I can understand that the transmit filter may be placed before S/P converter, but I could not for the receive filter. I mean, in regular systems, we first filter and then sample, right?
Another question, regarding CP, do we add it after the IDFT at the transmitter, and we remove it before the DFT at the receiver? I mean, it is not entered in IDFT/DFT process, right? I see some papers on single-carrier frequency domain equalization, which is basically works in the same manner as OFDM, i.e.: b-base with DFT/IDFT units at the receiver to equalize the channel at the frequency domain and transform it back to the time domain, and they add at the end of the block a pseudo-noise (PN) sequence to force the linear convolution to be circular to apply the DFT, however, they do the DFT/IDFT for the whole block (including the PN) and then after the IDFT, the last L samples are dropped. Why not drop them before the DFT instead after the IDFT?