802.11 2.4ghz interference

[justanothercanuck]

With so many devices using the 802.11 2.4ghz, I'd be interested to see how today's devices combat the issue.

Yea or Nae? 

[Simon]

It's a cockup in short. If I transfer files to/from my NAS from my PC the mouse stops working because boh the wifi and mouse are 2.4 GHz, utterly stupid. Encryption can only do so much and crossed wifi channels does cause problems, especially these days as wifi N can reach further and you can only get 2-3 networks on the chanel range because they take 4 channelsor more up

[Psi]

I suspect those type of "blocks" (where one device jams another) only occur with cheap RF electronics using the same exact frequency with no spread spectrum/frequency hopping at all.


i have a wireless keyboard & mouse, two wifi networks and multiple portable phones of different brands all on the 2.4Ghz spectrum and ive never had any issues where one of them causes another to stop working properly.

[Simon]

I think myproblem is when the wifi is belting out at full speed, it is fairly close to the mouse receiver and is taking all the bandwidth it can and even if they use slightlydifferent frequency the power and proximity will overload the other receiver.

If you take an FM radio under a transmitter no matter what you tune to you will pick up that one station because it over powers the receiver.

[JoannaK]

It's quite possible to build a meter to measure the intereference/signal levels.. At some years back we used one of these, and they seem to work quite nice.

http://www.metageek.net/products/wi-spy/

Obviously, any decent Spectrum analyzer + software would be more flexible and accurate, but the basic wi-spy is quite inecpensive (relatively, that is).

[notsob]

And here's a scanner project

http://geoffg.net/ISM_Scanner.html

[NiHaoMike]

Isn't 802.11 supposed to have provisions to coexist with other 802.11 networks? Also, many recent chipsets support coexistence with Bluetooth. Adding a little more intelligence to the wireless chips can help a lot for relatively predictable interference sources. For example, microwave oven leakage is just pulses of 2.4GHz at 50 or 60Hz, so a smart chipset can detect that and schedule transmissions during quieter periods. (That's something my friend Tiffany Yep worked on. The most interesting part is that a lot of the benefits are realized even if only one side is equipped with the technology.)

Phased arrays help a lot by directing most of the transmit power where it's needed and allowing the receiver to reduce off axis interference. Also, newer buildings are often insulated with insulation that has aluminum backing, which works very well at attenuating RF. (Great for 802.11 and other indoor networks, not so good for TVs and cell phones. It also causes a lot of reflections, but every modern wireless network is designed to adapt to it.) Even double pane windows nowadays are coated with a thin layer of metal to reflect infrared, which also attenuates RF a little. (If RFI is a big problem, you can replace the fiberglass window screens with aluminum window screens.)

[jerry507]

There's a big difference between "802.11" and "2.4ghz". Your mouse is, as someone said, probably just a cheap transmitter/receiver pair and isn't some kind of spread spectrum system. If it's 802.11, then it's spread spectrum which improves reliability a lot. Spread spectrum systems have a great property where narrowband interference just looks like a moderate increase in the overall noise level. This is what allows them to reject microwaves and other very narrow frequency interference. A cheap tx/rx set in a mouse that just uses FM or something will see a general rise in background noise from the accumulation of spread spectrum devices, and if another narrowband source fires up they may be completely jammed.

So while many 802.11 networks in the same area are fine, you'll see issues with the proliferation of cheap rx/tx pairs.

[Simon]

Well this was quite an expensive wireless mouse from Logitech, I paid £30 from a cheap shop so there should have been budget for a decent receiver - after all they made an effort to make a mouse that can run for over a year on one set of batteries.

My wifi gear is from Tenda which is crap. I'm not sure how spread spectrum works but does that require that your not using the full bandwidth ? I have no problems with normal use but as soon as I transfer file to my nas using up all the available bandwidth problems arise.

[jerry507]

Is it one of the unified receiver units? I'm a big fan of those and I haven't had any problems. That hardly means anything though According to Wikipedia it uses bluetooth that's been heavily locked down. It SHOULD be spread spectrum and fairly resistant to interference. If you've ever done a site survey though, you might find there are a ton of strong signals around. If you're hovering right on the edge of good SNR, using the full bandwidth certainly could cause the SNR to drop down. They're pretty low range too. I use one on my HTPC and PC to couch is about 10 ft max. Sometimes it misses key presses and such.

The wifi gear will be much higher power, therefore higher SNR, less of a problem.

[Simon]

The mouse receiver is no more than 8 inches below the mouse and 6 inches forward of the mouse but the wifi adapter plugged into the front of the PC at the bottom of the case about 50cm below causes a problem for it.

Moving the mouse forwards helps as it gets some of the PC case in the way so acts like a screen and it's then directly over the receiver, I'm thinking of finding an old USB "thing" and using the plug to make a plug in ground shield to go in the socket above the one with the wifi dongle in. if I get round to it before I bring the phone socket and router upstairs and wire the PC in so it has better access to the NAS