Hello Experts.
5G CSI-RS supports only 32 ports, so how to use 64 or 128 antenna ports configurations?
Don’t confuse csi-rs ports with antenna elements 256, 384 or even 1024.
I am talking about 64 or 128 antenna ports, not antenna elements.
When people say 64 TR system or 128 TR system.
Then do we really have 64 or 128 port csi-rs?
Max 32 csi-rs ports, not possible more.
I think this picture below will help to understand the transition from logical antenna ports to physical antenna ports:
From C to D.
Most of time we get confuse with available beam for selection which is obvious high compare to number of CSI RS port available.
Here number of beams available for selection depends on n1 n2 and overshampling factor.
I think the antennas can be grouped into sub sets, each being managed independently.
4 two-port 32 units can be combined to make a 128 configuration.
Yes each 4 antenna element of a subset having same phase shift.
Like in picture above.
Transition from C to D.
Subset means a group of antenna elements like a green rectangle in picture.
Thank you! I understood.
People should call it 32 TR solution only then.
It is indeed one of the most confusing concept in 5G.
In this how they map 32 csi-rs port to 64 T?
MU-MIMO is also not easy to get how is it possible to send 16 PDSCH layers simultaneously without interfering each other.
But once you get spatial multiplexing, it is ok.
Not to mention, how different users can get 2x2 or 4x4 MIMO within those layers.
Is there any video explaining MU-MIMO in detail?
Wireless Future channel in YouTube: 
This is how you radiate CSI-RS using 32 port when your antenna is 64T64R
Ericsson is radiating CSI-RS using 32 port and there is only one CSI RS beam across the one cell. ( N1: 8, N2: 2)
Nokia is radiating CSI-RS using 8 port and they are using 4 CSI RS beams in a cell i.e. in Nokia CSI RS transmission is beamformed.
So eventually Nokia is also using 32 port CSI RS.