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Efficient spectrum utilization can be achieved in several ways, one of which is a better spectrum access. In this paper we propose a subband adaptive filtering method for effective spectrum access and dynamic spectrum sharing in cognitive radios (CR). Based on an interleaved spread spectrum orthogonal frequency division multiplexing (ISS-OFDM) multiple subband transmission signal and subband adaptive filtering technique, some interfered subbands of the transmission signal are filtered and dropped off. The other subbands without interference or with interference less than a predetermined threshold are used for information transmission. The flexibility of the adaptively selecting transmission subbands provides users with the ability to fill in spectrum holes with appropriate number of subbands. Consequently, the spectrum utilization efficiency is improved. We simulate the system bit error rate (BER) performances and demonstrate the improvement on spectrum utilization efficiency by using this subband adaptive filtering method, when different numbers of subbands are used for information transmission.