Constellation expanded active interference cancellation technique for suppression of out-of-band radiation in OFDM based cognitive radios

Cognitive radio is a novel technology to address the problem of spectrum under-utilization, by allowing the secondary users to dynamically use the spectrum of the primary users. OFDM is a potential candidate for the physical layer of cognitive radio, due to its inherent features of spectrum shaping, spectrum analysis and robustness to multipath. OFDM based cognitive radio, however suffers from out-of-band radiation (OOBR). In cognitive radio, suppression of OOBR is much more important as the interference to the primary users needs to be kept to the minimum possible level. In the literature, time and frequency characteristics of the transmitted signal have been exploited to minimize the OOBR. In this paper, we investigate the possibility of combining merits of the constellation expansion (CE) technique and the active interference cancellation (AIC) technique for suppression of OOBR. We show through simulations that the joint technique based on CE and AIC achieves much better OOBR reduction, with a slight degradation in error performance.