Cognitive radio (CR) has been proposed as an effective technology for flexible use of the radio spectrum. The interference among primary users and CR users, however, becomes a critical problem when they are operating nearby using adjacent frequency channels with different transmission powers. In this paper, a CR-based bandwidth sharing architecture is proposed, which can effectively suppress adjacent channel interference (ACI) between them. This new approach is characterized by the adaptive frequency spreading, and the adaptive time spreading with power control for the subcarriers near the borders of the CR user's spectrum. The frequency spreading scheme provides with extra power gain against ACI, whereas the time spreading with power control guarantees the minimal interference to primary users from CR users. By computer simulation, it has been proved that the proposed system outperforms the conventional OFDM systems in both throughput and BER performance.
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