What is the difference between Rank indicator (RI) and layer indicator (LI)?

Hi Guys,
What is the difference between Rank indicator (RI) and layer indicator (LI) reported by UE in CSI reporting in 5GNR?

From 5G in Bullets:

The Layer Indicator (LI) identifiesi the strongest layer from the set of layers indicated by the reported Rank Indicator (RI).
For example if the UE reports rank4, then the LI identifies the strongest of those 4 layers.


What is the diference?

It says LI is the “most occurring value of Layer Indicator”.

It say LI is the strongest layer.

Also from 5G in Bullets:

The Base Station can take advantage of the Layer Indicator when transmitting the Phase Tracking Reference Signal (PTRS).
The performance of the PTRS is maximized if it is transmitted usgin the layer with the best channel conditions.
If the PTRS is transmitted using port 1000, while the UE reports that layer 3 has the best channel conditions, then Base Station can map antenna port 1000 onto layer 3.


Oh, good to know. Thanks. :wink:

Also: gNB use layer indicator for what purpose?

To report best layer index.
(As far as I remember)

For that we have another similar indicator as CRI i.e. csi- rs resource indicator.

It is LI which tells best layer.
CRI seems for best beam.

Hi Hainm, I have one question about layer indicator. according to 3gpp, bitwidth of layer indicator is
it means its value is used to indicate the best layer within reported rank. for example we are using 8X4 mMIMO, it means we have 8 CSI-RS antenna port, if reported rank is 4(reported bit value is 11), then what’s the meaning of layer indicator value 11(last layer in reported 4 layers)? we have 8 CSI-RS antenna port, how could we know to which one reported 4 layers should be mapped?