How Best To Deal With WiFi Interference? 451
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?"
Hack your AP (Score:5, Funny)
Increase the power. Then only your neighbours will have interference problems.
Re: (Score:2, Informative)
Actually, you're wrong. Increasing the transmit power will decrease your S/N ratio. It's actually better to lower the transmit power a bit, since there will be more signal and less noise.
Re: (Score:2)
Re:Hack your AP (Score:5, Funny)
magic.
Re: (Score:3, Interesting)
More likely the amplifier used was cheap, and with more power came more wave distortion.
Think of a guitar amplifier - put on the overdrive and it sounds very different. Now try to get the original signal from that wave... good luck!
Cheat (Score:4, Interesting)
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.
Re: (Score:3, Informative)
Re:Hack your AP (Score:5, Funny)
Homeopathy.
Re:Hack your AP (Score:5, Funny)
Homeopathy
Hey, magic [slashdot.org] had already been suggested!
Re:Hack your AP (Score:5, Informative)
Because when you increase your transmit power a bunch, all your neighbors' wifis become useless and they unplug/return them. *ding* Many of your sources of interference go away and you can turn your power back down, yielding a more favorable s/n ratio.
But on a lighter note, from one who works in radios a lot, increasing your transmit power is only generally useful if BOTH ends of your hardware do it. It's totally useless to be able to receive the AP's signal clear as a bell if the AP can't hear you back. In many cases, the AP already has better power and a better antenna anyway, so if you could only bump one end of the conversation, you would probably get more mileage by doing it at the laptop/desktop end. I've seen people astounded that adding an amplifier on their end didn't magically improve their set's range, because while others could now hear them whereas not before, they could not hear their replies.1
But all other factors being equal and in marginal cases where a small improvement would do, the station that is closer to the interference needs the OTHER station to transmit higher power, to make it over the nearby interference that is jamming its receive.
Lastly, trying to move the units to different locations or reorienting their antennas can yield amazing results. Or improve your antenna(s). I was recently at a customer's house and he had a desktop upstairs on one end of the (large) house and a base downstairs in the other corner and was having problems. His card happened to have a removable duck antenna and I swapped it out for the large mag mount I carry in my bag, and he got signal fine then. Those ducks on the back of PCI cards in slots on desktops have terrible range because the metal case is so close to the antenna. (and in his situation, it was physically blocking line of sight to the base)
And don't underestimate the loss of signal in coax at these high frequencies. Running an antenna to the roof to get a good outdoor signal will butcher the signal more than a higher antenna ever could help. If you want to get the antenna a good distance from the computer, get a USB wireless stick and move it and the antenna. Run a long USB cable to the computer, since digital signals do not degrade over distance. (tho USB itself has distance limit cutoffs) You can get a self-contained 20+dbi gain directional antenna with integrated 802.11 wireless transceiver on ebay for under $150, and I've been able to run USB for over 50ft with good cables.
Re:Hack your AP (Score:5, Funny)
Lastly, trying to move the units to different locations or reorienting their antennas...
For example, getting a long antenna cable so you can locate the AP's antenna right next to your machine(s) should work great.
Re: (Score:3, Funny)
> But on a lighter note, from one who works in radios a lot[...]
Wow, you must be really small!
Re:Hack your AP (Score:5, Informative)
What's going on here is that:
a) Clients are still transmitting at normal power, so the AP can't hear the clients.
b) Many APs are built with circuitry that doesn't like to be pushed very far beyond factory defaults with transmit power: the signal really does get "noisy" at high power settings.
Too bad the default Kamikaze 7.09 OpenWRT firmwares kills any and all (six!) WRT54GL routers that I put it on (previously ran White Russian brilliantly). Apparently flashing these things with said firmware out of the box defaults the output power to 150mW (default is 28mW), and fries the transmitter circuitry. There's no option to fix this, you're supposed to install a package onto the router called "wl" and hack a call to this utility in the init script for yourself that sets the output power at bootup.
Re:Hack your AP (Score:5, Funny)
Too bad the default Kamikaze 7.09 OpenWRT firmwares kills any and all (six!) WRT54GL routers that I put it on (previously ran White Russian brilliantly).
You didn't learn after the first five?
Re:Hack your AP (Score:4, Funny)
Too bad the default Kamikaze 7.09 OpenWRT firmwares kills any and all (six!) WRT54GL routers that I put it on
Did you expect something named Kamikaze NOT to kill itself?
Re:Hack your AP (Score:4, Interesting)
Re:Hack your AP (Score:4, Funny)
Incorrect.
