Battery-Assisted Backscatter Devices: Energy Management and Outage Performance Analysis

Backscatter communication (BC) has been deemed a solution for ambient Internet of Things. In this paper, we consider a BC system, where a battery-assisted backscatter device (BD) is capable of harvesting and storing energy for information transmission. Our first contribution is to propose a novel energy management protocol that enables the BD to make real-time decisions for minimizing unnecessary transmissions, thereby saving energy for future transmissions and improving the outage performance. The core of this protocol is an optimization problem where the BD decides whether to backscatter information or harvest energy exclusively, based on the satisfaction of the quality-of-service (QoS) constraint, energy causality constraint, and power reflection coefficient (PRC) range constraint. We solve this problem and obtain the optimal PRC. Our second contribution is to evaluate the impact of the proposed protocol on the BD's information transmission in terms of outage probability (OP). To this end, we model the BD's battery as a discrete Markov Chain, derive its state transition matrix and stationary distribution, and obtain the exact OP, along with an approximate expression using GaussianChebyshev approximation. The simulation and theoretical results demonstrate that the proposed energy management protocol outperforms the baseline schemes, and reveal the impact of system parameters such as the battery discretization level on the OP of the BD.