**What is the multipath?**

- Due to the signal propagation phenomena, like reflection or diffraction, a receiver can receive several delayed versions of the same signal.
- This creates Inter-Symbol Interference (ISI).

The multi-path impact is an overlapping of 2 symbols, called Inter-Symbol Interference (ISI).

The modulation is based on the amplitude and on the phase, so in case of overlapping there are 2 different

The modulation is based on the amplitude and on the phase, so in case of overlapping there are 2 different

amplitudes and phases.

The receiver is not able to decode the state of the symbol.

The receiver is not able to decode the state of the symbol.

- The guard time is called the Cyclic Prefix (CP). It permits to facilitate demodulation.

- The cyclic prefix transforms the classical channel convolution into a cyclic convolution which permits easy demodulation after FFT.