The 5G spectrum that each cellular network operator has license to will have ramifications for the 5G mobile telephony infrastructure they will have to build. Here we’ll take a look at what the industry knows about the behavior of signals at 5G frequencies and what that might mean for their deployment plans.


Editor’s Note: After perhaps a decade in research labs and drawing boards, 5G is on the verge of deployment. Indeed, early deployments of the technology are coming online now. You can tell because the marketers have sunk their teeth in and started promoting it. With 5G moving out of the lab, the team at AspenCore looks at what it will take to reach full deployment—from technical, supply chain, carrier, and policy perspectives.


From the moment that the wireless industry decided it would make use of higher frequencies for 5G transmission, everyone has known spectrum would have some ramifications for those deployment plans. One issue, it turns out, will probably not be that big of a deal, the other somewhat more consequential, but neither is addressed very often. Both derive from what’s commonly known: the higher the frequency of a wireless signal, the less well it propagates and the less able it is to penetrate obstacles. So as a practical matter:

  1. In contrast to deploying 3G and 4G, deploying 5G will require distinct indoor and outdoor strategies.
  2. 5G base stations will have to be spaced more closely, necessitating more of them, especially in densely populated areas.

That first concern would have been a much bigger problem for 5G but for a solution already widely adopted in response to another issue entirely. When operators of 4G networks got concerned they would become strapped for capacity, they began to support dual mode (cellular / Wi-Fi) handsets. A significant amount of what would have been wireless network traffic is now shunted off to Wi-Fi. Dual-mode operation represented a relief valve for the growing traffic problem.

Also, and it doesn’t happen all that often, but there are indoors areas where 4G reception is diminished or lacking. Dual-mode operation has been the answer for that, too.

And that points to why dual-mode operation is a blessing for operators evolving their networks to 5G. Indoor reception problems are guaranteed with 5G; higher-frequency millimeter wave signals in particular will not penetrate walls. If dual mode hadn’t already become a common feature, the industry would have had to introduce it.

An alternative would have been to create small cells that combine 4G and 5G (and probably Wi-Fi anyway). Wireless network operators have been considering small cells for more than 15 years, but if small cells were the best solution for anything we’d have them already. Nobody will deploy extra customer premise equipment (CPE) if they can get out of it to avoid the costs to buy and maintain it.

One other thing: network operators will be retaining all their 4G infrastructure. When 5G wireless phone subscribers who don’t enable Wi-Fi end up in 5G dead spots, they’ll be connected via 4G instead. So the bright 5G future for an awful lot of mobile phone use will actually be Wi-Fi and 4G. Feel the 5G excitement yet?

Weak signal propagation with 5G frequencies is the more serious constraint for mobile telephony, however, and it turns out that mmWave frequencies are not all created equal.

Buildings, hills, trees and other physical objects – even people (especially people, where there are crowds) will obstruct any mmWave signal.

Water vapor – humidity – will cause signal loss at 24 GHz. Oxygen is an impediment at 60 GHz. You read that right – the stuff in the atmosphere that is an absolute requirement for life on Earth can be a problem (see Figure 1).

As a practical matter, under most circumstances, water vapor and oxygen might ding a link budget by only a decibel or so, but then there will be circumstances in which it will be serious; rain fade has to be taken into account. “While a strong signal will not suffer, a weak or marginal signal may become unusable in heavy rain conditions,” reported Joel Conover, senior director of Industry Solutions & Digital Marketing at Keysight Technologies, in a recent EDN article.

There are other challenges when moving into mmWave frequencies, some outlined in the same story. For example, when a 5G receiver is moving at speed (say, 30 mph), channel coherence at frequencies of 6 MHz and below will be measured in milliseconds. In the millimeter range, that drops to microseconds. Not impossible to deal with, but it will have to be dealt with.

Previous estimates have been that the average distance between 5G base stations might be 250m to 300m. With combined effect of all the potential impediments, most equipment designers are targeting 150 meters to 200 meters apart everywhere, simply to get adequate coverage, Conover reports.

