Case Study: Some STAs Cannot Connect to the Wi-Fi Network Due to Radar Interference

Symptom

Most STAs fail to connect to the Wi-Fi network. Only a few STAs can successfully connect to the Wi-Fi network but the network is congested.

Relevant Alarms and Logs

Related log:

Cause Analysis

According to laws and regulations, when an AP detects a radar channel, it automatically switches to another channel to prevent radar interference. Channel switching, however, increases the delay of user service data and affects wireless services.

Procedure

1. Check that the channels of many APs are switched. The channel utilization of the APs is high, affecting the AP performance.
2. Use one of the APs as the test AP. After the channel of the test AP is reset, the number of associated STAs increases.
3. It is preliminarily suspected that channel switching occurs because radar channels are detected. To confirm this, collect and analyze logs.

   <AC> cd logfile/ 
   <AC> dir
   Directory of flash:/logfile/ 
     Idx  Attr     Size(Byte)  Date        Time       FileName
       0  -rw-      3,550,712  Feb 27 2018 19:28:07   log.log
       1  -rw-      5,967,814  Feb 27 2018 19:27:59   log.dblg
       2  -rw-        725,189  Feb 18 2018 10:09:48   2018-02-18.10-09-43.dblg.zip
       3  -rw-        693,111  Feb 18 2018 06:34:13   2018-02-18.06-34-08.dblg.zip
       4  -rw-        737,471  Feb 18 2018 13:24:11   2018-02-18.13-24-05.dblg.zip
       5  -rw-      1,025,468  Feb 18 2018 15:40:21   2018-02-18.15-40-15.log.zip
       6  -rw-        826,620  Feb 18 2018 16:26:25   2018-02-18.16-26-20.dblg.zip
       7  -rw-      1,148,944  Feb 18 2018 18:41:17   2018-02-18.18-41-11.log.zip
       8  -rw-        976,843  Feb 18 2018 18:53:07   2018-02-18.18-53-01.dblg.zip
       9  -rw-      1,240,399  Feb 18 2018 19:58:10   2018-02-18.19-58-04.log.zip
      10  -rw-      1,128,969  Feb 18 2018 20:55:27   2018-02-18.20-55-20.dblg.zip
      11  -rw-      1,236,041  Feb 18 2018 21:32:36   2018-02-18.21-32-30.log.zip
      12  -rw-      1,004,244  Feb 18 2018 23:11:35   2018-02-18.23-11-30.dblg.zip
   ……
   <AC> ftp x.x.x.x
   <AC> put log.log
   <AC> put log.dblg
   <AC> put *.zip

   According to the log analysis, the channel switching reason is In DFS, that is, the AP switches the channel to avoid a conflict with the radar channel.

4. If channels supported in a country or region overlaps with radar channels, radar channels must be avoided for APs.

Suggestion and Summary

The channels 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, and 144 can be used as radar channels. If the channels supported by a country or region and radar channels overlap, avoid using radar channels.