UNCORRECTED PROOFS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 Qusay H. Mahmoud c11.tex V1 - April 24, 2007 4:05 P.M. Page 271 11 Security Issues in Cognitive Radio Networks Chetan N. Mathur and K. P. Subbalakshmi Stevens Institute of Technology, NJ, USA 1. Introduction One of the primary requirements of cognitive radio networks is their ability to scan the entire spectral band for the presence/absence of primary users. This process is called spectrum sensing and is performed either locally by a secondary user or collectively by a group of secondary users. The available spectrum bands are then analyzed to determine their suitability for communication. Characteristics like signal-to-noise ratio (SNR), link error rate, delays, interference and holding time can be used to determine the most appro- priate band. After the spectrum band is selected, secondary transmission in that band takes place. If a secondary user/network detects a primary user transmission, it vacates the cor- responding spectrum band and looks for another vacant band. The process of handing off the licensed spectrum band to a primary user is called spectrum handoff. We later show that the delay associated with spectrum handoff causes many of the attacks proposed on cognitive networks. There are two basic types of cognitive radio networks: centralized and distributed. The centralized network is an infrastructure-based network, where the secondary users are managed by secondary base stations which are in turn connected by a wired backbone. In a decentralized architecture, the secondary users communicate with each other in an ad- hoc manner. Spectrum sensing operation in decentralized architecture is usually performed collaboratively. This type of architecture also encompasses coexistence of two or more wireless networks operating in unlicensed bands. An example of this type of network is the coexistence of IEEE 802.11 with IEEE 802.16 [20]. To analyze the security of cognitive networks, we start by introducing some basic security concepts in the context of cognitive networks. Some of the fundamental building Cognitive Networks: Towards Self-Aware Networks Qusay H. Mahmoud  2007 John Wiley & Sons, Ltd