gphysignal - I1070/T2000 Intro to Telecom Physical Layer:...

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I1070/T2000 Intro to Telecom Physical Layer: Signals Dr. Richard A. Thompson Telecommunications Program University of Pittsburgh
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Signals Carry information over a medium Communications: visual, audio Tele communications: electrical or photonic Need transducers (natural-electrical) Information value of some signal parameter Usual parameter is “intensity” Voltage, current, power (watts) But, can be frequency or phase
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Analog Signal  Signal intensity varies in a smooth fashion  over time, with no breaks or discontinuities Example: Analog Sine Wave Intensity v time No information Rotating hypotenuse Elementary
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Digital Signal Signal intensity maintains a constant level  for some period of time and then changes to  another constant level Example: Digital Square Wave Rectangle? Intensity v time: 1010 No information Period & frequency
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Periodic Signal Characteristics Amplitude (A) Maximum signal value, measured in volts Frequency ( f ) Repetition rate Measured in cycles per second or Hertz (Hz) Period (T) Amount of time it takes for one repetition, T=1/ f Phase ( φ ) Relative position in time, measured in degrees Changes as signal “travels” Yet another dead white male
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s(t) = (4/ π ×  {sin (2 π ft) + (1/3) sin (2 π (3f)t)}
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%%Frequency Domain Concepts Spectrum  of a signal is the range of frequencies  that it contains Absolute bandwidth  of a signal is the width of the  spectrum Effective bandwidth  contained in a relatively  narrow band of frequencies, where most of signal’s  energy is found. Commonly referred to just as  “bandwidth” The greater the bandwidth, the higher the  information-carrying capacity of the signal P P/2 power frequency Formal definition of bandwidth Not precise… There’s still signal out here Typical spectrum
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Bandwidth Width of the spectrum of frequencies that can be transmitted if spectrum=300 to 3400Hz, bandwidth=3100Hz Greater bandwidth leads to greater costs Limited bandwidth leads to distortion
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Voice/Audio Analog Signals Easily converted from sound frequencies (measured in loudness/db) to electromagnetic frequencies, measured in voltage Human voice has frequency components ranging from 20Hz to 20kHz For practical purposes, the telephone system has a narrower bandwidth than human voice, from 300 to 3400Hz
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Data Signal Transmission System A D D D A A Data, Signals, & Transmission Systems
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Data Communication Components Data Analog: Continuous value data (sound, light, temp) Digital: Discrete value (text, integers, symbols) Signal Analog: Continuously varying electromagnetic wave Digital: Series of voltage pulses (square wave) Transmission Analog: Works the same for analog or digital signals Digital: Used only with digital signals
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gphysignal - I1070/T2000 Intro to Telecom Physical Layer:...

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