Interference versus filtering distortion trade‐offs in OFDM‐based cognitive radios

Abstract

ABSTRACTCognitive radio (CR) and opportunistic radio access came as a solution for the underutilisation of radio resources. An expected consequence is that the interference management procedures obtain high priority in CR research. While the vast majority of studies focus on interference phenomena towards the licensed primary system (PS), this paper analyses the effects of adjacent primary user (PU) signals to a CR system that uses orthogonal frequency division multiplexing (OFDM) modulation. The lack of orthogonality in OFDM receivers increases out of band interference. The ‘near PU–far CR’ scenario is introduced, an inverse equivalent to the ‘hidden terminal’ problem that may cause serious degradation in the receiver operation. An analytical interference model is developed, and direct filtering of the conventional OFDM waveform is investigated as a means to control interference from PU signals. Closed‐form expressions of the induced distortion are extracted. The results are used to evaluate a filtered‐based OFDM receiver via simulation and to prove that high‐rank filters at CR receivers may be quite beneficial even though OFDM modulation generally avoids their use. Copyright © 2013 John Wiley & Sons, Ltd.