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Spectrum: The Gift That Gives You Faster 802.11ac

By Matthew Gast in · HiveMind Blog · January 11, 2013

I think I have an engineer-crush on FCC Chairman Julius Genachowski. Wi-Fi exists because unlicensed spectrum was allocated by the FCC, and it’s been in short supply ever since. The relatively small 2.4 GHz band is tapped out, and we are in the process of moving Wi-Fi to relatively clean 5 GHz spectrum with 802.11ac.

Today I need to thank the Chairman for his belated Holiday Gift of Unexpectedly Large Size. Yesterday at the Consumer Electronics Show (CES) in Las Vegas, Chairman Genachowski announced an effort to open up an additional 195 MHz of spectrum. For this much new spectrum, it’s ok for the gift to arrive in January. I’ll wait. Don’t worry, Chairman, we won’t be returning it!

For Wi-Fi, open spectrum is the electronic equivalent of the American frontier. More spectrum equals better speeds because there is more ability to carry the traffic. This gift of 195 MHz of spectrum is like the Airbus A380 of spectrum.  It’s the Autobahn of spectrum in a two-lane highway world.

The size of the new blocks were a bit of a surprise to me, even though the Chairman has long supported efforts to keep unlicensed spectrum available. During a 2011 trip to Silicon Valley, Genachowski repeatedly returned to Wi-Fi as an example of what he wants to see the FCC do, noting that unlicensed spectrum was a necessary ingredient in the creation of Wi-Fi.

Although the FCC’s action isn’t an official regulation yet, the announcement points towards the most important elements. Here’s a rundown on the unlicensed 5 GHz band available after the FCC action takes effect:

  • 5.170 – 5.330 GHz. This is already available as channels 36 – 64, so you have eight 20 MHz channels.
  • 5.350 – 5.470 GHz is 120 MHz of new spectrum available for Wi-Fi use. Although I haven’t taken a detailed look at the channel map, it’s likely about six new channels, probably numbered 72, 76, 80, 84, 88, and 92.
  • 5.490 – 5.725 GHz. This is the existing worldwide harmonized (DFS) band with twelve 20 MHz channels. This retains is current channel map, but we’ll get back the Doppler weather channels, restoring our ability to use channels 120 through 128.  In some ways, this is the biggest part of the announcement for 802.11ac because it brings back one of the two 160 MHz channels and makes that width more viable.
  • 5.735 – 5.835 GHz. This existing band has five 20 MHz channels, and was not changed by the announcement.
  • 5.850 – 5.925 GHz. This is 75 MHz of new spectrum, which will accommodate four new 20 MHz channels, probably numbered 170, 174, 178, and 182.

For the terminally curious, you can look at these new bands in the 2003 spectrum allocation chart, maintained by the NTIA’s Office of Spectrum Management.

Another way to look at the announcement is the additional channels made available. With the two new bands and the restoration of the “hole” in the DFS band, it’s a big chunk of spectrum: 13 new 20 MHz channels. By restoring blocks of contiguous spectrum, the situation is even better than what the FCC press release mentions. Although they correctly note the amount of spectrum is going up 35%, the number of available channels is going up by much, much more.


Matthew Gast (@MatthewSGast)

Matthew Gast is Director of Advanced Technology at Aerohive Networks. He currently serves as chair of both the Wi-Fi Alliance's security task groups, was the first chair of the Wireless Network Management Marketing task group, and is the past chair of the IEEE 802.11 revision task group. Matthew is also the author of 802.11 Wireless Networks: The Definitive Guide (O'Reilly), which is now in its second edition and has been translated into six languages. His companion book, 802.11n book, 802.11n: A Survival Guide (O’Reilly), was recently published and provides information on how 802.11n works and what it means for the WLAN planning process. Most recently, Matthew completed 802.11ac: A Survival Guide (O'Reilly).


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