  This paper presents the current state-of-the-art of massive antenna array
architectures with significant front-end hardware savings, as an enabler for
future small and powerful cell nodes that will be able to carry massive MIMO
technology. Radio frequency (RF) hardware architectures with a single power
amplifier are reviewed, compared, and found superior to conventional MIMO
implementations in terms of cost, dissipated heat, and physical size. This
progress on the RF-side allows to merge the two competing cellular concepts of
virtual and massive MIMO into a hybrid approach of remote radio heads with
massive MIMO arrays.
