On the Placement of Intelligent Surfaces for RSSI-Based Ranging in Mm-Wave Networks

We study the received signal strength indicator (RSSI)-based ranging performance of a cellular user in a millimeter-wave (mm-wave) network aided by reconfigurable intelligent surfaces (RISs). First, we propose an optimal RIS deployment strategy that minimizes the joint blockage probability of the user to the base station (BS) link and the user to the RIS link. Then, we provide a bound-based characterization of a ranging strategy in which the BS estimates the distance the user in the direct link in case it is in the line of sight (LOS) state, whereas in case the direct link is blocked, the BS estimates the user distance via the reflected, i.e., RIS-aided link. In literature, for maximizing the path-gain the RIS deployment is recommended to be in close proximity to the BS. In contrast, our study shows that in the presence of blockages, close locations of the RIS and the BS is sub-optimal.