I have been wondering for years if “MIMO” will always be a term exclusively used by engineers and a few well-informed consumers, or if it eventually becomes a word that most people are using. Will you ever hear kids saying: “I want a MIMO tablet for Christmas”?
I have been think that it can go either way – it is in the hands of marketing people. Advanced Wifi routers have been marketed with MIMO functionality for some years, but the impact is limited since most people get their routers as part of their internet subscriptions instead of buying them separately. Hence, the main question is: will handset manufactures and telecom operators start using the MIMO term when marketing products to end customers?
Maybe we have the answer because Sprint, an American telecom operator, is currently marketing their 2018 deployment of new LTE technology by talking publicly about “Massive MIMO”. As I wrote back in March, Sprint and Ericsson were to conduct field tests in the second half of 2017. Results from the tests conducted in Seattle, Washington and Plano, Texas, have now been described in a press release. The tests were carried at a carrier frequency in the 2.5 GHz band using TDD mode and an Ericsson base station with 64 transmit/receive antennas. It is fair to call this Massive MIMO, although 64 antennas is in the lower end of the interval that I would call “massive”.
The press release describes “peak speeds of more than 300 Mbps using a single 20 MHz channel”, which corresponds to a spectral efficiency of 15 bit/s/Hz. That is certainly higher than you can get in legacy LTE networks, but it is less than some previous field tests.
Hence, when the Sprint COO of Technology, Guenther Ottendorfer, describes their Massive MIMO deployment with the words “You ain’t seen nothing yet”, I hope that this means that we will see network deployments with substantially higher spectral efficiencies than 15 bit/s/Hz in the years to come.
Several videos about the field test in Seattle have recently appeared. The first one demonstrates that 100 people can simultaneously download a video, which is not possible in legacy networks. Since the base station has 64 antennas, the 100 users are probably served by a combination of spatial multiplexing and conventional orthogonal time-frequency multiplexing.
The second video provides some more technical details about the setup used in the field test.
3 thoughts on “Massive MIMO is Becoming a Marketing Term”
Softbank started calling their 8×8 MIMO in Japan as Massive already. So while 64 is still a long shot from 1024, it is definitely considered Massive in the current climate, and may be one reason why Softbank is trying to acquire as many TDD network operator (e.g. Sprint) as possible.
Massive MIMO is definitely on the offensive this year from a Marketing Perspective, while I have no idea in US, literally every operator has been marketing their coming Massive MIMO improvement in Japan, Korea, China, Hong Kong etc. Notice all these are extremely densely populated areas, and hence Massive MIMO should makes some dramatic improvement.
And it was some of this marketing information that got me to ask my previous questions. Most of the TDD operators in the region are already testing 128×128 MIMO, while FDD are left with 32×32, this alone is a massive difference in capacity, let alone the deficiency between FDD and TDD in MIMO performance. And from all the information in press notes, it seems TDD 128×128 base stations will be faster to market then the 32×32 FDD solution.
(All 128×128 field tests are from Huawei, and all FDD solution are from Ericsson, I haven’t seen any announcement mentioning Nokia.)
It also appears that, apart from China Mobile, most TDD operators are the smaller and less market dominant ones. This should give them massive headroom to give more data for the same price, assuming they don’t offer unlimited data plans yet.
I have some doubts concerning the first video. I believe that the spatial separation of closely-spaced users especially in open areas will be hard. Because most probably we will have a LOS wireless channel and since the users are close to each other. So, we may end up with a channel matrix of high condition number hence, we may not be able to separate data of different users efficiently. I am looking forward to hearing your opinion about this scenario.
I recommend Chapter 7 in “Fundamentals of Massive MIMO”, which shows how to analyze the angular separation of users in LOS channels. What matters is how large the angular differences are between the users as seen from the base station. If the base station is close to the users, the angles become larger than if it is far away. And if the array has a large aperture, it will be better at separating users.
But I don’t think this is a big deal in practice since the risk of having such closely spaced users is not so large.