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 pre-coder is presented for non-contiguous OFDM transmitter, which has the effect of relatively small distortion of the data symbols modulating the subcarriers. The authors discuss degrees of freedom in the pre-coding-matrix design. The quasi-systematic 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.