Physical Layer Security of THz Orbital Angular Momentum MIMO Systems with a Successive Interference Cancellation Eavesdropper

Spatial multiplexing is not always feasible in terahertz and sub-terahertz (THz) MIMO channels due to the primarily line-of-sight propagation, but recent works have explored the possibility of using orbital angular momentum (OAM) to enable multiplexing in line-of-sight scenarios. This paper explores a certain physical-layer security risk and a corresponding mitigation strategy for THz MIMO systems using orbital angular momentum (OAM). A novel successive interference cancellation eavesdropping attack is introduced for OAM-MIMO THz systems, and simulations demonstrate that the security of the link decreases in the far field. A security countermeasure is introduced and proven to be effective in physically protecting the communications link.