In OFDM based cognitive radio(CR) systems

the large sidelobe of frequency spectrum of secondary users (SU) may cause severe interference to the primary user and the sidelobe spectrum must be suppressed.Active interference cancellation (AIC) can't null the spectrum deep enough and it is sensitive to the cyclic prefix (CP).In this paper

a non-orthogonal AIC (NAIC) technique is proposed for the sidelobe suppression of OFDM CRs.In NAIC

cancellation carriers (CCs) are inserted at the locations which are non-orthogonal to the subcarriers of the SU such that the sidelobe can be more significantly suppressed.Moreover

the windowing technique is used to reduce interference effects from non-orthogonal CCs (NAIC-win) to SU and more deeply suppress the sidelobe spectrum of SU.NAIC-win can obtain sidelobe suppression depth 50dB more than AIC with very little inter-carrier interference (ICI).Compared to EAIC-CP

NAIC-win can suppress the spectrum sidelobe deeper

increase the spectrum efficiency

and lower the computation burden with shorter CP

less CC and ICI.Theoretical analysis and numerical simulations validate that NAIC-win method significantly outperforms the conventional AIC and EAIC-CP methods in sidelobe suppression for OFDM CR systems.