Underlay Spectrum Sharing with Spatially Random Users and Cooperative Wireless Power Transfer

This paper investigates a large-scale cognitive radio network with primary users (PUs) and secondary users (SUs) spatially and randomly distributed. All the PUs need to harvest wireless energy from their associated access points (APs) before transmitting information. To combat the low efficiency of wireless power transfer caused by the severe path-loss, we propose to apply an energy cooperation zone (EC) around each PU, wherein the best SU is selected to transfer wireless power along with the AP. Therefore, each PU can accumulate a predefined amount of energy more quickly to support the data transmission to its AP. To avoid the SUs causing strong interference, each active AP is protected by a guard zone, and only the SUs outside all the guard zones could access the channel together with all the active PUs. Numerical results show that the energy cooperation from SUs can greatly improve the area throughput of primary system and more opportunities can be achieved for the SUs' transmissions.