Wireless Access

We have a dense 5GHz deployment in several multi-story buildings.  I'm finding a lot of MAC errors and seeing high retransmission rates in many areas.  I found in several areas where the noise floor is higher than it should be, according to AirWave.  AirWave flags any radios with a noise floor of < -90 dBm.  Some noise floors are as high as -81, but most high noise areas are around -85 <> -89.  I believe that the cause is due to our dense deployment in our multi-story offices.

One thing that we've done on 5GHz to improve channel utilization and re-use was to disable 40MHz channels.  This really helped since all APs on a floor typically hear APs about 2 floors above and 2 floors below, making for at least 10 5GHz neighbors.

My questions are:

Is -90 dBm really a good threshold for 5GHz noise floor?

What can be done to improve the noise floor in dense multi-story offices?

Are MAC errors and high retransmission rates the result of noise floor?  I just want to be sure I'm attacking this problem the right way.

Well that noise floor shoudl be okay...

Channel Noise Floor is above 80. If Noise Floor is lower then too much non-802.11 interference

How is your Channel Frame Retry Rate %? it   is below 30%.?  If higher then too much interference...

You can check it by running
show ap active ip-addr <ap ip address>

Guess you already know that  :) but still put it....

How is the channel utilization?

You should be able to see it on the dashboard but if you got RF protect license and can put an AP on spectrum analysis on where you see more issues you can then use the channel utilization trend graph to see it... or if you got an air checker of fluke or something like that  you can see that right away with it :)

Check that the channel utiliization is not that high....

Also How many users are plugged in one AP on the 5ghz band?  what kind of apps you running over wifi? are you using VOIP phones and stuff like that?  or running HD video over wifi? those things affect how many users its recommended to have in that band on one AP.

For example if you using VOIP phones is not recommended to have more than 20 users on one AP per band...

Cheers

Carlos

The other thing you mention is that the AP can see at least 10 5ghz neightbor...

If you got your system profile by default you will have like 9 5 ghz channel for use.... not the 23 channels... you can enable some for more capacity, but the other that are not on by default are DFS channels..

you might want to enable more channels but you need to be careful with it.... ensure they either know they will not be impacted by radar.

Cheers

Carlos

Asnwering your question

Noise floor would be non 802.11 Interfence

To improve the noise floor you must find what is cuasing that non 802.11 interference and the spectrum analyzer of the aruba can help you with it.

The channel frame retry is too much interference in general, i mean interference or RF noise in the ap enviroment...

Ifyou got too many phy/mac errors  i mean that it exceed the provisioned thresholds on the controller they could trigger an immediate channel change if a better channel exist(which i think it will disconnect clients if it suddendly change channels)

Well its a good threehold i mean 90 is really few non 802.11 interference.. but if it like 79 there is TOO much non 802.11 interference...

At least on the advance troubleshooting course the mention that we should ensure that the channel noise is above 80 otherwise that means too much non 802.11 interference, thats like the threhold, but if you want like the optimum performance above 90 should be the threhold :)   but as far i konw 85 or 89 its okay.

Cheers

Carlos

I would pay good money for a noise floor in the high 80's :)

Thanks for the input.  I'd like to revisit this as I'm seeing a high noise floor at another location, now.

On about 4 APs, the 5Ghz noise floor starts at -81 and goes to -85.  I consulted my my CWNA book, which indicates that both 802.11 radios and non-802.11 energy sources are capable of affecting the noise floor.  So I started to look into both 802.11 and non-802.11 sources of interference and here is what I came up with:

1. Turned off all APs except for one reporting -81.  Let sit for several minutes to see if noise floor changed.  Nothing.
2. Set min/max TX power for all APs to better match client transmit power and keep some APs from transmitting so loud.  No help.
3. Turned hybrid mode on for the AP reporting -81.  Used the spectrum monitor to look for sources of interference.  None of the graphs were helpful in determining either radio or non-802.11 interference.  The swept spectrogram graph did look a bit dirty at times, but it was not helpful in finding a source.

So I'm all out of ideas.  I know the noise floor isn't terrible, but it certainly could be improved.  I have several environments where the noise floor is -90 to -94 for the majority of APs.  That's what I'd like to achieve considering that would be a gain of +10 SNR for some clients!

Any thoughts on what I could do?

What kinds of non-802.11 5GHz sources of interference even exist?  I've read on the Internet that some lights can cause interference along with the temperature of a room, but I'm not sure how trustworthy those sources of information are.

This issue has been resolved.  I had been disabling 40MHz channels incorrectly, which caused ARM to provide suboptimal results.  See my post, message #10, in this thread where I explain what I did.  After making the changes, I'm seeing a 4dB improvement on APs that had a very high noise floor before!