Joint resource allocation and UAV placement in UAV-assisted Wireless Powered Sensor Networks using TDMA and NOMA

Widely employment of UAV-assisted communications along with the energy harvesting technology in the next generation of telecommunication networks, is one of the promising solutions to provide improved metrics whereas it brings new challenges. In this paper, we consider UAV-assisted Wireless Powered Sensor Network (WPSN) in which the sensors are distributed in the area and harvest their energy from the UAV above, during downlink wireless energy transmission (DL-WET) phase and transmit the gathered data to the UAV during uplink wireless information transfer (UP-WIT) phase under TDMA and NOMA protocols. The total uplink sum-rate for both protocols are calculated, and then, the joint resource allocation and UAV placement optimization problems are defined over time schedule and power parameters under minimum data rate and energy constraints. The optimization problems turns out to be non-convex and intractable to be solved. Therefore, we separate the problems into two subproblems which could be solved through regular methods. An iterative algorithm with fast convergency characteristic is proposed to obtain the suboptimal solutions for the optimization problems. Comparing the numerical results for the NOMA and TDMA approaches shows that in a power limited scenario, NOMA-based approach outperforms the uniform resource allocation while it is as the same as TDMA-based one.