Re: [Discuss-gnuradio] integral frequency shift correcting in ofdm_frame_equalizer_vcvc_impl.cc

[Martin Braun]

Tiankan,

this corrects the coarse freq offset propagation due to the CP.
As 'i' increments, this represents later times. So, in a sense, this is
in time direction.

M

On 09/02/2014 04:14 PM, Tiankun Hu wrote:
> Hi All,
> I found "ofdm_frame_equalizer_vcvc_impl.cc" use below code to correct
> integral freq shift(IFO) in freq domain, but as I known, the IFO only
> cause signal cyclic shifting in freq domain, why this block use gr_expj
> to correcting IFO in freq domain? might be blow code should be done in
> time domain.
> 
>    // Correct the frequency shift on the symbols
>    gr_complex phase_correction;
>    for (int i = 0; i < frame_len; i++) {
>        phase_correction = gr_expj(-M_TWOPI * carrier_offset * d_cp_len /
> d_fft_len * (i+1));
>        for (int k = 0; k < d_fft_len; k++) {
>            out[i*d_fft_len+k] *= phase_correction;
>        }
>    }
> 
>