Flexible quasi-systematic precoding for the out-of-band energy reduction in NC-OFDM

The reduction of spurious emission is an important issue in future OFDM-based systems, especially in the context of cognitive radio, when the primary users must be protected from the interference. In this paper, flexible quasi-systematic precoder is presented for non-contiguous OFDM transmitter, which has the effect of relatively small distortion of the data symbols modulating the subcarriers. We discuss degrees of freedom in the precoding-matrix design. The quasi-systematicy allows for not only the reduction of the out-of-band emission, but also flexible reception with high performance, either with or without the knowledge of the coding-matrix.