Side Lobe Suppression in NC-OFDM Systems Using Variable Cancellation Basis Function

In non-continuous orthogonal frequency division multiplexing (NC-OFDM)-based cognitive radio system, the sidelobe suppression methods use the fixed length rectangular windowing functions for canceling carriers (CCs) like the extended active interference cancellation (EAIC) and active interference cancellation (AIC) methods. The AIC and its EAIC methods reduce the interference a lot, but the CCs in different frequency have a non-uniform assignment for sidelobe suppression. To overcome this problem a novel variable basis function proposed in which the CCs are grouped by frequency positions and modeled with different waveforms of different length to suppress NC-OFDM side lobes effectively while reducing inter carrier interference (ICI) at the same time. Simulation results show that using variable basis functions of the proposed method, -60-dB sidelobe suppression depth is reached even with higher order 64-QAM symbol mapping and the ICI caused by the subcarriers is almost negligible.