As I continue to get ready for my own venture into 11ac, I came across some pretty fascinating information about 5 GHz. I’ve been brushing up on how the state of 5 GHz spectrum applies to the Wi-Fi realm now, and what People of Lofty Title are wrestling with regarding future use of this slice of frequencies. Standby, because I’m going to dazzle you with some pretty darn macho terminology. (As a bonus, I shall invoke the name of Matthew Gast thricely in the following paragraph.)
But first, let’s set the stage.
WLAN designers and admins (hopefully) know about subjects like DFS (Dynamic Frequency Selection) and TPC (Transmit Power Control) and how they relate to weather radar in 5 GHz (cue the Matthew Gast music there, Part I). Also, hopefully we are all familiar with the last announcement about the WLAN world possibly being gifted with a fat swath of additional 5 GHz frequencies for the greater wireless good, made by ex-FCC Chairman Julius Genachowski (cue the Mathew Gast music again, Part II and Part III). It’s all great stuff, very relevant, and is techno-fodder that you should care about given the channel-hungriness of 802.11ac. But that’s not why we’re gathered here on this page.
As I was poking around, I came across this rather dry (at first glance) looking document by the Department of Commerce. It gets deeper into the many challenges of sharing more of the unlicensed 5 GHz goodness with WLANers while also protecting the interests of the licensed/federal/important users that also happen to be in this spectrum. And here’s where it gets interesting. Sure, weather radar is important- but the list of other users in 5 GHz is a veritable Who’s Who of cool stuff.
In all fairness to those of you who don’t know- I spent 10 years in the US Air Force in the Electronic Warfare career field, and maybe that’s why this sort of detail jazzes me (yes, some of what I did back in the day is on this list). Feast your eyes on the other occupants that live on 5 GHz Street, as noted in the unclassified Dept. of Commerce document:
- Highly mobile ground-based, shipborne, and airborne radar systems
- Range and tracking radars at DoD test and training ranges (get to know the C-Band)
- DoD comms systems
- Naval tactical radars like surface search, navigation, and fire control
- A bunch of stuff on Coast Guard cutters used in law enforcement, search and rescue, etc
- NASA- test and launch instrumentation, tracking of rockets, missiles and satellites
- NOAA’s Hurricane Hunters have systems in 5 GHz
- A whole range of operational goodies dealing with Unmanned Aircraft Systems (UAS) like data links, video targeting
- Spaceborn Synthetic Aperture Radars, including Canada’s RADARSAT (fascinating if you don’t know about this one)
- Electronic Warfare systems
- Lots more…
Some of these are site-specific and one-of-a-kind. Others are widespread, mobile, and out of the public eye. But they all use 5 GHz (albeit different discreet bandwidths within 5 GHz), so it’s amazing that the WLAN community has been able to come this far in the U-NII bands at all. It’s even more amazing that we’re likely to get more freqs made available, knowing who also uses it.
The Commerce Doc is really a great read if this stuff interests you, and I recommend it. If the specifics are too heavy for you, just go back through my abbreviated list here and apply “oohs” and “aahs” as you see fit.
(Note- the Doc projects completion of the co-existance studies later in 2014… let’s see what happens.)
wirednot 
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Amateur Radio is in the 5 GHz band and the larges Amateur Radio users run Television links and repeater outputs.
Thanks for the add, Mike!