Case Study: Wi-Fi Cannot Be Used Due to Other Interference in the Installation Environment

Symptom

APs are close to the carrier's mushroom-like antennas, generating severe interference on 2.4 GHz channels and deteriorating Wi-Fi experiences of some users.

Relevant Alarms and Logs

Alarm about interference from other devices: WLAN_1.3.6.1.4.1.2011.6.139.16.1.1.1.11 hwOtherDeviceInterfDetectedTrap

Cause Analysis

2.4 GHz channel 1 is close to the carrier's signal frequency band and has strong interference. As a result, the coverage signal is weak.

Procedure

1. Adjust the installation positions of APs and keep the APs away (a recommended distance of more than 5 m) from the carrier's indoor antennas.
2. Configure 5 GHz-prior access and increase the 5 GHz radio power to increase the proportion of 5 GHz access STAs.

   # Enable 5G-prior access. This function is enabled by default.

   <AC> system-view
   [AC] wlan
   [AC-wlan-view] vap-profile name wlan-net
   [AC-wlan-vap-prof-wlan-vap] undo band-steer disable 
   [AC-wlan-vap-prof-wlan-vap] quit

   # Manually set the transmit power of 5 GHz radios on APs.

   [AC-wlan-view] ap 0
   [AC-wlan-ap-0] radio 1
   [AC-wlan-radio-0/1] calibrate auto-txpower-select disable  //Disable automatic power calibration.
   [AC-wlan-radio-0/1] eirp 20  //Adjust the value according to the actual situation.
   [AC-wlan-radio-0/1] quit

Suggestion and Summary

The channels used by carrier signals, mobile phone hotspots, and home routers often overlap with 2.4 GHz channels, causing greater interference to 2.4 GHz channels with poor channel resources. With the promotion of 802.11ac and 802.11ax, most terminals in the market support the 5 GHz frequency, so enabling these terminals to access the 5 GHz radio can greatly improve user experience.

Additionally, antenna spacing can be properly controlled based on the site requirements to avoid signal interference. The following common guidelines are recommended:

[Outdoor scenarios]

• If antennas are installed on different poles and face opposite directions, it is recommended that the horizontal spacing be greater than 1.5 m.
• If antennas are installed on the same pole and face the same direction, it is recommended that the vertical spacing be greater than 5 m.
• Keep antennas at least 2 km away from carriers' 4G signal towers.

[Indoor scenarios]

• Ensure that antennas are deployed at least 7 m away from each other.
• Keep antennas at least 5 m away from carriers' 4G antennas.
• Keep antennas away from electronic equipment that may cause antenna interference, such as microwave ovens.

[Vehicle-mounted scenarios]

• Deploy antennas at least 5 m away from each other.
• Keep antennas at least 5 m away from carriers' 4G antennas.

[Trackside installation scenarios]

• At the same trackside, place antennas with the same direction at least 50 m away from each other, and place co-located antennas facing opposite directions at least 20 cm away from each other.
• Ensure that the height difference between trackside antennas and vehicle-mounted antennas does not exceed 0.5 m.