Wireless congestion cochannel interference and signal strength

I work at a school and we have between 30 and 60 AP's at each school.
We have a high concentration in order to get 20 or more kids on line in each room.
The issue I am having is dropped connections due to cochannel interference from my other AP's as well as those outside the schools.(I am in the city)

All my devices must work on the 2.4Ghz band so I am limited to  channels..

my question is..
What is the delta I should be shooting for when I have 2(or more) AP on the same channel(or other access points outside my school)

I am getting at least -70db in all my classrooms but some of the rogue AP's as well as others in my organization might be sitting at  -80db on the same channel..  I need some hard numbers so management will understand that external forces are causing connections to drop not the equipment/design.
Screenshot-2014-11-07-09-26-03-kindlepho
sullendAsked:
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Craig BeckCommented:
Unfortunately there's not much you can do there.  I would happily confirm that you're going to be suffering from lots of co-channel interference there which will cause drop-outs all day.

I'd suggest that if you have an AP on the same channel with a RSSI of around -85dBm it's not going to affect you too much, but anything higher than that will give you issues.

Out of interest, where are you located?
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sullendAuthor Commented:
St. Louis..
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sullendAuthor Commented:
So anything  below -85 in the same channel really wont impact me if its in the same channel is that a fair statement?
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Craig BeckCommented:
Pretty much... -85dBm really is a weak signal.  Your AP and clients should be able to cope with that signal and still decipher its own conversation.  A -91dBm signal is practically useless.

For info we aim for a signal to be at least around -67dBm if we want voice-quality wifi, and -75dBm for a steady data network.  If you can see the SNR value when a client is connected it really should be at least around the 20dB mark; 25dB is the target and anything above that is great.  If the SNR is below the 20dB mark that usually implies that there is noise (interference from other sources).  To try to counter that you can change the channel (not feasible in your environment), or increase the transmit power at your APs.  I wouldn't advise that though as it'll just make the situation worse here due to the sheer amount of noise in the area.
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