We're doing a project in which we're sending an OFDM frame, modulated to some appropriate carrier, over a channel. Before modulating, we are instructed to upsample and low-pass it. Is there a good explanation this should be done? We have full control over sample rates at both Tx and Rx.
I guess it has something to do with an interpolated signal resembling a smooth signal more, which makes it somehow more appropriate for multiplying by a modulating function. But this is very imprecise and hand-wavy.
Can anyone explain why one would want to upsample, given that there are no differences in sample rate between transmitter/receiver?