Constant–er Lens Beamformer for Low Complexity Millimetre–Wave Hybrid MIMO
The utilization of unused millimetre–wave (mmWave) spectrum is inevitable, due to the unavailability of required bandwidth in the conventional RF band to support the high data demands in 5G networks. at mmWave frequencies, large antenna arrays with beamforming capabilities are required to compensate for the high path–loss. We are on the verge of a massive mmWave radio front-end deployment, and low–complexity, low–cost hardware beamforming solutions are required more than ever.
In this paper, we therefore demonstrate the capabilities of a constant–er lens in an attempt to realize a low complexity RF front–end for mmWave MU–MIMO. We present a high performance and low complexity lens-based beamformer consisting of constant dielectric material (er) with antenna feeds for multi–beams operation. We developed a prototype based on the classical synthesis approach and in line with the requirements of mmWave hybrid multi–user multiple–input multiple–output (MU–MIMO) systems. We performed a characterization at 28 GHz wherein uplink signal–to–noise–ratio of user terminals was evaluated with the zero–forcing (ZF) baseband signal processing.
With the measurements of the lens beamformer, we predicted the end–to–end system performance of hybrid MU–MIMO architecture in terms of ergodic sum spectral efficiency for 9 UE terminals. To draw a comparison, we used the performance of previously reported classical analogue Rotman lens-based beamformers connected to ULA and URA. Our results depict the superiority of the constant–er lens in terms of cost, complexity and performance. We show that the constant–er based beamformer solution is simple, yet significantly outperforms conventional antenna array beamformers with analogue phase shifter network. The capacity gains acquired with our proposed solution, when coupled to the mechanical and thermal properties of the lens beamformer, suggest that it is a useful engineering solution for mm-wave beamforming in hybrid massive MIMO systems.
This innovative approach is an evolution of our 28 GHz two-stage Roman Lens beamformer design, for which we were awarded the Grand Prize of the global Mobile World Scholar at MWC19 in Barcelona this year.
Please contact Norbert Sagnard at Queen’s University Belfast (Centre for Wireless Innovation) for detailed information [firstname.lastname@example.org].
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