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					                Data vs Signals
     Periodic Analog Sine Wave
                 Digital Signals




Data Communications and Networking:
       Data & Signals - Part I

               Somjet Suppharangsan

        Department of Electrical Engineering,
      Faculty of Engineering, Burapha University


                       19 June 2012




         Somjet Suppharangsan      Review of Data and Signals 1
                               Data vs Signals    Data
                    Periodic Analog Sine Wave     Signals
                                Digital Signals   Periodic vs Non-Periodic Signals


Outline

  1   Data vs Signals
        Data
        Signals
        Periodic vs Non-Periodic Signals
  2   Periodic Analog Sine Wave
        Sine Wave
        Time vs Frequency Domains
        Composite Signal
        Bandwidth
  3   Digital Signals
        Transmission of Digital Signals
        Baseband vs Broadband Transmissions
        Transmission Impairment


                        Somjet Suppharangsan      Review of Data and Signals 1
                             Data vs Signals    Data
                  Periodic Analog Sine Wave     Signals
                              Digital Signals   Periodic vs Non-Periodic Signals


Data




  Types of Data
      Analog Data : continuous values e.g. analog clock
       Digital Data : discrete values e.g. digital clock




                      Somjet Suppharangsan      Review of Data and Signals 1
                            Data vs Signals    Data
                 Periodic Analog Sine Wave     Signals
                             Digital Signals   Periodic vs Non-Periodic Signals


Signals




  Types of Signal
      Analog Signal : an infinite number of values in a range
      Digital Signal : a limited number of values




                     Somjet Suppharangsan      Review of Data and Signals 1
                            Data vs Signals    Data
                 Periodic Analog Sine Wave     Signals
                             Digital Signals   Periodic vs Non-Periodic Signals


Periodic vs Non-Periodic Signals




  Definition
      Periodic : complete a pattern within a period
      Non-Periodic : no pattern over time




                     Somjet Suppharangsan      Review of Data and Signals 1
                                                  Sine Wave
                               Data vs Signals
                                                  Time vs Frequency Domains
                    Periodic Analog Sine Wave
                                                  Composite Signal
                                Digital Signals
                                                  Bandwidth


Outline

  1   Data vs Signals
        Data
        Signals
        Periodic vs Non-Periodic Signals
  2   Periodic Analog Sine Wave
        Sine Wave
        Time vs Frequency Domains
        Composite Signal
        Bandwidth
  3   Digital Signals
        Transmission of Digital Signals
        Baseband vs Broadband Transmissions
        Transmission Impairment


                        Somjet Suppharangsan      Review of Data and Signals 1
                                                Sine Wave
                             Data vs Signals
                                                Time vs Frequency Domains
                  Periodic Analog Sine Wave
                                                Composite Signal
                              Digital Signals
                                                Bandwidth


Periodic Sine Wave



  Facts
  y (t) = A sin(2πft + φ)
                                                                               1
      frequency and period are the inverse of each other : f =                 T
      phase (φ) describes the position of the waveform relative to
      time 0
      wavelength: λ = c , where c is the propagation speed e.g.
                       f
      light speed = 3 × 108




                      Somjet Suppharangsan      Review of Data and Signals 1
                                               Sine Wave
                            Data vs Signals
                                               Time vs Frequency Domains
                 Periodic Analog Sine Wave
                                               Composite Signal
                             Digital Signals
                                               Bandwidth


Time vs Frequency Domains



  Time vs Frequency Domains
      Time Domain: plotting between time and amplitude
      Frequency Domain: plotting between frequency and amplitude

  Fact
  A complete sine signal in the time domain can be represented by
  one single spike in the frequency domain. A composite signal is the
  signal made of many simple sine signals.




                     Somjet Suppharangsan      Review of Data and Signals 1
                                                Sine Wave
                             Data vs Signals
                                                Time vs Frequency Domains
                  Periodic Analog Sine Wave
                                                Composite Signal
                              Digital Signals
                                                Bandwidth


Composite Signal


  From Fourier analysis,
  Any composite signal is a combination of simple sine waves with
  different frequencies, amplitudes, and phases.

