Efficient Technique for Sidelobe Suppression and PAPR Reduction in OFDM-Based Cognitive Radios

Orthogonal Frequency Division Multiplexing (OFDM) is a transceiver technology able to achieve spectrally efficient and high data rate wireless transmissions. It is also able to transmit in a non-contiguous (NC) fashion by utilizing several separate spectral whitespaces. Cognitive radio (CR) is an efficient solution for solving the spectrum scarcity problem, while OFDM based CR system, i.e. NC OFDM system is used as modulation scheme. NC-OFDM has two significant problems, high peak to average power ratio (PAPR) and high sidelobe power, which cause out of band radiation and interference with primary users (PU). Many solutions were proposed for solving either of these problems while in this paper, an efficient technique for reducing both PAPR and sidelobe power is proposed. This technique is based on using the Advanced Cancelation Carriers combined with signal set expansion and gives an efficient reduction for both PAPR and sidelobe power. A modified version is also proposed which reduces the transmitted power and decreases the complexity but gives a little reduction for PAPR. Simulation results cover the PAPR and sidelobe reduction for both the proposed technique and its modified version for comparison purposes.