Hello Everyone. I have a question.
When the rank of MIMO channel gives rank of 1, this means that the layer should be one layer?
And how the rank of channel changes as UE gives a feedback of it?
I need to undertand the concept of this process.
In MIMO-OFDM 5G NR.
Rank 1 means 1 stream of data.
Network and device can still be using 2 or 4 antennas (for spatial diversity).
As UE RF condition improves, network can start sending separate stream for each of antenna receiver (if 2 antenna receiver Rank 2 will make 2 separate streams of data, thereby doubling throughput).
Concept is same across technologies. Mechanism can be different.
Stream of data means layers. If one stream, then it is one layer. If 2 separate streams, mean a layers and yes you are doubling the throughput.
Yes, I understand.
You mentioned important point. Depends on RF condition at UE, the UE will give rank feedback to transmitter.
Right?
I personally do not prefer word ‘layer’. Not sure but don’t think its a standard term.
When you get to MU-MIMO with CA, word 'layer gets a whole lot confusing.
So for purpose of this, yes stream is a layer.
Yes.
You are right.
Because most of people are confusing😅 with word layer that layer is part of OSI Model.
Then, its clear to me 
In CA you have layers of data for individual carrier.
MU-MIMO has layers for each user in 1 TTI.
MU-MIMO with 2x2 has layers of data for individual user.
You see it’s gets very confusing.
Because if you have 2 layers means you have 2 indepented data streams.
So if you have rank of 2 mean you get 2 layers with indepented data streams for each layer.
Just use word stream or be prepared to explain what you mean by layer.
See you are confusing it. Just remember Rank 2 means there are 2 streams of data, that’s it.
Yes, you are right.
It’s confusing and I got your point.
I know what you mean. layers is basically if you have two layers, you are disturbing the modulated data stream into 2 indepented data streams
You are using word stream rather than layer, but it is same concept here
But, thanks for your information about ranking. 
I have slight disagreement on layer and stream definition. As an example , for rank 1 case - there can only be 1 layer but 1,2 or 4 streams. These 1,2 or 4 streams are in case of transmit diversity with 1,2 or 4 antenna support. Layers and streams will map 1 to 1 in case of spatial multiplexing,ex 2 layers = 2 streams.