Power Minimization in Multi-Antenna Transmitter Aided Bidirectional Tag-to-Device Communications for IoT

Bidirectional device-to-device (D2D) communications with energy-constrained devices hold the potential to revolutionize the low-power communication landscape and provide a means to realize the aim of Internet-of-Things (IoT). In this paper, we aim to explore a communication environment where a multi-antenna transmitter facilitates communication between two users equipped with two different technologies — backscattering and radio frequency based energy harvesting. Under such a setting, we aim to minimize the transmit power over a set of constraints by considering the traditional linear and the more practical nonlinear (sigmoid) energy harvesting model. Henceforth, we propose a novel optimal solution approach, exploiting the geometric interpretation of constraints and interdependency of optimization variables and the performance metric, to solve the formulated non-convex problem for the multi-antenna transmitter case for both the energy harvesting models considered. In addition, we revisit the power minimization problem for the single-antenna transmitter case, solved in our previous work, to demonstrate the applicability of the current solution approach. Furthermore, to establish a fair balance between the performance and the computation-intensive nature of the proposed optimal solution, we present two low complexity sub-optimal solution approaches leveraging the analysis carried out for the single antenna transmitter case. Finally, using the numerical simulations, we assess the performance of our system and present a comparison between the proposed solution approaches by varying some key parameters of our simulation setting.