Combined spatial-temporal energy harvesting and relay selection for cognitive wireless powered networks

In order to improve the Energy Efficiency(EE) and spectrum utilization of Cognitive Wireless Powered Networks(CWPNs), a combined spatial-temporal Energy Harvesting(EH) and relay selection scheme is proposed. In the proposed scheme, for protecting the Primary User(PU), a two-layer guard zone is set outside the PU based on the outage probability threshold of the PU. Moreover, to increase the energy of the CWPNs, the EH zone in the two-layer guard zone allows the Secondary Users(SUs) to spatially harvest energy from the Radio Frequency(RF)signals of temporally active PUs. To improve the utilization of the PU spectrum, the guard zone outside the EH zone allows for the constrained power transmission of SUs. Moreover, the relay selection transmission is designed in the transmission zone of the SU to improve the EE of the CWPNs. In addition to the EE of the CWPNs, the outage probabilities of the SU and PU are derived. The results reveal that the setting of a two-layer guard zone can effectively reduce the outage probability of the PU and improve the EE of CWPNs. Furthermore, the relay selection transmission decreases the outage probabilities of the SUs.