Troubleshooting Air Interface Quality Issues
The air interface environment is affected by factors including the received signal strength indicator (RSSI), signal-to-noise ratio (SNR), and channel independence of different TX+RX antenna combinations in the MIMO system.
In most cases, higher RSSI and SNR values indicate better performance. When the MIMO system works, higher channel independence indicates better performance.
Air interface quality affects the WLAN communication system, which is represented by the link setup rate, MCS statistics, RSSI, and channel utilization.
Interference Check
It is recommended that the test environment interference be checked before a test. Signals on the same or neighboring channel as the channel under test are considered as interference signals.
Try to perform the test in a place without any signals. If no such an environment is available, ensure that no signals exist on the channel under test and the RSSI on channels other than neighboring channels is lower than –95 dBm.
Check interference as follows:
- For Wi-Fi interference signals: Install the inSSIDer software on a laptop that supports 2.4 GHz and 5 GHz bands or install the CloudCampus APP on a dual-band mobile phone to check for Wi-Fi interference signals.
- For non-Wi-Fi interference signals: Use a WiFi Spy network adapter or a handheld spectrum analyzer to check for non-Wi-Fi interference signals.
PHY Rate Check
After a STA goes online, run the display station all command on the AC to check PHY rates. In the command output, Rx/Tx indicates the uplink/downlink PHY rates on the air interface. Note that the Rx/Tx values obtained when traffic is transmitted can reflect the actual performance.
<AC> display station all Rf/WLAN: Radio ID/WLAN ID Rx/Tx: link receive rate/link transmit rate(Mbps) ---------------------------------------------------------------------------------------------------- STA MAC AP ID Ap name Rf/WLAN Band Type Rx/Tx RSSI VLAN IP address SSID ---------------------------------------------------------------------------------------------------- 14cf-9208-9abf 0 1047-8007-6f80 0/2 2.4G 11n 215/208 -26 10 10.10.10.253 tap1 ---------------------------------------------------------------------------------------------------- Total: 1 2.4G: 1 5G: 0
To obtain the extremum single-user performance of the air interface, ensure that actual PHY rates are the same as the theoretical PHY rates in What Are PHY Rates on the Air Interface?.
If the theoretical rate cannot be reached, check environmental interference and adjust the relative antenna positions of the AP and STA.
MCS Statistics Check
MCS statistics include the packet transmit and receive rates of an AP. You can run the display wifi radio-statistics-sdk radio radio-id command in the diagnostic view to query the MSC value of each packet in the receive/transmit direction.
To ensure data accuracy, run the reset wifi radio-statistics sdk radio radio-id command in the diagnostic view to clear historical statistics before checking MCS statistics. Run the display wifi radio-statistics-sdk radio radio-id command to query MCS statistics after traffic is transmitted for a period of time.
<Huawei> system-view [Huawei] diagnose [Huawei-diagnose] display wifi radio-statistics-sdk radio 1 ... Rx MCS STATS: mcs 0- mcs 4 STATS: 0, 0, 0, 0, 0, mcs 5- mcs 9 STATS: 0, 0, 37, 0, 17595, Tx MCS STATS: mcs 0- mcs 4 STATS: 0, 0, 0, 0, 0, mcs 5- mcs 9 STATS: 16, 10, 16, 381, 48989,
The optimal situation is that 95% of MCSs are the highest-order MCSs. To adjust the environment, check environmental interference and adjust the relative antenna positions of the AP and STA.
Signal Strength Check
A high RSSI value is a guarantee for the highest air interface rate. The recommended RSSI ranges from –45 dBm to –30 dBm.
- The downlink RSSI refers to the RSSI of signals received by the STA and can be obtained using inSSIDer or Wifi Analyzer on the STA.
- The uplink RSSI refers to the RSSI of signals received by the AP from the STA and can be obtained by running the display station all command on the AC.
<AC> display station all Rf/WLAN: Radio ID/WLAN ID Rx/Tx: link receive rate/link transmit rate(Mbps) ---------------------------------------------------------------------------------------------------- STA MAC AP ID Ap name Rf/WLAN Band Type Rx/Tx RSSI VLAN IP address SSID ---------------------------------------------------------------------------------------------------- 14cf-9208-9abf 0 1047-8007-6f80 0/2 2.4G 11n 215/208 -26 10 10.10.10.253 tap1 ---------------------------------------------------------------------------------------------------- Total: 1 2.4G: 1 5G: 0
If the RSSI does not meet the preceding requirement, shorten the distance between the AP and STA (3 m or less can achieve a high RSSI in indoor scenarios) and increase the AP transmit power (APs use the maximum transmit power by default).
Channel Utilization Check
Channel utilization can be checked to detect interference on the channel to be tested. Run the following command on the AC to check channel utilization:
<AC> display ap traffic statistics wireless ap-id 1 radio 1 ----------------------------------------------------------------------- ... Wireless channel utilization(%) :0 ... -----------------------------------------------------------------------
When the DUT is not working, channel utilization should be 0. If a non-zero value is displayed, interference exists on the current channel.
Additionally, a professional Fluke USB network adapter can be used to check channel utilization.
