Connection Density Enhancement of Backscatter Communication Systems with Relaying

Backscatter communication is a promising technology for energy-efficient communications. It enables the Internet of things (IoT) devices to send their data by backscattering and modulating the incident radio frequency (RF) signals. In this paper, we propose a scheme for improving the connection density of backscatter communication systems, i.e., increasing the number of backscattering-enabled IoT devices that meet a minimum threshold of the received signal-to-noise ratio (SNR) at the serving base station (BS). The aforementioned goal is achieved by allowing the user equipment (UE) devices to relay the backscattered signals from the IoT devices. A UE superimposes its own uplink data with the data from an associated IoT device using power-domain non-orthogonal multiple access (NOMA). Since the UEs are mobile and have higher transmit power, the IoT devices utilize the nearby UEs to relay their data. In addition, using UEs as relays helps the BS to support more backscattering-enabled IoT devices. We formulate the connection density maximization problem to pair the IoT devices with the available UE relays. The formulated problem is a mixed-integer linear programming (MILP) problem. Although the formulated problem can be solved optimally, it has an exponential complexity. Hence, we propose a suboptimal algorithm which decomposes the original problem into smaller subproblems that can be solved by low complexity algorithms. Simulation results show that the proposed scheme with UEs as relays can increase the connection density by up to 65% compared to deploying fixed relays.