Need More Spectrum

Wireless spectrum is like freeways: the more you build, the more traffic you get. There was certainly a time when the 110 freeway through downtown Los Angeles was synonymous with smooth sailing at 55 miles per hour, but for decades, the world’s highest-capacity freeway network has filled every additional lane that got built with twice as much traffic as before.

I noticed this tweet from Stephen Lawson a couple of days ago that suggests cellular operators are running up against the same problem:

Stephen has a number of other comments from his trip to CTIA, including what might seem like a surprising statistic: wireless subscriptions have achieved 105% penetration in the United States. Surprising when I think back to my summer job with a CDMA operator in 1998 where everyone wondered if cell phones would ever achieve 30% market penetration; unsurprising given that today I have three wireless subscriptions.

With so many wireless devices in service, it’s definitely no surprise that we’re running out of spectrum, especially as more and more of these mobile devices are used for high-bandwidth video applications. And while allocating a significant amount of additional spectrum could solve the problem in the short-term, that’s not a simple solution – roughly 1 GHz of total cellular bandwidth has been set aside worldwide, but in any given country, it is shared with dozens of other wireless applications, including television, radio, satellites and navigation. (This 2003 chart of United States frequency allocations is very instructive!) The pace of clearing spectrum to open up new cellular bands is very slow because it often requires completely changing existing technology in a band – think about how long it took to switch to digital television, which created the already at-capacity 700 MHz LTE bands.

Fortunately, 5G WiFi presents a solution to this problem. The 5 GHz band, where 5G WiFi operates, offers another 1 GHz of spectrum that can potentially be used to offload high-bandwidth cellular usage to Wi-Fi. Much of this band is already open for Wi-Fi use in the United States and other countries, and the remainder may be licensed in the near future. The even better news is that the capacity of the 5 GHz band is even greater than a similar amount of cellular spectrum: there are significantly fewer users in this band than there are in cellular bands, and the reduced range of Wi-Fi relative to cellular (several hundred meters vs several kilometers) allows even more users to share the spectrum. While it’s difficult for cellular spectrum allocations to keep up with the growth in a carrier’s customers, for example, 5G WiFi presents an opportunity to quickly build 10 times as many freeways, so to speak. Even Los Angeles would have smooth traffic with that kind of increase in capacity.

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