Precoding with interference suppression sequence scheme for OFDM-based cognitive radio systems

Orthogonal frequency division multiplexing (OFDM) is considered to be one of the promising schemes for cognitive radios (CR) systems, due to its flexibility in spectrum shaping. However, the traditional way of spectrum-notching failed to suppress out-of-band leakage enough, resulting in interference with licensed users (LUs). A novel spectrum shaping scheme is proposed in this article, where a precoder with interference suppression sequence (ISS) is for the first time introduced for shaping the spectrum of OFDM signals in OFDM-based CR systems. The precoder matrix together with ISS matrix is obtained by minimizing the power of out-of-band interference, which results in the sufficient interference suppression of OFDM signal to LUs. Analysis and simulation results show that the proposed scheme can significantly suppress the interference power to LUs at a little cost of precoding efficiency. Meanwhile, the peak-to-average-power-ratio (PAPR) is invariable and the bit-error-rate (BER) performance over Rayleigh fading channel is improved.