Millimeter Wave Performance Will Keep Getting Better

It would be fair to say that U.S. mobile operators deploying millimeter wave spectrum remain in a learning mode. So far, it seems there is evidence of signal attenuation worse than expected as well as better than expected.

T-Mobile US, which has significant low-band assets with which to deploy 5G, argues that millimeter wave will never be used in rural areas for 5G support. But we are just at the beginning of commercial use of millimeter waves for mobile communications.

Historically, one would have been more accurate being an optimist than a pessimist about microwave signal propagation, it is fair to say. And we will have to use millimeter waves, to increase the amount of bandwidth mobile networks can supply.

Ignoring the vested interests and assets each mobile service provider possesses and touts,  many note there is a lack of available U.S. lower-band spectrum to devote to 5G.

In this illustration by Anokiwave, the orange blocks represent the 11 GigaHertz of new spectrum to be allocated by the U.S. Federal Communications Commission, and most nations eventually will do something similar. The big takeaway is how much more new spectrum will be available, compared to all mobile spectrum available up to 4G.

The skinny blue bands to the far left show currently-allocated mobile spectrum. Basically, more than an order of magnitude (10 times) more mobile bandwidth is being commercialized. And that new bandwidth is more efficient, in terms of bits per Hertz, than in the sub-3 GHz bands by perhaps three times, based on antenna techniques, alone. Modulation also makes a difference, but sheer bandwidth also matters.

The Nyquist rate  

source:  Anokiwave

The red and green blocks show spectrum already allocated to defense entities, for satellite or aerospace purposes.

Even as some argue 5G will be spectrum agnostic and can use “all frequencies,” some insist there is a real disadvantage to using millimeter "versus" lower-frequency spectrum. Ignore for the moment the obvious marketing stances taken by firms with different assets. Firms will tout what they have.

Some larger realities are not changed by 5G. There always is a trade off between capacity and coverage, when using wireless spectrum at any frequency. Networks always can get more-extensive coverage using lower frequencies, at the expense of potential bandwidth. Conversely, they always can get greater capacity, at the expense of lesser reach, with higher frequency spectrum.

And since “everyone” agrees a wide variety of low, medium and high frequency spectrum will be used by 5G operators, it makes sense to figure out what use cases (beyond coverage and capacity in general) are best suited to which frequency bands.

The area of greatest discovery will be in the millimeter wave bands, which have never been commercially viable for mobile services in the past. Millimeter wave spectrum will enable the greatest changes in capacity (bandwidth), and likely will be the area where the greatest number of new use cases will be developed.

Generally speaking, the gigabit speeds touted by 5G backers will be possible only when using millimeter wave assets. Generally speaking, lower-frequency spectrum will offer speeds higher than 4G, but perhaps not typically more than twice as fast.

That might suggest it is fruitful to look at 5G using lower or mid-band spectrum as important for supplying faster mobile internet for smartphone users, but not, in itself, a huge driver of new applications. One might argue that the higher bandwidth will make visual apps more compelling, and that is correct, so long as tariffs allow the higher usage.

In other words, much-faster speeds will not lead to as much innovation unless tariffs for usage are low enough that barriers to usage are not created. As one example, 5G might enable mobile TV. But consumers will constrain usage unless tariffs and usage plans encourage--or at least do not discourage--such usage.

Different use cases beyond “faster consumer smartphone access”  will tend to require millimeter wave. It will be hard to make a decent business case for fixed wireless--as a substitute for fixed network internet access--without using millimeter wave assets. There simply is no way to replicate the low cost per bit of fixed network services without millimeter wave capacity gains.

Latency performance should not vary between services at any frequency, but will be affected by the presence or absence of infrastructure edge computing facilities. Enterprises using their own edge computing platforms and private 5G will not generally have to worry about latency.

Visual applications and real-time control operations likewise are areas where millimeter wave should have relevance, often in conjunction with edge computing to control overall latency when analytics must be applied.

