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  • LV Digital Comm display tagshide tags

    This module is included inLens: Analog / Digital Communications with National Instruments LabVIEW
    By: Sam ShearmanAs a part of collections:"SubVI Specifications for "Communication Systems Projects with LabVIEW"", "Communication Systems Projects with LabVIEW"

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    ""Communication Systems Projects with LabVIEW" features ten projects that draw upon a library of over 40 subVIs constructed as part of the project activities. Each module in this manual completely […]"

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regen_ExtractPreamble.vi

Module by: Ed Doering. E-mail the author

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Summary: Build a LabVIEW subVI to detect and extract the preamble from a baseband signal.

Table 1
LabVIEWtop.png This module refers to LabVIEW, a software development environment that features a graphical programming language. Please see the LabVIEW QuickStart Guide module for tutorials and documentation that will help you:
• Apply LabVIEW to Audio Signal Processing
• Get started with LabVIEW
• Obtain a fully-functional evaluation edition of LabVIEW

Note:

Visit LabVIEW Setup to learn how to adjust your own LabVIEW environment to match the settings used by the LabVIEW screencast video(s) in this module. Click the "Fullscreen" button at the lower right corner of the video player if the video does not fit properly within your browser window.

LabVIEW SubVI: regen_ExtractPreamble.vi

  • Description: Detect and extract the preamble from a baseband signal. A preset number of alternating 1s and 0s (also designated as marks and spaces) typically starts the preamble to "wake up" the receiver's carrier sync and bit sync subsystems. This subVI assumes the received signal is quiet (nominally zero) prior to the preamble.
  • Category: Bitstream regeneration ("regen" prefix)

Inputs (Controls)

  1. signal in -- waveform
  2. Tb [s] -- DBL
  3. bit intervals to skip (4) -- I32
  4. bit intervals to keep (32) -- I32
  5. threshold (0.1) -- DBL

Parentheses ( ) indicate default value; square brackets [ ] designate units.

Outputs (Indicators)

  1. preamble out -- waveform
  2. preamble detected? -- Boolean

Required Behavior

  • signal in is scanned from the beginning to detect when the signal amplitude exceeds threshold. If the input signal never exceeds the threshold, preamble out returns an empty waveform and preamble detected? returns F.
  • Once a valid threshold crossing is detected, preamble out extracts a portion of signal in of duration bit intervals to keep times the bit interval Tb; the extracted signal begins at the location of the first threshold crossing plus bit intervals to skip times the bit interval. The Boolean indicator preamble detected? is set to T.

LabVIEW Coding Tips

View the screencast video in Create a SubVI in LabVIEW to learn the mechanics of subVIs.

Refer to the Figure 1 screencast video for LabVIEW coding tips and techniques specific to this subVI.

Figure 1: [video] LabVIEW coding tips and techniques for regen_ExtractPreamble.vi
Figure 1 (subVI_regen_ExtractPreamble-vi.htm)

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