Wi-Fi Cards Can Now Detect Microwave Ovens

An anonymous reader writes "Researchers at UW Madison have used regular WiFi cards to detect non-WiFi interference sources like microwave ovens, Bluetooth devices, cordless phones, Xbox controllers and video cameras. They call their software Airshark. Current products like Wispy, Spectrum Expert are expensive and need extra hardware, whereas Airshark is a software-only solution that can directly work on the Wi-Fi cards on your laptops and APs. This also paves way several interesting applications. For example, your WiFi network will not be affected anymore just because your neighbor switched on a microwave oven or a cordless phone — the newer WiFi APs will be able to switch the channels and adapt to the interference accordingly."

Comments

If only all wifi devices could work cooperatively

[Skinkie]

Then the entire spectrum problem is solved, and everything would be autoconfigured for the basic paradigm: connectivity. Now I don't expect a microwave to give me food-over-ip, but I would expect a neighbor wifi cell, helping my AP to extend the signal, if my client would move out of range (aka: has more noise).

Like IMing in the same house

[EmagGeek]

"Honey, did you leave the microwave on?"

"I don't know, Dear, let me log into my PC and check."

Re:Like IMing in the same house

[maxume]

Right, because no one has neighbors in close proximity or anything silly like that.

Re:Like IMing in the same house

[grub]

The fuse would still pop. Hey I was 25ish and stupid. Now I'm 45 and stupid.

Re:If only all wifi devices could work cooperative

[morcego]

The technology allows for this already. However, the security and privacy implications are big. Not to mention bandwidth limitations. And switching capability. And routing tables. And ARP tables. And those are the problems I though about while typing this. I'm sure there are several others.

Why is there still microwave oven interference?

[vadim_t]

I thought that shielding was well understood and in fact a good reason of the part why microwave ovens are a common household item.

Could anybody with experience in these matters explain where the leak is coming from, and why do they still exist? Is it impractical or physically impossible to have perfect shielding for some reason?

Re:Why is there still microwave oven interference?

[stms]

I don't have much experience with this kind of thing but from what I can extrapolate from this wikihow article it's just that some microwaves are poorly designed or are old.

Re:Why is there still microwave oven interference?

[bbn]

WIFI is only allowed to transmit 100 mW (0.1 watt).

Even if only 0.01% of the microwave is leaking it is still more powerful than the WIFI. And even less is required if you do not have a perfect WIFI signal to begin with.

Re:Why is there still microwave oven interference?

[networkzombie]

Really? I installed my Whirlpool microwave and neither my cell nor my GF's cell (ATT & Verizon) receives any text, call, or email while in the microwave. I test it often. If I were you I would stop using your Samsung microwave, or at least get a remote control for it so you can cook from down the street.

Re:Why is there still microwave oven interference?

[complete loony]

Why else do you think 2.4 Ghz wifi is unlicensed spectrum? It's mainly *because* microwaves make it useless for much else.

Re:Why is there still microwave oven interference?

[bill_mcgonigle]

Even if only 0.01% of the microwave is leaking it is still more powerful than the WIFI.

Usually it's not any leaking from the cooking chamber, those are pretty well shielded, but the power supplies, which aren't well shielded.

I've read that it has to do with the AC duty cycle, but I previously had a Panasonic that ran on a DC inverter (supposed to make the microwave cooking better, but didn't) and it had terrible WiFi interference.
  'Microwave robustness' and 802.11g didn't do a darn bit of good (maybe because there was no duty cycle?).

Anyway, I set out to buy new microwave ovens and return them until I found a clean one, and got lucky on a Kenmore the first time. It's the gigantic one with the rounded inside corners, and I can sit at the table less than 10 feet away and not see a dB loss on the WiFi. IIRC it's made by one of the Korean companies (LG, Samsung?) It can handle a 9x13 casserole dish too, so double-plus good.

I've done this plenty

[ModernGeek]

When my downloads get slow and I can't refresh slashdot, it means it's time to take a break because mom is making me a snack upstairs.

If you buy one of the CHEAP WiFi Detectors

[MindPrison]

(not to be confused with the WIFE Detector(tm) )

then you can indeed detect a microwave oven, and pretty much anything that spews out parasitic signals from 1500-3000 Mhz.

