At a customer site, there are over 300 2.4GHz Wi-Fi devices connected to the network. In this scenario with multiple access points (APs) , AP placement becomes crucial. APs need to be configured with different channels to avoid interference. So how should this be done? The channel range for 2.4GHz Wi-Fi is typically 1-13 , but regulatory policies may differ in different countries / regions (e.g., the US only allows channels 1-11 , while Europe and China support 1-13 ). However, not all channels are "interference-free." Here are the key points:
I. 2.4GHz Channel Distribution
• Frequency range : 2.400 GHz ~ 2.4835 GHz
• Channel spacing : Each channel has a width of 5MHz , but actual transmission requires 20MHz of bandwidth (i.e., adjacent channels overlap).
Channel number and center frequency :
II. Non-interference (non-overlapping) channels
The only completely non-overlapping channel combination is: 1 , 6 , 11
Reason : Each channel occupies 20MHz bandwidth, and adjacent channels are spaced 5MHz apart . If the center frequency interval between two channels is ≥ 25MHz (i.e., 5 channels apart ), then there is no overlap.
• Illustration :
• Misconceptions:
Some people mistakenly believe that channels 1 , 5 , 9 , and 13 are also non-overlapping channels, but in fact these channels still have some frequency band overlap (for example, channel 5 overlaps with channel 1/6 ).
III. Channel Planning Recommendations for High-Density Networks
1. Multi - AP deployment:
• Alternate between channels 1 , 6 , and 11 to ensure that adjacent APs use different channels.
Example (honeycomb layout):
2. Reduce co-channel interference:
• Adjust the AP transmit power to 15-20dBm to reduce the coverage area and decrease the probability of channel overlap.
• Use spectrum analysis tools (such as Wi-Fi Analyzer ) to detect and avoid interference sources such as Bluetooth and microwave ovens.
3. Disable unnecessary channels:
• If the device only supports channels 1-11 , channels 12 and 13 can be disabled (to avoid compatibility issues).
IV. Special Circumstances and Precautions
• Channel 12/13 compatibility : Some devices (such as US version iPhones ) may not support channels 12/13 and need to be adapted according to the terminal.
• 40MHz channel bonding : Forcibly bonding 40MHz in the 2.4GHz band (such as channel 3+7 ) will occupy more spectrum and cause serious interference . It is strongly discouraged to use this method.
• Dynamic Channel Selection ( DFS ) : DFS is not supported at 2.4GHz and manual planning is required.
V. Summary
• Standard non-interference channels : only 1 , 6 , and 11 .
• Deployment principles : Multiple APs should be strictly allocated alternately in a 1/6/11 manner to control coverage and disable redundant functions (such as 40MHz ).
• Verification tools : Use NetSpot or Acrylic Wi-Fi to scan for channel occupancy in a real-world environment.
