Efficient methods of interference suppression for spectrum pooling cognitive radios using OFDM signals

Cognitive radio networks are promising systems to enable efficient use of spectral resources, thanks to identification of Primary Users (PU) possessing guaranteed radio resources and Secondary Users (SU), trying to use temporary unused channels. Assuming that PU traffic is low, it can switch off specific subcarriers in OFDM signal and this subbands can be used by SU. The proposed method is based on spectrum pooling, assuming that secondary users spectrum access is flexible and should not degrade performance of the licensed user link. As an adaptive modulation scheme, a use of OFDM modulation is proposed, but to use this technique it is necessary to reduce out of band interference. This paper compares four methods and present results of laboratory tests on real OFDM signals.