Co-Channel vs Adjacent-Channel Interference
See why a neighbouring AP on the same channel only costs airtime while one on a nearby channel corrupts frames, with the spectral mask, preamble and energy detect, and 2.4 GHz channel plans.
How to use this tool controls and what to look for
Put a neighbouring AP on the same channel or a nearby one, and see whether it costs airtime or corrupts your frames.
Controls to change
- Band: choose 2.4 or 5 GHz.
- Neighbour's channel: move the neighbour from your channel to the ones next to it.
- Neighbour's transmitter: choose At the mask limit or Typical (10 dB cleaner).
- Your signal: set your signal and the Neighbour's signal strength.
- Preamble detect (CCA): compare −82 dBm (standard), −86 dBm (a more sensitive radio) and −72 dBm (802.11ax spatial reuse); energy detect stays at −62 dBm.
- Neighbour busy: set how much of the time the neighbour transmits.
What to look for
- On the same channel your radio decodes the neighbour and waits: CCI costs airtime, but every frame arrives clean.
- On a nearby channel the leak is too weak to decode but strong enough to corrupt frames: ACI.
- Overlapping 2.4 GHz plans (such as 1, 4, 8, 11) do worse than everyone sharing one channel.
- Two APs mounted close together on adjacent channels can still disrupt each other.
About this tool
A neighbouring access point on the same channel and one on a nearby channel hurt a Wi-Fi network in opposite ways. This tool draws both channels with the 802.11 spectral mask, shows how much of the neighbour's energy lands in your channel, and works out whether your radio waits for it (preamble detect and energy detect), your airtime, your SINR and data rate, and your throughput, including a comparison of 2.4 GHz channel plans.
What you'll learn
- Why co-channel interference (CCI) costs airtime but leaves every frame clean, while adjacent-channel interference (ACI) corrupts frames
- How the transmit spectral mask sets how much a neighbour on another channel leaks into yours
- How preamble detect and energy detect decide whether your radio waits, and why the gap between them is where ACI does its damage
- Why overlapping 2.4 GHz channels are worse than sharing one, why 1, 6 and 11 is the usual plan, and when 1, 5, 9 and 13 works
Common questions
Is co-channel or adjacent-channel interference worse?
Often adjacent-channel. With CCI your devices decode the neighbour and take turns: you lose airtime, but frames stay clean. With ACI they can't decode it, so unless it is strong enough to trigger energy detect they don't wait, frames overlap and get corrupted on both sides. Partly overlapping 2.4 GHz channels such as 1 and 3 are the worst case.
Can 5 GHz channels cause adjacent-channel interference?
Yes. Neighbouring 20 MHz channels don't overlap, but every transmitter leaks a little outside its channel (the spectral mask allows −28 dBr at the next channel). When the neighbour is much stronger than your own signal, such as two APs mounted close together, that leakage is enough to lower your data rate.
Why use channels 1, 6 and 11 in 2.4 GHz?
The rule comes from 802.11b, whose signal is 22 MHz wide and needs 25 MHz of separation. OFDM signals are narrower, so 1, 5, 9 and 13 also work where all 13 channels are allowed and every nearby network uses them; in the US, 1, 6 and 11 is the only three-channel plan that fits.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.