PDSCH is number of layers.
LL1 PDSCH Demod Config Info Pri. Component Carrier M(Tx) x N(Rx) Ant No.
This from Qualcomm Tree gives me 2 Tx, i.e. 2x4.
And here it is Tx antenna and not layers, that’s the confusion.
The air interface will become like a diagonal matrix
So what you see there will be the diagonal matrix that 2x4 or 2x2
Read the SVD for matrix.
Here it is explained on Sharetechnote:
https://www.sharetechnote.com/html/Communication_ChannelModel_SVD.html
It’s math basically, but able to transform any air interface matrix (with strong interference between transmitters and receivers) into a single diagonal matrix without interference.
The rank of the diagonal matrix is the rank in 4G or 5G.
So with DSP (precoding at transmitter and equalizer at receiver) be able to transform any air interface matrix into a diagonal air interface matrix.
After SVD matrix is like having the diagonal matrix with a direct line between pairs of (transmitter antenna and receiver antenna) with zero interference between one to another.
This is where the gain comes from and this is how UE is able to receive data from a single TX antenna on a single RX antenna without being interfered by other TX antenna signals.
But this works only as long as there are uncorrelated multipaths between TX and Rx antennas so for a rank number of layers.
This can be as bad as 1 layer or ideal 4 layers.
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Guys, i got a new doubt:
As per picture shared earlier, can we say that with tm3/tm4 mode we can’t use 8x8 or 8x2 MIMO?
8x2 MIMO possible with tm9 only?
Is it correct to say?
Yes TM9 and TM10 only have 8 layer support in LTE.