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. Goal of Modulation Techniques
Modulation is difficult task in hostile channels like the mobile radio channels
Small-scale fading and multi-path conditions.
The goal of a modulation scheme is:
To transport the message signal through the radio channel with best possible quality.
To occupy least amount of radio (RF) spectrum.

4. Multipath Propagation
signal at sender
signal at receiver
LOS pulses
multipath
pulses
short term fading
long term
fading t
power

5. Wireless channel
Effective channel depends on both physical environment and bandwidth!