I took an AP and cranked it up to max power on 802.11g channel 1. (way over limit) and left it running that way for 2 months. I had my second ap set for the other end of the band and lived with crappy signal during that time.
when I revisited it in 2 month and I shut down my splattering and jamming AP and did a scan, EVERYONE moved away from the jamming frequency.
So I put my real AP at the jamming frequency and now have AWESOME signal.
you just need to presuade the neighbors to change their settings away from yours. you can ask, or you can force their hand by making them not have any Wireless connectivity until they change it.
Re: (Score:3, Interesting)
wouldn't it be easier just to change your own wireless AP setting? making everyone else change their frequencies is just being an asshole. if everyone behaved like that, then none of you would ever get a decent signal.
of course, the best solution is just to:
a.) consolidate your WiFi networks so you have 1 or 2 shared WiFi networks rather than 10-12 different competing networks. that's one advantage to having municipal WiFi/WiMax--there's less crowding of the spectrum. additionally, you have greater wireless
Re:Hack your AP (Score:4, Funny)
Or an old micro-wave oven that you run with the shielding off.
Should do the trick nicely.
You have to wear gloves and googles though. Remember that power tools are dangerous.
Re:Hack your AP (Score:5, Funny)
actually I found that since my neighbors had NO idea how to secure their AP's I went into each one with the default password (most were Linksys) I changed their frequencies all to 11 and made mine the loan AP on 1 - worked great !
Re: (Score:3, Interesting)
Re: (Score:3, Funny)
Weren;t you trying not to loan your AP?
Solution (Score:4, Insightful)
Re:Solution (Score:4, Funny)
He lives in a condo. Going to wired may not be practical.
So, I recommend he place his router in a Faraday cage. His interference problems will be over!
Re:Solution (Score:4, Informative)
Re: (Score:3, Informative)
Re: (Score:2, Interesting)
And in case TP cabling is impractical, consider a network over powerline solution like HomePlug. Frankly, if you have a problem with your wireless being slow and unreliable, you shouldn't be using wireless. Wireless is great for intermittent asynchronous low bandwidth communications, like the occasional mail or web page on a laptop, but being slow and unreliable is pretty much part of its nature in many cases.
Re:Solution (Score:4, Interesting)
Right. I also gave my wireless up and go back to wired.
I live in Hong Kong where ~500sq ft apartment, 30+ floors residential building is the norm, I got 20+ visible AP in the list when I turn on the network search. The number does not include AP with SSID hide.
So as you can imagine, there is simply too much thing squeezed in the frequency and making stable wifi connection almost impossible. I then shut my FON, went back to the 1Gbps wire I had.
Re:Solution (Score:5, Insightful)
Upgrade to N or A and call it done.
in fact I find at a friends place A is perfect as B,G,N are full, but A is an open wasteland.
Re: (Score:3, Informative)
Re:Solution (Score:4, Interesting)
I just run the ethernet cables along edge of the ceiling with tacks, that way my rats don't eat them.
Using cables similar to the wall colour makes the eyesore minimal.
Re:Solution (Score:5, Funny)
You know, some people get fish for pets.
Re:Solution (Score:5, Funny)
i'm pretty sure that his way prevent fish to eat them too ...
Re:Solution (Score:4, Funny)
i'm pretty sure that his way prevent fish to eat them too ...
Fish are pretty dangerous too. The man wants us to believe that all those cable cuts were caused by anchors but those of us who have raised fish know better......
Re:Solution (Score:5, Funny)
Re: (Score:3, Funny)
Re:Solution (Score:5, Insightful)
It should be, yes, but nowadays I see wireless being installed everywhere, even when not needed. I know people who connect their desktop to the modem 10 feet away by wireless. And two months ago I went to a big store to buy a simple ethernet card and they told me "nobody produces them anymore, get wireless".
I have a Cat5 from my living room to my bedroom (65 feet) across the ceiling and it's great, I get incredible speeds in transfers from one computer to the other!
Re:Solution (Score:5, Funny)
Lemme guess: Circuit City?
Re:Solution (Score:5, Insightful)
"And two months ago I went to a big store to buy a simple ethernet card and they told me "nobody produces them anymore, get wireless"."
A classic salestard in action, and yet another reason to shop online.
Re:Solution (Score:4, Insightful)
Hey, wait.. I do that. The AP is literally ~12 feet away from the computer that uses it. 12 feet, mostly vertical.
Seriously, though, If you've only got one or two computers, wires are pretty unsightly, and the only way to get rid of them is a *lot* of work and considerable up-front expense (compared to a chap wireless route) if you don't already have the tools or know someone with the tools. And how many people have fish tape, really.
Get a MIMO hub (Score:3, Informative)
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.
