Joint PAPR reduction and sidelobe suppression in NC-OFDM based cognitive radio using wavelet packet and SC techniques

Abstract

Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is an appropriate transmission technique for cognitive radio (CR) systems. It guarantees an efficient spectrum utilization for high data rate wireless systems. However, NC-OFDM system suffers from two main problems, which are the high peak-to-average power ratio (PAPR) and the high sidelobe level. In this paper, two techniques are proposed to jointly reduce the PAPR and suppress the out-of-band (OOB) radiation caused by the high sidelobe levels. In both of the two proposed techniques, an inverse discrete wavelet packet transform (IDWPT) is used, once with the signal cancellation (SC) for the first proposed technique (IDWPT-SC), and once again with the sub-signal cancellation (Sub-SC) for the second proposed technique (IDWPT-Sub-SC). The use of the IDWPT helps decreasing the fluctuations in the transmitted signal, and hence reduces the PAPR and the OOB radiation. The simulation results show that, the proposed techniques provide better PAPR and sidelobe cancellation performance compared to the other techniques. Moreover, the two proposed techniques also conserve almost the same computational complexity as the other techniques.