Energy Utilization Efficient Frame Structure for Energy Harvesting Cognitive Radio Networks

Abstract

This letter proposes a novel saving-sensing-transmitting (SST) frame structure for energy harvesting cognitive radio networks. As in the conventional SST, the proposed SST takes the energy causality constraint (EC-constraint) into consideration, which is referred to as the normal mode in this letter. Besides, it includes the other two modes, sensing mode and sleeping mode, to make full use of the residual battery energy and ensure enough time for sensing and transmission. These two modes are activated based on the residual battery energy and a predefined save-ratio threshold. For the normal mode, we maximize the energy utilization efficiency of the secondary user by jointly optimizing the save-ratio and transmission power under both the EC-constraint and the minimum throughput constraint. This problem is solved by first determining the best save-ratio in closed-form and then optimizing the power allocation using Dinkelbach method. The sensing mode is optimized using a similar method. Finally, numerical results validate the efficiency of the proposed SST.