Some Massive MIMO Antennas Might Be a Little Too Massive

Mike Dano
2/19/2019

Massive MIMO antenna technology has been heralded as unlocking dramatic improvements to wireless networks, boosting users' speeds and operators' network capacity. However, according to some of the technicians in charge of actually hoisting these new antennas on to cell towers, they can get fairly portly.

For example, one national contractor charged with installing new Massive MIMO antennas said that they're so big and heavy that the company is installing larger frames to hold the antennas and using cranes to get them into position.

"They are bigger from a wind-area standpoint, which is the main driver for tower loading. They are certainly heavier because of the additional elements and parts that are in them, but it ranges. I've seen massive MIMOs that are 40 to 65 pounds heavier than traditional broadband antennas," Bernard Borghei, EVP of operations and co-founder of Vertical Bridge -- the largest private tower company in the US -- told Light Reading. Following standard practice in the tower industry, Borghei didn't provide details about the wireless network operators involved in Vertical Bridge's Massive MIMO operations.

But Massive MIMO antennas come in a variety of shapes and sizes, and antennas for one operator and one spectrum band might look much different from antennas for another operator using a different spectrum band.

"The form factor for Massive MIMO is actually small and compact. As a broad industry generalization, it's probably fair to think Massive MIMO units will be physically larger, but this does not apply to Sprint," a Sprint representative wrote in response to questions from Light Reading. "Because of the physics around spectrum, Massive MIMO is great for us because it is more easily deployed on TDD-LTE 2.5GHz due to the smaller size of the radios. Also, when you add the weight of the antenna plus existing non-massive MIMO radio together, it is actually the same as the integrated Massive MIMO radio that we're using. The integration of the radio and the antenna system improves reliability by eliminating jumper cables between the radio and antenna."

Nonetheless, now is the time to evaluate the Massive MIMO landscape because many of the major operators in the US are in the early stages of a serious rollout of the technology.

What – and where – is Massive MIMO?
Massive MIMO technology has been around for years, and can be applied to LTE as well as 5G. The technology essentially replaces a handful of antennas on a cell site with dozens or hundreds. Shorthand for regular MIMO is often 2x2 or 4x4 and shorthand for Massive MIMO is often 16x16 or 64x64, with the numbers denoting the number of available antennas. The result is that, instead of having to share an antenna with a bunch of other people, you get to share an antenna with just a few other people. If you're lucky (like, it's late at night and no one is around) you might get an antenna or two all to yourself. Further, technologies like beamforming can be added to Massive MIMO antennas, thus allowing each of the antennas to point themselves at users to deliver an even better, faster connection.

So what do you get out of all that? A 64x64 configuration could result in an 8x boost in uplink speeds and a 5x boost in download speeds, according to Nokia. Further improvements can be had through the application of more antennas and other technologies.

And that's why some operators are in the midst of deploying the technology into their networks.

Sprint, for its part, has been an early and vocal supporter of Massive MIMO. The company's CTO, John Saw, discusses the technology at almost every opportunity, explaining that Massive MIMO is Sprint's stepping stone to 5G because it will provide much faster speeds on the company's existing LTE network.


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Specifically, Sprint said recently it has hundreds of massive MIMO radios on air in a few markets -- sporting 128 antennas (64 transmitting and 64 receiving, or 64X64) -- and has found a 4x average speed and capacity increase and up to a 10x peak increase. That's up from Sprint's earlier 16 antenna MIMO configurations.

Sprint isn't alone though. Verizon last year boasted of its Massive MIMO deployment that involved 16 transceiver radio units driving an array of 96 antenna elements supplied by Ericsson. The deployment uses a 20MHz block of AWS spectrum in Irvine, Calif., on Verizon's LTE network. The operator's vendor added at the time that Massive MIMO is a "key technology enabler for 5G."

AT&T too has hinted at its Massive MIMO ambitions, including in the context of its CBRS 3.5GHz deployment plans.

And though much of T-Mobile's MIMO work has been in the 4x4 area, the company has said it will make the jump to Massive MIMO if it is successful in acquiring Sprint.

Globally there are at least 87 projects that have involved testing Massive MIMO in the context of 5G, according to the Global Mobile Suppliers Association.

Not surprisingly, all of this noise around Massive MIMO is like music to the antenna vendors, tower companies and construction crews that will be required to get Massive MIMO from the lab and up onto commercial cell sites.

