Non-data aided adaptive channel shortening for efficient multi-carrier systems

Multi-carrier (MC) systems are known for being very effective in cancelling intersymbol and multi-user interference provided that a cyclic prefix (CP) of length at least equal to the channel order is inserted at the beginning of each transmitted block. However, this insertion causes a reduction of the transmission speed which is not negligible when the channel delay spread is not small with respect to the block-length. We propose an algorithm for designing time-domain pre-equalizers which shorten the channel impulse response. The method requires neither the a-priori knowledge of the channel impulse response nor the transmission of training sequences. The only basic assumption underlying our method is that the transmitted MC stream contains (virtual) sub-carriers, a condition which is verified in many current MC transmission systems.