What sometimes is overlooked in discussions of “millimeter versus lower-band spectrum” is that many new use cases depend as much on edge computing as they do on bandwidth or latency. Millimeter wave communications will have a huge advantage where bandwidth intensity is high, but also will tend to be use cases where local processing also is necessary, hence edge computing will be necessary.

And many use cases said to be candidates for millimeter wave and edge computing (virtual reality, augmented reality, visual health applications) also will occur either indoors or in stationary or low-speed settings ideally suited to private 5G or small cell supported public networks, with local processing (edge computing).

The point is that many of the brand-new use cases (beyond faster mobile internet) will happen in settings where millimeter wave coverage is not a great issue. Most usage happens in a small number of cell sites for any network (2G to 5G). Those cell sites always are in urban areas. So 5G “coverage” is a bit of misplaced concern.

Even when wide area 5G coverage is supported, the really-high bandwidth features (gigabit or higher) will not be supported everywhere. The trade offs of coverage versus capacity remain.

So the place to look for truly-new use cases is in areas other than “faster smartphone access.” It is the urban places, indoors and outdoors, where millimeter wave and edge computing exist, where the new use cases and revenue opportunities will emerge.

The point is that ubiquitous 5G coverage is not necessarily required for the development of most new 5G-enabled apps and use cases. Those are going to happen in the dense urban areas--or inside enterprise facilities--where most economic activity takes place.

Without Millimeter Wave, the Mobile Business Model Breaks

Some technology innovations are important because they either keep an existing business model from breaking, or threaten to break business models. Low earth orbit satellite constellations, in principle, represent new competition to virtually every internet service provider on the planet.

Cable modems and hybrid fiber coax have been a major means for breaking the bandwidth limitations of digital subscriber line, as advanced forms of DSL in turn extend the usefulness of copper access.

Small cell architectures have been the primary way mobile operators have intensified their use of available spectrum.

Likewise, millimeter wave spectrum might help mobile operator business models from breaking (for lack of sufficient capacity to support mobile internet access).

Verizon has faced criticism in some quarters related to the performance of its millimeter wave fixed wireless service, which remains in early commercialization. The general tenor of the critique is that signal propagation is not good enough, and take rates too low, to support the business model.

We also sometimes forget that the state of the art for fiber to the home was 10 Mbps, and that deployment costs were double what they are today.

The conclusion some seem to reach is that millimeter wave is not useful for 5G. That flies in the face of global movement to commercialize millimeter wave spectrum for 5G and all following mobile network generations. At WRC 2019, the International Telecommunications Union is looking at a wide range of millimeter wave spectrum.

In the following illustration, the width of the blue bars roughly illustrates the amount of capacity at different frequencies. The horizontal axis represents the frequency spectrum from approximately 1 GHz to 90 GHz on a relative scale (mobile services tend to use frequencies at 600 MHz to 800 MHz at the low end).

The orange bars show the approximately 11 GHz (capacity, not frequency)  of new spectrum released by the FCC for both licensed and unlicensed use. Note that the total amount of new bandwidth is orders of magnitude more than all bandwidth presently available for mobile purposes.

Europe and Asia are working towards commercialization of much of that spectrum as well.The EU recently authorized 26 GHz for 5G, for example. 

The red and green blocks show frequency allocations for the aerospace, defense and satellite communications industries, parts of which might ultimately be available using shared spectrum mechanisms.

source: Anokiwave

The point is that there will be growing pains as millimeter wave technology--never used commercially before--is deployed. But there also can be little doubt that in addition to small cell architectures, there is little additional spectrum available to accommodate growing mobile data use, except in the millimeter wave regions.

