Adaptive precoding for spectrum shaping of OFDM-based cognitive radio signals

In this paper, a novel adaptive precoding scheme for spectrum shaping in OFDM-based cognitive radios (CR) system is proposed. The proposed adaptive precoder is designed using singular value decomposition (SVD) optimization method to minimize the power interference of OFDM signal to licensed users (LUs) while keeping the extension power at an acceptable level. Analysis and simulation show that the proposed scheme can significantly reduce the power interference to LUs at the expense of a little precoding efficiency. At the same time, the bit error rate (BER) performance of the proposed system over Rayleigh fading channel is improved due to the frequency diversity and the peak-to-average power ratio (PAPR) is invariable.