Joint Sidelobe and Peak Power Reduction in OFDM-Based Cognitive Radio

Abstract

Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is an effective transmission method for cognitive radio systems. It can provide high bandwidth utilization and robustness against time dispersive channels. However, NC-OFDM inherits the problems of high sidelobes and peak-to-average power ratio (PAPR) of the OFDM signal. If not accounted for, this introduces leakage into a primary user (PU) band and distorts the signal of the secondary user (SU). This paper proposes a joint sidelobe and PAPR reduction method that can simultaneously reduce the inherent OFDM out-of-band (OOB) radiation and the OOB radiation caused by a nonlinear power amplifier. In this method, selected mapping (SLM) sequences, which are generated from sequences with a low average sidelobe power, are used to improve the PAPR performance. The key idea is to generate multiple representations of the transmit signal and select a sequence with low OOB radiation and PAPR. We examine the performance of the proposed method taking into account the effects of non-ideal (i.e. non-linear) power amplification. The simulation results show that the proposed technique can significantly reduce OOB radiation while improving the PAPR and bit error rate (BER) for NC-OFDM signals.