And that is why the strategic direction (use millimeter wave and small cells) Verizon is taking is correct, absolutely correct. Starting with 5G, and continuing forward, ability to support ever-higher data demand will hinge on use of millimeter wave resources.

source: Accton

Bands under consideration for mobile service on a primary basis include 24.25-27.5 GHz, 37-40.5 GHz, 42.5-43.5 GHz, 45.5-47 GHz, 47.2-50.2 GHz, 50.4-52.6 GHz, 66-76 GHz 81-86 GHz.

Bands under consideration that may require additional allocations for mobile service on a primary basis include 31.8-33.4 GHz, 40.5-42.5 GHz, 47-47.2 GHz.  

As with any major new platform, and especially for deployment of spectrum resources that in the analog era simply could not be used at all, millimeter wave platforms will go through an experience curve (learning curve). By moving early, Verizon might well get ahead of others on that experience curve. AT&T is on the same curve as well.

That is not to say other alternatives, in an ideal world, might not have been preferable. Verizon and others might well prefer mid-band solutions that are coming, but not available today.

Since capacity and coverage always are inversely related, mid-band is a blend of coverage and capacity, where low-band is better for coverage, but lacking in terms of capacity. Millimeter wave frequencies are best for capacity, worst for coverage.

Though we might prefer not to have to rely on millimeter wave assets, ultimately we have no choice. Capacity is an obvious and growing need, and there is little low-band or mid-band spectrum left to use for that purpose, absent a major reconfiguration of usage rights.

Spectrum clearing is both expensive and time consuming. And we might not have either time or sufficient capital for such major spectrum clearing.

Also, we are 10 years away from 6G, in any case, as we launch the next-generation mobile network about every decade. Millimeter wave involves no significant spectrum clearing hurdles.

Give Verizon Credit for Knowing What it Has to Do in Terms of 5G Capacity and Coverage

Sometimes we do not give Verizon enough credit for knowing precisely what it has to do, capacity-wise, and for having a rational strategy to deal with those challenges. Observers have noted for years that Verizon “needs more spectrum.”

Verizon’s answer has been to use millimeter wave spectrum, small cells and spectrum sharing, in addition to acquiring new millimeter wave assets and refarming 3G spectrum. There is an unsaid ability to possibly augment with other assets as well, but Verizon is moving ahead on the assumption it must do so without spectrum asset acquisitions from other service providers.

“One of the most important features that I have talked about is of course the dynamic spectrum sharing that will come during next year, where you basically also can use, deploy wherever you are with 5G and then you don't need to allocate certain spectrum to certain technology,” said Hans Vestberg, Verizon CEO.

An important point is that there are a growing number of ways to increase effective bandwidth beyond buying spectrum licenses. Small cells, dense fiber networks, spectrum sharing and spectrum aggregation all can expand capacity.

That said, both AT&T and Verizon have committed to lots of new spectrum in the millimeter wave regions. Some have criticized such moves, arguing that volume production of radios and devices eventually be strong in the mid-band spectrum areas. There is some merit to such arguments.

But it also is true that future 5G capacity growth will have to come from the millimeter wave region, and that this will be a global trend, not something mostly limited to the United States.

Verizon realizes millimeter wave spectrum “is not the coverage spectrum,” Vestberg said. That is one reason why “spectrum sharing will be the next step for us to see that we have all the assets to deploy our strategy on 5G to meet the different type of use cases.”

No 5G service provider in the mobile business can escape an iron law of bandwidth, namely that lower frequency spectrum is better for coverage, while higher frequency spectrum is better for capacity, and mobile service providers need both.

That means operators always must balance coverage and capacity. But there are lots of moving parts. End user demand always changes, but most of the demand for capacity happens when users of smartphones are stationary, at home or at work. So most of the demand for capacity happens at home and at work.

“Remember, the majority of all the traffic is in dense urban areas, where we are now initially are focusing” its millimeter wave deployments, said Vestberg.

The point is that observers sometimes do not give Verizon strategists enough credit for having thought through capacity expansion alternatives and approaches.

