Peak to Average Power Ratio and Out of Band Radiation Reduction in OFDM Based Cognitive Radio

Orthogonal frequency division multiple-xing (OFDM) is an effective transmission method for cognitive radio system. This method provides high bandwidth and robustness against time dispersive channel. But OFDM inherits the high side lobe power and peak to average power ratio. High side lobe power of primary user (PU) distorts the signal of the secondary user (SU). In this paper we reduce the side lobe power and peak to average power ratio. To reduce the side lobe power and high PAPR we use the multi-choice sequence method (MCS) and hyperbolic tangent sigmoid transfer function for companding transform. By changing the value of parameter k we can get better Peak to average power ratio (PAPR). the BER performance of proposed companding transform of NC OFDM signal without side lobe power reduction is 3.5x10 for SNR 14 that alittle batter than mu law companding transform. the proposed method reduce PAPR more as the parameter k increase by varing value of k from 0.3 to 0.45 can improve papr by 2.5 to 6 db with respect to original OFDM system. Keywords—Average Power Ratio, Band Radiation Reduction, OFDM Based Cognitive Radio.