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How Best To Deal With WiFi Interference?
marciot writes "I live in a condominium where I get interference from my neighbors' WiFi. I understand that 1, 6 and 11 are the only non-overlapping WiFi channels, but how does this translate into real-life best practices? When you must overlap, is there a 'good' way to do it? With nine access points, for example, is it better to have three APs each on 1, 6 and 11, so that each completely overlaps with only two others? Or is it best to distribute those APs across nine channels such that they only partially overlap others (but potentially overlap more APs in total)? Do use patterns affect interference? For example, is it best to overlap a channel with multiple APs that rarely transfers data, or to share a channel with one person who downloads torrents 24/7? Does maximum data rate affect interference or robustness to interference? I found out by accident that setting my access point to '802.11b only' mode appeared to give me a vastly more reliable connection that leaving it in 'mixed 802.11b/g.' Is this a fluke? Or does transmitting at 10 Mbps when everyone else is using 54 Mbps (for their 3 Mbps DSL pipes!) give you a true advantage?"
Increase the power. Then only your neighbours will have interference problems.
Go back to wired, if you can. Really, you will enjoy the speed increase.
Worked for me. Don't need MIMO-compatible clients to get some benefit either.
Also, careful placement of your hub can help - minimising obstacles between the hub and the target devices, away from sources of interferece, that sort of thing.
If all else fails, use a cheap mimo hub as a repeater.
The 5GHz band has been basically forgotten by the mainstream. This is your chance. Equipment supporting 802.11a is a little bit more expensive and 5GHz doesn't work so well through walls, but other than that it's pure upsides.
Finally! A year of moderation! Ready for 2019?
I detect five AP's here, mostly from my neighbours and I still have a really good connection with my own wireless router. I haven't had a problem with interference at all, even when other PC's working in the same channel.
All the AP's occupy another channel (except 6), so the four channels I see are 1, 4, 6 and 9. My own AP is also in 6. So I guess the best solution is to spread them.
Also, and I don't know wether I could work, but you could use channel 64 ( 5.32 GHz ). Most likely, nobody is using that one but maybe your router will not support that. I know mine does.
As long as there are slaughterhouses, there will be battlefields.
If there's lots of 802.11b/g networks around you on the 2.4ghz band, and probably a lot of other 2.4ghz non wifi equipment (lots of wireless cameras use an analog transmisssion on the 2.4ghz band for instance), why not try using 5ghz 802.11a instead?
I can't detect any 802.11a networks here other than my own, so i get much better performance than on the crowded 2.4ghz bands.
http://spamdecoy.net - free throwaway anonymous email - avoid spam!
They will increase the signal power you transmit in a particular direction. They will also reduce the amount of power you receive from your neighbour. Be careful that the directional antenna's don't cause you to exceed legislated limits for EIRP.
As others have suggested, MIMO will also help your cause. MIMO resolves antennas in space, which means that once the MIMO receiver has completed its channel measurements it can reduce the level of interfering signals based on their physical location.
You can't trust what you can see in the wireless network list to be an accurate representation of the noise level.
As another poster pointed out, the re are plenty of other devices that mucks up the signal in a condo. For instance, in my previous flat some caring neighbor bought a wireless surround system and since he was on the dole he pretty much watched TV all the time he was awake. And his sleep pattern was plaid.
The big problem with these automatic systems is that some of them will dynamically allocate a channel for itself when it is turned on and any channel you have previously chosen might be garbage now.
You can find autodetecting systems for wireless, but you might have to dig around a bit to find them.
Me, I use to hop channels and instead of trusting the channel strength and such I run a ping to a known host outside for each channel and then select the one with the least interference. But if your neighbor gets a noisy microwave or an anarchistic stereo, that could become a rather tedious hobby.
You can minimize interference, but don't expect too much.
First, I don't know what type of antenna's you use, but escaping from vertical polarization (which is 'default'), to horizontal one.
Difference in signal level between these two are 20 dbm. So, if you'r getting signal level from your neibh. -70, you will be getting -90, which will greatly improve your wifi stability.
Next, use channels that have lesser bandwidth consumption. It's not important how many ap's are on one channel, it's important how many data frames are going in and out on that channel.
I tested few days ago, my wifi nodes are receiving data from 3 channel bellow/above me, so cuz I use 11, that means I get data from channel 8, but not from 7 that much. Some packets get through, but that's nothing. Which means, if there's traffic on channel 6, you can safely use channel 9, and you won't feel interference blocking you.
