A hybrid technique for joint PAPR reduction and sidelobe suppression in NC-OFDM based cognitive radio systems

Abstract

Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) based Cognitive Radio (CR) system automatically identifies available frequency gaps in spectrum and utilize them to meet the requirement of higher data rates in 5G technology. It allocates some unauthorized users to access those frequency gaps without causing interference to the adjacent users. Besides the advantages of NC-OFDM based CR system, it suffers from two main drawbacks which are high Peak-to-Average Power Ratio (PAPR) and large spectrum sidelobe power. In order to overcome these drawbacks, we propose a hybrid technique that jointly reduces PAPR and sidelobe power. This technique involves a two level or modified clipping scheme for PAPR reduction. For sidelobe power suppression, signal cancellation symbols are generated by calculating Error Vector Magnitude (EVM) that are added to the original data bits. Here, the problem of sidelobe suppression can be formulated as a quadratically constrained quadratic program (QCQP), and the optimal solution can be obtained by the standard interior-point method. By combining two techniques we can solve these two issues in NC-OFDM based CR system simultaneously. From the simulation results, it is inferred that our proposed method outperforms interms of both PAPR, sidelobe power suppression over other existing methods and also improves the BER performance of the system.