Reduction of out of band radiation using carrier-by-carrier partial response signalling in orthogonal frequency division multiplexing

Abstract

Orthogonal frequency division multiplexing (OFDM) is a mature and one of the most popular multicarrier modulation (MCM) techniques. Also, it is the main candidate for physical layer of cognitive radio (CR) networks. CR is a new method to satisfy ubiquitous demand for wireless services while there is no enough unlicensed spectrum. However, the most important shortcoming of OFDM-based CR systems is the high level of out of band (OOB) components that originate from simple fast Fourier transform (FFT)-based implementation. In this study, the authors propose a novel method to reduce side-lobes of OFDM spectrum. In this method proper carrier-by-carrier partial response signaling is used on the modulated symbols across the time. This method will allow for using other techniques for OOB radiation or peak-to-average power ratio (PAPR) reduction, while does not require high complexity at the transmitter, i.e. just the receiver should have either maximum likelihood sequence detector (MLSD) in case of no pre-coding or a simple slicer in case of pre-coding. Moreover, it will not affect the PAPR but will increase word error rate (WER). Simulation results show that about 7 dB reduction in OOB components can be expected by this method.