Changing data rate, means changing signal modulation. If you use G or A(if you can, use 802.11a), OFDM modulation kicks in, which from my experience deals better with noise. Latency is far more better then on any modulation of B.
So, try putting your devices on G, then fix the rate to 11mbps.
Basically ... there's no real escape from noise. I'm dealing with it for years now, and I'm getting sick of it ... even polarisation changes aren't effective anymore. That's why, I recommend to switch to 802.11a, there's more then 30 non overlaping channels.. or go above/bellow frequency range. Like .. channel 15 on 2.4. It's possible to do.
ok this is not legal in the USA, but it doesn't require you buying anything new. which is why I like it.
1. Flash your wifi equipment with firmware meant for jap versions. that enables the 2 extra channel's above ours.
2. ???
3. PROFIT!
Then you can use channels 12 and 13, which will have a touch less interference
Hack your neighbours access point, turn wifi off and change all the passwords. Bonus points if you can upload custom firmware with different factory password so that even reset doesn't grant them access.
This
From my sofa, iStumbler shows 15 different networks, all at 2.4Ghz. Switching to an AEBS with 802.11n at 5 ghz made a huge improvement for me. YMMV.
802.11n also supports the 5ghz band.
Oh, wait, no it doesn't...you have to guess.
No sig today...
I spend a lot of time in hotels. When I have problems getting WIFI was it always form interference. I have solved the problem by using external USB adapter (with a 12ft USB cable). Relocating the antenna (adapter) is usually all that is needed to solve the problem. In extreme cases I need to use the "foil sheet". I keep a sheet of aluminum foil in an 8.5x11 plastic sleeve in my laptop case. The sheet will block WIFI from one direction, and make a USB adapter that is directional.
What's the reasons for using the older "A" (5GHz ODFM) technology instead of the still-draft (2.4/5GHz ODFM with MIMO) technology?
I've googled and saw many "G vs N" articles, and some technical info on the 5GHz bands, but ... let's just say, one good explanation from an experienced Slashdot writer, is far better.
Put 3 access points on channel 1.
Put 3 access points on channel 6.
Put 3 access points on channel 11.
Nothing at all inbetween as that will destroy the communication on these channels.
If you put the wifi-ap's on the same channel, they will recognize each other and only transmit when the medium is free. Thus the packages will get through although there are some negotiation.
If you spread them on channel 1,2,3,4,5,6,7,8... they will not be able to see and talk to each other, they will only see high background noise. Thus they will start to transmit and really interfer with each other. Large packets will all the time be destroyed and require re-transmission which does not really help up the bandwidth problem at all.
Try to use the highest common standard all basestations/clients understand as they deploy more advanced protocol techniques.
I don't know exactly what a 'condominium' is in America but if running ethernet isn't an option it might be an option to try a homeplug network device?
I have my ADSL router downstairs but all my PCs upstairs with 2 x 200mbit Devolo Homeplug devices taking the ethernet through my power sockets and I've been much much happier than when I tried to WIFI to downstairs.
Get Homeplug devices with good encryption and make sure you set it up to use it and you'll do well.
the dude asked how he can optimise his existing wireless solution - not whether he should buy new wireless hardware or switch to a wired network.
(clearly im not answering the question either... but at least im not karma whoring and trying to pose as an answer)
Example: Netgear WNHDE111
Bonuses:
--Whizzmo
Talk to your neighbors. Pick the AP with the highest wattage, unplug the rest, grab a 15dbi omni, form 1 single larger network, and everyone share 1 internet connection. You'll all save a few bucks too.
How much better? If you're using one fifth of the bandwidth over the same channel, you can withstand a noise level that's five times higher. At least in theory.
If you don't need the bandwidth, just use 802.11b.
Reality is the ultimate Rorschach.
I thought that IEEE 802.11n used OFDM to help prevent this sort of thing from being a problem?
XML is like violence. If it doesn't solve the problem, use more.
The answers are generalities, since each situation is unique. As others have already said, the real solution to your problem is spelled "5 GHz." However, if we add the condition that you must remain at 2.4, here we go:
In general, the former is best. Most site planning is done this way, with the (I hope obvious) additional condition that the cochannel APs are physically separated as much as possible.
Yes, use patterns affect interference. In general, the former is best, since the channel has more idle time available for "your" data.
