There is one industry statistic that isn’t getting a lot of press – the fact that cellular data usage is more than doubling every two years. You don’t have to plot that growth rate very many years into the future to realize that existing cellular networks will be inadequate to handle the increased demand in just a few years. What’s even worse for the cellular industry is that the growth is the nationwide average. I have many clients who tell me there isn’t nearly that much growth at rural cellular towers – meaning there is likely even faster growth at some urban and suburban towers.
Much of this growth is a self-inflicted wound by the cellular industry. They’ve raised monthly data allowances and are often bunding in free video with cellular service, thus driving up usage. The public is responding to these changes by using the extra bandwidth made available to them.
There are a few obvious choke points that will be exposed with this kind of growth. Current cellphone technology limits the number of simultaneous connections that can be made from any given tower. As customers watch more video they eat up slots on the cell tower that otherwise could have been used to process numerous short calls and text messages. The other big chokepoint is going to be the broadband backhaul feeding each cell cite. When usage grows this fast it’s going to get increasingly expensive to buy leased backbone bandwidth – which explains why Verizon and AT&T are furiously building fiber to cell sites to avoid huge increases in backhaul costs.
5G will fix some, but not all of these issues. The growth is so explosive that cellular companies need to use every technique possible to make cell towers more efficient. Probably the best fix is to use more spectrum. Adding an additional spectrum to a cell site immediately adds capacity. However, this can’t happen overnight. Any new spectrum is only useful if customers can use it and it takes a number of years to modify cell sites and cellphones to work on a new spectrum. The need to meet growing demand is the primary reason that the CTIA recently told the FCC they need an eye-popping 400 MHz of new mid-range spectrum for cellular use. The industry painted that as being needed for 5G, but it’s needed now for 4G LTE.
Another fix for cell sites is to use existing frequency more efficiently. The most promising way to do this is with the use of MIMO antenna arrays – a technology to deploy multiple antennas in cellphones to combine multiple spectrum together to create a larger data pipe. MIMO technology can make it easier to respond to a request from a large bandwidth user – but it doesn’t relieve the overall pressure on a cell tower. If anything, it might do the exact opposite and let cell towers prioritize those that want to watch video over smaller users who might then be blocked from making voice calls or sending text messages. MIMO is also not an immediate fix and also needs to work through the cycle of getting the technology into cellphones.
The last strategy is what the industry calls densification, which is adding more cell sites. This is the driving force behind placing small cell sites on poles in areas with big cellular demand. However, densification might create as many problems as it solves. Most of the current frequencies used for cellular service travel a decent distance and placing cell sites too close together will create a lot of interference and noise between neighboring towers. While adding new cell sites adds additional local capacity, it also decreases the efficiency of all nearby cell sites using traditional spectrum – the overall improvement from densification is going to be a lot less than might be expected. The worse thing about this is that interference is hard to predict and is very much a local issue. This is the primary reason that the cellular companies are interested in millimeter wave spectrum for cellular – the spectrum travels a short distance and won’t interfere as much between cell sites placed closely together.
5G will fix some of these issues. The ability of 5G to do frequency slicing means that a cell site can provide just enough bandwidth for every user – a tiny slice of spectrum for a text message or IoT signal and a big pipe for a video stream. 5G will vastly expand the number of simultaneous users that can share a single cell site.
However, 5G doesn’t provide any additional advantages over 4G in terms of the total amount of backhaul bandwidth needed to feed a cell site. And that means that a 5G cell site will get equally overwhelmed if people demand more bandwidth than a cell site has to offer.
The cellular industry has a lot of problems to solve over a relatively short period of time. I expect that in the middle of the much-touted 5G roll-out we are going to start seeing some spectacular failures in the cellular networks at peak times. I feel sympathy for cellular engineers because it’s nearly impossible to have a network ready to handle data usage that doubles every two years. Even should engineers figure out strategies to handle five or ten times more usage, in only a few years the usage will catch up to those fixes.
I’ve never believed that cellular broadband can be a substitute for landline broadband. Every time somebody at the FCC or a politician declares that the future is wireless I’ve always rolled my eyes, because anybody that understands networks and the physics of spectrum can easily demonstrate that there are major limitations on the total bandwidth capacity at a given cell site, along with a limit on how densely cell sites can be packed in an area. The cellular networks are only carrying 5% of the total broadband in the country and it’s ludicrous to think that they could be expanded to carry most of it.