Power Minimization for Half-Duplex Relay in Fluid Antenna System

The exploration of Sixth Generation (6G) networks has led to a paradigm shift, emphasizing the synergy between next-generation reconfigurable antennas and wireless communications. Notably, Fluid Antenna System (FAS) stands out as a promising solution for advancing 6G networks. One of the unique features of FAS is its ability to instantly reconfigure the antenna’s position over a given area, enabling extreme spatial diversity with just one antenna and one Radio Frequency (RF)-chain. This spatial diversity can be harnessed to create an energy-efficient system. While FAS has been explored in various scenarios, its performance as a half-duplex relay remains unclear. In this letter, we investigate the application of fluid antennas in half-duplex relays, considering both Amplify-and-Forward (AF) and Decode-and-Forward (DF) schemes. Moreover, we jointly minimize the total transmit power of the Base Station (BS) and relay through optimal port and transmit power for both schemes, while ensuring the user rate requirement is met. We demonstrate that optimal port and transmit power can be determined using a one-dimensional search for AF and a closed-form expression for DF. Simulation results show that FAS relay is more energy efficient than Traditional Antenna System (TAS) relay with fixed-position antenna.