Clipping of Precoded OFDM in Cognitive Radios

Abstract

To provide reliable and opportunistic utilization of the radio electromagnetic spectrum, cognitive radio (CR) has been proposed as an intelligent technology that provides dynamic spectrum access for users by opportunistically utilizing even the licensed spectral bands. Orthogonal frequency division multiplexing (OFDM) is considered by many to be an effective multicarrier transmission technique for the implementation of CR system transmissions due to its flexible spectrum access. Out-of-band (OOB) radiation of an OFDM signal is one of the major concerns which has to be addressed as this causes interference to the adjacent spectral users. OFDM also has a demerit of high peak-to-average power ratio (PAPR) which results in increased system complexities. In this paper, methods to simultaneously reduce both OOB radiation and PAPR are being discussed. Iterative clipping and filtering (ICF) and spectral precoding of OFDM is combined in different ways to investigate the optimum reduction of OOB radiation as well as PAPR and their effect on bit-error rate performance is also mentioned.

Keywords: Cognitive radio, orthogonal frequency-division multiplexing, out-of-band radiation, spectral precoding, peak-to-average power ratio