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Q&A: What the FCC's Wi-Fi expansion means for you

And why Aerohive's Matthew Gast has an engineer's crush on the FCC chairman

By , Network World
January 23, 2013 10:04 AM ET

Page 2 of 4

5.350-5.470MHz: 72, 76, 80, 84, 88, 92

5.850-5.925MHz: 170, 174, 178, 182

So, pre-announcement you had 22. Post announcement, you have 22+3+10=35, an increase of 62%. It's a much bigger improvement than just the [added] spectrum, and that's way more important to me as Wi-Fi engineer.

Why is that important?

First of all, we now have 60% more channels for high capacity networks. I once did a Wi-Fi network for a tradeshow, when everyone had 11b and 11g devices on the 2.4GHz band, in a football-field sized exhibition hall, with in effect just three channels. With Wi-Fi today, if any one person is transmitting on a channel, no one else can "say" anything. [So] it's basically impossible to lay out any kind of high capacity network with just three channels. That's why the 5GHz band is so important.

Secondly, you increase the speed available. The next generation of Wi-Fi, 802.11ac, uses wider channels than 11n [11n can combine two 20MHz channels into a "fatter" 40MHz channel; 11ac can combine 40MHz channels into 80MHz channels]. The table in my blog post shows the higher capacity of the wider 80 and 160MHz channels. With the existing spectrum, we don't have that many 80MHz channels. That lack of wider channels will take the big speed increase off the table for 11ac users. But with the new spectrum [and added channels], 11ac networking just got the ability to carry much larger amounts of data.

How else does this affect Wi-Fi networking?

There's another interesting but a bit subtle effect. In Wi-Fi, the big factor is the signal-to-noise ratio [SNR], which has to do with how well you [meaning "a radio"] can "talk" above the ambient electrical noise in your area. As SNR improves, you can perceive finer differences in the signal, making it easier to talk above that background noise. The more SNR improves, the faster you can go.

And that has another related effect, dealing with the higher, 256 QAM modulation [introduced] in 11ac. To do 256 QAM, you have to pick out very fine distinctions. It's like throwing darts at a dart board that has more, but finer concentric circles: the more accurately you're able to throw, and the less air disturbance between you and your dart board, the better it is.

The No. 1 cause of "noise" in Wi-Fi is other Wi-Fi devices: we "hear" each other transmitting. If you transmit, I can't. It's like being in a party that's in a small room, where you can hear this burble of noise from one or more groups talking around you. To be heard, you have to "talk over" that burble.

But with the new spectrum and more channels, it's like moving this party into a much larger room. When that happens, everyone is [in effect] spread out. So all the groups can talk more quietly, and you can recapture the subtlety in what you're talking about: you don't have to talk louder. And less interference means better speed.

So how will this change the Wi-Fi experience for end users?

Right now, these products exist only in laboratories. Imagine you have two 11ac products. One supports these new 5GHz Wi-Fi channels and one doesn't. For the radio that doesn't, it will have a choice of 20 channels, which also will be sought by 11a and 11n clients. It will auto-select a data rate and it will not be able to use 256 QAM.

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