Spectral Sculpting for OFDM Based Opportunistic Spectrum Access by Extended Active Interference Cancellation

To enable coexistence between an OFDM based opportunistic spectrum access system and a primary user, we proposed two novel methods called EAIC (Extended Active Interference Cancellation) and EAIC-H (EAIC-Hybrid) for spectral sculpting of OFDM signal. In EAIC and EAIC-H, cancellation signals are added to OFDM signal to cancel interference in target spectrum band caused by data tones, so that interference perceived by primary user can be limited. The cancellation signal (EAIC tones) has longer time duration than that of OFDM symbol, which enables a better notching capability than that of most existing methods. Optimal weights of EAIC tones have been analyzed and given in this paper. Simulation results show that the proposed methods can obtain very deep spectral notches of about 80 dB. Although the EAIC tones cause certain interferences to OFDM data tones, the SNR degradation of OFDM system is very limited and it can be acceptable for high order modulation such as 64 QAM. Compared with EAIC, EAIC- H provides a better tradeoff between notching performance and SNR degradation for high order modulation.