Principles of Communications
NCTU EE Tzu-Hsien Sang
• Website: http://126.96.36.199/phpBB2/
• Please register with your student ID number.
• My office Hours: Thursdays 3:30~5:30pm.
• TA: 黃俞榮，鐘譯賢 ED 317A (Office
• Grading (tentative): Homework 25%; Midterm
35%; Final 40%
• Five best homework scores will be chosen
(each counts for 5%).
A Few More Things…
• Please ask questions! I am eager to have your
feedback. If you have any issues, please speak up.
Don’t wait until it’s too late!
• To encourage the exchange on class, each reasonable
response to my question will be credited with 1 extra
point on the final grade. Each student is eligible to
receive up to 5 extra points.
“In the beginning there was the word…”
• Define “communication.”
• Goal: conveyance of “information”
• Methods: signals and systems
• Define “information”
• What do we care: information value or
• More too often we take the convenience of
modern communications for granted.
Remembrance of Things Past…
Source: Fernand Braudel “15至18世紀的物質文明、經濟和資本主義”
The Value of Information
• In 1815, the Rothchilds (a Jewish banking family) received in
London the news of Wellington’s victory at the battle of
Waterloo a full day ahead of the government’s official
messengers. (Dump the franc, bought in the British pound, and
made a hell lot of money.)
• In 2002, Dave Cummings moved his firm's (Tradebot)
computers in Kansas City to buildings in New York and New
Jersey that house central computers for two big electronic
stock exchanges. (Save about 20 ms. Enough to intercept
orders before they get matched. Make $20,000,000 per year.) 6
More on Two Perspectives
Physical Interface Abstract Level
0 1 0 1 1 0 0 0 1 1 1 1 ...
“We are what we can do…”
• How are we going to study these two subjects?
• How to represent a signal?
• How about the noise?
• How to measure the amount of information?
• How to “visualize” the information space?
• How to put a whole system together?
• We’ve got two powerful weapons alright.
My Little Two Pennies
• Linearity & Probability
• How to study a complicated thing?
• First, dissect it! But you need to put it back.
(The paradigm of analysis/synthesis)
• What can you say about things that you really
don’t know much, e.g., the noise?)
• Know thy dice! (Make the uncertainty
principle your best friend.)
• Review of signals and systems
• Analog signal transmission and reception
• Random processes
• Effect of noise on analog communication
• Information sources and source coding
• Introduction to digital communications
“The inevitable has come…”
Let’s Learn Some Names
• Input Transducer
Messages: analog or digital
Message conversion: e.g. speech voltage variations
Purpose: couple the message to the channel
Primary functions: modulation, filtering, amplification, and
(1) for ease of radiation
(2) to reduce noise and interference
(3) for channel assignment
(4) for multiplexing or transmission of several messages over a
(5) to overcome equipment limitations.
• Channel: Signal degradation.
• Receiver: Primary functions are demodulation and
• Output Transducer: Loudspeaker, tape recorders, personal
computers, LCD screens, etc.
• Noises (Three major sources listed below)
Internal noise: noise generated by components within a
communication system, such as resistors and solid-state active
devices. (Thermal noise, shot noise, and flicker noise)
External noise: Atmospheric noise; Man-made noise (Ignition
noise; Switching noise; Radio-frequency interference (RFI),
Extraterrestrial noise: Solar & cosmic noise
• Signal degradation: Fading
“How many lines do you get?”