  Data rate requirements for cellular communications are expected to increase
1000-fold by 2020, compared to 2010. This is mainly because of the rapid
increase in the number of wireless devices and data hungry applications
per-device. This creates a formidable bandwidth crisis. Milimeter-wave (mmWave)
systems with massive multiple-input multiple-output (MIMO) operation are two
complementary concepts poised to meet this exploding demand, as verified by the
wealth of investigations by both industry and academia. Nevertheless, existing
MIMO processing techniques, requiring a dedicated radio-frequency (RF)
up/down-conversion chain per antenna, results in prohibitively high complexity
and cost of the mmWave prototypes. The primary objective of this paper is to
present a complete feasibility study on alternative beamforming techniques
targeted to reduce the system complexity without drastically compromising its
performance. More precisely, at 28 GHz, we investigate the end-to-end
performance of two different lens-based beamforming topologies. Our study is an
amalgam of theoretical modelling, electromagnetic design, and prototype
manufacturing, yielding a comprehensive mmWave, massive MIMO performance
evaluation.
