Revisiting Active Cancellation Carriers for Shaping the Spectrum of OFDM-based Cognitive Radios

Orthogonal frequency division multiplexing (OFDM) is widely used in wireless communication systems, and it is a candidate for Cognitive Radios (CR). Shaping the spectrum of OFDM-based CR is needed to reduce the out-of-band radiations and reduce the interference delivered to the licensed user (LU). In this paper, shaping the spectrum using windowing and active cancellation carriers is discussed. It is shown that the use of windowing alone for large band is a better choice. The window choice in case of large number of subcarriers spanned by a LU is investigated and it is shown that the Harming window outperforms the raised cosine window by 7dB. Computational complexity analysis is introduced and it shows a huge advantage by using windowing alone for large frequency bands and multiple bands vis-A-vis cancellation carriers. Simulations show that such technique offers no effect on the bit error rate performance.