APs fighting each other for airtime
very common
“They added APs because it was slow and now it is worse. Everything is on channel 1 and 6 and the whole floor is talking over itself.”
Likely causes
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Self-interference: your own APs reusing channels within earshot of each other
35%From one spot you hear three or more of your own APs on the same channel above -85 dBm. Utilization is high and retry-heavy, and it degrades at busy times rather than with distance. Above -85 dBm they defer to each other, which means they share one channel's airtime.
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40/80/160 MHz widths burning the channel plan
20%5 GHz radios at 80 MHz. How many non-overlapping 80 MHz channels you actually get is regional: in FCC regions roughly six with DFS in the plan and two without, under ETSI about four with DFS and one without, because there is no U-NII-3 and the upper band is narrower. Read the AP's own regulatory/country channel table for this site rather than trusting a remembered count. Either way, reuse collides immediately: drop a test radio to 20 MHz and utilization falls even though the headline rate does.
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2.4 GHz off plan, or running 40 MHz
15%Scan shows APs on 3, 4, 8 or 9, or a 40 MHz 2.4 GHz radio. Overlapping-channel energy does not show as clean utilization; it shows as a raised noise floor and frames failing CRC.
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Auto-RF churn
10%Channel and power change events logged every few minutes and complaints that move around the building day to day. Either the RRM interval is too aggressive or something (rogue containment, a DFS hit) is making it flap.
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DFS channels disabled, so everything crowds into the non-DFS blocks
10%Only the bottom and top non-DFS channels in use and the whole DFS range empty. Nine times out of ten somebody disabled them after an earlier radar drop and never revisited it.
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The neighbouring tenant's network
10%The strongest co-channel BSSIDs are not yours: different SSID and different BSSID prefix. You cannot fix theirs, so you narrow your channels, lower your power and pick the least-used channels.
What to bring
- Wi-Fi analyzer or survey tool showing channel, width and utilization
- hand-held spectrum analyzer
- controller access with RRM and event logs
Steps
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Step 1: Scan from where the users actually sit
At desk or cart height, not ceiling height. List every BSSID with channel, width, RSSI and utilization. Anything you can hear above roughly -85 dBm on your channel is competing for your airtime.
If that doesn’t do it
Nothing co-channel above -85 dBm and it is still slow: go back to Full signal, no usable throughput and check SNR and the wired path.
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Step 2: Count your own co-channel neighbours, per band
Write down how many of your APs share each channel and how loud they are from that spot. One strong AP per channel is the goal. Three is why the room is slow.
If that doesn’t do it
Your plan is clean and the loud co-channel BSSIDs belong to somebody else: skip to step 3 and live inside a narrower, quieter footprint.
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Step 3: Narrow the channels before you touch hardware
2.4 GHz to 20 MHz, always. 5 GHz to 20 or 40 MHz anywhere dense. Retest utilization and per-client throughput in the same spot: more usable channels beats a bigger headline rate every time in a busy building.
If that doesn’t do it
Narrowing helps but is not enough: continue to the channel list and power.
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Step 4: Put the DFS channels back in the plan
Re-enable the DFS range in the auto-RF channel list: 52-144 in FCC regions, the 5470-5725 band under ETSI. In FCC regions that takes 5 GHz from about two usable 80 MHz channels to about six; under ETSI from about one to about four. Confirm what this site is actually allowed from the AP's country table. It is the single biggest free win available on most sites.
If that doesn’t do it
Clients start dropping in bursts after re-enabling: that is radar, not a fault. Go to Everyone drops at once, then it is fine and exclude only the specific channels taking hits.
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Step 5: Fix the plan, then the power, then the radio count
2.4 GHz on 1, 6 and 11 only, and disable the 2.4 radio on most APs where they sit closer than about 12-15 m: three channels cannot feed six co-located radios. Then bring TX power down so cell edges land near -67 dBm instead of overlapping three rooms deep.
If that doesn’t do it
Plan and power are right and utilization is still pinned when the room fills: that is capacity, not interference. Go to Wi-Fi dies when the room fills up.
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Step 6: Re-measure and hand over the numbers
Target: utilization under 40-50% at busy hour, retries under 15%, and one of your own APs audible per channel above -85 dBm from any given spot. Same tool, same spots, before and after.
If that doesn’t do it
Numbers still out after all of the above: you are short on radios or long on clients, not on channel plan. Also confirm no AP came up in the wrong regulatory domain: see AP will not join, or joins in the wrong country.
References
- IEEE 802.11-2020
- 47 CFR 15.407
- ETSI EN 301 893 (outside FCC regions)
- TIA TSB-162-A