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  1. #1
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    OFDM sub-carriers data: conjugate or independt?

    in 802.11a, 48 sub-carriers are used to transmit data, and they are not carrying conjugate data on index like sub-carrier(x) and sub-carrier(N-x).

    also in some thsis I come across designs that transmit conjugate data on sub-carriers that are symmetric around the FFT size N, which results in waste of half the bandwidth. But the method outputs real signal.

    I have two questions.
    1. if not transmitting conjugate data on fft bins that are symmetric around N, the overall output signal would be complex. By decomposing the OFDM symbol into I and Q component, then the overall transmiited signal would be I * cos(wt) + Q * sin(wt). Now if I want to perform FFT at the receiver side, it seems I have to extract I and Q separately by multiplying cos(wt) to I, sin(wt) to Q, then filter them and add together. Then it's possible to do the FFT. Anything wrong here?

    2. what is the common practice in the practical systems, conjugate data or not?

    thans in advance.
    Last edited by bravoegg; 8th November 2016 at 02:57.

    •   Alt8th November 2016, 02:33

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  2. #2
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    Re: OFDM sub-carriers data: conjugate or independt?

    I got it wrong. The padded 0s ars just to smooth and center the IFFT subcarriers.
    At the trasmiiter and recever side, one does have to do sine and cosine multiplication.



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