Massive profit in Massive MIMO?
Executives from some of the nation's biggest tower companies -- companies that make money by renting space for cellular equipment on their "vertical real estate" -- offer differing views on whether Massive MIMO antennas represent a big new revenue stream.

"We have begun to receive amendment applications for new MIMO antennas, which are just now becoming available in higher performance designs and that will facilitate much faster speeds using existing low and mid band spectrum," said Jeff Stoops, CEO of tower company SBA Communications, last year, according to a Seeking Alpha transcript of his remarks. "These new MIMO antenna are generally wider and deeper than current antennas and in some cases way over twice as much."

And will that cost extra?

"I'm not a product expert, but to my knowledge there is no single radio unit and certainly no single antenna unit that covers the spectrum, covers the range of spectrum that will be deployed by the combined company, so you're looking at multiple units to cover that full array of spectrum and then if you start to get to the desired MIMO configuration on the antennas that actually could add quite a bit of weight and that -- obviously depending on the load of things like that that will impact the price, so that there that there could be a wide range of about outcomes there," Stoops said.

But other tower company CEOs are striking a less gleeful tone.

"They could solve the same thing by using more sites or different types of equipment depending on what spectrum bands they use and how they choose to do it. So just in isolation, I wouldn't necessarily assume that would be a large revenue driver for us," explained Crown Castle CEO Jay Brown earlier this year in a response to a question about possible revenues from the installation of Massive MIMO antennas, according to a Seeking Alpha transcript of his remarks.

"Carriers have been installing Massive MIMO antennas on our towers for a while now. We have around two to three dozen sites where we have received -- and approved -- applications to install such antennas," said Vertical Bridge's Borghei.

And what of the cost? "Rent is determined by the amount of wind loading that tenants cause on the tower and/or have rights to. … If installing a Massive MIMO antenna exceeds the wind load entitlement of the tenant, then the rent for that site would be adjusted accordingly," he said.

Ken Schmidt, president of tower consultancy firm Steel in the Air, said that Massive MIMO antennas often require tower modifications if the tower's structural capacity is exceeded. "This is particularly problematic in that carriers will want Massive MIMO in the same areas as each other and on same towers," he said.

Schmidt added that some Massive MIMO antennas create permitting or zoning approval difficulties if they're in aesthetically sensitive areas where concealment is required.

Others haven't seen that problem, at least not yet. "I'm not aware of any instances to date where our tenants have faced unusual difficulty obtaining permits, and we have seen Massive MIMO antennas installed across several states, coast-to-coast," Borghei said. "So at this time, I don't believe these antennas cause additional permitting issues or challenges aside from the normal zoning process that carriers go through."

For its part, Sprint acknowledged that, because the shape of its Massive MIMO antenna is different than its existing equipment, "we do go through a site acquisition process for leasing/zoning/permitting to add Massive MIMO to our sites. Any related changes are built into our budget," the carrier said.

But Sprint added that "the permitting/zoning process is generally no different than for other upgrades we are performing."

Putting the 'Massive' in MIMO
But for the nation's tower technicians -- those tasked with actually putting Massive MIMO antennas on top of cell towers, the work is significant.

"Based on the feedback I have received from a nationwide company who has installed over 300 of them, Massive MIMO antennas are smaller than existing antennas, but heavier in weight. The antenna is heavier because the radios are inside the antenna. The dimensions of MIMO antenna are typically: 26-inch height x 20-inch width x 9-inch deep, and weigh 103 pounds," wrote Todd Schlekeway, executive director of the National Association of Tower Erectors (NATE), in response to questions from Light Reading. The association represents tower companies and the contractors around the country that actually climb those towers.

Schlekeway added that one of NATE's members, one that has installed over 300 Massive MIMO antennas, said it has not experienced an increase in cost or fees, and described the work as a relatively simple swap of antennas.

But other NATE members are taking a different view, he said. "Some of the mid-sized companies who I reached out to (who have yet to do this work) indicated to me they anticipate that these heavier antennas will warrant an increase in costs due to the heavier mounts and larger pipes designed to support these antennas as well as potential crane costs to lift to elevation," he said.

And one NATE member described the antennas as "MUCH heavier" and requiring cranes to install.

Finally, there also seems to be some debate over whether Massive MIMO antennas are living up to their billing as a massive improvement in services. Schmidt, of the firm Steel in the Air, said that some antennas aren't performing in the field as promised, and often require more adjustment.

