Misalignment-Robust OAM Multi-Mode Multiplexing With Index Modulation Based on UCA Samples Learning

Orbital angular momentum with index modulation (OAM-IM) presents an innovative information modulation scheme for OAM wireless communications, which is expected to achieve superior spectral efficiency (SE) and energy efficiency (EE) by utilizing a set of activated OAM modes to carry additional information based on the principle of IM. However, in the existing OAM-IM communication systems, the accurate alignment between the transmitter and receiver is required to avoid a larger performance penalty. To break the bottleneck, we present a novel misaligned OAM multi-mode multiplexing with IM (OAM-MMUX-IM) scheme based on uniform circular arrays (UCAs), including the generation of OAM-MMUX-IM signals and the multi-mode OAM detection. At the transmit UCA, the OAM-IM signals are designed to carry additional information by activating a subset of the available OAM modes. According to the characteristics of IM, the multi-layer back-propagation neural network (BPNN) is applied to the misaligned receive UCA for the first time to achieve the OAM multi-mode detection. The simulation results from MATLAB show that the presented OAM-MMUX-IM scheme can flexibly identify multiple OAM modes in the misaligned OAM system and achieve excellent SE and error performance.