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Homework Help: Qpsk modulation

  1. Mar 19, 2012 #1
    Hello, I have attached a diagram of QPSK modulation angles. I was wondering how would the red and yellow dots be interpreted.
    Those dots are not exactly on either of the 4 different phase angles. But I understand QPSK has a discrimination of 90 degrees so would the red equate to 45 degrees and the yellow to -45 degrees ? Is that how it works or would the red equate to 135 degrees and the yellow to 45 degrees ?

    Thanks for confirmation.

    Attached Files:

  2. jcsd
  3. Mar 20, 2012 #2


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    Science Advisor
    Gold Member

    Points at these locations only occur when the SNR is abnormally low or there is some kind of corruption, indicating that they are probably not valid. A simple decoder would assign them to the closest location, but it is likely that they will give symbol errors.
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