Green Wireless Powered Sensor Network through Joint Power Beacon and Sensor Activation.

The technology of wireless powered communications is essential for the energy-sustainable sixth generation (6G) wireless networks. However, due to the generally low end-to-end wireless energy transmission efficiency from the power beacons (PBs) to the wireless sensors (WSs), the PBs are required to adopt high transmit power or deploy densely to meet the WSs' energy demands, which may result in intolerantly high energy consumption at the PBs. To investigate the optimal design tradeoff between the WSs' energy-sustainable communications and the PBs' energy-efficient wireless energy transmissions, this paper jointly optimizes the PBs' activation probabilities and the WSs' duty cycles in a wireless powered sensor network (WPSN), to minimize the overall energy consumption at the PBs. Using tools from stochastic geometry, we derive the WSs' successful transmission probability in each frame, which is a joint probability of being sufficiently charged by the PBs in the idle phase and sending information successfully in the transmission phase. However, the PBs' energy consumption minimization problem under the WSs' successful information transmission probability constraint is shown to be non-convex, and thus is difficult to solve. By studying the problem structure, we manage to find the optimal solutions efficiently. Numerical results are also provided to show the energy consumption performance of our proposed scheme.