Maximum data rate has a major effect on interference robustness. As you've found, in general lower rates can tolerate higher levels of interference than can higher rates. More explicitly, there's a range of interference levels (low) at which both will work. Above this is a range of interference levels (medium) at which the low rate will work and the high rate won't. Above this is a range of interference levels (high) at which both will not work. What you've found is that you're in the medium category, in which your system will work at 10 Mbps in the presence of interference from your neighbor's 54 Mbps system, but your system will not work at 54 Mbps in the presence of the same interference.
A second phenomenon may also be present, one specific to the 802.11g standard. To make it backwards compatible (i.e., so that an 11g AP would work in a network having one or more 11b devices) the 802.11g folk mandated a behavior in which an AP checks first to see what's around it. If it hears an 11b device, it downshifts into 11b. This, of course, slows the entire 54 Mbps network down to 10 Mbps. You may be experiencing a side effect of this -- all the checking and upshifting and downshifting takes time, so if 11b devices come and go frequently (as they might in your scenario) the net throughput can be less than if one stayed at 11b speeds in the first place.
One of our client wanted to have wireless clients from the start. It was easy, but now the number of clients are spreading like rabbits and currently I have to use 5-6 AP to cover the whole area.
What is the best configuration in this case?
Love many, trust a few, do harm to none.
Get ath5k or rt73, linux, and run off-frequency. I can run at 2192mhz w/o problems w/ rt73usb right now... just don't tell the FCC.
Do you and your neaghbors all need your own seperate LAN's ?
If all you are doing is a bit of surfing, it might be worth knocking on doors and offering to set up an open access point. Of course, some will need a private LAN of there own, but most will probably jump at the chance to split the ISP bill with you and reduce the interferance.
Remember, they will be suffering with crap wireless just as much as you are. If you are a geek, you will be the one in the best position to help everyone out.... and meet your neigbours for a beer in the process
Anyone quoted by a reporter knows how little they understand
Don't believe what you read is the truth.
In the first part of my comment, I said, "...the cochannel APs are physically separated as much as possible."
This, of course, is true only both APs are part of your LAN, and isn't really appropriate here. (*sigh* You can take a horse to "Preview," but you can't make him think.) In your case, one might consider the opposite strategy: Place your cochannel AP as close to your neighbor's as possible (e.g., on the other side of the wall from his), and use a directional antenna (pointed into your place, of course). This would tend to produce a constant signal-to-interference ratio throughout your place, hopefully high enough to be useful, while not producing interference in your neighbor's place high enough to corrupt his network. I guess while you were buying directional antennas you could buy one for your neighbor, too, which could only help matters.
Of course, the contrarian view is to place your AP against the wall with its present antenna, and force your neighbor to worry about interference, buy antennas, etc. :-/
Use NetStumbler http://www.netstumbler.com/ to determine the signal strength of all the other access points to see if any of the channels will have low interference. Although you may see lots of access points, they could be very feint signals because beacon frames are short at about 50 bytes (compared to 1500 for a typical data frame) so they're a lot easier to receive. The strong signal from your own apartment/condo should be able to drown out the noise from all the feint AP signals but if the people next door to you have an AP then it could slow you down so that's why you need to check for strong signals with NetStumbler.
Title correction: Pick the one with the LEAST interference
Connect to your neighbor's unsecured wireless routers, log into the web administration panel with the default password, and set them all to channel 1. There will be one neighbor who secured his, and he will be using channel 11. Set yours to channel 6. No more problems!
Go green: turn off your refrigerator.
Install a bigger antenna. Oh 12 db gain should do nicely.
Nuff said.
As previously mentioned, try switching to 5GHz if you can. It won't go through walls, which means that you need to locate the AP carefully to make sure you have coverage where you need it. But it does mean that your neighbors APs, if they switch to 5GHz as well, won't interfere as much with you.
Run your APs at the lowest power possible to still cover where you need, and have your neighbors do the same. Many people want to push the power up and up when they have problems. But that just leads to an arms race and more interference.
I only use the non-overlapping channels.
I use 802.11g on 2.4GHz, using the theory that sending the data in a smaller time will decrease the overall contention. However, 802.11b may be more robust.
If your systems have a setting for "Interference robustness", try using it.
Try setting the RTS threshold, possibly to a very low number.
