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16 QAM and OFDM

Discussion in 'Radio and Communications' started by thavamaran, Sep 3, 2010.

  1. thavamaran

    thavamaran New Member

    Jan 24, 2008
    hi guys, currently im building a passband system of 5 GHz, so I have simulated 16 QAM and its perfectly working fine at 5 GHz.

    But I am very new to OFDM, I have been studying on the background of OFDM and all of them only talking about baseband OFDM. Im not interested with using the MATLAB function to generate baseband 16-QAM, cause I have to analyse the changes of BER and EVM with changes of frequency.

    So my question is, the generated 16 QAM signal are not in complex value, cause I have summed the I and Q channel at the end, so from the summation of this I and Q channel, I actually got the 16 QAM signal which is very trivial.

    Then I have to shift from serial to parallel before performing IFFT in OFDM, but my question is, my signal is not complex, how could I IFFT my signal? should I FFT after the serial to parallel conversion and IFFT back again, but it doesnt make sense.

    Please advice me on this. Thank you! Cheers!
  2. RCinFLA

    RCinFLA Well-Known Member

    Jul 23, 2009
    FLA, USA
    Simple summing I and Q channels will not create QAM. Vector summing (multiplication) will create the necessary polar (vector) waveform.

    To demodulate you must convert the polar vector waveform back to I and Q components. This is typically done with double balanced mixers fed by quadrature local oscillator.

    Any frequency offset rotation and DC offsets that must be corrected. Within limits, these can be corrected in I and Q digitized channel processing.

    OFDM is very processor intensive and most real OFDM receivers have extensive hardware math accelerators to accomplish the demodulation.

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