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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?"
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.
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.
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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.
802.11n also supports the 5ghz band.
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.
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.
No reason to go with A, as long as you make sure the N-equipment you buy actually supports 5GHz.
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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.
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!
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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
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.
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4 overlaps with both 1 and 6. 9 overlaps with both 6 and 11.
Time makes more converts than reason
Not if he gets Powerline AV Ethernet Adapters. My Netgear ones work great in my ~30 year old home.
netsh wlan show networks mode=bssid
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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.
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.
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It's not the first time I've heard this, but it comes from people who've observed degraded performance after increasing their AP's power output (usually with a 3rd-party firmware).
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.
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.
The gear only works within a certain range of space (wires), so it is unlikely to leave the building and it's possible it would not cover the whole building. Furthermore, they offer encrypted subnetwork connections.
A is a great solution if you don't have too many walls to go through. I seem to remember reading that A has better transmit speeds at greater distances. The trade off is that signal doesn't pass through buildings as well due to the larger waves.
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 frequency (that frequency was once bellowed to broadcasters technical transmission), we were under 1W of power, but we had to switch this off as the Gendarmerie asked us to do so.
(Sorry my bad French) Je fais parler les Guignols de l'Info. Le pied, quoi.
It's not the first time I've heard this, but it comes from people who've observed degraded performance after increasing their AP's power output (usually with a 3rd-party firmware).
What's going on here is that:
a) Clients are still transmitting at normal power, so the AP can't hear the clients.
Actually, a huge problem with wireless networks is that an antenna is NEVER able to receive transmissions while also transmitting. The power from the AP's own signal will by far overpower any other signals. This is why a collision avoidance system (RTS/CTS) is used, as opposed to collision detection that would be used on a wired network.
One approach which worked for me (but which may or may not be directly useful to the OP, since my particular issue was poor reception in a large building built out of metal/foam sandwich panels) was to buy myself a repeater and an omnidirectional 7dBI antenna like this which I stuck to a ceiling at an appropriate location. I had to tweak the output level of the originating AP down a bit so that my laptop didn't insist on trying to use that signal instead of the "louder" one.
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.
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).
Hrmm, considering I have 12 WRT54GLs installed in commercial locations with 7.09, I feel the urge to call BS. Perhaps you got the wrong package.
If your router has UK options that would work as well since UK has those as options too.
I don't get it.