Cyclic Prefix: To make possible the use of OFDM in LTE is FFT/IFFT. To reduce the Inter Symbol Interference in channels we add cyclic prefix in signal.
What is cyclic prefix in LTE ? (Difference is in last paragraph)
Just copying the last part of each OFDM symbol with the length of a guard interval forms a cyclic prefix (CP). It consumes both a bandwidth and power penalty.
In summary, the use of the cyclic prefix entails data rate and power losses. The “wasted” power has increased importance in an interference-limited wireless system, causing interference to neighboring users.
Where L is the power used for non CP transmission. In the case where there is a large delay spread, e.g. due to large cell radius, an extended CP option can be used.