Opportunistic Spectrum Sharing With Wireless Energy Transfer in Stochastic Networks

We consider underlay spectrum sharing with wireless energy transfer in a large-scale cognitive radio network, where each primary user (PU) can harvest radio frequency energy from its associated access point (AP). An energy cooperation zone is applied around each PU, wherein the secondary user (SU) with the best channel quality toward PU is selected to cooperatively transfer wireless energy. With SUs' assistance, each PU can harvest a predefined amount of energy in a shorter time, so there will be more concurrent primary links in the network. We analyze the transmission probability of PUs by properly modeling their energy statuses using Markov chain. Furthermore, a guard zone is applied around each active AP to prohibit the nearby SU transmissions to avoid strong interference, and SUs outside the guard zones of all the active APs can access the spectrum opportunistically. Under the constraint that the area throughput of primary system should be improved by at least a certain degree, the area throughput of the secondary system is maximized by jointly determining the SUs' density and the guard zone radius. Numerical results show that our scheme can well accommodate SUs' transmissions while guaranteeing PUs' performance requirement.