Performance of a 28 GHz Two–Stage Rotman Lens Beamformer for Millimeter Wave Cellular Systems
Phase shifter–based hybrid beamforming has received a lot of attention at millimeter–wave frequencies for cellular communications. Nevertheless, the implementation complexity of such beamformers is rather high due to the complexities involved in designing and fabricating the required radio–frequency (RF) circuits. In contrast, lens–based RF beamformers significantly reduce the implementation complexity, as all active circuits can be replaced by a passive device. In this paper, researchers of the Centre for Wireless Innovation at Queen’s University Belfast present the sum spectral efficiency performance of an uplink multiuser multiple–input multiple–output (MU–MIMO) system with a 28 GHz Rotman lens. An asymmetric two–stage stacked design is fabricated with a 15 element (3×5) uniform rectangular array feeding 9 RF down–conversion chains towards baseband.
Zero–forcing processing is employed at baseband for interference nulling and multistream recovery. Our results show that the MU–MIMO gains are substantially more pronounced for the two–stage architecture relative to a single–stage design due to the inclusion of the elevation multipath components. They also show that the asymmetric design can help further reduce the implementation complexity, since the conventional beam selection network can be omitted from the RF front–end.
This novel approach won the Grand Prize of the global Mobile World Scholar award at MWC19 in Barcelona in February 2019. Please contact Norbert Sagnard for more info [n.sagnard@qub.ac.uk].
©2019 Queens University Belfast.
