Blocking Probability in Obstructed Tunnels with Reconfigurable Intelligent Surface

In the obstructed tunnels, the signal transmission will suffer the risk of ray-path blocking caused by the obstacles owing to the Snell's law. In this letter, the reconfigurable intelligent surface (RIS) that can reflect the electromagnetic waves to any specific directions is introduced to mitigate the signal blocking. The closed-form expressions for blocking probability (BP) for one reflection with single RIS and multiple RISs under various scenarios are derived. Compared with the case without RIS, significant reduction of BP can be found with proper configuration of the RIS. Moreover, the impact of the location of RIS, the height of the transmitter, and the location of the receiver, on the BP is investigated. Finally, the case of multiple obstacles with different distributions is discussed to further verify the effectiveness of RIS on reduction of BP.