You might want to try setting up an AP on two or 3 of the non-overlapping channels, with the same ESSID. Your systems *MAY* switch from one to the other if they run into interference.
See this URL for more information on what I've had success with: http://www.tummy.com/Community/Articles/pycon2007-network/
Sean
Sean
Cover all interior walls with tin foil. Seriously. As an added benefit, you will have mirrors everywhere so that you can see when you have left "your barn door" open. It's also great when making out with your signficant other.
Some other things you "could" do (but not as fun are:
1)Use some of that paint that blocks cell phone calls. (works for wifi also)
2)Use magnetic paint (has iron oxide in it) and then put a coat of "normal" paint for the color of your choice.
Didn't I see a post on Slashdot at one point about a paint that mimics a faraday cage? Paint that on the inside of the outer walls of the house...
Mind you a house will never be a complete cage, but it should limit the external noise and minimize the external wireless signals...
I have not actually seen any of this paint on the market but I haven't looked either...
If this is set up in an apartment you may not have this option however (and it wouldn't help at all for anyone living above/below you unless you also painted the ceiling and floors))...
--- When you start with the conclusion that you want, then throw out any facts that don't agree, is it true?
- what are the most busy bands in term of actual usage.
- what is the strength of the interfering AP's.
- what is the actual SNR for your computer in the locations you work normally.
having this information you can use some of the methods above:
- directional antenna
- selecting the correct frequency
- setting the power
changing to a band can be an interesting idea but its more expensive than the others.
Daniel
http://design-to-last.com/
If you're wireless is being difficult and you're unable or unwilling to run cable, think about using Homeplug bridges.
Homeplug is basically ethernet over the power lines in your house. They usually sell the adapters in pairs which act as a bridge. So you could have one adapter in the office with the modem and your access point, and another in your living room going to a switch for your xbox/ps3/wii/laptop. So it basically turns any electrical outlet into a potential bridge point..
I've got two sets of Dlink's DHP-301 and they're fantastic. (It was the first product I'd bought in a long time that 'just worked'). Most adapters also support encryption if you're worried about anyone watching the traffic since you might be on the same electrical circuit (I don't remember what exactly its called).
The obvious solution is to line your walls with tin foil, of course! ;)
-Ghostis
Computer Science is all about trying to find the right wrench to bang in the right screw. -T.Cumbo?
If you have Linksys WRT54G wireless router and have flushed it with DD-WRT Firmware, you might be able to increase Xmit power of your wireless transmission to effectively suppress any interference. Now, the idea is to not go overboard and piss the neighbors off by making it so strong that it suppresses reception of their own signal in THEIR own apartment.
Although it's not a long term solution if masses of people follow your lead I can tell you moving to something OTHER than the 2.4Ghz spectrum range made a big difference for me.
Netstumbler is a great little program. I'm not sure how the author of the article could control how other people set up their routers (yes he could ask but would people actually cooperate?), so at least he could pick the channel with the least competition. A technically inclined person could also install this and increase the transmission power over the default. Swamp your neighbor's wifi signal! Impress your friends!
I have not actually installed or used this, since my wife would kill me if I accidentally bricked our router.
I have mod points. The reign of terror begins now.
...because there won't then be a wireless access that you can change their passwords with!
The Cisco 1200 series I use put out 100mw at 802.11b rates and only 30mw at 802.11g rates. This partly explains it's better range/penetration.
When I install WIFI networks for hotels I generally use 802.11b radios in the Cisco APs for this reason (there Internet connection is way slower than 802.11b anyway).
In the field I frequently find that locking the radios into 11 or 5.5mbps rates will improve connection stability.
Other things to try, low rts threshold and a low fragmentation threshold.
See if neighbors will coordinate, put all the 802.11b stuff on one channel and use the others for 802.1gG stuff.
I can see a dozen 802.11g networks around us, but I'm the only a/n 5GHz network that I can see. It doesn't penetrate walls as well, but that's good enough in our condo. (The upside of lower penetration is that it's harder to intercept, and we interfere less with any neighbors who might move to 5GHz.)
We use a/n because my first-gen Intel Macbook does a/b/g but not n.
In no particular order
The best way to avoid interference is to not use wifi at all. You can get wifi around the place if you use a ethernet-over-power adapters. This nice things basically allow you to plug in an ethernet cable into your outlet at the end by your router/switch/firewall/whatever then at another outlet by where you will be plug in your laptop. This gives you similar freedom of movement as wifi with the trade-offs being no wifi interference for goood throughput at the expense some reduced mobility.
