**OutlineBackgroundCognitive radio technologySecurity issues in cognitive radiosSpectrum sensing in cognitive radiosPrimary user emulation attack

**BackgroundWireless communication system design requires higher data rate and larger channel capacity as well as better quality of service and spectrum utilization efficiency to meet the needs of wireless users.Security issues have drawn much research attention in wireless communications due to its open air nature.

**Cognitive Radio TechnologyMotivation 1. Frequency spectrum a scarce resourceFigure 1. Frequency allocation chart in US as of 2003

**Cognitive Radio TechnologyMotivation 2. Spectrum access is a more significant problem than spectrum scarcity.

Figure 2. Measurements of spectrum utilization in downtown Berkeley

**Cognitive Radio TechnologyDefinition Cognitive radio [1] is a technology of wireless communications in which a network or a user flexibly changes its transmitting or receiving parameters to achieve more efficient communication performance without interfering with licensed or unlicensed users.

1. J. Mitola and G. Maguire, Cognitive radio: Making software radios morepersonal, IEEE Communication Magazine, vol. 6, no. 4, pp. 1318, Aug. 1999.

**Cognitive Radio TechnologySpectrum holesFigure 3. Illustration of spectrum holes

**Cognitive Radio TechnologyAdvances of cognitive radiosJ. Mitola I. AkyildizS. HaykinQ. Zhao

**Cognitive Radio TechnologyMain functions

**Cognitive Radio TechnologyCognitive cycle

**Security Issues in CR NetworksChallenges The intrinsic properties of cognitive radio paradigm produce new threats and challenges to wireless communications [2]. Spectrum occupancy failures; Policy failures; Location failures; SensorFailures; Transmitter/Receiver failures; Operating system disconnect; Compromised cooperative CR; Common control channel attacks.

2. T. Brown and A. Sethi, Potential cognitive radio denial-of-service vulnerabilities and protection countermeasures: A multidimensional analysis and assessment, IEEE International Conference on Cognitive Radio Oriented Wireless Networks and Communications (CrownCom), Aug. 2007, pp. 456-464.

**Spectrum Sensing in Cognitive RadiosDefinition Spectrum sensing is to obtain awareness about the spectrum usage and existence of primary users in a geographical area.

**Spectrum Sensing in Cognitive RadiosSpectrum opportunity

Figure 4. Multiple dimensional spectrum opportunity

**Spectrum Sensing in Cognitive RadiosSpectrum sensing A classical signal detection problemchannel gainnoiseprimary signal

**Spectrum Sensing in Cognitive RadiosSpectrum sensing methods

**Spectrum Sensing in Cognitive RadiosTransmitter detection 1) Matched filter detection

Advantages: Better detection performance and less time to achieve processing gainDisadvantages: Priori knowledge of primary signal is required (such as pilots, preambles or synchronized messages).

**Spectrum Sensing in Cognitive RadiosTransmitter detection 2) Energy detection

Decision statistic Y follows Chi-square distribution

**Spectrum Sensing in Cognitive RadiosTransmitter detection 2) Energy detection False alarm probability and detection probability

is decision threshold

**Spectrum Sensing in Cognitive RadiosTransmitter detection 3) Cyclostationary detection Exploits built-in periodicity of modulated signals couple with sine wave carriers, hopping sequences, cyclic prefixes and etc. Advantages: better performance than energy detection Disadvantages: more computational complexity and longer observation time.

**Spectrum Sensing in Cognitive RadiosCooperative detectionFigure 5. Transmitter detection problem

**Spectrum Sensing in Cognitive RadiosCooperative detectionFigure 6. Cooperative detection model

**Spectrum Sensing in Cognitive RadiosInterference temperature detectionFigure 7. Interference temperature detection

**Spectrum Sensing in Cognitive RadiosChallengesPrimary users detection in spread spectrumDetection capabilityDecision fusion in cooperative detectionSecurity issues

**Primary User Emulation AttackDefinition An attacker occupies the unused channels by emitting a signal with similar form as the primary users signal so as to prevent other secondary users from accessing the vacant frequency bands [4].4. R. Chen, J. Park, and J. Reed, Defense against primary user emulation attacks in cognitive radio networks, IEEE Journal on Selected Areas in Communications, vol. 26, no. 1, pp. 2537, Jan. 2008.

**Primary User Emulation AttackDetection of PUEA

Distance ratio test & distance difference test

Walds sequential probability ratio test

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***Primary user Secondary user******************