Inter-Mode Interference Suppression Employing Even-Numbered Modes for UCA-Based OAM Multiplexing

This paper proposes an inter-mode interference suppression method that employs only even-numbered modes for uniform circular array (UCA)-based orbital angular momentum (OAM) multiplexing. Given that interference from adjacent OAM modes becomes severe when the beam axis is misaligned, the proposed method uses only the even-numbered modes while leaving the odd-numbered modes unused, which effectively prevents the inter-mode interference. Moreover, we verify the effectiveness of the proposed method by applying it to multiple-input and multiple-output (MIMO) with zero-forcing (ZF) alone or ZF with successive interference cancellation because severe inter-mode interference is caused by transmitting multiple streams from multiple UCAs in each mode. The effectiveness of the proposed method compared with the traditional method, which uses all OAM modes, is demonstrated in terms of the system capacity through computer simulations.