The impact of node position on outage performance of RF energy powered wireless sensor communication links in overlaid deployment scenario

In recent years, ambient radio-frequency (RF) signal has been accepted as a new potential solution to support green communications. However, due to the increasingly severe spectrum scarcity, the ambient RF signal is not only an energy source but could also be an interference to the supported communication systems. In this paper, we focus on the study of the node position impact on the performance of the overlaid wireless sensor communication link where the nodes are powered by RF energy harvested from an existing wireless system operating over the same frequency, providing insights into node configuration strategy and relay selection scheme for the network deployed in such a overlaid scenario. A point-to-point communication link which consists of a sink node and a sensor node is fundamentally studied in our works. The effect of sink position on the link outage performance is investigated in detail. Through theoretical analysis, three rules are proposed for the sink position adjustment to reduce the link outage. Subsequently, we extend our works into a two-hop relay communication scenario, where a RF energy powered relay is added between a sensor node and a sink node. By adopting decode-and-forward (DF) relaying protocol at the relay, the impact of relay node position on the link outage performance is investigated. To reduce the link outage, the optimal relay position is proven to be collinear with the source and the sink. Based on this property, a suboptimal position of the relay is provided. Finally, numerical simulations are conducted to verify our theoretical analysis.