Q. On slide 24 of topic 3a, you mentioned that for OFDM modulation, the FFT is performed at the transmitter and the IFFT at the receiver in wireless systems. As I was curious to learn more about OFDM, I looked at several resources online, including the reference below. In these sources, I noticed that the IFFT is typically applied at the transmitter, while the FFT is used at the receiver. [Springer, Advanced Optical and Wireless Communications Systems Chapter 7: OFDM for Wireless and Optical Communications https://link.springer.com/chapter/10.1007/978-3-319-63151-6_7 ] I would greatly appreciate it if you could clarify which implementation is correct.
A. In reality, the Fourier Transform (and hence the FFT) is a self-inverse except for a sign change; doing it four times becomes the identity function. So the distinction is ultimately a matter of convention. Given the common definition/concept of the Fourier Transform as converting from time domain to frequency domain, you are right to point out that I should have labelled the boxes the other way around. I shall update the slide.
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