Blind channel shortening for zero-padded OFDM

When the channel delay spread is larger than the guard interval of zero-padded (ZP) OFDM transmissions, interblock interference (IBI) might lead to significant performance degradation. Without altering the signal design, a time-domain equalizer (TEQ) can be applied at the receiver to shorten the channel for IBI suppression. In this paper we study several known designs of blind channel shortening in the ZP-OFDM context, exploiting the signal redundancy in the form of guard zeros in the time domain, or null subcarriers in the frequency domain, or both. Numerical results show that blind channel shortening algorithms can catch up or even exceed the performance of a benchmark scheme assuming perfect channel knowledge. Only time-invariant channels are considered in this paper; channel shortening for time-varying channels with large delay spreads such as underwater acoustic channels is an interesting subject that warrants further investigation.