By way of contrast, 4G cells in densest urban areas might be as close as 400 meters to 800 meters apart (in more open areas they might be a kilometer or two apart, or more).

Wireless operators are going to have to install more 5G base stations than they did to support 4G, they’re going to have to install more 5G base stations than they originally estimated. This is going to increase the expense of rolling out 5G.

It is instructive to consider this when regarding wireless companies’ efforts to induce the Federal government to force local jurisdictions to reduce or eliminate pole attachment fees.

What does this mean for each wireless provider?

The only competitor that might possibly eke some edge out of all of this is T-Mobile. T-Mobile stocked up on licenses for spectrum at 6 GHz and below (< 6 GHz), and it plans to have its initial rollout of 5G services reliant almost solely on that spectrum. It also says it will use mmWave spectrum (assuming it wins the licenses it desires) at some later date to expand its 5G coverage.

Using mostly spectrum at < 6 GHz, T-Mobile might be able to establish its 5G network with greater spacing between cells, which would mean it will be able to get up and running having installed fewer cells at a lower total cost. It might end up with more reliable service, though that remains to be seen.

T-Mobile will eventually have to install more cells more closely packed when it does finally supplement its 5G coverage using mmWave spectrum, true, but at the very worst the company seems to have charted a path with the most measured approach possible to 5G-related capital expenditures.

The other major wireless network operators appear on a course where they will be mixing-and-matching <6 GHz and mmWave coverage sooner rather than later.

It makes no sense to install multiple, distinct sets of base stations, with each set dedicated to transmission at a single frequency. It would be exceedingly expensive, and exceedingly difficult from a logistics perspective, given the complexity of the process of siting cells.

Since every major wireless network operator will be mixing and matching 5G spectrum to get maximum coverage, all of them (with the possible exception of T-Mobile – and then only in the short term) wireless network operators will be compelled to space their 5G base stations at 150m-200m distances, regardless of the spectrum they have license to use.

Back in February, when companies were still early in the process of field testing 5G transmission systems, the Small Cell Forum estimated that by 2025, the industry will have installed 13.1 million 5G or multimode small cells. That is almost certainly now an undercount.

The Federal Communications Commission (FCC) is currently in the process of selling licenses to 24 GHz and 28 GHz spectrum in separate, parallel auctions. There are 40 companies who have lodged bids for licenses in one or both; most are small regional companies. As has been the case with almost every US spectrum auction thus far, the biggest companies are expected to win the vast majority of licenses.

AT&T, Verizon Wireless, Cox Communications, T-Mobile, U.S. Cellular and Windstream are the biggest companies competing for licenses for 24 GHz spectrum. Another notable bidder is Starry, an ambitious startup.

Verizon already has licenses to quite a bit of 28 GHz spectrum through its $1.8 billion acquisition of XO Communications in 2017. The list of network operators likely to snap up the majority of the remaining 28 GHz spectrum is almost, but not quite, the same as the list for the 24 GHz auction: AT&T (through AT&T Spectrum Frontiers), Verizon Wireless, T-Mobile, U.S. Cellular, Frontier Communications and Windstream.

Check out the articles showing how 5G is coming along and the issues it still faces.

5G test gears up
As products emerge and networks assemble, the test-equipment industry must keep up with standards, production, and deployment.

 

5G: Where is it and where is it going?
Despite the oncoming hype, 5G has a considerable way to go given that deployment is just beginning. We still need much of systems to get into full production. Then, businesses and consumers will have to buy the products.

 

Could local fees kill 5G?
The costs wireless carriers will have to pay to install small cells could be a hinderance to deployment and a windfall to local governments.

 

Optical interfaces to address 5G test
ODI is now positioned to address difficult challenges in 5G communications, mil/aero systems, and high-speed data acquisition

 

5G Networks Under Construction
Engineering managers from AT&T and Verizon share their experiences designing and deploying their first 5G cellular networks.

 

Building the Early Supply Chain Path to 5G
Although it may be months or even years before 5G takes its place in the market, it’s not too early to start to get the supply chain prepared. Building the right supplier relationships and talent pool are critical.