ASUS RTAX88U Wi-Fi6 MCS index selection

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New Around Here
Dear Wi-Fi enthusiasts,

Recently, I have been investigating ASUS RTAX88U Wi-Fi6 MCS index selection. I have created a conducted test-setup to measure this. I am running a downstream TCP iperf to another ASUS RT-AX88U in bridge mode (aka Wi-Fi station).
I have added a step attenuator between the AP and Wi-Fi station so that I can induce an MCS drop.
On the X axis in the graph below, 0 dB attenuator corresponds to -20 dBm RSSI measured on the Wi-Fi station. Y-axis is the percentage of HE-SU (data packets detected).
I am very surprised by the data as I had expected all the detected data packets to be MCS11 (upto 33 dB attenuation).


Anyone has seen this before? Any comments are appreciated.



Part of the Furniture
Is this testing of your own design? Is it expected to give you the results you seek?

What exactly is this going to help with, in actual use?

Given the results you got, does it affect your Wi-Fi environment in any tangible way with regards to speed, stability, or other?


New Around Here
Dear L&LD,
Thanks for your reply.
I was expecting to see a higher percentage of MCS11 data packets sent upto -60 dBm received signal level.
What I see is a mix of MCS rates being selected even when the SNR requirements are fulfilled. Seeing this in conducted measurements is not expected as there is no channel variation. I have also tried disabling MIMO and beam forming, but see the same trend.
It does affect the peak throughput rates which can be achieved by Wi-Fi6 router. Transmitting at lower MCS rates occupies more air-time, translating into a peak throughput drop.
I would design a Wi-Fi6 system which always selects MCS11 rates at least in controlled conducted measurements, to maximize the throughput performance.

Have you or anyone ever checked for MCS index selection in a sniffer ?

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