Spectrally balanced OFDM precoders for communications over unknown multipath channels

The problem of transmitting a single block of data over an unknown multipath channel is considered. It is explained why the transmitted signal should look white if the channel parameters are unknown, and it is proved that this can be essentially achieved by using a zero padding precoder. A novel canonical representation for linear precoders is then used to decompose this zero padding precoder into a form better suited to multipath channels. Adding a cyclic prefix to this precoder results in what is called a "spectrally balanced OFDM precoder"