There is a simple reason why millimeter wave frequencies will prove important for 5G, and essential for 6G and future networks. Simply put, even if most of the sub-2 GHz spectrum were not already allocated to other users, low-band spectrum is limited where it comes to bandwidth.
If mobile networks must keep supplying ever-faster speeds, millimeter wave and mid-band spectrum are key ways much more bandwidth can be supplied without dramatically increasing cost per bit, both supplied and consumed.
As always, the other means for increasing mobile network bandwidth is to shrink the size of cells. Millimeter wave networks will use both techniques, of necessity. Simply put, millimeter wave requires small cells.
Put simply, unless lots of millimeter wave spectrum is made available, the mobile business model breaks.
The fundamental constraint is that more bandwidth has to be supplied at constant prices, for the most part. Consumers simply cannot, and will not, pay much more for mobile bandwidth, even as their consumption grows fast.
An analysis of U.S. mobile service provider 4G speeds illustrates nicely the inverse relationship between frequency and capacity. In every case but one (explainable for reasons other than frequency itself), capacity--and therefore speed--is higher as frequency is higher, and lower as frequency is lower.
The other issue is channel width, with a direct relationship between channel bandwidth and speed. Wider channels are capable of higher speeds. And channels in the millimeter wave bands, as outlined by the 5G standard, will be far wider than has been the case for 2G, 3G and 4G networks.
One hears a lot of noise, much of it uninformed, about use of millimeter wave spectrum to support 5G (and all subsequent mobile next-generation networks). A growing number of voices warn that millimeter wave spectrum is the “wrong way” to implement 5G.
Such comments have a point: all other things being equal, lower-frequency 5G signals have a coverage advantage. Wider coverage, at lower cost, will be possible when sub-1 GHz assets can be used.
But coverage and capacity always are trade offs. A 5G network using sub-1 GHz assets will not be able to provide the capacity of millimeter wave assets.
Also, millimeter wave assets are the future of all future mobile networks. The need will not be as obvious in some markets as in others, but it represents the future.
That is obvious, even when voices question its use in early deployments.
What observers often forget is that mobile networks must offer both coverage and capacity. And there are a limited number of spectrum assets available to support coverage requirements. There is, however, a nearly-infinite requirement for increasing capacity.
And that capacity can only come from use of millimeter wave assets, as the International Telecommunications Union, even when urging circumspection about where 5G will make sense, attests.
Back in 2018, the International Telecommunications Union noted “concern that 5G is premature.” A report indicated “operators are sceptical about the commercial case” and “high-levels of investment.”
But the report also contains the rationale for 5G. Simply, a new mobile next-generation network is introduced about every decade. That does not mean it gets introduced everywhere, nor at the same time. But nothing is going to stop 5G from being deployed, simply because network capacity demand drives it.
New use cases always are a feature of each touted digital network, but the practical reality is that, of the two main tools for increasing capacity--smaller cells and new spectrum--each next-generation network has brought additional spectrum resources.
Also, despite much concern that millimeter wave communications will be too hard to deploy commercially, even the ITU has noted that 5G--and all subsequent networks--will have to use millimeter wave assets.
Though many spectrum bands will support 5G--lower frequency including 600 MHz or 700 MHz, mid-band assets in the 3 GHz to 4 GHz region and millimeter wave region--capacity needs, even after spectrum refarming, will leave only the millimeter bands available for most of the future capacity supply.
Much of the concern about millimeter wave assets, and the supposed “path to 5G,” is misplaced. Millimeter wave assets will anchor every generation of mobile network from now on, for capacity. There are a limited number of coverage bands, and those bands will not be able to support capacity requirements easily.
Some of us might draw the opposite conclusions others do related to the wisdom of early user of millimeter wave technology and platforms. Specifically, millimeter wave is the future. Also, millimeter wave is the best way to supply needed capacity, going forward.
Some worry Verizon and AT&T err in emphasizing millimeter wave. On the contrary, some of us might argue, it is a tool those two carriers must use, as a practical matter. With most of the subscribers, those two firms have the greatest needs for additional capacity and spectrum.
Longer term, both will acquire operating experience that might well prove useful in the future, since all mobile generations from now on will have to rely on millimeter wave for capacity requirements.
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