Energy-Efficient Adaptive Transmissions in Cognitive Radio Networks with Energy Harvesting

In this paper, we propose an adaptive transmission scheme to improve the energy efficiency (EE) of bidirectional information transmissions in cognitive radio (CR) networks. In the proposed scheme, two end-source secondary users (SUs) select a high energy-efficient transmission mode between the direct transmission (DT) and the two-way relaying transmission based on physical-layer network coding (PNC). Meanwhile, the two-way relay harvests energy from the two end-source SUs to improve the EE. We derive the EE expressions of DT and PNC modes. The results show that the EE of PNC mode is not always higher or lower than that of DT mode. It proves that our proposed adaptive transmission scheme is necessary and effective to improve the EE of bidirectional cognitive transmissions. The results also show that energy harvesting (EH) can improve the EE of the PNC transmission by compared with the PNC transmission without EH.