TDD Massive MIMO is already going wide at SoftBank Japan, yielding a 4x-10x capacity improvement on a single channel. Eric Zhao believes Massive MIMO is often the right choice where you need high capacity. Zhao finds early 32 antenna system averaging 450% more capacity in a single band. Many leading engineers agree MM is the way to go.
Worldwide, chief technologists are enthusiastic about Massive MIMO. At Huawei's MBB Forum, Hidebumi Kitahara of SoftBank confirmed the reported results, especially in crowded cells. Later in the day, Huang Yuhong of China Mobile also reported success. Her performance improvement estimates were "only" 3x, but it's early days for the technology. At SoftBank owned Sprint, Günther Ottendorfer reports a 10x improvement. Sanyogita Shamsunder of Verizon a year ago told me, "We must have massive MIMO." Nasser Al Nasser of Saudi Telecom in the release below reports a 6x improvement.
The varying estimates correspond to the varying performance of MIMO. MIMO results are drastically different depending on the terrain. They will go up. There are dozens of ideas how Massive can be improved, many still just technical journal articles. There's plenty of room to improve before reaching the Shannon Law limits.
Where the demand isn't that high, Zhao recommends 4x4 MIMO. Qualcomm is promoting "4x4 Everywhere." Huawei is now shipping systems with four antennas that average 40% to 75% more capacity than two antenna systems. They also offer an interesting alternative, an eight antenna system optimized for phones with two antennas. deploying at Viva in Kuwait Four antenna phones are just beginning and there won't be many in the field for a while.
You can add capacity with more sites (small cells,) antennas (MIMO,) spectrum, software (256 QAM,) and improvements to all of the above SASSi, As I write in April 2017, most carriers are adding carrier aggregation (spectrum,) 4x4 MIMO (antennas,) and 256 QAM (software.) Together, they can deliver close to a gigabit peak.
Looking forward, CTOs seem to be looking most at Massive MIMO or small cells, including 5G.
SAUDI TELECOM COMPANY (STC) ANNOUNCES RECORD THROUGHPUTS IN ITS 4G LTE NETWORK THROUGH THE SUCCESSFUL DEPLOYMENT OF MASSIVE MIMO TECHNOLOGY, IN JOINT PARTNERSHIP WITH HUAWEI.