Re: (Score:3, Informative)
There is no such thing as a hub with wifi. Hubs are devices that are "dumb" and essentially just extend a physical wire. Wifi has no wires so the wifi equivalent of hubs would be repeaters. Most consumers have wifi routers though.
Escape to A (Score:5, Interesting)
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.
Not just A (Score:2, Informative)
802.11n also supports the 5ghz band.
Re:Not just A (Score:4, Informative)
Re:Not just A (Score:5, Informative)
that's because N at 270Mbps only works on the 5GHz band, if you have a cheap AP it will only have 2.4 and work at 120mbps. You need a dual-radio, I have a WRT600N and I get full speed. The WRT600N is great: 3 antennas with 3 independent radios. MIMO, N, 2.4+5.8, etc. Plus you can flash it with DD-WRT and get some extra functionality (warning: only one particular old version of dd-wrt gives 270mbps, it's a known bug, I don't know if it has been fixed). I suggest that AP/router hands down. Don't get the WRT610N, while it might seem a little better (610 > 600, right?), it only has internal antennas.
Re:Not just A (Score:4, Interesting)
I have an airport extreme and it supports the 5ghz band, as does my macbook pro (the two are designed to work together) but i don't get 270mb speeds out of it either...
My eee 901 will do 802.11n but only on the 2.4ghz band, annoyingly.
Re:Not just A (Score:4, Informative)
People also would do well to note that, just like hard disk sizes, wireless speeds are a big fat lie.
http://www.oreillynet.com/pub/a/wireless/2003/08/08/wireless_throughput.html [oreillynet.com]
5GHz (Score:2, Interesting)
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.
Re:5GHz (Score:4, Informative)
No reason to go with A, as long as you make sure the N-equipment you buy actually supports 5GHz.
Re: (Score:3, Interesting)
N probably won't become final anytime soon. All the manufacturers promise software upgrades of pre-N to standard-N, and that looks fairly impossible now (except for the companies which get lucky and have something close to their version ratified). If standard-N appears, they have to deliver on their promises, so it's best for everyone if that doesn't happen.
Re: (Score:2, Interesting)
transmitting 802.11a outside at non trivial power levels requires a special licence , in the uk.
Re: (Score:3, Informative)
In France, WiFi is in the Army band. I can tell you that even Army abandonned wavelengthes are always monitored. Some of the WLAN frequencies are not for public usage in some departements. The law say you must stay under 300mW in power, and can't link between networks.
When I was in charge for the maintenance of a local FM radio, a specialised hardware seller put us a 900MHz link transmitter between our studio and the FM broadcast system. It was outside the GSM use, we didn't find any transmitter on this fre
Or channel 14 (Score:5, Interesting)
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.
Re:Or channel 14 (Score:4, Funny)
Re: (Score:3, Insightful)
"Any idea how big the FCC fine is for transmitting on a licensed band without a license? Do they send you to PMITA prison?"
Any idea if they have the time and money to spend sniffing for transmissions that don't step on people who have the slightest way to know they are being stepped on and hence will never report it? :)
Re: (Score:3, Interesting)
"Any idea how big the FCC fine is for transmitting on a licensed band without a license?
Common is $10,000.
Do they send you to PMITA prison?"
Doubt it for just that, and if they did it wouldn't be a PMITA prison but a Federal Prison Camp where there are no cells but dorms instead. Like being in an armed service without weekend passes and you don't have to salute the guards.
Any idea if they have the time and money to spend sniffing for transmissions that don't step on people who have the slightest way to know
Spread the channels (Score:5, Interesting)
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.
Re:Spread the channels (Score:4, Informative)
It might be possible that your WiFi AP has support for Channel 14-- not found usually on US gear, unless you flash the AP with the International Version (hint). The second thing you can do is to get cheapo antennas to put on the AP (~$10 at a local Frys or eBay) to boost the output in a particular direction. My suggestion is to boost it in a direction away from adjacent neighbors.
And while 802.11a sounds good as it probably has little interference, the hardware is a bit expensive compared to 802.11b/g/n.... N is nice if you can find cheaper hardware and it's the first time that I finally put away the Ethernet cables and went truly wireless around my house. YMMV.
Re: (Score:3, Interesting)
IMHO, i would use ddwrt and pick an unused channel, get an external antenna and boost your signal, use mac-based filtering, and disable SSID broadcast.
Re:Spread the channels (Score:4, Informative)
4 overlaps with both 1 and 6. 9 overlaps with both 6 and 11.
Re: (Score:3, Insightful)
With that many visible, why even deal with your own...use one of theirs! :)
802.11a, 5ghz (Score:4, Informative)
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.
Get directional antennas (Score:5, Informative)
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 [wikipedia.org].
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.
