We usually care about the spectrum flatness for OFDM transmitter, to ensure its baseband/modulater design is good. But what if the frequency response is not flat due to RF front end (PA, filter, antenna...), what is the impact to receiver?

 

We usually care about the spectrum flatness for OFDM transmitter, to ensure its baseband/modulater design is good. But what if the frequency response is not flat due to RF front end (PA, filter, antenna...), what is the impact to receiver?

That is the beauty of OFDM. OFDM is robust to non-flat channel (or so called multi-path channel). If the channel is not flat, the symbol will suffer only an amplitude and phase distortion as long as the maximum path delay is less than the guard interval. The receiver just needs a one-tap equalizer to eliminate the amplitude and phase distortion.

Nevertheless, the modulator may need to have a flat output spectrum. Pre-emphasize in base-band could be utilized to obtain flat-spectrum.