Precoded OFDM systems robust to spectral null channels and vector OFDM systems with reduced cyclic prefix length

The performance of OFDM systems may be degraded when ISI channels have spectral nulls. Also, when ISI channels have many taps, the data rate overhead due to the insertion of the cyclic prefix is high. In this paper, we propose a precoded OFDM system that may improve the performance of the OFDM systems for spectral null channels. We also propose size K/spl times/1 vector OFDM systems that reduce the cyclic prefix length by K times compared to the conventional OFDM systems. The precoding scheme is simply to insert one or more zeros between each two sets of K consecutive information symbols, although it can be generalized to a general form. This precoding scheme may be able to remove the spectral nulls of an ISI channel without knowing the ISI channel. When no zero is inserted between each two sets of K consecutive information symbols and only each K consecutive symbols are blocked together, we obtain vector OFDM systems.