What is Rank Indicator in 5G?
My friend: Hi Ibrahim, I have a question for you.
Me: Please, go ahead.
My friend: I was wondering what is meant by Rank Indicator in 5G?
Me: Rank Indicator (RI) is a special type of UE measurement that is reported by the UE to request a specific number of MIMO layers. RI is included in the CSI feedback sent from UE side towards the 5G BTS with other information such as CQI and PMI. For example, if UE reported RI=1 (RANK1), so that means only one stream of data will be assigned to the UE, while if UE reported RI=2 (RANK2), so two streams of data will be sent to the UE (2x2 MIMO), RI=4 means 4x4 MIMO and so on, please check the below snapshot.
My friend: But, how does UE determine the rank to be used whether it is 1, 2 or anything else?
Me: Simply, UE will determine the correlation between the different signals received at each receive antenna and best performance happened when signals are not correlated and worst performance happens when signals are correlated. Here, correlation means causing interference to each other. The number of useful layers depends upon the propagation channel conditions. So, transferring a high number of layers requires a corresponding high number of uncorrelated propagation paths between the transmitter and receiver.
My friend: Thanks a lot, you made it very clear.
Me: You are most welcome.
From :https://www.linkedin.com/feed/update/ur ... erlay=true