5G is here. China Mobile and Softbank plan thousands of sites. At Huawei's remarkable Tokyo Mobile BBF, both Softbank Japan and China Mobile showed enthusiasm. These are the first large moves in 5G, pulling Massive MIMO at least one year ahead of high-frequency millimeter wave. I believe my report Softbank's Giga Monster Massive MIMO: World's first commercial 5G is not highband millimeter wave was the first in the West. I have since learned that Huawei, as well as ZTE, provided equipment.
Gear that triples capacity (or better) at modest cost is now in production from both Huawei and ZTE. Softbank has 100 base stations up and running. They are mostly in Tokyo but also in several other cities. China Mobile has working systems in two cities.
Their early reports are that 128 antenna Massive MIMO today increases capacity 3X to 10X. Expect considerably better results over time. MIMO inventor Paulraj of Stanford two decades ago realized that MIMO could enormously increase capacity in a given amount of spectrum. Remarkably, the additional throughput requires minimal additional power.
Respected engineers - Henry Samueli, Andrea Goldsmith, Vint Cerf - two years ago were comfortable with predictions that wireless capacity would soon increase 50X. MIMO is crucial to that goal.