OAM-MIMO Multiplexing Transmission System for High-Capacity Wireless Communications on Millimeter-Wave Band

This paper presents the performance analysis and experimental demonstrations of our orbital angular momentum-multiple-input multiple-output (OAM-MIMO) multiplexing system. OAM is a fixed orthogonal basis set, so OAM multiplexing has a high affinity to analog processing. We extend OAM multiplexing to OAM-MIMO multiplexing technology, which effectively combines the advantage of OAM multiplexing with that of MIMO-based digital signal processing with multiple uniform circular arrays (multi-UCAs) for line-of-sight wireless transmission. Basically, OAM-MIMO is classified as a practical form of analog-digital hybrid MIMO technology. Our multi-UCA-based OAM-MIMO multiplexing transmission system has two hybrid analog-digital architectures. We evaluated its performance through a comparison with different antenna arrangements and configurations. We implemented antennas of quadruple UCAs, with each UCA having a broadband Butler matrix circuit that generates and separates OAM modes as an analog part of hybrid MIMO on a 28-GHz frequency band. We experimentally demonstrated 130-Gbit/s wireless data transmission with 11 streams using five OAM modes (0, ±1, ±2) at a distance of 10 m. We also demonstrated simultaneous use of OAM-MIMO and polarization multiplexing and achieved wireless transmission over 200 Gbit/s with 21 streams. These results indicate the practicality and effectiveness of our system for high-capacity wireless communication.