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In this paper, the emerging interference alignment technique is applied into the prevailing cognitive radio system. Dynamic spectrum access enables the secondary users to coexist with the licensed primary user in a cognitive radio system. However, to mitigate the intrinsic network interference of secondary users is becoming a challenge, even for the secondary network itself. Moreover, the primary user offers limited resource to share with secondary users. Here, a novel interference-oriented and alignment-based scheme is proposed, which explores the impact of propagation delay on the degrees of freedom of cognitive radio and is called interference draining scheme. On one hand, the secondary users network try to share the same interference draining space at the primary user; on the other hand, the secondary users network aligns its own internal interference. Delicate cooperation between primary user and secondary users network is implemented. A temporal paradigm illustrates a successful interference draining procedure. The interference draining efficiency manifests a surprising increase with the number of secondary users.