Orthogonal frequency division multiplexing (OFDM) is a promising technique for multi-antenna broadband systems, since it significantly reduces receiver complexity by providing orthogonal subchannels. A drawback of OFDM systems is the performance/rate reduction due to the cyclic prefix overhead. We propose receiver structures that exploit the cyclic prefix to increase the performance of the link. The proposed structures use the standard OFDM transmitter, and the modifications are only made at the receiver. Optimum receivers in both the least-mean-squares and least-squares senses are presented, and they do not result in any extra processing complexity compared to the standard OFDM receiver. The proposed architecture is further extended to a MIMO OFDM structure. Simulation results validate the improved performance of the proposed receiver.