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Quardrature Amplitude Modulation

  1. Feb 3, 2005 #1
    Quardrature Amplitude Modulation.

    I know the basic techniques, like when you have 1 point and only two signals are to be multiplexed. But the constellations got me a bit confused. My text-book doesn't explain it thoroughly, and there isn't much deep information about it on the internet.

    "The number of "dots" in the constellation is given as a number before the QAM, and is always an integer power of two -- from 2^1 (2QAM) to 2^12 (4096QAM)."

    This is from wikipedia site. I'm just wondering, each point adds two signals? or multiply the number of signals mulitplexed by two??

    This is an example exercise:

    An analog passband channel can pass a maximum of 20 KHz. If the channel is used for transmission of digital data, what is the minimum number of points in a QAM constellation if 5 ADPCM signals are to be multiplexed in an the analog channel?

    In both cases of my interpretation, the answer would be 3 points, no??
  2. jcsd
  3. Feb 3, 2005 #2
    erm, that would be 2^3=8 points.

    8 points have the ability to multiplex 16 signals or 2^8= 256??
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