This blog presents the results of the new MCS table updated to include all the new 802.11ax data rates. It also presents how these data rates are calculated.
Complete MCS Table
As you can see, the table is getting very big. In fact, 802.11ax is introducing 2880 new data rates. However, not all data rates will be used in the real world. In order to focus on what will be most useful to Wi-Fi Engineers, I have created some smaller tables which only focuses on sections of the complete table.
MCS Table up to 3 Spatial Streams
802.11ax MCS Table
802.11ax MCS Table (OFDM)
802.11ax MCS Table (OFDMA)
The Math Behind It
Here is the formula we can use to calculate which data rate is used for both 802.11n and 802.11ac:
- A new symbol duration is used: 12.8µs
- Different Guard Intervals are used: 0.8µs, 1.6µs and 3.2µs
- The size and number of data subcarriers is not the same (especially with the different RU sizes introduced by OFDMA.
Even though the formula doesn't change much, the IEEE does define 2 different formulas depending on if OFDMA is used or not. When OFDMA is not used, we can used the formula previously presented above.
Here is the formula we can used when OFDMA is used (it is pretty much the same except that we define the number of data subcarriers per RU and not per channel):
- Index 10: when the 1024-QAM modulation is used with a coding of 3/4
- Index 11: when the 1024-QAM modulation is used with a coding of 5/6
The phone is a Samsung GS10 which supports 802.11ax and up to 2 spatial streams. The AP used is an Aerohive AP630. I have configured it with an 80MHz wide channel. OFDMA is not used here because ODFMA was not activated at the time of this capture.
So based on this information, we can determine some of the variables required to calculate the data rate and narrow down the data rates that will be used by this device:
- Number of Data Subcarriers for an 80MHz wide channel: 980
- Number of Coded bit per subcarrier (Modulation): we don't know yet
- Coding: we don't know yet
- Number of Spatial Streams: 2
- OFDM Symbol Duration: 12.8µs
- Guard Interval: we don't know yet
So here is the list of possible data rates used by this device when connecting to this AP:
- MCS 11 was used
- 1024QAM with a coding of 5/6 was being used
- A guard interval of 0.8µs was used
- IEEE 802.11ax Draft D4.0 ($400): https://www.techstreet.com/ieee/standards/ieee-p802-11ax?gateway_code=ieee&vendor_id=7180&product_id=2019792
- "802.11 OFDM Data Rates – The Math Behind The Numbers" great article from Renzo Notter: http://dot11.exposed/2018/11/29/802-11-ofdm-data-rates-the-math-behind-the-numbers/
- MCS Table by Keith Parsons at WirelessLAN Proffesionals: https://d2cpnw0u24fjm4.cloudfront.net/wp-content/uploads/802.11ac-VHT-MCS-SNR-and-RSSI.pdf
- Clear To Send Podcast - 802.11ax OFDMA Subcarriers: https://www.cleartosend.net/802-11ax-ofdma-subcarriers/
- Clear To Send Podcast - 802.11ax OFDMA Resource Units: https://www.cleartosend.net/802-11ax-ofdma-resource-units/
- 802.11ac Missing MCSs by Jérôme Henry: https://www.youtube.com/watch?v=vTIy-rjopY8