New use cases might require significant amounts of additional bandwidth when users are fully mobile, but that will occur over time. For the most part, mobile bandwidth has to grow, but not at the same rate as “tethered but not moving” bandwidth demand. And that appears to be where spectrum farming and spectrum sharing will be crucial.

If Sprint and T-Mobile US do not talk as much about that, at the moment, it is because they face different challenges and own different assets.

AT&T and Verizon have heavily-loaded networks and require more bandwidth because they have more customers.

T-Mobile US and Sprint networks are relatively lightly loaded, and therefore can get by with less incremental bandwidth.

Service providers also tend to own distinct blocks of spectrum. AT&T and Verizon have more lower-band spectrum than T-Mobile US and Sprint, but that spectrum also is heavily loaded. T-Mobile has more flexibility in that area. Sprint has lots of mid-band spectrum, but not enough customers to justify aggressive deployment of those resources at the moment.

Some have noted that Verizon has less capacity per account than does AT&T, and “needs” more mid-band spectrum. Verizon technologists have run the numbers and concluded that small cell architectures--always a practical way to expand bandwidth--will do much of the job. Millimeter wave spectrum and spectrum sharing will help: the former with capacity needs, the latter for coverage.

Beyond that, there are additional mid-band resources potentially available. Dish Network’s spectrum remains a wild card. It always is possible that a T-Mobile US merger with Sprint is approved with significant spectrum sales. That remains a possible source of additional Verizon spectrum.

But none of that is essential. Every 5G service provider eventually has to supply both coverage and capacity. Capacity has to come in different ways than coverage. Verizon knows that.

"Fiber to the Light Pole" Might be the Required Backhaul Network for Millimeter Wave Access Networks

If, as expected, millimeter wave small cells have a transmission radius of about 50 meters (165 feet) to 200 meters (perhaps a tenth of a mile), it is easy to predict that an unusually-dense backhaul network will have to be built (by mobile network standards).

In the past, mobile operators have only required backhaul to macrocells to towers spaced many miles apart. All that changes with new small cell networks built using millimeter wave spectrum (either for 5G mobile or fixed use, or for ISP fixed access).

Keep in mind that street lights are spaced at distances from 100 feet (30.5 meters) to 400 feet (122 meters) on local roads.

As a rough approximation, think of a small cell, in a dense deployment area, spaced at roughly every other street light, up to small cells spaced at about every fourth light pole.

That suggests the sort of dense backhaul network that also will be required. You can argue that a new “fiber to the light pole” network must be built. You can argue that a new mesh backhaul network must be built. You can argue that some other leased backhaul (cable TV network) could be feasible.

In all cases, there are potential business model costs in the backhaul and small cell transmission network that exceed anything engineers have had to design, yet. That is why ots of people now are asking very-practical questions about millimeter wave spectrum and its potential impact on access network business models.

People want to know how far signals will reach, how much rain or snow will affect signal levels, how signals will bend or otherwise get around line of sight issues and how backhaul will be provided.

Impact on the business model for existing and new Internet service providers lies at the heart of those questions. And those are important questions.

With some 29 GHz of new spectrum for communications set for release by the Federal Communications Commission (including 7 GHz or more of unlicensed spectrum, spectrum sharing set to add additional spectrum in the 3.5-GHz band, there are potentially-disruptive changes in network costs, revenues and competition in the works.

What remains unknown is how much propagation distances might change as 28 GHZ is adapted for small cell network architectures, instead of point-to-point links. In an earlier period, reach of 1.5 miles was routine for point-to-point links, and distances up to three to five miles sometimes were possible.

In a new small cell deployment, transmitting at lower power, distances of 1,000 meters (about 0.6 miles) might be possible. Others think reasonable distances will more likely be in the 50 meters to 200 meters range.

Potential bandwidth is among the key differences between bandwidth in the below-6 GHz frequency bands and those millimeter bands in the 24-GHz and higher bands.

