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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.
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.
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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.
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.
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.
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.
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.
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.
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
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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.
If he doesn't know enough to answer his question, there's a reasonable chance he also doesn't know enough to ask the right questions. It's quite valid to give answers to questions he should have asked, but didn't.
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.
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
Shouldn't you be troubleshooting your soundcard or something?
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.
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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.
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