Hybrid Beam Focusing for MIMO OAM Communications

For millimeter or Tera-Hertz communications, channel capacity is often found limited by its channel diversity due to the sparse or line-of-sight transmission conditions in these frequency bands. This diversity problem exacerbates particularly in future non-terrestrial communications. Wireless communication that exploits the diversity of orbital angular momentum (OAM) in electro-magnetic waves is considered one of the potential technologies to push the limit despite the skepticism for its long-rang transmissions in free space. Inspired by the recent advances on hybrid beamforming, we propose a novel OAM beam focusing method to explore the feasibility of multiple input multiple output (MIMO) OAM wireless transmissions. With the proposed optimal beam focusing and power allocation scheme and the use of a concentric uniform circular array (CUCA) of diameter 1.2 meters (m), we show that signals of up to three OAM modes can be delivered to a receive uniform circular array of diameter 20 cm at a distance of 500 m, which presents the potential of MIMO OAM for future 6th generation communication systems.