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CS601 - Data Communication - Lecture Handout 13

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Related Content: CS601 - VU Lectures, Handouts, PPT Slides, Assignments, Quizzes, Papers & Books of Data Communication

Frequency Spectrum / Bandwidth

  • Frequency Spectrum: of a signal is the collection of all the component frequencies it contains
  • It is shown using a Frequency domain graph
  • Bandwidth: of a signal is the width of the frequency spectrum
  • In other words ,Bandwidth refers to the range of the component frequencies and Frequency Spectrum refers to the elements within that range

How to calculate Bandwidth?

  • To calculate Bandwidth, subtract the lowest frequency from the highest frequency

How to calculate Bandwidth

Example 4.8

If a periodic signal is decomposed into five sine waves with frequencies 100, 300, 500, 700, and 900 Hz, what is the Bandwidth?

Solution

Solution

Other Definitions of Bandwidth

  • 3 dB Bandwidth or Half Power Bandwidth

H( f )

3 dB Bandwidth or Half Power Bandwidth

  • Equivalent Noise Bandwidth

The width of a fictitious rectangular spectrum created to have the same power in the rectangular band as the power of the signal in positive frequencies

Equivalent Noise Bandwidth

  • Null-to-Null Bandwidth or Zero Crossing Bandwidth

Null-to-Null Bandwidth or Zero Crossing Bandwidth

  • Power Bandwidth

Frequency Band in which 99% of the total power resides

Power Bandwidth

  • Digital Signals

In addition to being represented by Analog Signals, data can also be represented by a Digital signal

  • Bit Interval and Bit Rate

Most digital signals are aperiodic and thus Period and Frequency are not the appropriate terms to describe them

    • Bit Interval (seconds)
      • Time required to send one single bit
    • Bit Rate (bps)
      • Number of bits sent per second

    Bit Interval and Bit Rate

     

    Frequency Spectrum of a Digital Signal

    • Frequency spectrum of a digital signal contains an infinite number of frequencies with different amplitudes
    • Ideally we want to send all the components but if we send only those components whose amplitudes are significant , we can still recreate the digital signal with reasonable accuracy at the receiver

    Frequency Spectrum of a Digital Signal

    Summary

    • Frequency Spectrum and Bandwidth
    • Other Definitions of Bandwidth
    • Digital Signals

    Reading Sections

    • Section 4.4, 4.5, 4.6 “Data Communications and Networking” 4th Edition by Behrouz A. Forouzan

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