Sorry for this question, I'm still new in signal processing area.
In OFDM system, let $x$ be the received signal, what do we call the process of multiplying the received signal $x$ by $e^{-j2\pi F_c t}$ , where $F_c$ is frequency carrier and $t$ is interval 0 : sampling rate: sampling rate * length of signal.
So the question, what is that function? and why do we use it.