A survey on MAC protocols for complex self-organizing cognitive radio networks

Complex self-organizing cognitive radio (CR) networks serve as a framework for accessing the spectrum allocation dynamically where the vacant channels can be used by CR nodes opportunistically. CR devices must be capable of exploiting spectrum opportunities and exchanging control information over a control channel. Moreover, CR nodes should intelligently coordinate their access between different cognitive radios to avoid collisions on the available spectrum channels and to vacate the channel for the licensed user in timely manner. Since inception of CR technology, several MAC protocols have been designed and developed. This paper surveys the state of the art on tools, technologies and taxonomy of complex self-organizing CR networks. A detailed analysis on CR MAC protocols form part of this paper. We group existing approaches for development of CR MAC protocols and classify them into different categories and provide performance analysis and comparison of different protocols. With our categorization, an easy and concise view of underlying models for development of a CR MAC protocol is provided

Toward Cognitive Coexistence: Optimal Sensing-Based Resource Management

The rapid growth of wireless communication systems makes the coexistence of heterogeneous technologies more and more important. This dissertation studies how cognitive radio concepts may provide an efficient framework for accessing and sharing spectrum by sensing and predicting temporal activity patterns. In this way, the spectrum access of interfering devices can be coordinated implicitly and coexistence be improved. The efficacy of this approach is studied for two common coexistence scenarios. First, we address the coexistence of a frequency hopping cognitive radio with a set of parallel ad-hoc bands, a setup that has conceptual similarities with interfering local and personal area networks. Temporal idle periods that remain between adhoc transmissions are reused efficiently by the cognitive radio through predicting ad-hoc radio activity and dynamically adapting the hopping pattern. Second, we address the coexistence of infrastructure and ad-hoc networks. Motivated by the superior resources of the infrastructure system, we study how its centralized resource allocation may accommodate the ad-hoc links based on adjusting the power and transmission time allocation. Despite adapting its behavior to coexist with the ad-hoc links, the infrastructure system maintains a specified quality of service level for its users by imposing rate constraints. Both of the above formulations are based on a two-state continuous-time Markov chain model for the ad-hoc system's temporal behavior which approxi- mates the carrier-sense multiple access typically employed in such systems. The model is discussed in detail and corroborated through empirical analysis of a practical system. Our analyses are based on the mathematical tools of constrained Markov decision processes and convex optimization and are validated by systemlevel simulations. Further, a real-time test bed has been developed for the cognitive frequency hopping protocol which enables us to corroborate model assumptions experimentally and gain further insight into fundamental tradeoffs. The results presented in this dissertation demonstrate a significant performance gain compared to reference schemes without sensing capabilities. While various implementation details remain to be addressed in future work, our study clearly shows the conceptual merits of this framework and the importance it might play in future wireless systems

Cognitive radios for dynamic spectrum access - dynamic spectrum access in the time domain: Modeling and exploiting white space

Dynamic spectrum access is a promising approach to alleviate the spectrum scarcity that wireless communications face today. In short, it aims at reusing sparsely occupied frequency bands while causing no (or insignificant) interference to the actual licensees. This article focuses on applying this concept in the time domain by exploiting idle periods between bursty transmissions of multi-access communication channels and addresses WLAN as an example of practical importance. A statistical model based on empirical data is presented, and it is shown how to use this model for deriving access strategies. The coexistence of Bluetooth and WLAN is considered as a concrete example