WiFi Interference

While we are trying to stay cool this week, I had some time to do some wireless tests at the Strom world HQ. And when I started to add up all the wireless stuff that I have beaming radio waves around here, I was impressed that everything just sorta works, given all the crossed signals.

Let’s make a list, shall we, of the wireless stuff that is in a typical house: besides the wireless LAN, there are Bluetooth headsets, wireless mice and keyboards that may be running on infrared or some other signal, remote controls to the TV and stereo, cordless phones, microwave ovens, and let’s not forget garage door openers too. Heck, my wife just bought a fan yesterday that had a wireless remote control, which got me thinking about all this wireless stuff out there.

A nice article that covers some of the basics with dealing with interference can be found here by Network Computing’s Jameson Blandford.

If you are in the market for a new cordless phone, make sure you get one that operates at the higher 5 GHz frequencies if you can — you will get a clearer signal and stay out of the WiFi band that your network operates on. That is, unless you have an 11a network.

What about the wireless LAN — that has its own idiosyncrasies. Most of you are probably not aware that the current crop of wireless LANs operates on three non-overlapping frequencies out of all 11 frequencies that are available — channels 1, 6, and 11. It is best to do a site survey and figure out if you can move your own access point/router to some other frequency that will have better reception. In my case, I had plenty of neighbors who were using channels 1 and 6, but only one on 11.

How do you do a site survey? If you have the Canary WiFi spotter, you can do it easily in about two minutes, because this handy device tells you immediately what channel everything is talking on. And you can move from one side of your house to the other easily and see how the signals change. Failing that, you can bring up your laptop’s wireless control panel and root around for a while seeing if you can make sense of the information it is telling you while walking around your house.

Once you get the frequency, you will have to dig out your wireless router’s manual and figure out how to connect to its management interface and make the change to its parameters on the right page. While you are on this page, if you have a wireless router that operates on more than one protocol, such as a b/g or a/b router, now is the time to turn off the ones that your computers don’t use. If you have those 5 GHz phones, then turn off the 11a signals and you will get better reception, provided none of your laptops are running 11a cards. Got that?

Finally, there is Bluetooth, which operates at near the same frequencies as our wireless 11b/g networks in the 2 GHz ranges, along with microwave ovens. Now, most of us aren’t on our Bluetooth headsets all that long anyway, but some new ones are coming out there that can do double duty — such as answer calls from our desk phones and also be used to connect to our PC audio to listen to music or make VOIP calls. I tried out the GN Netcom GN9350 and it worked well, even on my Mac that isn’t promised in its manual. The one downside is there are a lot more wires on my desk, and the unit doesn’t do caller ID on its futuristic base station. I could roam all over the house with this unit, which is very nice, but I wonder how my wireless LAN connectivity is affected. Blandford’s article talks about a 10% hit in his tests.

Have fun with your wireless networks, and enjoy your summer.

0 thoughts on “WiFi Interference

  1. Unfortunately, your advice regarding picking a WiFi channel will
    not work in practice. Many devices operate on 2.4 GHz but will
    not be detectable via a Wi-Fi scanner.

    The best tool for the job is a spectrum analyzer, which is what
    we use.

    However, for indoor networking it really doesn’t make much
    difference if a neighbor is on the same channel. Walls
    attenuate the signal too much for it to cause much interference.

    –Brett Glass

  2. Interesting article by Bladford. I would echo his comments that other WiFi networks are the big problem, especially because you don’t control them.

    I’ve been setting up WiFi for folks for some years now and it’s amazing to watch the saturation. In NYC, in the early days of WiFi, I’d put one up and I’d be unlucky if there was 1 other WLAN nearby. The last NYC setup I did a few months back in a multi-tenant office building, I recall seeing about 30 nearby WLAN’s!!!

    So it’s nice to do an initial site survey to pick the least used
    (interfered with) 1/6/11 channel, but that choice can become obsolete the following day. It’d be nice if future generations of low-end WiFi AP’s would watch channel congestion for you and alert you if there’s a problem or suggest/make a channel change.

    BTW, I use a freeware called NetStumbler to do site-surveys. Haven’t tried Canary but NetStumbler has been good enough.

    -Rich Roller

  3. Here is a short note about our de-wiring the Croisette in Cannes.

    For over a year, I had been operating a hotspot over one corner of the old port of Cannes. From there I was able to shoot down on the port, but not over the Palais with the legal 20dB signal. Actually, it was only really reliable for someone who had high gain on the connecting yacht…which there were only a few of at the time.

    But I was able to get one high-profile CEO’s yacht connected during the Film Festival a few years ago, among others. And, they were able to grab the signal from across the bay in the newer Port Canto.

    The next year the engineers for his new boat asked for more service, but couldn’t pick it up well. I came aboard and found out why. I attached a medium gain antenna to a Buffalo WiFi to Ethernet Converter and found nearly 100 signals available in the bay. Long story short, I eventually attached a yagi, pointed it at my site, found the cleanest channel and got them happy.

    One of the channels that was broadcasting was a leftover from a previous project. A partner company bought rights from the city for several spots along the Croisette including the Mayor’s building, and a couple museums and hotels. We wired up the spots with antennas and repeaters from a reputable company, and got everything working using my site as the source. The big introduction was to be the GSM show. The day before everything checked out; you could walk anywhere on the Croisette and download with up to 3 Meg service (which we then clamped down so no one could take it all.)

    That worked fine until about 10AM the day of the show. Then, while online downloading mail or a website with no problem, suddenly you would start getting errors and eventually, the connection would stall. Turns out that as every booth in the Palais lit up their private wifi site, as well as those set up in private sites in the hotels, solid connections became impossible. The hardware supplier couldn’t figure it out, whether it was the mesh taking the hit, or what it seemed to me; that there were just too many signals floating around in too little space. I’ve had the same thing happen in convention sites, where too many booth sites compete against the official supplier.

    We rerouted the mesh to take signal from a different source, but it made no difference. In those days it wasn’t legal to put 802.11a into open air spaces, and as that was the manufacturers only solution after months of trying to work with the ‘g’ signal, we were forced to take down the system. I eventually closed my site over Cannes as well. Whether the manufacturer has found that ‘a’ solves all, I don’t know. I suspect that we are in for a lot of saturation problems when these city-wide sites get up.

    C J Flynn
    Internet Marine, SARL
    Sophia Antipolis, France

  4. In our home our next door neighbor’s signal (Channel 11)is one bar lower than our own, and when we use any channel other than 11 (1 or 6), things stall completely, even though our connection signal strength is excellent and our network is mac address secure.

    What’s up?

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