If there is no way to keep all involved APs completely isolated, you want to consider who is using the most frequent bandwidth and how many clients are talking to each AP. There is only so much RF capacity and try to the avoid the more populated channels if possible. If your AP and client(s) can see the other APs and their respective clients that will be the best so everyone can talk in harmony otherwise if your AP can see you and other clients but your client cannot see the others then they are likely to step on each other without even knowing it.
Another thing you can do that will potentially make it a little more cumbersome to use depending on how you are actually using your wifi is to get directional atennas instead of omni antennas at the AP and your client. This will help to extremely reduce the amount of the interference you and your AP will see as you can only "see" the interference if it is coming from the direction your antenna is directed vs thru the walls to the side or what have you. This obviously does not allow you to as easily just roam around your place.
If you can get your APs and client(s) with more powerful transmitters and antennas with higher gain you will also be better off.
Or you can coat your neighbor-facing walls with the anti-wifi paint
ZERO ZERO ONE ZERO ONE ZERO ONE ONE! Just brushing up for my next big invention: Ethernet over Voice (EoV)
I found out by accident that setting my access point to '802.11b only' mode appeared to give me a vastly more reliable connection that leaving it in 'mixed 802.11b/g.' Is this a fluke?
No, because the 802.11b signal requires less bandwidth than 802.11g. Since the channel spacing remains the same, this means that you've got more "space" in a given channel to fit that bandwidth.
A not-totally-inaccurate analogy would be that 802.11g is like writing smaller to fit more information on a page - sure, you can write more in the same space but it's harder to read, especially in a poor light or if the ink is faint. If you use 802.11b then the writing is bigger, and easier to pick out in a noisy background.
I do not respond to cowards. Especially anonymous ones.
set up a WDS network and put and put a bunch of routers everywhere?
CSMA lockdown!
Only run 3 networks on channel 1, 6 and 11 (and 14 if you want, it is actually spaced as far as 1 is from 6 etc etc, regardless of channel number! Although may be illegal, unless in Japan). Running more than one AP on the same channel in the same area will cause CSMA lockdown and you will be disappointed.
Changing your beacon interval to 101 keeps your wifi networks beacons perpetually out of sync with your neighbors wifi noise. The problem every one is having is errors like unable to find access point, connection error, and being dropped from your access point. This single change makes all of the other tweaks esoteric and uneccessary. Access points know how to deal with noise and interference. Access points do not know how to deal with an excessive amount of lost beacons. And they shouldn't.
http://freegnu.blogspot.com
http://identi.ca/freegnu
Leave the WIFI on, fix the channel to the one you don't you. They won't replace it then. But then for the finishing touch:
Shart using it to share movies and music and let the MPAA and RIAA go sue them into bankruptcy.
Fight Spammers!
Don't forget there ARE non technical solutions.
-- Programming with boost is like building a house with lego. It's a cool but I wouldn't want to live in it
With all the interference at 2.4GHz or possibly even 5GHz, a better solution would be to rely on light waves.
Ok seriously, go with 802.11a or 802.11n operating in the at 5.0GHz frequency band.
w00t
Not necessarily. Given that this is an apartment, the user will be in close proximity to his AP and many others. It is possible that boosting his power (in the presence of other interference) could simply overdrive the Wifi receiver in the laptop (driving it into compression). This creates an even higher noise floor (resulting from third order intermods) which desensitizes the receiver (and will of course reduce throughput). This will happen to even the most linear, low noise amplifier if you drive it hard enough. A properly designed receiver should have enough analog attenuator range to prevent this, but it could be a crappy/low cost design.
Most plebes don't know how to tweak their north american firmware/drivers for channel 14, but us 133t /. d00ds do. The hardware all supports it (tell it you're in Japan), and 14 is far enough from 11 that you're only getting a bit of overlap, and only on one side.
Just don't tell the FCC.
Do daemons dream of electric sleep()?
In my old apartment my laptop offered me the choice of 45 access points to connect to, and my wireless still worked fine - I did set the channel away from the highest signal access points...
Is a different band.
Chicken wire tied to a ground! Faraday cage bitches.
