A Novel Adaptive Mode PAPR Reduction Scheme for NC-OFDM Based Cognitive Radios

Non-contiguous orthogonal frequency division multiplexing is an adaptable multicarrier modulation technique that achieves high data rates using non-contiguous subcarriers and can be the very suitable modulation technique to be used at the physical layer of cognitive radio. However its main drawback is high peak to average power ratio (PAPR). Different techniques have been used to combat this problem but all have some tradeoffs. An adaptive mode PAPR reduction algorithm has been proposed using tone reservation technique where some subcarriers called peak reducing carriers (PRCs) are reserved to reduce the signal´s high peaks instead of data transmission. Different methods (including second order cone programming (SOCP), gradient and geometric) are used to generate these PRCs. The proposed algorithm uses adaptivity within and between these methods. This adaptive selection is based on the PAPR value of the signal and gives better PAPR reduction. The novelty in this approach is that the transmission of PRCs and secondary users will be through the use of underlay and overlay transmission respectively. PRCs shall share the bands occupied by the primary users at power levels so low that primary users in the same bands are not effected (underlay transmission) while the secondary users access the spectrum unoccupied by the primary users through dynamic spectrum sensing (overlay transmission).