Signals and Systems

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					        Lecture 1
       Introduction

Principles of Communications
           Fall 2008
 NCTU EE Tzu-Hsien Sang

                               1
              Managerial Stuff
• Website: http://140.113.225.188/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
  Hours: TBA)
• Grading (tentative): Homework 25%; Midterm
  35%; Final 40%
• Five best homework scores will be chosen
  (each counts for 5%).

                                             2
             A Few More Things…
• 作業是為了讓學生熟練內容而非考倒學生,若作
  業做不出來,請儘量利用助教,找我也行。
• 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!
• 這裡是交通大學,不是交大補習班。請勿期望我
  會做重點提示或考前總整理。
• 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.
                                                          3
    “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
  amount?
• More too often we take the convenience of
  modern communications for granted.
                                              4
                  Remembrance of Things Past…




                                                 5
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
Modern Communications




                        7
8
     More on Two Perspectives


     Signal                 Information
Physical Interface        Abstract Level
   Waveform                    Bits
    Filtering                Coding
  Equalization                  ...
        ...

                     0 1 0 1 1 0 0 0 1 1 1 1 ...



                                                   9
          “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.

                                                10
            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.)
                                                    11
                Subject Matter

•   Introduction
•   Review of signals and systems
•   Analog signal transmission and reception
•   Random processes
•   Effect of noise on analog communication
    systems
•   Information sources and source coding
•   Introduction to digital communications
                                               12
“The inevitable has come…”




                             13
             Let’s Learn Some Names
• Input Transducer
  Messages: analog or digital
  Message conversion: e.g. speech  voltage variations
• Transmitter
  Purpose: couple the message to the channel
  Primary functions: modulation, filtering, amplification, and
  coupling.
• Modulation:
  (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
  single channel
  (5) to overcome equipment limitations.
                                                               14
                      More Names

• Channel: Signal degradation.
• Receiver: Primary functions are demodulation and
  amplification.
• 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),
  etc.)
  Extraterrestrial noise: Solar & cosmic noise
• Signal degradation: Fading
                                                              15
“How many lines do you get?”
    Channel Conditions




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