Joint Design of Aerial Reconfigurable Intelligent Surface aided URLLC Systems

Ultra-Reliable Low-Latency Communication (URLLC) has imposed significant challenges on the Internet of Things (IoT) networks due to its stringent Quality of Service (QoS) requirements. Conventionally, to support the latency and reliability requirements, the IoT devices have to leverage the transmission power, which significantly shortened the battery life. As a promising candidate for the future mobile communication systems, reconfigurable intelligent surface (RIS) is preferrable to be deployed in the IoT networks to reduce the power consumption, thanks to its ability in reconfiguring the propagation environment. In this paper, we focus on the design of an aerial RIS aided URLLC system where the RIS is deployed on an unmanned aerial vehicle (UAV). The system operates on the time division multiple access (TDMA) protocol, and the transmission power minimization problem is investigated. A low-complexity algorithm is proposed to jointly optimize the RIS phase shifts, transmission time duration, and the UAV location. Simulation results demonstrate that by deploying aerial RIS in the IoT network, the transmission power at the IoT device can be significantly reduced. The effect of the TDMA frame length is also discussed. When the TDMA frame length is large, the optimal transmission time duration could be much shorter than equal allocation, which implies that our proposed design is able to simultaneously reduce both the average power consumption and the transmission latency.