Video card + 3D game = dropped 802.11 (wifi) link?

It seems I have no luck at all with bizzare problems lately.

So, I’m on vacation, and there’s an 802.11g network here that I’m using for my network link. Where I’ve got my laptop, it’s really right on the fringe of coverage, just barely able to maintain a stable link. The manufacturer’s 802.11 diagnostics utility reports signal as -87 ~ -88 dBm, and noise as -87 dBm in this configuration; not exactly ideal RF conditions. (There exist no other SSID-broadcasting 802.11 networks in close proximity, at least as far as I can tell without downloading some sort of more specialized (and capable) link sniffing software.)

Anyways, the connection is usable like this, although it’s as I said on the very edge of tipping over into losssy or just plain lost link land. I’ve determined that, for instance, using Bluetooth A2DP to my headphones injects enough traffic into the 2.4GHz RF environment to push the 802.11 link to doing something like ~10-20% packet loss (not exactly all that friendly for TCP). Without A2DP streaming audio, packet loss is somewhere around ~1% or less, which is usable, although the link doesn’t appear to be able to do more than half a megabit reliably. Again, not all that great, but it at least works.. mostly.

That is, until I start any program that kicks the video card (a GeForce 7950 Go GTX) into high gear. If I do that, the 802.11 diagnostics utility immediately registers somewhere in the neighborhood of a 4-6dBm increase in noise, which is enough to completely swamp the already relatively weak net signal and cause the link to drop entirely shortly after. I guess that the video card is not quite sufficiently shielded relative to the 802.11 antenna on my laptop. (In this particular case, my box is the only system on the 802.11 link; it’s definitely not a problem related to someone else on the same AP.)

To better illustrate the problem, I took a screenshot of the combined signal and noise graph history from the 802.11 diagnostics utility; you can very clearly see when I had a program using the video card up and running:

802.11 Noise Graph Screenshot

Now, normally, this isn’t a problem when I use 802.11 at my apartment, even with playing games or watching video over 802.11, but then again I’m normally well into the “green” as far as signal goes there, and my apartment 802.11 link uses a superior radio technology to boot compared to where I’m staying right now (802.11n as opposed to 802.11g).

So, naturally, frustration ensues. I can do whatever I want on the link, except (of course!) play games. And, of course, since it’s vacation, that sucks all the more – so much for retiring from a long day of plane flights to blast some bad guys in a video game.

Well, that’s overstating it a bit. I can always sit my laptop down elsewhere, but the problem was curious enough that I decided to investigate why my network connnection was magically disappearing the moment I tried to play any game. (Update: It actually appears to vary based on how intensively the game uses the video card, which makes sense as it’s a laptop video card that’s supposed to conserve power as much as possible. For example, starting Quake 3 only creates enough noise to cause significant packet loss, but World of Warcraft causes the video card to generate enough noise above that to result in the link flaking out entirely.)

It’s actually a kind of interesting problem, though, if one that caught me totally off-guard. I have to wonder what other operations will generate enough internal noise in a laptop to noticibly affect 802.11. It also makes you wonder if someone might be able to guess when you’re, say, slacking off and playing games on the office 802.11 link by observing indications of link quality from your machine (irrespective of whether your traffic is encrypted or not)…

3 Responses to “Video card + 3D game = dropped 802.11 (wifi) link?”

  1. Good Point says:

    This king of analysis has been around since the 50s.

    http://en.wikipedia.org/wiki/TEMPEST

  2. Skywing says:

    Definitely some interesting reading there. Kind of sucks that so much of it is apparently still classified, though…

  3. Ron says:

    Hey,

    I already told you this on MSN, but for the benefit of anybody else here I gave it a shot (on Linux, with a Mobility Radeon video card), and saved the results to the following file:
    http://www.javaop.com/~ron/tmp/linkquality2.txt

    Although it isn’t a huge difference, one definitely exists.

    Happy research! :)

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