  Fact
  If the composite signal is periodic, the decomposition gives a series
  of signals with discrete frequencies; if the composite signal is
  non-periodic, the decomposition gives a combination of sine waves
  with continuous frequencies.




                      Somjet Suppharangsan      Review of Data and Signals 1
                                               Sine Wave
                            Data vs Signals
                                               Time vs Frequency Domains
                 Periodic Analog Sine Wave
                                               Composite Signal
                             Digital Signals
                                               Bandwidth


Bandwidth



  Definition in Hertz
  The bandwidth of a composite signal is the difference between the
  highest and the lowest frequencies contained in that signal.

  Definition in bps
  The speed of transmission, showing in a number of bits passed in
  one second.




                     Somjet Suppharangsan      Review of Data and Signals 1
                               Data vs Signals    Transmission of Digital Signals
                    Periodic Analog Sine Wave     Baseband vs Broadband Transmissions
                                Digital Signals   Transmission Impairment


Outline

  1   Data vs Signals
        Data
        Signals
        Periodic vs Non-Periodic Signals
  2   Periodic Analog Sine Wave
        Sine Wave
        Time vs Frequency Domains
        Composite Signal
        Bandwidth
  3   Digital Signals
        Transmission of Digital Signals
        Baseband vs Broadband Transmissions
        Transmission Impairment


                        Somjet Suppharangsan      Review of Data and Signals 1
                            Data vs Signals    Transmission of Digital Signals
                 Periodic Analog Sine Wave     Baseband vs Broadband Transmissions
                             Digital Signals   Transmission Impairment


Digital Signals as a Composite Analog Signal




  From Fourier analysis,
  If the digital signal is periodic, the decomposed signal has a
  frequency domain representation with an infinite bandwidth and
  discrete frequencies; If the digital signal is non-periodic, the
  decomposed signal has an infinite bandwidth and the frequencies
  are continuous.




                     Somjet Suppharangsan      Review of Data and Signals 1
                            Data vs Signals    Transmission of Digital Signals
                 Periodic Analog Sine Wave     Baseband vs Broadband Transmissions
                             Digital Signals   Transmission Impairment


Baseband vs Broadband Transmissions



  We can transmit a digital signal by using either baseband
  transmission or broadband transmission (using modulation).
  Facts
      Baseband Transmission: sending a digital signal over a channel
      without changing to an analog signal - Low-pass channel
      Broadband Transmission: change digital signal to analog
      signal before sending - Bandpass channel




                     Somjet Suppharangsan      Review of Data and Signals 1
                             Data vs Signals    Transmission of Digital Signals
                  Periodic Analog Sine Wave     Baseband vs Broadband Transmissions
                              Digital Signals   Transmission Impairment


Baseband vs Broadband Transmissions

  Basedband transmission
      preserving the shape of the digital signal is possible only if we
      have a low-pass channel with an infinite or very wide
      bandwidth.
      the required bandwidth is proportional to the bit rate; the
      more bit rate, the more bandwidth required

  Broadband transmission
      If the available channel is a bandpass channel, we cannot send
      the digital signal directly to the channel; we need to convert
      the digital signal to an analog signal before transmission.
      the required bandwidth is proportional to the bit rate; the
      more bit rate, the more bandwidth required

                      Somjet Suppharangsan      Review of Data and Signals 1
                            Data vs Signals    Transmission of Digital Signals
                 Periodic Analog Sine Wave     Baseband vs Broadband Transmissions
                             Digital Signals   Transmission Impairment


Transmission Impairment

  Types of Impairment
      Attenuation: a loss of energy showing in decibel
                      P2
      (db) = 10 log10 P1
      Distrotion: signal changes its form or shape e.g. phase
      difference.
      Noise: thermal noise, crosstalk, and impulse noise i.e. spike.

  Signal-to-Noise Ratio(SNR)
      the ratio of the signal power to the noise power
              average signal power
      SNR =   average noise power
      SNRdb = 10 log10 SNR


                     Somjet Suppharangsan      Review of Data and Signals 1

				
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