I have been reading about MCS rates and there is one thing i dont understand. In multiple white papers, i could see the values given upto 32 index only. After that, they give an example of MCS 33 (which is same in almost all whitepapers i have read) that
For e.g. MCS 33 includes 16-QAM on stream 1 and QPSK on another.
i tried looking at multiple places, but i dont see MCS 33 to 76 defined anywhere. Are they totally random and its coincidence that everyone is giving the same example for MCS 33?
The un-equal modulation rates you are talking about were only proposed for 802.11n. The idea was deprecated in 802.11ac as apparently few, if any, manufacturers ever used it.
If you look in the IEEE 802.11n-2009 standard starting at about page 349, you will find several pages that list the various possibilities.
RIFS was also deprecated.