5G is rolling along nicely for what it is, for the moment. Sub-6 GHz (mostly low and low-midband) up to about 3 GHz has been its playing field. But much of what 5G is supposed to be needs a lot more bandwidth and spectrum. Some of that is being addressed in the CBRS spectrum, around 3.5 GHz, which will be coming online this year once the technical and political issues are ironed out (the mix of general authorized access [GAA] and priority access licenses [PAL], environmental sensing capability [ESC] and eventually, incumbent-Informing capability [IIC] in next several years).
CBRS currently has 70 MHz available. There is talk of as much as 120 MHz eventually. But much of this is still in the works. While 70 MHz of spectrum is certainly nothing to sneeze at, it is only slight relief for 5G. In reality, we need a lot more, at least gig, for meaningful gains to augment existing low and midband. Plus, CBRS is not clean. It has many incumbents, and the spectrum was thrown out there against a fair amount of opposition. And its utilization is dependent on sharing technologies.
Most experts agree that it will certainly help the 5G use case for platforms such as enhanced mobile broadband (eMBB), and typical cellular use cases. But sub-6 GHz need more breathing room.
CBRS is attractive because its performance is good when it comes to propagation footprints for standard cellular-type deployments. With all things being equal, the propagation model of the 3.5 GHz signal is about 50 percent of that of a 1.8 GHz signal. That is still suitable for many of the denser 5G deployments. And it works with the existing tower infrastructure.
But the rising star being seriously looked at for low and midband relief is the 6 GHz band.
It is all about mobile data
Statistics suggest that mobile data traffic will increase by 15 to 25 times by the end of this decade. The next five years will give us a pretty good look at what we can expect going into 2030. The current expectation is that we will see Zettabytes (ZB) of data per month, perhaps more, by 2030.
This prognostication is likely to be at least correct if not conservative. Why, well take into account all the emerging platforms (Internet of Anything/Everything (IoX), smart “X”, smart and autonomous vehicles, edge networks, private networks, unlicensed, and so much more).
One of the challenges to managing that 25X increase in sub-6 GHz spectrum is that, even with all of its next-generation technologies (such as Massive MIMO, network slicing, spectrum aggregation, dynamic spectrum allocation, etc.), the networks are expected to be able to handle 20, to 40 percent of that. There are economic challenges to this, as well.
The industry is looking at some tricks to better manage and allocate this sub-6 GHz spectrum. Massive MIMO and beamforming being some of the more visible and easiest to implement. These technologies allow operators to optimize the RF signals and better focus them while reducing interference.
However, Massive MIMO and beamforming is not enough. Neither are some of the other options (spectrum aggregation, being one). Massive MIMO and beamforming will work better in the mmWave spectrum where large chunks of contiguous spectrum are available. But other tricks are necessary to manage the anticipated monthly ZB load as we approach the end of this decade.
The knight in shining armor
Six gigahertz is being eyed as the white knight riding to the rescue (5.925-7.125 GHz). But will it live up to what is needed to hit that ZB number?
The current thinking is to allocate 1.2 GHz of that spectrum. It is being identified by WRC-23 IMT as between 6425 – 7025 MHz for consumers, enterprises, and industries with 600 MHz of that for next-generation WiFi networks.
There is an argument for allocating all of the 6 GHz spectrum to unlicensed. Proponents argue that it will require that much to provide some breathing room for the sub-6 GHz spectrum. Translated that simply means offloading as much of the data as possible to smaller networks such as edge networks and small cells using unlicensed spectrum.
The hope for mmWave to offer some relief is still in the early stages. Millimeter-wave-based 5G NR technologies need better economic models before operators jump in with both feet. And such systems will need to target dense deployment to make economic sense.
As well, there are other challenges in mmWave deployments that are not necessarily technical. There are concerns about antenna placement, powering the cells, municipality policies and regulations, even health concerns. So, there is still a fog around its clarity.
The overarching challenges is just how 5G will evolve. Early history suggests it will take anywhere from a bit, to much longer for it to reach the levels where expanding platforms, its advanced technologies, and ubiquity will happen.
The GSMA is putting its eggs in the 6 GHz spectrum basket by claiming it will be what puts the full spectrum of 5G technologies on the map. While I believe it will go a long way in accomplishing that, without mmWave, I do not see that as the coup de pouce that will enable full-fledged 5G.
Without a doubt, that 1.2 GHz of spectrum will go a long way in unshackling the potential of 5G in the lower spectrum. How to optimally use it is under discussion. While all this shakes out, the focus needs to continue to be on mmWave, where the real 5G action can happen.
Ernest Worthman is an executive editor with AGL Media Group, a senior member of IEEE and an adjunct professor at the CSU Walter Scott Jr. College of Engineering.