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This tutorial shows the idea of analog time domain OFDM. My question is if we can sample the analog signal and use time-domain OFDM in a similar fashion. Why do we need to apply IFFT/FFT to the signal at transmitter/receiver?

I understand that it is more efficient to use the FFT at the receiver side, but why do we transform the original data to a complex number by some modulation technique and then use the IFFT (instead of just sending it in the time domain)? There has to be some benefit beyond efficiency.

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  • $\begingroup$ I personally think the question does not deserve a downvote. As @Deve has provided a concise answer, the advantage of DFT implementation is the low cost of receiver (or simply money!!). You may find this paper of OFDM history interesting ... researchgate.net/publication/… $\endgroup$ – AlexTP Oct 23 '18 at 12:51
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Even if you synthesize the time-domain OFDM signal with N analog oscillators, you still need the frequency domain representation at the receiver to recover the subcarrier symbols. After sampling, the FFT is the most efficient way to obtain the frequency domain signal.

Similarly, the IFFT is generally much easier to implement than N analog oscilllators with N Pulse shapers at transmitter side.

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