It is well known that secondary users can take advantages of spectrum opportunities from primary users via cognitive radio technology. However, general sense cognitive radio networks allow all users to cooperatively relay the packets, especially primary users are aware of existence and activity of secondary users. Secondary users may act as cooperative relays for primary traffic. We propose a relay selection criteria such that cooperation is beneficial to both primary and secondary systems. With the suitably chosen relays, power consumption in primary transmissions is reduced and simultaneously interference from primary traffic decreases exposing spectrum opportunities for secondary traffic. We characterize the performance improvement of secondary network due to the extra spectrum opportunities by analyzing the extension of its connectivity region through percolation theory. Such self-motivated cooperation leads the way toward self-organizing wireless networks.
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