Saturday, September 25, 2010


  • Description: Create a raised cosine pulse shape suitable for a pulse amplitude modulation (PAM) transmitter.
  • Category: Pulse amplitude modulation (PAM) ("pam" prefix)

Inputs (Controls)

  1. Tb, bit interval (0.01) [s] -- DBL
  2. alpha, excess bandwidth factor (0.5) -- DBL
  3. N, bit intervals for support (4) -- DBL
  4. fs, sampling frequency (1000) [Hz] -- DBL
Parentheses ( ) indicate default value; square brackets [ ] designate units.

Outputs (Indicators)

  1. pulse shape -- 1-D DBL array

Required Behavior

  • "pulse shape" is an array containing the raised cosine pulse shape defined by the equation p(t)=sinc(2B0t)(
  • B0 = Nyquist bandwidth, the minimum possible transmit bandwidth achieved by a sinc pulse
  • B0=
    , where Tb is the bit interval
  • α = roll-off factor (also called excess bandwidth factor), 0α1 (alpha = 0 creates an unmodified sinc pulse, and alpha = 1 creates a fully damped sinc pulse with twice the Nyquist bandwidth).
  • The "alpha" control value must be limited to the range 0 to 1 and be incrementable by steps of 0.1.
The raised cosine pulse shape is fundamental to digital communication systems. Its name derives from its frequency-domain shape. Refer to the Figure 1 screencast video to learn more about the raised cosine pulse.
Figure 1: [video] Explanation of raised cosine pulse
Figure 1 (subVI_pam_RaisedCosinePulse-explained.htm)

LabVIEW Coding Tips

View the screencast video in Create a SubVI in LabVIEW to learn the mechanics of subVIs.
Refer to the Figure 2 screencast video for LabVIEW coding tips and techniques specific to this subVI.
Figure 2: [video] LabVIEW coding tips and techniques for
Figure 2 (subVI_pam_RaisedCosinePulse-vi.htm)

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