Signals Are Poor

To address the problem of low signal strength, use scanning software to scan surrounding signals and check the signal strength. Usually, the RSSIs of the wireless signals should be larger than -75 dBm in common coverage areas. If the RSSI cannot meet requirements, adjust the AP power or replan the network.

Networks with low-RSSI signals are of low quality. You need to adjust AP power on these networks.

If automatic radio calibration causes low AP power, you need to plan the channel and power of the AP properly, and set the radio calibration mode to fixed mode.

Poor signal quality seriously affects user services, causing association failures, forced logout, and low network access rate. To solve these problems, perform the following operations:

• Association failures

  Check whether the performance of the terminal NIC or AP power is low.

  • If the performance of the terminal NIC is low, update the NIC drive or replace the terminal.
  • If the AP power is low, adjust AP transmit power to provide signals with proper RSSIs.
  • If the poor signal quality is caused by neither of the preceding problems, go to the next step.
• Forced logout

  The methods are the same as those specified in the preceding step.

• Low network access rate

  Perform ping operations and check whether long forwarding delay or packet loss occurs. If the packet loss ratio is larger than 5% or the average delay is longer than 500 ms, the terminal has low performance.

  Ping statistics for xxx.xxx.xxx.xxx:
      Packets: Sent = 21, Received = 19, Lost = 2 (9% loss),
  Approximate round trip times in milli-seconds:
      Minimum = 157ms, Maximum = 351ms, Average = 271ms

If poor signals are caused by interference in the radio environment, use the scanning tools to scan the radio environment and check whether there are conflicting channels.

Common scanning tools include the following: WirelessMon, inSSIDer, Network Stumbler, and CloudCampus APP on mobile phones.

If interference in the surroundings cannot be detected by scanning tools, locate whether non-Wi-Fi devices exist in the surroundings, such as Bluetooth and infrared ray devices, and microwave ovens, which may cause severe interference to the WLAN. You can also enable the interference detection function.

WLAN wireless channels are often affected by the radio environment, and the service quality is therefore degraded. Interference detection allows APs to send an alarm to an AC when co-channel interference, adjacent-channel interference, or STA interference exceeds the alarm threshold.

Interference detection can detect AP co-channel interference, AP adjacent-channel interference, and STA interference.

• AP co-channel interference: Two APs working in the same frequency band interfere with each other. For example, on a large-scale WLAN (a university campus network), different APs often use the same channel. Co-channel interference exists in overlapping areas among these APs, degrading network performance.
• AP adjacent-channel interference: Two APs with different center frequencies have overlapping areas, resulting in adjacent-channel interference. Therefore, if APs are placed too close to each other or they have strong signals, more noise will be produced, degrading network performance.
• STA interference: If there are many STAs that are managed by other APs around an AP, services of the STAs managed by the local AP may be affected.

The following figure shows alarms generated due to co-channel interference and STA interference.

[AC6605-wlan-view]
Sep 6 2013 22:25:53+08:00 AC6005 WLAN/4/AP_COMMON_FREQUENCY_DISTURB:OID 1.3.6.1.4.1.2011.6.139.3.24.1.5 Jan of common frequency is detected notify.(APID=0, APID=0, RadioID=0, APMAC=[e4.68.a3.4f.6b.a0 (hex)], APChannel=11, BssID=[dc.d2.fc.f8.c5.e0 (hex)], RSSI=45)

[AC6605-wlan-view]
Sep 6 2013 22:25:53+08:00 AC6005 WLAN/4/STATION_DISTURB:OID 1.3.6.1.4.1.2011.6.139.3.24.1.9 Jan of station is detected notify.(APID=0, APID=0, RadioID=0, APMAC=[e4.68.a3.4f.6b.a0 (hex)], APChannel=11, StatMACList=0039-3310-1560,2cd2-e7a6-d2aa,8c70-5a47-9cb0,64a7-6970-5d85,9021-55d8-ee4a,cc53-b5ee-39ef,) 

After interference sources are located through the preceding steps, make corresponding adjustments to improve the radio environment.

• Wi-Fi interference

  Replan channels and adjust AP power to prevent co-channel and adjacent-channel interference. If many channels interfere with each other or channel overlapping cannot be avoided, discuss with customers to change the locations of other Wi-Fi devices.

  As shown in the following, set values of channel 20mhz XX and power-level to adjust the channels and AP power.

  [AC6005-wlan-radio-0/0] display this  
  # 
    radio-profile id 0  
    channel 20MHz 13
    power-level 2
  # 
  return 

• Non-Wi-Fi interference

  Non-Wi-Fi interference refers to the interference from non-Wi-Fi devices, such as the Bluetooth devices and cordless phones. Avoid using these devices during the working period of APs or remove the interference devices.