Holographic-Inspired Meta-Surfaces Exploiting Vortex Beams for Low-Interference Multipair IoT Communications: From Theory to Prototype

Meta-surfaces, also known as reconfigurable intelligent surfaces (RISs), have emerged as a cost-effective, low-power consumption, and flexible solution for enabling multiple applications in Internet of Things (IoT). However, in the context of meta-surface-assisted multipair IoT communications, significant interference issues often arise among multiple channels. This issue is particularly pronounced in scenarios characterized by Line-of-Sight (LoS) conditions, where the channels exhibit low rank due to the significant correlation in propagation paths. These challenges pose a considerable threat to the quality of communication when multiplexing data streams. In this article, we introduce a meta-surface-aided communication scheme for multipair interactions in IoT environments. Inspired by holographic technology, a novel compensation method on the whole meta-surface has been proposed, which allows for independent multipair direct data streams transmission with low interference. To further reduce correlations under LoS channel conditions, we propose a vortex beam-based solution that leverages the low-correlation property between distinct topological modes. We use different vortex beams to carry distinct data streams, thereby enabling distinct receivers to capture their intended signal with low interference, aided by holographic meta-surfaces. Moreover, a prototype has been performed successfully to demonstrate a two-pair multinode communication scenario operating at 10 GHz with quadrature phase shift keying (QPSK)/16-QAM modulation. The experiment results demonstrate that, even under LoS conditions, the isolation between the two-pair channels exceeds 21 dB. This allows receiving users to undertake simultaneous, same-frequency multiplexed data transmission under extremely low-interference conditions, with a real-time demodulation bit error rate (BER) remaining below 3.8 ×10-3 at achievable signal-to-noise ratio (SNR) conditions. Through the convergence of holographic meta-surfaces and vortex beams, we present a fresh perspective on achieving efficient, low-interference multipair IoT communications.