Simply, compared to 2-GHz (mobile) or 3.5-GHz signals, potential bandwidth is from five times to an order of magnitude higher. The trade-off is propagation distance.

The bandwidth differences are based on frequency itself: Basically, the waves oscillate between their high and low states much more often as frequency increases. And, in principle, every oscillation is the foundation for representing a physical bit.

On the other hand, as frequency increases, the waves start to act more like particles, in a sense, and are affected by physical objects, which stop them, and by oxygen and moisture in the atmosphere, which absorb them.

Those trade-offs mean it is not easy to model the potential business impact of abundant millimeter wave spectrum on business models.

source: YateBTS

Professor Robert Heath, Jr.

“The beauty of these frequencies is that the new bandwidth they make available is tremendously large,” said Alpaslan Demir, InterDigital principal engineer. “You are talking about Mbps or multiples of- 100 Mbps bandwidths, with up to 2 GHz bandwidths, or multiples of 2 GHz, especially at 70 GHz.”

“The definition of capacity should not be limited to bps/Hz but it should involve space as another dimension,” he also argues. “For example, if there are 50 links deployed over one sq km, each with 10 Gbps over 2 GHz channel bandwidth, then the total capacity can be defined as 500 Gbps/sq km.”

The bottom line for millimeter wave access networks: lots of bandwidth but limited physical reach.

Also, in the U.S. market, 7 GHz of unlicensed spectrum will be released, with obvious impact on the cost of such an access network.

The business model issues, aside from the new small cell radio network, is the requirement for some sort of "fiber to the light pole" backhaul network. It doesn't have to be optical fiber as the physical medium, but tht's the right sort of thinking about the density of a millimeter wave access network backhaul requirement.

As always, cost and revenue will get a hard look. In fact, the ability for a mobile operator to create a new fixed Internet access business--using the same infrastructure required to support mobility services--is one major reason fixed access likely will be a key feature of 5G mobile networks.

New revenue is required to pay for the new dense small cell networks, and cannibalizing fixed Internet access might be one way of doing so.

Why Millimeter Wave Matters

Propagation issues notwithstanding, millimeter wave frequencies will be vital for mobile operators. The pressure to achieve lower cost per delivered bit will not cease, forcing service providers to continually deploy new solutions for bandwidth with a lower cost per bit profile. 

Millimeter wave does that. Eventually, so will teraHertz frequencies. 

 

source: GSMA Intelligence 

To be sure, 4G capacity increases will continue for a while. Eventually, though, 4G runs out of gas. Fundamentally, that is why 5G is “necessary.” Beyond all the other new use cases enabled by vaster-lower latency, core network virtualization or 5G-enabled edge computing or internet of things, 5G will supply bandwidth at lower costs than 4G networks. 

Cost per bit matters because customer bandwidth demand grows as much as 40 percent a year, while consumer willingness to pay is limited, essentially remaining flat, year over year. 

If access providers must supply 40 percent more bandwidth per year, while revenue grows one percent per year, bandwidth efficiency must increase significantly. That is the value of millimeter wave spectrum. 

That need for efficiency would be true if access providers owned all the apps used by their customers. In the internet era, access providers own almost none of the apps used by their customers. 

So connectivity providers generate relatively small amounts of revenue from applications they own, and at the same time must supply bandwidth for third party apps at prices their customers consider fair. 

In that context, since most of the bandwidth consumed is video entertainment, and since video is the most bandwidth-intensive app, prices per bit must be low, and constantly get lower. Video economics are dominated by the fact that users will not pay very much for video entertainment, in relation to the bandwidth consumed to support its use. 

For owned apps, revenue per bit for messaging and voice can be as much as two or more orders of magnitude higher than for full-motion video or Internet apps. By some estimates, where voice might earn 35 cents per megabyte, revenue per Internet app might generate a few cents per megabyte. 

