Intrasymbol interference in OFDM

Orthogonal Frequency Division Multiplexing (OFDM) systems usually insert a guard interval between transmitted symbols in order to avoid intersymbol interference (ISI) produced by multipath propagation. Some authors have claimed that the addition of a guard interval into an OFDM system to combat multipath may not perform the desired task as previously thought, and that instead, this bandwidth could be used to convey more information. The present paper tries to clarify that even though it is true that interference of an OFDM symbol with delayed versions of itself causes serious impairments in reception, these can be fixed by adaptive channel estimation, and that the guard interval is still necessary to avoid interference of an OFDM symbol with delayed versions of the previous ones.