Lecture 2- Transmission Fundamentals -2.ppt

Frequency domain concepts any electromagnetic signal

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Frequency-Domain Concepts Any electromagnetic signal can be shown to consist of a collection of periodic analog signals (sine waves) at different amplitudes, frequencies, and phases The period of the total signal is equal to the period of the fundamental frequency
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Relationship between Data Rate and Bandwidth The greater the bandwidth, the higher the information-carrying capacity Conclusions Any digital waveform will have infinite bandwidth BUT the transmission system will limit the bandwidth that can be transmitted AND, for any given medium, the greater the bandwidth transmitted, the greater the cost HOWEVER, limiting the bandwidth creates distortions
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Data Communication Terms Data - entities that convey meaning, or information Signals - electric or electromagnetic representations of data Transmission - communication of data by the propagation and processing of signals
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Examples of Analog and Digital Data Analog Video Audio Digital Text Integers
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Analog Signals A continuously varying electromagnetic wave that may be propagated over a variety of media, depending on frequency Examples of media: Copper wire media (twisted pair and coaxial cable) Fiber optic cable Atmosphere or space propagation Analog signals can propagate analog and digital data
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Digital Signals A sequence of voltage pulses that may be transmitted over a copper wire medium Generally cheaper than analog signaling Less susceptible to noise interference Suffer more from attenuation Digital signals can propagate analog and digital data
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Analog Signaling
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Digital Signaling
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Reasons for Choosing Data and Signal Combinations Digital data, digital signal Equipment for encoding is less expensive than digital-to- analog equipment Analog data, digital signal Conversion permits use of modern digital transmission and switching equipment Digital data, analog signal Some transmission media will only propagate analog signals Examples include optical fiber and satellite Analog data, analog signal Analog data easily converted to analog signal
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Analog Transmission Transmit analog signals without regard to content Attenuation limits length of transmission link Cascaded amplifiers boost signal’s energy for longer distances but cause distortion Analog data can tolerate distortion Introduces errors in digital data
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Digital Transmission Concerned with the content of the signal Attenuation endangers integrity of data Digital Signal Repeaters achieve greater distance Repeaters recover the signal and retransmit
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