*Technical explanation coming up*
This is due to the cheap construction of those So Called WiFi detectors, they're not digital, they're in fact analog receivers that only detect any modulation on the band (very VERY wide-band / BroadBand reception)... it's just a glorified Crystal Radio with a small half-coil, 3-4 transistors to amplify anything...any signal picked up by the small 1 cm internal antenna, and 1 transistor to switch on a led (or 3-4 resistors, if it's sophisticated and have 3-4 leds...ha ha) ;)

There...now the Chinese can mass-produce them, I just literally gave you the schematics for it... ...oh wait!

Re:If only all wifi devices could work cooperative

[tuxicle]

802.11a devices (operating at 5.45 GHz) are already supposed to detect radar signals and switch channels if one is found. This is particularly a problem in Europe, where most weather monitoring radars are C-band, and share the same frequency band as 802.11a.

Re:If only all wifi devices could work cooperative

[complete loony]

Hi, I'm working for The Serval Project, and like other projects related to wifi mesh routing, we do have high level goals like this. And we're actively trying to make them a reality.

One of our staff just returned from a presentation to IEEE, to propose a more open standard for the next 802.11 spec.

The basic premise of our proposal is that the protocol for using wifi devices to route traffic should be dealt with in kernel or user space. Not in the radio spec. And that adhoc, and 802.11s are useless for this task (Damn you BSSID, why you change?). We also think that security and perhaps even error correction should be dealt with via a VPN or baked into the application layer.

We want the next wireless spec to include a basic packet radio mode, operating in any unlicensed white-space spectrum, that gives as much control as possible to higher levels of the OS. So that new interesting ideas are easier to experiment with and implement.

And we've been invited to the next IEEE working group to help make it happen.

Eh, what?

[russotto]

First of all, switching channels to avoid a microwave is futile... the magnetron isn't all that frequency stable and the peak tends to wander across the band as a result.

Second, 802.11g/n uses OFDM. You get narrowband interference, you reduce the rate on the affected subcarriers. It's built in.

Third, I'm fairly sure using a wifi card as a spectrum analyzer has been done before.

How about one that can't

[Hentes]

This is cool but I would be far more interested in a card that does NOT detect microwave signals.

Re:Easy fix

[YrWrstNtmr]

So, how am I supposed to make popcorn, eh?

Bag of regular popcorn.
Medium size pot, with lid
Oil, or I prefer bacon grease

Put it on the stove, on just above medium *
Put a thin layer of oil in the bottom
Put two and only two kernals in it.
When the first one pops, turn the heat down a little *
Put in one and only one layer of kernals on the bottom
Put the lid on the pot
When it is 2 seconds between pops, it is done.
During popping, you may give the pot one and only one shake.

* your stove settings may vary

True Story

[flatulus]

In 1992 I was at an IEEE 802.11 meeting (that's WiFi, if you didn't know it by that name). My company was presenting a "pre-standard" wireless LAN design that we were developing, to be considered as a contribution to the standard.

Someone asked "Why does your design have so much error correction coding? Are you expecting the RF environment to be that bad?"

I replied, "Well, I haven't seen any 'Listen Before Cook' microwave ovens out there!"

This got a few chuckles and we moved along.

Many years later, I was doing some patent searches, and I came upon Patent number 6,346,692, titled "Adaptive Microwave Oven"

I'll be damned! Somebody actually patented the "Listen Before Cook microwave oven!"

So now we have WiFi devices detecting microwave ovens. That seems obvious to me. But I'm still waiting for a commercially available microwave oven that will avoid stomping on my WiFi signal :-)

FWIW, The 802.11 Media Access Control (MAC) protocol effectively avoids microwave ovens most of the time, because the magnetrons in consumer microwave ovens only operate on a "half wave" basis. This means they're off at least half the time. A microwave oven during its "on" time looks indistinguishable from another WiFi transmitter, and so your WiFi device simply waits until the microwave oven turns off before transmitting the next packet. This results in slower throughput, but isn't a show stopper.

The bigger problem is that since the microwave oven doesn't listen before turning on its magnetron, it tends to "stomp on" your WiFi signal occasionally. This, combined with the fact that the majority of IP based communications is TCP (and TCP sees every packet loss as congestion, causing it to slow down for the next few-to-tens of seconds), results in more throughput loss than is strictly related to the number of packets "stomped upon."