Cyclic Prefix problem in LTE

The problem is fixed by adding a guard time between each symbol to avoid the ISI.
The ISI is still present but is not disturbing for the receiver.
Principle : add a prefix to absorb channel effect and avoid ISI Cyclic prefix permits to facilitate demodulation
The cyclic prefix transform the classical channel convolution into a cyclic convolution which permits easy demodulation after FFT
 

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