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
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.
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