PlantUML Diagram2.4 GHz Channel Overlap
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A conference room on the third floor consistently has terrible Wi-Fi during meetings. Speed tests in the adjacent hallway are fine. The AP is healthy. What's going on?
That pattern — good in the hallway, bad in a specific room when occupied — is the signature of RF interference. Bodies are 60% water and absorb 2.4 GHz and 5 GHz signal. Twenty people in a conference room effectively create a wall of attenuation between the AP (likely mounted in the ceiling outside the room) and the clients inside.
2.4 GHz has 11 channels in the US, 13 in Europe, 14 in Japan. But channels overlap heavily — each 20 MHz channel spreads across 5 channels worth of spectrum. Only three (1, 6, 11 in the US) don't overlap with each other. Using any other combination guarantees adjacent-channel interference.
5 GHz offers around 25 non-overlapping 20 MHz channels (varies by regulatory domain). 6 GHz adds ~59 more. Unlike 2.4 GHz, where you're forced to reuse 1, 6, and 11 in dense deployments, the higher bands give you plenty of clean channels. This is why modern designs push clients to 5 GHz and 6 GHz.
| Type | Cause | Effect |
|---|---|---|
| Co-channel interference (CCI) | Two APs using the same channel, close enough to hear each other | Both must share airtime — reduces throughput |
| Adjacent-channel interference (ACI) | Overlapping but different channels | Garbled signals — worse than CCI |
| Non-802.11 interference | Microwave ovens, Bluetooth, cordless phones, video cameras | Random packet loss and retransmissions |
| Self-interference | Too many APs at max power in a small area | Constantly changing channel or retry rate |
Adjacent-channel interference is worse than co-channel. In CCI, the two APs hear each other and politely share — CSMA/CA makes them take turns. In ACI, they hear partial signal, fail to decode it as 802.11, and transmit anyway — causing collisions the hardware can't manage.
Wider channels give more throughput per association but reduce the number of usable channels and increase the chance of interference. In an office with many APs, 20 or 40 MHz channels are often better than 80 MHz. In a home with one AP, 80 MHz is usually fine.
You're deploying 12 APs in an open-plan office on the 2.4 GHz band. Non-overlapping channels available: 1, 6, 11. What's the best channel plan?
Select the safest next action.
RF planning is as much art as science. Walk through any large office with a Wi-Fi analyzer app and look at the channel graph. You'll see why 2.4 GHz is crowded — a dozen APs from your building, plus neighbors, all sharing three usable channels. 5 GHz is where the air is quiet.
Finish the lesson once you have worked through the material. This awards ★ 40 XP.