An RIS Deployment Strategy to Overcome Static Obstacles in Millimeter Wave D2D Communication

Use of millimeter waves for short range device to device (D2D) communication is one of the most promising ways to provide high data rates. But millimeter waves are susceptible to blockages due to high penetration losses and hence require almost a line of sight (LoS) communication to provide such high data rates. When the direct LoS of a pair of devices is blocked by an obstacle, a reconfigurable intelligent surfaces (RIS) in the vicinity can be exploited to bypass the obstacle and achieve an indirect LoS between them. In this paper, we develop a strategy for placing minimum number of RISs in an environment filled with obstacles such that any pair of devices in the environment who does not have direct LoS can communicate via these RISs by establishing an indirect LoS. We convert this RIS placement problem to a set cover problem and give a greedy algorithm to get a near optimal but practical solution. This is done as a preprocessing step before the actual devices are deployed in the region. Next we present a strategy which knowing the actual deployment of the devices, selects a subset of the deployed RISs for operation together with their channel coefficients and phase shifts such that the system sum throughput of the devices is maximised. Finally simulation results show that strategically placed RISs can significantly improve system throughput in comparison to the existing deployment strategies.