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

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

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. Channel coding 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. Different definition of bandwidth:
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