Cognitive Radios play very important role in military applications due to their capability to adapt intelligently according to the prevailing environmental conditions. Relays form the main communication enablers in infrastructure-less networks. In this paper, relay selection for increasing the energy efficiency of a cognitive radio network is considered. The proposed approach considers the multiple - relay selection scheme with strict outage probability constraints. Energy maximisation is posed as an optimisation problem, the solution to which shows that relay selection under outage constraints is different from the one without such a constraint. It can be observed from the simulations that energy efficiency and outage behaviour follows trade-off relations. Moreover, the original Branch and Bound algorithm has been re-designed for faster convergence. It has also been demonstrated that when strict outage constraints are imposed, the optimal number of relays selected will be more in comparison to the case where there is no outage consideration.
Energy efficiency (EE) has now become one of the essential parameters in the design of 5G and other next‐generation communication networks mainly due to economic and environmental concerns. In this paper, we develop an EE maximisation algorithm for the orthogonal frequency‐division multiplexing (OFDM)–based cognitive radio (CR) systems where the PU activity is highly dynamic. The problem is formulated as a joint optimisation problem in 3 variables: sensing duration, transmission duration, and transmit power on the subcarrier, with statistical constraint on the primary user (PU) interference. The statistical interference constraint frees the CR transmitter from the additional burden of obtaining the instantaneous channel quality feedback from the PU receivers. Furthermore, PU mobility, which is the main consideration of this work, closely portrays a real and practical CR network. We analyse how the mobility of the PUs affect their Quality of Service, particularly in terms of the interference impinged on PUs by the SUs. Moreover, the mobility of the PUs has been modelled, and PU interference constraints are reformulated by considering collisions between the PUs and SUs during their overlap period. Moreover, closed‐form expressions for secondary throughput and EE have been derived. The original problem, which is mathematically intractable due to its nonconvexity, is reformulated in terms of 3 alternately iterating subproblems. Numerical results show that with the proposed optimal algorithm, CR users can achieve significantly higher EE compared with existing algorithms. The suboptimal algorithm guarantees reduced complexity with a performance gap close to zero with the original optimal problem.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.