Re: (Score:3, Funny)
Also, great for making popcorn.
Don't trust the network list! (Score:5, Informative)
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 ... (Score:5, Interesting)
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.
Re: (Score:3, Interesting)
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.
How do you check that?
Buy a European AP (Score:4, Interesting)
Then you can use channels 12 and 13, which will have a touch less interference
Stop interference at the source (Score:4, Funny)
Re:Stop interference at the source (Score:4, Interesting)
Better yet, hack their APs and reduce their signal strength to something more agreeable. Change their channel too if necessary. If you're going to be evil, be evil constructively. (Hey, is that Google's new motto? j/k)
Reduce your own AP's radio output too while you're at it, if you can. You're in a frickin' condo, there's no need for every AP to shout.
Or just use Ethernet. Cables are your friend.
Switch to 802.11n at 5ghz (Score:5, Interesting)
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.
Luckily Windows shows your neghbour's channel (Score:2)
Oh, wait, no it doesn't...you have to guess.
Re: (Score:3, Informative)
netsh wlan show networks mode=bssid
Re: (Score:3, Funny)
Ohh, but linux is hard, windows is easy and noone ever needs to use the commandline on windows... Commandline is so archaic!
Re:Luckily Windows shows your neghbour's channel (Score:5, Funny)
Shouldn't you be troubleshooting your soundcard or something?
Make a DIY Directional Antenna (Score:5, Insightful)
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.
Comment removed (Score:5, Funny)
Use only channel 1,6 and 11. (Score:2, Informative)
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 no
Re:Use only channel 1,6 and 11. (Score:4, Informative)
On the lowest level you have the radio spectrum. Channel 1, 6 and 11 does not interfere with each others frequencies at all. Channel 3 interferes with both channel 1 and 6 (with the wider 802.11g channels)
On the next level you have the orthogonal keys, they make this transmission look as random noise to other transmissions on the same radio channel. On such a radio channel you have a Signal to Noise ratio that basicly limits the amount of information you can transmit. The more random noise you have, the less S/N you have and the less data you can transmit. Compare it to a room with too many talkers, the noiselevel increases and less gets communicated. It does not really help that your neighbour starts talking to his neighbour in another language. You will be able to filter that out, but you will still have problems talking english to those you wish to talk to since he sometimes is silent and suddenly burps out in Swedish and you have to repeat yourself in english once again.
By placing the communication on the same radio channel, you can make use of the simpler protocols were you raise your hand and is then allowed to talk. Never mind the language you speak. All of the speakers understands the handsignalling.
The standard practice is thus to use only 1, 6 and 11 as traffic on channel 2,3,4,7,8,9,10 hides the handsignalling that is used on 1,6 and 11 by those parties.
But yes, orthogonal keys do reduce the problems a bit, but not enough in a tight environment.
Possible Alternative (Score:2, Informative)
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.
amazing (Score:3, Insightful)
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)
Re: (Score:2)
Considering the cost of wireless equipment, it may be the best option though and it is obviously something he did NOT think of....
Re:amazing (Score:4, Insightful)
Get a 5ghz 802.11 a/n access point (Score:2, Insightful)
Example: Netgear WNHDE111 [netgear.com]
Bonuses:
Put EVERYTHING on 1 channel (Score:3, Interesting)
Should be theoretically better at 10Mbps (Score:2)
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.
IEEE 802.11n (Score:2)
I thought that IEEE 802.11n used OFDM to help prevent this sort of thing from being a problem?
Answers, in order... (Score:5, Informative)
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 more thought (Score:5, Interesting)
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. :-/
Share your connections? (Score:5, Interesting)
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
Pick the one with the interference (Score:5, Interesting)
Use NetStumbler http://www.netstumbler.com/ [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.
Re: (Score:3, Interesting)
I like InSSIDer [metageek.net].
fix the problem yourself (Score:3, Informative)
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!
Here's what I've done, for me and 600 of my closes (Score:5, Informative)
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/ [tummy.com]
Sean
Sean
802.11b is actually best here (Score:4, Interesting)
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 don't do it, so they must not either" BS (Score:3, Insightful)
Change your beacon interval to 101 (Score:5, Interesting)
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
In real life? (Score:3, Informative)
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.
Re: (Score:3, Interesting)
Or buy "magnetic paint" and paint the walls towards the problem.
Magnetic pain has a very VERY high iron content to the point that magnets will stick to the wall. if you GROUND the painted wall (paint into the electrical box and get it to touch the ground wire, or run a wire down to a copper pipe) it will further increase the effectiveness of the "Shielding"
Did this for a client in a end condo. got interference from the upstairs and south neighbors.. ordered him some paint and his painter repainted the