Sidelobe power and PAPR reduction for CR systems with NC-OFDM

Abstract

The non-continuous orthogonal frequency division multiplexing OFDM (NC-OFDM) based cognitive radio (CR) system has many advantages but also suffers from the problems of high peak-to-average power ratio (PAPR) and large sidelobe power of the transmission signals. In this paper, a novel method is proposed for jointly reducing sidelobe power of signals in licensed user bands (LU) and PAPR for the CR system with the NC-OFDM scheme. A method to construct a precoding matrix for reducing PAPR values by choosing a proper shaping pulse is developed first. A replacement procedure through the singular value decomposition (SVD) is executed to modify the precoding matrix for further achieving the minimum bit error rate (BER) performance. Second, two pseudo random sequence assignment algorithms, the Random Circular Sequence (RCS) and Quadratic Permutation Polynomials (QPP) algorithms, are proposed in the Multiple Choice Sequences (MCS) scheme for suppressing sidelobe power of signals in LU bands. Both algorithms have low complexities in computation and are easy to perform with only requiring a small amount of side information. Simulation results show that, by combining the optimum precoding matrix with the MCS procedure, decreasing the PAPR values and sidelobe power of signals in LU bands can be achieved simultaneously. Without introducing signal distortion, the proposed algorithms have better effects in sidelobe power suppression than the phase approach, and almost the same performance as the random assignment method.