Intelligent Reflecting Surface-aided Phase-Shift Backscatter Communication

Intelligent reflecting surface (IRS) is a 2D surface made up of metasurface, on which passive elements such as varactor diodes interact with incoming electromagnetic waves and manipulate them to behave according to user objectives. Ambient backscatter communication (AmBC) utilizes both ambient RF source and spectrum without additional infrastructure. In this paper, we propose a system that integrates AmBC with IRS technology to overcome the fundamental coverage limitation of conventional backscatter communications. Specifically, we replace the antenna-switching tag with such IRS elements. As IRS is already known to aid in passive beamforming and relaying, we aim to enable secondary information transmission while relaying primary information. A novel idea here is splitting the primary transmitter power to send additional unmodulated carrier along with its message signal. We maximize the spectrum efficiency of the secondary system subject to the minimum spectrum efficiency of the primary system through optimization of the power-splitting factor. Numerical results validate that the IRS-aided backscatter system outperforms conventional ones.