Overcoming the Near–Far Effect for Backscatter Communications: RIS or Relay?

Backscatter communication (BackCom) has gained increasing attention due to its low power consumption and low cost. However, its performance is severely degraded by the near-far effect due to the limited backscattering power at the tag side. In this paper, we consider two effective methods to solve the above problem by using the reconfigurable intelligent surface (RIS) and the relay. The objective is to maximize the received signal-to-noise ratio (SNR) subject to the transmit and circuit power control. To gain insight into both schemes, we derive a closed-form expression for the coverage radius of RIS-aided BackCom. Furthermore, considering the relay as a competing technology to the RIS, we compare their performance in terms of transmission performance, required transmit power, and quantify the number of reflecting elements needed for the RIS to outperform the relay. Simulation results demonstrate the RIS-aided BackCom with a sufficiently large number of elements achieves a superior performance, offers greater deployment flexibility, and is suitable for high self-interference levels.