I live in an apartment. I have had a WWVB 60Khz Nixie clock for a couple of years. Early October 2008, it quit getting time updates. Seems there is enormous nighttime interference out there these days. I have a different audio WWVB radio and that now only plays static. Sometimes in early morning just after daylight, things are pretty good. I suspect its from nearby lighting assemblies on a nearby interstate.
HELP!! Any suggestions for a RF detector that can target my 60KHz interference? How to make one; a) that shows direction and b) detects 60Khz?
Also I need to get my local radio club to help with an oscilloscope to create a better 60Khz tuned antenna. The current tiny antenna is directional and in a non helpful square box.
Thanks,
Jim
You can't really reduce or eliminate interference very well without a lot of effort (like special wall materials that block wireless signals), but you can work around the interference well enough by using a wireless spectrum analyser to determine where the interference is the weakest. Me, I use a very cheap (and limited) spectrum analyser like device called 'Wi-Spy'. This is basically a wireless reciever tuned to the same frequency range used by 802.11g wireless networks, combined with software that graphically illustrates the wireless signal strength throughout that spectrum. Using the data gathered with this tool I was able to configure my wireless router to use a channel which had the least ammount of outside interference in my area. This has worked great for me.
- James
cause most routers default to channel 6, so move yourself to 1. Seriously.
I have been getting a lot of calls for this recently. I had a guy who was 6ft, LOS from his router w/ interference issues. We bumped him down and he's been fine ever since. I had another client who everytime they picked up and turned on their wireless phone, the internet would drop, and when they reconnected the wireless network the phone would drop cyclicly. Same issue, except, they had about 13 discovered networks using the "windows" tool. Now he makes phone calls, uses the internet, and we lined his walls w/ lead paint from china to seal in the signal.
(That last bit was a joke)
How much is your data worth? Back it up now.
How Best To Deal With WiFi Interference?
Find out where the bastard lives and what equipment he has that's causing the interference, and then send a couple of your boys around to help him take it apart.
The higher the technology, the sharper that two-edged sword.
To answer the question, there are two things going on.
One is the interference from the transmissions, which lowers the signal-to-noise ratio if you are on the same (or an overlapping) channel. The lower that gets, the more errors and the worse your performance. So to combat that, you can either use a different channel (1, 6, and 11 are probably the best to try, but you could just measure your performance on all of them and use whatever is best), or as you said force the use of a lower data rate (a lower data rate is more tolerant of low signal-to-noise ratios). Obviously there's a trade-off between having a more reliable connection with a lower data rate and having an unreliable connection with a faster data rate.
The second issue is channel reservation. Because of how 802.11 works, you can end up with a situation where one user is getting an unfair amount of bandwidth by basically telling the other users to be quiet. There are various settings which you may have access to depending on your router, such as the RTS/CTS threshold (try setting it to a very small value, may be better or worse depending on the situation), the backoff window size (which tunes aggressiveness), preamble (a long preamble helps when there is interference), etc.
So yes, just try different settings and you should be able to get an improvement.
The Tomato firmware lets you scan each channel and identifies all wireless networks (including hidden w/o ssid) before you pick the channel you will use.
Among many other seriously cool features. You didn't see fit to include a link to the Tomato firmware so there it is. Check the list of supported routers to make sure yours is in there, and then flash it in. Blows the stock firmware out of the water.
The higher the technology, the sharper that two-edged sword.
If all the radios around you are tuned to non-overlapping channels (1,6, 11) and you look "down the spectrum through time" you have 3 distinct bands that all the radios can tune and demodulate easily. When people use an intermediate channel like 3, it doesn't get them away from the channel 1 signal so much as it fills in the spectrum that makes the neighbor channels tunable. Intermediate channels just interfere with 2 channeles, it doesn't get you clear of either. Tuning is difficult when the spectrum is filled out without separation, it's like trying to listen to a distant flute concerto while you're in the shower.
The best way I know to really tune your wireless environment: Run Kismet on a linux laptop in one window, and run Wi-spy Chanelyzer in a vmware unity windown next to it. The USB wispy works perfectly in a virtual machine, and you can correlate the Kismet traffic to the radios you see in the spectrum graph. Makes it real obvious what the problems are, and what the best solutions will be, assuming you have good solutions available. In a crowded environment, the unregulated microwave spectrum can be a noisy mess, but until you see what a radio sees, your actions are likely to be little better than random changes.
