Eero – More Than Meets the Eye

I’ve been fascinated by the Eero for some time, mostly because I love the idea of dirt-simple wireless mesh access points. That’s a challenging space to operate in, and if it’s done well, it has the potential to do a lot of good in putting crappy wireless repeaters out of the marketplace before they convince someone to do impossible things with Wi-Fi.

Recently, though, I’d read some odd things about them, and I wanted to see if I understood the whole situation. First up was something specifically I’d read: they use 40 MHz channel widths in the 2.4 GHz spectrum. My primary experience with devices that work like that has been finding them in use at various corporate sites where they’re just blotting out entire swaths of a very crowded spectrum. It lead to this slide’s existence:

40MHz Channel Widths in 2.4?! Weehawken, Dawn. Guns, Drawn.

It’s safe to say that I feel strongly about this.

Weirder, though, the Eero doesn’t move from its channel position at channel 1 no matter the situation. While 2.4GHz does only have three channels in 2.4 that are unencumbered by adjacent channel interference, it seems odd to pick one and lock right down to it. I asked the CEO of Eero about this on Twitter, and he came back with evidence: “Across now thousands of networks, the best channel has been 1.” In addition, while it will default to 40 MHz widths in 2.4 GHz, if things are crowded, it will dial it back to a standard 20 MHz width.

Fascinating, right? Wait ’til you see what else they’re doing.

802.11ac in the 2.4GHz band?!
802.11ac in the 2.4GHz band?!

Yes, that graphic is right. They are using 802.11ac in the 2.4GHz range! HOW?!

Well, for one, Eero is not Wi-Fi Alliance certified, which means their gear isn’t necessarily adhering to every part of the 802.11 set of standards as designed and approved by the IEEE. That means that they can choose to do more innovative things with their units, at the cost of a pretty and recognizable badge on their box.

Now, why’s this all matter at all? The culmination of our Wi-Fi deck at Cascadia was the definition of transmit speeds, which depend on the guard interval, the encoding and modulation scheme, the channel width, and the number of spatial streams available. Like a mathematical equation, these group together to give us a decent result. Wi-Fi works by encoding signals through amplitude modulation and phase-shift keying, which combine to put the wave in a specific position in a given polar chart, like so:

64QAM Chart
64QAM Chart

Depending on how the amplitude and phase are shifted together, you can line up each symbol in one of 64 positions, which a fourier transform can quickly calculate. That’s how Wi-Fi works. But until 802.11ac – which is a 5GHz technology by specification – 64-position Quadrature Amplitude Modulation was the limit. With 802.11ac, when conditions are right, everything upshifts to 256-position QAM, and the chart gets a whole lot denser:

256QAM
256QAM

Sure enough: 2 spatial streams, with a short guard interval, in a 40MHz channel in the 2.4 GHz band, at 256QAM 5/6, gets you a 400Mbps Tx Rate, and that’s what Wi-Fi Explorer sees in this test provided by a friend-of-a-friend.

It’s a pretty neat trick to make 802.11ac work in the 2.4 band, especially when you think they’re flouting the standards to prove a point. I’m interested to see a little more about how these handle the backhaul between units, but I’m not sure I want to spend $500 to find out more.

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