Physical Layer

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Physical Layer
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Position of the physical layer
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Service
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Analog and Digital

• Analog and Digital Data To be transmitted, data
  must be transformed to electromagnetic signal
• Analog data Human voice, pressure, video, etc.
• Digital data Text, integer
• Analog and Digital Signal
• Analog signal infinite values in the range
• Digital signal limited values in the range
• Periodic and Aperiodic Signal
• Periodic pattern repeated over time s(tT)
  s(t)
• Aperiodic pattern not repeated over time

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Analog and Digital Signal
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Periodic Signal
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Aperiodic Signal
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Analog Signal

• Sine Wave
• Peak Amplitude
• Period and Frequency
• Phase
• Time and Frequency Domain
• Composite Signal
• Frequency Spectrum Bandwidth

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Sine Wave
S(t) A sin (2ftØ)
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Peak Amplitude

• Maximum strength of the signal

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Period and Frequency

• Frequency rate of change of the signal
• Period time for one repetition
• Unit cycles per sec. (Hz)
• f 1/T

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Phase

• The position of the waveform relative to time
  zero
• Phase t/T
• 360 degree 2 radian

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Sine Wave Example
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Sine Wave Example

• Question
• A sine wave is offset one-sixth of a cycle with
  respect to time zero. What is its phase in
  degrees and radians?
• Sketch s(t) 0.5 sin(6t/4)

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Time and Frequency Domain
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Composite Signal

• Signal is usually made up of many frequencies
• The components are sine waves
• Fourier Analysis can show that signal has many
  frequencies

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Composite Signal
Square Wave
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Frequency Spectrum and Bandwidth

• Spectrum range of frequencies contained in
  signal
• Absolute bandwidth the width of the spectrum
• Effective Bandwidth Bandwidth, narrow band of
  frequencies containing the most energy
• DC component component of zero frequency

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Frequency Spectrum
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Square waves The Difference
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Signal Corruption
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Bandwidth

• The property of the medium
• The difference between highest and lowest
  frequency

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Bandwidth
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Example of Bandwidth

• Example a periodic signal is decomposed into
  five sine waves with frequencies of 100, 300,
  500, 700, and 900 Hz, what is the bandwidth? Draw
  the spectrum, assuming all components have a
  maximum amplitude of 10 V.
• Solution B fh - fl 900 - 100 800 Hz. The
  spectrum has only five spikes, at 100, 300, 500,
  700, and 900

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Example of Bandwidth
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Questions of Bandwidth

• A signal has a bandwidth of 10 Hz. The highest
  frequency is 60 Hz. What is the lowest frequency?
  Draw the spectrum if the signal contains all
  integral frequencies of the same amplitude.
• A signal has a spectrum with frequencies between
  1000 and 2000 Hz (bandwidth of 1000 Hz). A medium
  can pass frequencies from 3000 to 4000 Hz (a
  bandwidth of 1000 Hz). Can this signal faithfully
  pass through this medium?

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Digital Signal

• To be continued