By the way, you can't really trust your wireless card to give you a good picture of the spectrum. It misses all noise that is not its own protocol, it tunes 1 channel at a time and scans and samples slowly, and even when it recognizes a signal the strength that it reports to the driver may not be calibrated in a meaningful way.
If you're in a condo with microwave-transparent walls and lots of neighbors, your best answers are
1) Wire it and
2) 802.11a or 5Ghz 802.11n. These have more channels, penetrate walls more poorly and your neighbors are less likely to be on it -- especially the 5.1-5.2Ghz channels, which are not used by cordless phones.
Yeah, the equipment costs a bit more. But actually having useful wireless is worth it.
In any given modulation scheme used in 802.11, the lower speeds are more resistant to interference than the higher speeds. 802.11g uses two different modulation schemes, DSSS and OFDM. Theoretically, OFDM (used only in G) is more resistant to interference than DSSS (used in B), so reducing the speed but leaving the AP in G mode should do better than putting in in B-only-mode. This depends on your AP supporting that feature of course.
If you have to share a channel, it's far better to share one with an AP which is rarely used; most of the time, such an AP will not be transmitting anything and the spectrum will be available.
With 9 APs, you're pretty much screwed; no matter what you do you'll have major overlap. With 4 APs, it has been found that 1,4,7, and 11 works reasonably well, but you'd need control of those other APs.
Other answers (which may be illegal, immoral, impractical, or fattening)
1) Use higher-power APs (not hacked, but those designed for higher power) and cards.
2) Use high-gain directional antennas (a high gain omni may be practical on a single-floor condo)
3) Use channel 14 (illegal and generally requires firmware hacking to get 802.11g on it, as that's illegal everywhere)
4) Microwave-absorptive coating on walls/ceiling
5) Hack into neighbors APs and move them all to channel 1, then use 11 yourself.
Change the frequency you're running on to one that your less-technical neighbor can use.
Problem solved.
I want to delete my account but Slashdot doesn't allow it.
If you live in a condo, there's a condo association.
If there's that many APs, maybe the association should look into building-wide WiFi. Depending on what everyone is paying now, it might be cheaper than one-by-one solutions.
I'm not sure how you deal with inter-unit security. Ideally, you want each unit to only be able to see other computers in that unit, but let someone wander the building with their laptop and still be on "their network." I'll bet there's a way, though.
The preferred solution is to not have a problem.
None of you come up with the best solution, albeit somewhat illegal.
Run Japanese firmware at channel 14. Low interference there.. I should know :)
This is the only real world solution I had, unfortunately I don't know how legal it was.
I was in a Apartment building, and all channels were being user/overlapped. I kinda cheated, probably was breaking law too.
My router had a country/location choice, I choose Australia, that game me I think channel 12 and 13. I choose the unlucky 13. All was well.
Do at your own risk though.
There are ISPs that are happy to have you share bandwidth. Another poster mentioned Speakeasy; I'm using sonic.net. Some of them have deals where the roaming user pays for an account and the wired user gets credited for it, and typically the ISP gets to sell you a faster DSL link so you're all happy.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
Thanks - that was a useful post.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
As previously mentioned, try switching to 5GHz if you can. It won't go through walls, which means that you need to locate the AP carefully to make sure you have coverage where you need it.
Agreed. The 5Ghz spectrum always seems so open and free. Not to mention that 802.11a allows for dozens of *discrete* (read: non-overlapping) channels.
To help with the "not going thru walls well" problem of 802.11a, I've found that a simple reflector placed on every antenna of your WAP can boost your signal by 10 - 12 dB (in a single direction) -- This is enough to make it through walls of a condo. It also helps reduce noise coming into your WAP as well as pick up the signal from your devices better.
They're very simple and cheap to make, too. Instructions can be found at the Free Antennas website. The designs work great for all Wifi standards.
If you didn't, you could go to jail.
Of course, it's not like anyone will catch you, unless you do something like confess your crime on the public internets.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
If your condo association and your internet provider can agree to terms, your condo association can lay out a mesh network all on the same channel.
Whether this makes sense or not in your situation will depend on many local factors, both technical, economic, and political.
I don't think the FCC will let your condo association prevent members or their guests from using the same channels, but if you do it right very few will need their own wifi and those that do can use the other channels.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
InSSIDer is better and updated. NetStumbler hasn't been updated for years. I recall it was due to money. :(
Ant(Dude) @ Quality Foraged Links (AQFL.net) & The Ant Farm (antfarm.ma.cx / antfarm.home.dhs.org).
