Transmission mode switching for relay/RIS assisted device-to-device communication networks

Reconfigurable intelligent surface (RIS) is now envisioned as a promising strategy to enhance the performance of the traditional device-to-device (D2D) communication system. In this paper, taking the relay strategy into consideration, we propose a new mode selection scheme between three communication modes, including amplify-and-forward (AF) relay-assisted D2D communication mode, decode-and-forward (DF) relay-assisted D2D communication mode and RIS-assisted D2D communication mode, which always selects the mode with maximum achievable rate. The switching thresholds between three modes or any two modes are presented by closed-form expressions. The simulation result verifies the accuracy of the selection scheme and illustrates higher achievable rate performance under the proposed scheme.