Why Cell Networks Cut Out at the US Capitol Riot
As the mob descended on the US Capitol complex yesterday, did law enforcement jam cell signals to thwart communication? No, the networks were probably just overwhelmed. Here’s why.
By Sascha Segan
The riot in Washington, D.C. yesterday made clear the limits of 4G technology, and led to a few relatively reasonable conspiracy theories. As mobs stormed the US Capitol, plenty of people nearby reported their phones having no signal or non-functional connections.
Of course, when this happens at an event like this, it isn’t crazy to wonder if law enforcement is jamming communications. The answer is, they usually aren’t. As our senior analyst for software and security, Max Eddy, pointed out to me, the cops gain more by hoovering up location and messaging data than they do by cutting off video streams.
Instead, the networks were probably just overwhelmed. Here’s how the math works there.
According to wireless engineer Martin Sauter, a 4G LTE cell can realistically handle about 100 users. (Other similar posts on the net have come to similar conclusions.)
One cellular base station includes multiple cell sectors. According to CellMapper, a Verizon site just off the West Lawn of the Capitol has 12. Another two blocks south adds eight more. One a few blocks north adds five.
AT&T appears to have six sites near the Capitol grounds with two, three, four, five, and nine cells respectively. Cellmapper shows six T-Mobile sites, with five, five, five, five, nine, and nine, respectively. I also see seven Sprint sites, with eight, six, four, three, three, three, and three, respectively.
Total that up, and you get 107 cells probably able to serve about 10,700 people in a pinch. That’s a huge amount for a few blocks! It’s complicated by the fact that not all of those cell sectors are facing towards the Capitol, and I haven’t found CellMapper’s data on the shape and direction of cell sectors to be totally reliable. But let’s say around half of those sectors point toward the Capitol. Now we’re around 5,000 active connections on those blocks at once.
I haven’t been able to find a good count for how many people were outside the Capitol on Wednesday, but of course it wasn’t just mob members—it was also media, police, passers-by caught up in the mess, staffers, and even the guy running the concession stand I saw on Twitter. According to Google, the Capitol grounds are about 1,600 feet by 700 feet. So that’s about 1.12 million square feet.
At 16 square feet per person for a relatively tight crowd, you could theoretically fit 70,000 people onto the Capitol grounds. I’m not saying there were 70,000 people there, just how many people could fit in the space. But now let’s say that a fifth of those theoretical people are trying to use their phones. We’re at 14,000 simultaneous connections. So it would be relatively easy to overload the cell networks in an extreme circumstance.
The cops’ phones all keep working because they’re on a special part of the AT&T network called FirstNet, which gives priority to first responders. Heavy FirstNet usage would slightly reduce civilian device capacity at that location, though, because FirstNet comes first.
So why doesn’t this happen at other major protests or events on the National Mall? At most events, the carriers roll a line of truck-based cell sites onto the avenues surrounding the Mall (or the event in general). They’re commonly called COWs (cell on wheels) or COLTs (cell on light truck), and they’re designed to break up larger cells into smaller cells to serve more people.
On regular tourist days, a lot of people are also being handled by the in-building cellular systems in places like office buildings and the Smithsonian museums, which take stress off the outdoor networks.
It looks like the carriers didn’t roll those trucks in yesterday, out of lack of planning or fear of violence. (The fear would have been justified, as the mob members destroyed broadcasting equipment from CNN and other organizations, and conspiracy theories like QAnon tend to overlap with anti-5G conspiracy theories.)
5G Handles Crowds Better
5G could have helped in two ways.
The 5G protocol supports more active devices per cell, and the way 5G cells are designed can put more logical cells on each site. In terms of putting small cells on lamp posts to break up your cells, that doesn’t require 5G. It’s encouraged for millimeter-wave 5G, but it’s also done with 4G bands 46 and 48.
But this is yet another way current US 5G networks aren’t living up to 5G promises. All of the 5G networks in Washington are “non standalone,” which means they use 4G for setup and control channels. That means they operate under 4G device limits.
While T-Mobile says it has a standalone 5G network now, reading between the lines there shows it’s being used to increase coverage, not capacity. It’s extending low-band rural 5G coverage to areas where their 4G doesn’t reach, not improving capacity in already-covered 4G cities.
The blunt reason for this is that T-Mobile needs to combine 4G and 5G on your device to have decent performance. Many fast, “mid-band 5G” T-Mobile connections are really half 4G, which means they once again have those 4G device limits.
When will this change in urban areas? I’m thinking the end of 2021. For T-Mobile, true urban standalone 5G means it needs to be running 80–100MHz of mid-band 5G in these cities. For Verizon, it means standalone millimeter-wave 5G. Both have been promised for later this year.
Originally published at https://www.pcmag.com.
