  Cognitive Radio (CR) is a promising technology for next-generation wireless
networks in order to efficiently utilize the limited spectrum resources and
satisfy the rapidly increasing demand for wireless applications and services.
Security is a very important but not well addressed issue in CR networks. In
this paper we focus on security problems arising from Primary User Emulation
(PUE) attacks in CR networks. We present a comprehensive introduction to PUE
attacks, from the attacking rationale and its impact on CR networks, to
detection and defense approaches. In order to secure CR networks against PUE
attacks, a two-level database-assisted detection approach is proposed to detect
such attacks. Energy detection and location verification are combined for fast
and reliable detection. An admission control based defense approach is proposed
to mitigate the performance degradation of a CR network under a PUE attack.
Illustrative results are presented to demonstrate the effectiveness of the
proposed detection and defense approaches.
