulse Shaping Filters Line Encoder To Channel De- Modulator Receiver Filter Detector From Channel Carrier Ref. Signal at the user end Digital-to-Analog Converter Channel Decoder De- Multiplexer

  3. Analog versus Digital • Harder to separate noise from an analog signal than from a digital signal • If there is too much noise cannot discern a high voltage from a low voltage

  4. Original pulse Regenerated pulse Propagation distance Voice Data A bit is a bit! Media Analog versus Digital • Regenerator receiver • Different kinds of digital signal are treated identically.

  5. Analog versus Digital • Stability of components: Analog hardware change due to component aging, heat, etc. • Flexibility: • Perform encryption • Compression • Error correction/detection • Reliable reproduction

  6. Baseband signal Bandpass signal Local oscillator Bandwidth of signal • Baseband versus bandpass: • Bandwidth dilemma: • Bandlimited signals are not realizable! • Realizable signals have infinite bandwidth!

  7. Source coding • Encoder: mapping of the dig info at the source o/p with another dig form • One-one mapping, reduce redundancy • Decoder: inverse mapping • Advantage: a reduced bandwidth requirement

  8. Channelcoding • Encoder: map the incoming dig sgl into a channel input • Decoder: map the channel o/p into an o/p dig sgl, so that channel noise is minimized • Combnd role: provide for reliable communication over a noisy channel

  9. Half-power bandwidth • Noise equivalent bandwidth • Null-to-null bandwidth • Fractional power containment bandwidth • Bounded power spectral density • Absolute bandwidth (a) (b) (c) (d) (e)50dB • Different definition of bandwidth:

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