Wireless connection is Slow?

Modulation and Coding Scheme value is directly proportional to the client speed.

( check the website www.mcsindex.com )

Modulation and coding scheme(MCS) dependent on Signal to Noise Ratio (SNR) and Spatial Streams supported by the User Device.

Please check for Retry frames for specific user Device using below in Air captures

(wlan.addr contains <part of Client mac> && wlan.fc.retry == 1)

Retry frames deprecate the MCS value. (Similar TCP Window sizing).

Try to have a Benchmark value for the Retry frames percentage. In general, 5% of retry frames are acceptable for non-dense deployment.

Noise(like Bluetooth devices), Interference, frequent channel changes due to Radar inference, etc., can lead to the network's slowness.

If the user device fails to support all the AP/Infra channels, it may lead to Slowness.

Example: The user device connected to the farthest AP(AP01) than the AP(AP02), which is near to the user due to AP(AP02) is broadcasting SSID on the channel (like channel 100), user device does not support channel 100. The user device supported channels can be seen in the Association request.

The throughput of the users will be dependent on concurrent users on AP. The number of user connections on an AP is indirectly proportional to the users' throughput.

If any 802.11b clients connected to an AP on 2.4GHz will slow down the AP's users on 802.11g radio. We all know 802.11b clients work with lower rates, and to avoid 802.11b client associations to AP, lower rates below 12 Mbs on the 2.4 GHz are removed.

To conclude, to have expected throughput, we need to ensure the precise number of spatial streams both AP, the user device, consistent MCS value on the data traffic of the user device, and SNR.