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I am a volunteer network engineer working in a building housing refugees in Greece. It's an old school and is extremely densely populated (multiple families in each classroom). Many people have phones with WiFi.

There is one very good access point (Unifi) which is unproblematic, stays up and gives good coverage. I wanted to provide another access point to address a small area not already covered. I've tried four different consumer grade ones and they've all had the same problem. The signal fluctuates between full strength and nothing at all (using a WiFi analyser app, it shoots up and then disappears). Sometimes phones see it, sometimes they don't. Or you can see it and apparently connect but there is no internet access at all (you get the "device is offline" error).

The obvious answer is that the access point doesn't support enough clients but I've googled this and the symptoms of congestion are described as slowdown and latency. Could it also cause the symptoms I described?

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    It sounds like you have channel contention. Are you on a different channel than the other? Set the minimum data rate high enough so that distant clients don't try to connect. – Ron Trunk Jun 8 '16 at 1:03
  • 4 consumer grade APs would be cost equivalent to 2 more UniFi APs, and the UniFis will work together intelligently...so solution seems obvious. – Ecnerwal Jun 8 '16 at 3:46
  • @RonTrunk the channel is different from the other. I will try setting higher data rate and putting in another access point so less people try to connect to this one. – naomi Jun 8 '16 at 14:24
  • Increase the minimum data rate on all your APs to make the cell size smaller. This will reduce the number of clients on each AP and reduce channel utilization. Many small cells are better than a few large ones. – Ron Trunk Jun 8 '16 at 14:27
  • @RonTrunk what I ended up doing was this. The consumer one didn't have a max data rate setting but it did have a "coverage threshold" which I guess has similar effect. I raised it to -70 which helped. Then I turned down transmission power to 75%. This combination seemed to do the trick. I didn't touch the unifi one. Let's see what the users say over next few days. Thanks! – naomi Jun 8 '16 at 17:57
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It sounds like you have channel contention. Increase the minimum data rate on all your APs to make the cell size smaller. You want to disable low speeds so clients can't connect if signal is marginal. That has the effect of reducing the cell size. This will reduce the number of clients on each AP and reduce channel utilization. Many small cells are better than a few large ones.

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  • Right, and pay attention to what flavor WiFi you are serving up a/b/g/n/ac? Channel specifics vary based on flavor. – Ronnie Royston Jul 8 '16 at 18:39

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