The OFDM plays a very important role in communication. We used channel estimation for fast time varying channels based on BEM model using two dimensional prolate functions. We are using CP and UW for OFDM. Instead of the conventional cyclic prefix (CP), we use a deterministic sequence, which we call unique word (UW), as guard interval. We show how unique words, which are already well investigated for single carrier systems with frequency domain equalization (SC/FDE), can also be introduced in OFDM symbols. Since unique words represent known sequences, they can advantageously be used for synchronization and channel estimation purposes.