Hi, paresh_saxena:
In all familiar COFDM transmission methods (DAB, DVB-T, ISDB-T, WLAN, ADSL), both cyclic prefix (also called guard interval) and zero-padding (unused subcarriers set to zero) are being used.
The guard interval cannot be used for eliminating fading: there is nothing that can be done against fading apart from adding error protection to the data stream by means of upstream FEC (forward error correction) and distributing the data stream as uniformly as possible over all COFDM subcarriers in the transmission channel.
As the cyclic prefix (guard interval) is useful, viewed in the time domain, to avoid intersymbol interference due to echoes, the unused zero-information carriers helps for preventing adjacent channel crosstalk, by facilitating the filtering of the shoulders of the COFDM spectrum (frequency domain), and for adapting the bit capacity per symbol to the input data structure.
Regards.