Why QPSk ,16 QAM and 64 QAM are used in LTE and what is the significance of using these techniques? why not others?

Question

I found that LTE supports up to 64 QAM modulation scheme . From where this limitation comes out ?

Answer 1

From Bart - https://www.facebook.com/groups/LTE.Professionals/
The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to carry more bits of information per symbol.

Also the QAM 16/32/etc. variants are used to allocate dynamic number of subscribers per cell/antenna. Keep in mind that your vector used to spread/de-spread your data still has to be unique.

Long story short, the Intelligent eNB breaths, but this time modulation, not antenna power and it is still able to provide unique spread vector.