1. Digital Communication Chapter 1: Introduction
Fall 2011

2. Elements of A Digital Communication System
Modulation/ Demodulation
Channel Coding
Source Coding
Information Source
Source Encoder
Channel Encoder
Digital Modulator
Channel
Digital Demodulator
Channel Decoder
Source Decoder
Output Transducer
Output Signal

3. Information Source Analog Sources Digital Sources Voice, Video
Data Packet from Internet
Discrete content in CD

4. Source Coding Function Design Objective: Example
Convert the analog or digital information source to a bit sequence
Remove redundancy in the information source
Design Objective:
Use minimum number of bits to represent the source with minimum distortion
Example
JPEG, MPEG, PCM, etc.
Is introduced in a different course

5. Channel Coding Function Design Objective Example
Add redundancy to achieve reliable communication
Design Objective
Use minimum redundancy to achieve maximum reliability
To achieve larger coding gain
Example
Block Code, Convolutional Code, Turbo Code, LDPC
Is introduced in a different course

6. Modulation/Demodulaton
Function
Map the bit sequence to signal waveforms suitable for channel transmission
Design Objectives
Design modulation schemes and signal waveforms to achieve the channel capacity
Example
BPSK, QAM, PSK, CPM  Single Antenna
Space-Time Coding/Modulation  Multiple Antennas
Is the main focus of this course

7. Joint Source-Channel Coding
Information Source
Source Encoder
Channel Encoder
Digital Modulator
Channel
Output Signal
Output Transducer
Source Decoder
Channel Decoder
Digital Demodulator
Combine the source coding and channel coding to achieve better performance:
Source Coding  Remove Redundancy
Channel Coding  Add Redundancy
Have found applications in speech and video transmission

8. Coded Modulation Coded Modulation Information Source Source Encoder
Channel Encoder
Digital Modulator
Channel
Output Signal
Output Transducer
Source Decoder
Channel Decoder
Digital Demodulator
Combine the channel coding and modulation to achieve better performance:
Channel Coding  Reduce the data rate (add redundancy)
Modulation Improve the data rate (transmits more bits in a symbol)
Have found wide applications
Trellis Coded Modulation
Bit-Interleaved Coded Modulation

9. Channel Type of channels We cannot design the channel
Wireline Channel
Fiber-optic Channel
Wireless Channel
Underwater Acoustic Channel
Storage Channel
We cannot design the channel
One exception: Anechoic Chamber
We can design source coding, channel coding, modulation etc. to achieve optimum performance for one particular channel.

10. Layered Model Application Application HTTP, FTP, Email, VoIP, Video
Representation
Representation
Session
Session
Transport
Transport
TCP, UDP
Network Layer
Network Layer
IPv4, IPv6
Data Link
Data Link
MAC, LLC
Physical Layer
Physical Layer
Our Course
Channel

11. AWGN Channel
Ideal abstraction channel model, mainly used in design and analysis
Source of Noise
Mainly from the electronic components and amplifiers at the receiver

12. Band-Limited (AWGN) Channel
Bandwidth is limited by the linear filter
Example
Wireline Telephone Channel

13. Fading (Band-Limited AWGN) Channel
A special case commonly used
Example
Wireless Channel

14. Outline of The Course Deterministic and Random Signals TX Channel RX
Coded Bits
Modulated Waveform
Received Waveform
To Decoder
Modulation Schemes
Chapter 3*
Pulse Shaping
Chapter 9
Diversity Techniques
Chapter 14
AWGN Channel
Chapter 3, 4
Band-Limited Channel
Chapter 9, 10,
Fading Channel
Chapter 13,14
Detection
Chapter 4
Synchronization
Chapter 5
Equalization
Chapter 10,13,14
*The Chapter number is based on the Fifth Edition of Proakis’ Book