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Cognitive radio (CR) is an advanced technology for efficient use of radio resources. In the CR system, the spectrum pooling technique is used to enhance spectrum utilisation, which enables public access to the spectral ranges of the licenced frequency bands which are seldom used by overlaying an unlicenced user (unLU) on an existing licenced user (LU). The spectrum pooling system constructed by implementing wavelet-based orthogonal frequency division multiplexing (WOFDM) owns better flexibility and bandwidth efficiency. However, the interference between the LU and the unLU is severe in the multipath wireless channel. In the study, the intercarrier interference (ICI) interference energy of the spectrum pooling-based WOFDM is analysed and an optimal deactivated subcarriers algorithm for the guard bands is proposed to mitigate the ICI between the unLU and the LU by intelligently deactivating one or more of the optimal deactivated subchannels which generates the maximum ICI interference in the LU. The numerical and the simulation results show that the data transmission rate of the unLU is ensured, the ICI of the LU is reduced and the bit error rate performance of the LU is, respectively, improved by implementing the algorithm.