The cost of consuming a bit is infinitesimally small. Assume an internet access plan costing $50 a month, with a usage allowance of a terabyte. That, in turn, works out to a cost of about $0.000004 per byte. And even that cost will have to keep dropping. 

The reason is that consumer propensity to pay is only so high. Essentially, internet service providers must continually supply more bandwidth for about the same prices. 

source: GSMA Intelligence

Spectrum Policy is the Latest in a Long String of "U.S. is Falling Behind" Claims

Over the past few decades I have often heard observers expressing great worry about one or another divides or gaps that have U.S. service providers and consumers behind users and customers in other regions.

U.S. consumers were “behind” Europe and Japan in mobile phone use, text messaging, 3G use, internet access, broadband adoption and speeds, and always are “paying too much” for their services.

The U.S. is falling behind meme never goes away, where it comes to communications. The latest assertion is that the United States is falling behind in 5G. That claim has been made many times in the past, and always has proven wrong.

In the past, it has been argued that the United States was behind, or falling behind, for use of mobile phones, smartphones, text messaging, broadband coverage, fiber to home, broadband speed or broadband price.

It is an old pattern of claims. Consider voice adoption, where the best the United States ever ranked was about 15th globally, for teledensity (people provided with phone service). Does anybody think that was any kind of impediment to economic growth?

With the caveat that some rural and isolated locations never got fixed network phone service, not many would seriously argue that the supply or use of fixed network voice was an issue of any serious importance for the nation as a whole, though it is an issue for rural residents who cannot buy it.

Some even have argued the United States was falling behind in spectrum auctions.  What such observations often miss is a highly dynamic environment, where apparently lagging metrics quickly are closed.

The latest candidate is 5G spectrum policy. 

Over the past year there have been many shouts of alarm about the “choices” being made for 5G spectrum. Millimeter is the wrong spectrum, it has been said. Mid-band spectrum is the “right choice,” many have argued. 

Those criticisms are rather off point. Different countries are making different immediate choices largely because--of a range of permissible frequencies--mid-band is available. 

For historical reasons, the mid-band is not immediately available in the U.S. market, forcing early movers to rely on millimeter wave spectrum sooner than they might have preferred, even if the 5G standards clearly point to millimeter wave as the future of 5G, and subsequent platforms as well, simply because that is where most of the unencumbered spectrum exists. 

The U.S. Federal Communications Commission is not ignorant. It knows what resources can be made available now, and what has to happen to clear more mid-band spectrum. It is doing so. Clearing part of the C-band is among the actions the FCC is taking. But that takes time. 

Verizon, in particular, has had to rely on millimeter wave. Among the top four national carriers, it has the least spectrum, per customer. And after weighing its options for bandwidth, Verizon concluded that upgrading its terrestrial network with dense optical fiber, enabling small cells and hence millimeter wave radio networks, made more sense than bidding for lots of new spectrum. 

That does not mean Verizon or the other service providers will be shy about bidding on additional spectrum. “More” is always the answer, longer term. 

Still, Verizon believes the cost of its dense fiber network approach will work for capacity expansion. Verizon surely will rely on mid-band for coverage. AT&T initially relied on millimeter wave for its business-focused services, especially for fixed network substitution. 

Its consumer 5G will use 850 MHz low-band spectrum, and AT&T will acquire more mid-band spectrum when it is made available. 

T-Mobile, with relative plentiful new 600-MHz assets, will rely on low-band for its 5G launch. Sprint has lots of mid-band spectrum licenses, which will eventually be put to work by whatever company winds up owning it. 

The larger point is that no dangerous or wrong spectrum choices have been made by the FCC or service providers. Specific firms have made choices congruent with their assets and strategies. Long term, there is no “choice” to be made between millimeter wave and mid-band spectrum or low-band. All will be used.

But different service providers in different countries have differential access to low-band or mid-band spectrum. So the initial strategies and deployments will reflect those immediate realities. Longer term, all the choices will be in play.