Channel Deployment Issues for 2.4-GHz 802.11 WLANS
an investigation by cisco into some of the details of interference. over my head in places, but what i followed i found interesting.
in my apartment there were enough people on the default channels that i was unable to connect to my ap from a few feet away. i changed to a channel that looked empty and have had decent connectivity since. i didn't do a follow-up investigation, but came away from the experience with the feeling that it's better to try to fit in the spaces between when there are a lot of people on the defaults.
n.b. this is anecdotal and i am not a wifi expert by any means...
Get yourself a ham license, some special adapters for your AP from eBay, a 1 or 2watt bi-directional amplifier and a 15.4 Db gain omni antenna. Connect the AP (adapters) to the amplifier to the antenna. Set the AP on channel 1 (just inside the ham band), put your callsign in the AP SSID and 'ave at it. You will no longer have any problems but your neighbors will. If the peasants start an uprising have a trench broom at the ready.
When using my Inverter microwave, the strong WiFi signal is lost. I took a GE Inverter back because of this, and got a Panasonic, but the Panasonic would up also killing the WiFi. Yikes. It is probably not microwaves that are escaping from the oven, but probably a bunch of EMI from the inverter. Surely not ionizing but nasty enough to wipe out the WiFi.
Yah, instead of whoring for Informative or Interesting, you are whoring for Insightful.
Myself? I am going for Funny, here.
No, you can definitely sharpen these enough to be lethal if you're a ninja.
I am not devoid of humor.
Faraday cage
This post is LAW where prohibited by VOID. Prosecutors will be violated.
It's easier to stop creating problems than it is to avoid troublemakers. Tragedy of the commons? perhaps. But, if you were to get your ham radio license and transmit at maximum permissible power using ham modes on 2.4 ghz, you could jam the whole neighborhood. Note that doing this intentionally would be illegal.
So, to co-exist harmoniously, what everyone needs to do is this:
1) Filter the broadcasts that Microsoft operating systems are making over the next. They make a lot of noise, and the leaking of such information could be considered a security risk.
2) Turn off your SSID beacon, or set it to broadcast infrequently. Perhaps once per second. Beacons are sent at the lowest data rate, see below.
3) Not quite sure how to accomplish this with everyday routers, but most of the time you don't want to be connected at less than 11 mbps, so why even accept 1 mbps connections? Sure, the signal goes farther, but at a reduced efficiency - which means, it takes longer to send the same amount of data, which means that the band is more congested.
4) There are long and short preambles, sometimes these are settable. But I am going out on a limb here, I can't remember much about the preambles, but shorter would be better.
I know this is 'you should' information, and not a really concise 'how-to', which is what you and your neighbors need. But you're asking for free advice, so maybe you can do some in-depth research and find out how to implement the above methods. Remember, your neighbors are probably suffering too. If you can get everyone in the area to run a router with openwrt on it, then you'll have access to all the settings you'll need to minimize interference.
If you have a FCC Amateur Radio license, then your use of the radio trumps the use of others. They're broadcasting without a license on the basis that they cause no interference to any other signals. They have the burden of fixing any interference problems.
So get your ham license and then claim interference. They can't refuse legally to change their transmission channels if you ask it.
Fascism trolls keeping me up every night. When I starts a preachin', he HITS ME WITH HIS REICH!
Clearly all you need to do to protect yourself from wifi interference is to surround your entire house/apartment/unit with appropriately sized copper mesh, duh!
Mike gave us that one before wifi was even invented! Course, there might be a couple of small engineering challenges in implementation...
perhaps I need more sleep...
err!
jak.
I can't answer all your questions, and it seems no one else has either.
However you already know that APs cooperate when on the same channel, so the best thing you can do is get your neighbours to change to non-overlapping channels. I have done this by visiting my neighbours, explaining the problem and helping them to change channel. Result: reliable connection. You might prefer to get the concierge to advertise good wifi practice.
If you end up configuring all your neighbours then you get a chance to distribute signals intelligently: ie, reserve two channels for big downloaders, and the other reserved to ordinary users (even a single channel is more than enough for 20 people browsing the web).
Non-standard wifi and N: generally speaking it is best for these devices to be configured for g or b and disable the fancy feature which stomps on signals and acts like interference. They will do better not just you. Disable anything out of the ordinary.