Cognitive radio networks (CRNs) emerge as a promising solution for overcoming the shortage and inefficient use of bandwidth resources by allowing secondary users (SUs) to access the primary users' (PUs) channels so long as they do not interfere with them. The random availability of the PU channels makes the delay analysis of the SU, which accesses the channels opportunistically, plays a crucial role as a quality of service measure. In this paper, we model and characterize the total average delay the SUs experience in a CRN. The cognitive radio system is modeled as a discrete-time queueing system. The availability of the N independent and identical PU channels is modeled as a two states Markov chain. Our contributions in this paper is that we provide a solid performance evaluation that gives a closed-formula for the two delay components experienced by the SUs, namely the waiting delay and the service delay. We derive the waiting delay using the residual time concept. We characterize the service time distribution by considering the buffered-slotted-ALOHA systems. We also provide numerical results to show the effects of the analysis on the CRN design.
5G wireless networks will support massive connectivity mainly due to device-to-device communications. An enabling technology for device-to-device links is the dynamical spectrum access. The devices, which are equipped with cognitive radios, are to be allowed to reuse spectrum occupied by cellular links. The dynamical spectrum availability makes cognitive users switch between channels. Switching leads to energy consumption, latency, and communication overhead in general. The performance degrades even more when the network is under jamming attack. This type of attack is one of the most detrimental attacks. Addressing jamming while maintaining a desired quality of service is a challenge. While existing anti-jamming mechanisms assume stationary users, in this paper, we propose and evaluate countermeasures for mobile cognitive users. We propose two time-based techniques, which, unlike other existing frequency-based techniques, do not assume accessibility to multiple channels and hence do not rely on switching to countermeasure jamming. We achieve analytical solutions of jamming, switching, and error probabilities. Based on our findings, the proposed techniques out perform other existing frequency-based techniques.
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