Sprint, not surprisingly, disagreed with that assessment. "Absolutely not true," the company said when questioned about it. "In the world's first independent benchmark study on Massive MIMO, Signals Research Group recently found the benefits of our Dallas-area … commercial deployments 'real and meaningful generating significant increases in downlink and uplink throughput,'" the company added.

Schlekeway, of NATE, said that some of his association's members have found some performance issues. Specifically, they said that Massive MIMO antennas don't reliably transmit into buildings and other structures. "This is anecdotal evidence passed along and nothing scientific however," he cautioned.

"What I can say is that we haven’t seen too many changeouts of Massive MIMO antennas, post initial installation on our towers," added Vertical Bridge's Borghei.

Thus, it appears that the rollout of Massive MIMO technology is taking the same kind of bumpy, circuitous route that many new technologies take -- it works in some places, some of the time, for some people, and for others it doesn't. And, like the rollout of other technologies before Massive MIMO, that situation may smooth out over time.

And it's likely that 5G will follow a similar trajectory.

Mike Dano, Editorial Director, 5G & Mobile Strategies, Light Reading | @mikeddano

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Cloud 4G
Cloud 4G
2/26/2019 | 4:31:07 PM
5G is a weaving of spectra and technologies
What makes 5G more difficult to understand (swallow) is that unlike previous generations, it depends far more on a blending of multiple bands with multiple arrangements of technology that are applied to achieve multiple service profiles.  If you ask anyone what 5G is you get as many opinions as there are operators and the departments within them that are working on the broadened envelope of applications that depend on spectra and capital resources to leverage their unique position in marketshare.   

 

In 2G, 3G, 4G, operators had varying portfolios of spectra and capital but the motivating application was mobile phone service. 

 

Massive MIMO fits as part, but only part, of 5G.  It tends to have a higher impact when used in frequencies above about 2 GHz.  The higher up in frequency, as a general rule, the smaller the individual antenna elements and closer they can be packed within the arrays.  Signals also travel in more of a straight line with less interference because they can be more cleanly beamed despite the tendency to bounce more off of solid objects.  That makes for good use of Massive MIMO in 2.5-2.6GHz Band 41 help by Sprint.  However, that alone cannot fill in the needs for the building of competitive 5G networks.

 

5G is no single band or single prescription of multiple bands.  Rather, it is a long in development tiered network access system combined with network and user devices that implement multiple bands and multiple carrier band path radios and the supporting signal processing. M-MIMO can't defy laws of physics to bend high-frequency signals around hills and buildings.  M-MIMO works best in combination with massively distributed, multiple-tiered band networks that use large numbers of smallcells.  

 

Take a look back at Sprint's 'Network Vision' presentations: they look eerily similar to those of Ericsson, Nokia, Huawei for how to build a 5G network: use lower bands for coverage, mid-band for a combo of coverage and bandwidth, and high-band for xHaul and Gigabit wireless.  This is what is now proposed by New T-Mobile except that it takes what has been a futile effort by Sprint to use a preponderance of mid-band using M-MIMO and every other thing to make use of T-Mobiles broadband allocations (10x10 MHz or greater) to fulfill the coverage layer at low deployment cost and the greater simplicity, rapidity and low service cost.

Massive MIMO has been part of 4G-Advanced the makes better commercial sense as part of the expanded universe of 5G spectra and applications.  It has not been a game changer for Sprint.  It will be a part of what helps New T-Mobile change the competitive mix as one of the network layers.  The deployment and applications environment changes due to the combination more than the individual piece of technology. 
e2mbcorp
e2mbcorp
2/19/2019 | 12:10:15 PM
No Antenna Can Solve Packet Efficiency
Great story Mike, but as always, if we keep the discussion around the physical layer and bandwidth speed, then we are not focusing on the root cause of the problem.  This is because no amount of bandwidth speed can solve a problem in switch architecture.  The root of the problem is the collision detection mechanism.  5G's access channel uses ALOHA for that purpose, which results in approximately 50% packet efficiency at the MAC layer.  Fixing this bottleneck will have an automatic antenna improvement when layer 1 does not need to contend with the bottleneck at layer 2.  Or we can just keep throwing bandwidth at a problem it can't solve, which is what we've been doing for the last 30 years so I hope nobody is expecting a different result.
Mike Dano
Mike Dano
2/19/2019 | 11:08:08 AM
Re: MIMO Functionality
Wow what a nice comment. Thank you!
jamiekimble
jamiekimble
2/19/2019 | 10:58:35 AM
MIMO Functionality
Mike, another well written story that is fact based.  Thanks for publishing this article.