# Questions regarding OFDM, FFT, IFFT

The questions below are for OFDM, IFFT, FFT operations.

Example 1

In OFDM modulation, a stream of parallel symbols are input to an IFFT operation of size $M$ for example and the output is time domain samples of size $M$.

My question is:

Let us take for example, the fact that the input symbols to the FFT operation are QAM symbols. Then, at the output of IFFT I receive $M$ samples. Each sample is weighted sum of modulated subcarriers.

Does it mean that each QAM symbol (input of IFFT) is sent out on ONE subcarrier?

Example 2

I have seen a paper that take the time domain samples of an impulse response of channel of length $T_{CH}$ puts them into M-FFT operation and the result was $H(k)$ for $k\in[1:M]$ which the authors state are the frequency response of the $k$th subcarrier. Why is that the FFT generated the subcarrier frequency response? According to Example 1, each sample should be weighted sum of all input ?

Can anyone explain to me whats the connection between two examples?

Thanks and looking forward for your clarification.