weak signal due to sudden increase in overlapping external AP

[ejlbarcelon]

after some months there has been an increase (a lot) of other WLAN with the same channel as my APs SSIDs, thus this reduce the signal of my APs. is there a way to block these signal or strenthen my own APs signal? i was thinking of something like blocking external APs signal. by the way i have autonomous APs. because of this problem even if the device is close to the AP like 3 meters or less it only detects poor signal from my AP.

[Surendra BG]

Hi,

How do you know that the APs are using the same channel?? To measure the interference.. the best inbuilt tool that we hav on the AP is the CARRIER BUSY TEST, run this ans see what channels are heavily affected.. and configure the least congested channel on the AP and see if htat helps..

dot11 dot11radio 0 carrier-busy

or

dot11 dot11radio 1 carrier-busy

Then to assign the least congested channel..

en

conf t

int dot11 0 or int dot11 1

channel

end

2> Second option is to increase the security, this has nothing to do with interference but just for Security!!

lemme know if this answered your question..

Regards
Surendra
====
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[roxtonchapman]

Hi,

I would love to say use the 5GHz A radio, but that may not be an option for you? If you do, you will avoid all interference in the 2.4GHz band if that is the band you have a problem with.

You could use a tool like inSSIDer from Metageek to see what other APs are out there and what channels they are on. If you have a spectrum analyzer, even better as this will show you what non 802.11 interference is out there and on what frequency.

You will need to place your channels on 1,6 & 11 (if 2.4GHz) ideally and it will be worth checking your power settings on the radio as it might either be too high causing interference or too low not providing enough coverage.

You say that if a device is 3m away it has a low signal. If you mean RSSI (signal strength), then I would look at your hardware and antenna connections as your RSSI should be good, but the low SNR (signal-to-noise ratio) from other APs is causing reduced throughput.

Many thanks

Rocky

[ejlbarcelon]

Hi Surendra/Roxton,

I used inSSIDer to check the overlapping channels, please see attached, i used least congested frequency on the channel setting and I got the channel 8 as least congested.

I would like to use 802.11a but the problem is the device connecting are handled devices mostly iPhones and iTouch which are only 802.11b/g capable, thus using 802.11a for these devices are not possible. but for laptops the Wi-Fi signal are OK since they use 802.11a for connection.

I am not sure if this is being affected by external AP signals. or if this is antenna issue. I was also looking on how to enable only 802.11n and disable 802.11b/g since newer iPhone has 802.11n support.

[roxtonchapman]

Hi,

Yes, that's the problem with A at the minute, hopefully the client vendors will catch up soon and realise that the 2.4GHz range is overcrowded and add support for A

As for your inSSIDer output, I see very weak signals from everything, including your own AP! If you are close to your AP when you took the snapshot, then you may have to look at the power output or check your antenna connections. Try upping the power first (make sure this is within your EIRP), this should make ad difference, but won't help with interference from other APs as you will be effectively increasing your RF fingerprint by upping the power.

Channel 8 is a bad choice and you should not use this channel even if it is the least used according to your carrier busy test. The reason is because channels are 22MHz wide and overlap, so if any devices are on channels 4 to 12, they will all be interfering with your APs transmissions. Also, channels next to your own, known as adjacent channels are worse than using the same channel! This is because your AP won't be able to decode the other transmissions on overlapping channels and will see this as noise that will lead to more errors and layer 2 retransmissions.

If they are on the same channel, they can decode each others basic transmissions and avoid collisions, thereby increasing your throughput dramatically.

Looking at your output again, I don't see you having too many issues as the other signals are so weak, they should not cause too many issues. Move your AP to channel 1 and check your APs power and connections and test again. I would say if you within a few meters of your AP, you should be seeing about -50 to -60dB. If you still have issues, I would be looking at non-802.11 interference.

Disabling data rates is always a good plan, especially if you can rule out the legacy 802.11b protocol. This is done on the radio itself, but be careful as your clients need to support the data rates you choose otherwise they will not be able to connect.

Cheers

Rocky

[ejlbarcelon]

Hi Rocky,

I am not too good at configuring power and data rates, i have just basic knowledge of configuring access point, btw i am using autonomous AP. can you share your input on what data rates and what power should i set on the AP? clients mostly using the 802.11b/g are iphones and other handheld devices, since 802.11a is enabled laptops connect to this radio.

also for the non 802.11 interference what could i do with this and what should i use to check on this?

Thanks!

[roxtonchapman]

Hi there,

I would browse to the GUI of the AP you want to change and within there you should have the option to go into the 802.11a and 802.11g radio tabs.

This should be under network interfaces and then choose your radio - 802.11a/802.11g then go into setting where you can adjust power and data rates. I would start setting the power to max, then do some testing with InSSIDer, where you should now be seeing much better signals than you were, then you can lower the power down to something like 11dB for locally and for the client. You should be seeing at least -70dB in the area where your clients want to connect. If not, then I would be looking at moving the AP into a better position or it could be your hardware to blame.

1Mb, 2Mb & 5.5Mb can be disabled on the 802.11g radio as this means that you can still support 802.11b clients but only at 11Mb.

Look also at how and where your AP is located, maybe it is in a really bad place or maybe the antennas are damaged. If you have multiple APs around the place, then it may be worth investing in a site survey, as this will help design your network how you want it. If not, then a post site survey will also help raise alarms if your set up isn't right. I might be wrong here and you may have done this, but worth suggesting as wireless networks are becoming harder to design for given the amount and type of clients looking to connect and by definition, this places an important aspect on design.

Regarding RF interference, Spectrum Analyzers perform this duty. Metageek have a good range of affordable WiFi analyzers that can check out interference in the 2.4GHz & 5GHz range which WiFi uses. It will show you the ambient Radio Frequency noise on any given channel (microwave ovens are always a good example as they trash large parts of the 2.4GHz spectrum when in use), then you can move your APs away from such interference which will be harming your network. Saying this, you should still be able to see your AP at better than -80 or better still -70 regardless of how much noise is around as this is the energy that is required for initial connectivity over the air.

Many thanks

Rocky