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?"
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.
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: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.
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.
Firmware for Japs (Score:1, Interesting)
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!
Buy a European AP (Score:4, Interesting)
Then you can use channels 12 and 13, which will have a touch less interference
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.
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.
Put EVERYTHING on 1 channel (Score:3, Interesting)
Re:Solution (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:amazing (Score:1, Interesting)
Assuming that the poster is not to only slashdot reader, the answers may still be useful for other readers. WiFi is a common problem.
Using a combination of cheap switches, and using single (8 wire) ethernet cable for two 10/100 mbit links I was able to completely eliminate the wireless network in the house, with a minimum of cable work. The only computer that ever worked well with wifi was my Linux eee pc.
FC who? (Score:1, Interesting)
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
Re:Escape to A (Score:2, Interesting)
transmitting 802.11a outside at non trivial power levels requires a special licence , in the uk.
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. :-/
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:Spread the channels (Score:2, Interesting)
Currently I can detect between 11 and 16 on a regular basis, with maybe another 7 or 8 APs that only show up now & then depending on time of day/weather/phase of moon etc.
iwlist eth1 scanning | grep Channel:
Channel:1
Channel:6
Channel:6
Channel:9
Channel:11
Channel:11
Channel:11
Channel:1
Channel:6
Channel:5
Channel:6
Channel:6
Channel:11
On bad days I often get serious interference with signal quality dropping down to 1mbit, huge amounts of packet loss, varying delay between me & the router between 60 and 900ms... the situation sucks yet I cant do anything about it (strict landlord refuses to put in new phone lines so the only inet access I have is via the shared house wifi etc.)
Other days it's great, particuarly over the christmas holidays when (I presume) lots of people in the neighbourhood were away I had a very stable connection.
To a certain extent I blame this on the high-power wifi APs which are advertised as "stronger signal wherever you are in the house", the only problem is when you have 20+ of these in a small area mostly on the default channels which overall results in connection issues for everybody. I tried explaining this to a neighbour who was having wifi problems too, but the whole concept seems lost on them.
Personally I wish small lower-powered meshing APs were used and placed liberally around peoples houses depending on *where* they needed them so I wouldn't be able to pickup signals from 3 streets away.
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.
Re:Pick the one with the interference (Score:3, Interesting)
I like InSSIDer [metageek.net].
Re:Spread the channels (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: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: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.
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.
Re:you can ... (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?
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
Re:Hack your AP (Score:3, Interesting)
Re:They're reading my brain! (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 south wall and ceiling. interference dropped by over 25db.
Re:Hack your AP (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!
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:5GHz (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:Hack your AP (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 coverage by everyone sharing the same network and extending it with their own APs. instead of only being able to access the internet from home, you can access it anywhere. heck, you could install a WiFi-enabled system in your car so that you can stream internet radio while driving.
b.) merge proprietary single-purpose communication networks like TV, radio & cellular networks with the internet, which is general-purpose open network. this would free up a large chunk of the radio spectrum for WiFi networks, which could then be used for internet TV/radio and VoIP. this would replace a lot of redundant communication infrastructure and put shared resources to better use that gives maximum benefit to the public. additionally, WiFi protocols have far greater spectral efficiency [wikipedia.org] than either TV, radio, or cellular networks. so allocating these frequency ranges to WiFi devices would allow for more data to be transmitted over the limited radio spectrum that's available.
Re:Hack your AP (Score:4, Interesting)
Re:Or channel 14 (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 they are being stepped on and hence will never report it? :)
No, they don't have the time or money unless you interfere with someone that has paid for their license and you are causing them harm (i.e.: costing a business money or hampering public safety.)
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.