It will soon be a decade since the first trials of massive MIMO (mMIMO) in mobile networks, and yet there is still debate over how to deploy the technology optimally in different scenarios, as well as how to balance spectral performance against energy efficiency. There are even doubts over how far it is worth increasing array size, even though it has been fully proven beyond doubt that mMIMO does enhance spectral efficiency (SE) up to at least 32T32R (32 transmit and 32 receive) arrays in commercial networks. It is also clear mMIMO’s benefits scale with frequency, since smaller wavelengths enable reduced antenna size. mMIMO only enters the equation for mid band frequencies above 1 Gbps and becomes most compelling at…