When doing any WLAN Assessment or Remediation, we ALWAYS look at the spectrum. In about 60% of the WLANs we assess and remediate, we find interference from a device the customer didn’t know they had, or knew they had but didn’t know it was sharing the same spectrum as their Wi-F.
The complaints vary from Customers that have interference issues. We hear “I only have two bars”, “my wireless is slow” and “when I stand right here, my Wi-Fi doesn’t work”.
We’ll first start out with stating the obvious. The 5GHz UNII bands are license free, which means it is a free-for-all when it comes to who is doing what. Most of us all understand that. A company, or their neighbors, can pretty much deploy anything they want, as long as they abide by the rules.
When we first start out on an Assessment, we do what we normally call a WLAN Validation. We walk the entire facility with Ekahau’s ESS – or Site Survey Software. Ekahau recently updated their software to include Spectrum Integration, so here is our first look using it in the real world.
In this case, we have an area that we know we have WLAN Interference. We have looked at it with other tools, however since Ekahau is our tool of choice at the moment, we want to compare what we see with our new spectrum integration to what we are used to seeing in our legacy equipment. Here is a view of the area known to have an interferer on channel 40. We looked at our Survey Inspector, and the Spectrum Channel Power view. We clearly see something there, and can compare it with a quick glance to the other channels.
And now we are going to take a look at our Spectrum Utilization view. We scrolled up to another area of the survey/walkabout where we know we have another source of interference. Again, we can clearly see that there is an issue in another part of the building.
During our Spectrum Integration analysis, we notice another feature called RTFM. Forget what you know about this acronym, because it stands for Real Time Frequency Monitor. This is the kind of tool I would use if I had my survey rig in my backpack, and someone told me of an area that was having Wi-Fi issues. I don’t even need to build a project – I open ESS and hit the RTFM button, select the frequency I want to look at and give it a glance. Here’s what I see below. I must say, that’s a nice feature! Thank you Metageek (for the SpecAn) and Ekahau!
Now that I have seen the interference, I, for whatever reason, want to see it in my Spectrum Analyzer software. This is available from Metageek – where you would most likely purchase your SpecAn hardware. This view is with other known interference devices, all by the same manufacturer, turned on – for our testing purposes. As you can see, there is a lot of interference here, and some remediation and spectrum management needs to take place.
Now for a look from some of our legacy tools. As you can see, the view is not of the same exact slice in time, however I promise you that what you are looking at is all caused by the same equipment. This is a view of four devices energized, and one of them is changing channels. No wonder these folks are complaining about their Wi-Fi not working well for them!
Here’s a view of channel 40 from another Spectrum Analzyer. AS you can see, the numbers vary from tool to tool, but in each you can tell there is an issue.
Af first, it took us a while to track down the equipment, as we didn’t want to go into an operating room while they were doing their thing. After several days of intermittent troubleshooting, we finally came to the conclusion that our source was mobile. We tracked it down to Operating Room “towers”, which were mobile Endoscopy equipment. The gear has a wireless transmitter and a remote monitor or two, and those remote monitors were connected via the 5GHz spectrum. This equipment was moved around to whichever Operating Room need it.
Then we discovered something else. When the equipment was turned on, it searched for a channel to use. Not in a very Wi-Fi friendly way, though. It seems as if it always starts on channel 36, then works its way around the first eight channels until it finds “home”.
If you are good with math and have a great imagination, multiply this one source of interference, and what is does to your WLAN, by four. There were at least four of these devices being turned on and off during the course of any workday, each booting up and trying to find a channel to use. Stomping on the Wi-Fi as it went.
Something about these tools is worth mentioning. They are somewhat complicated and expensive to own – unless you use them on a weekly basis. They all do a great job of displaying to the operator what the electromagnetic spectrum looks like at a given frequency. However, there is no “magic button” that you can click on that will tell you what is wrong with your network and how to fix it. I highly encourage anyone interested in owning and operating these tools to first go to CWNP.com and purchase the CWNA curriculum and read it several times. Of course you also have to read the manual of the spectrum analyzer you finally end up purchasing. You can get the Spectrum Analyzer (and the software) that integrates with Ekahau ESS from http://www.metageek.com/
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