I have one question.
Does UE also report RI in RRC-connected mode but no data transmitted?
Depends wether CQI report configured is Periodic Or aperiodic.
You can check IE pmi-ri in rrc connection reconfiguration setup or not.
Generally it’s there with closed loop mimo, tm6, tm8.
Open loop also RI report.
Just no PMI.
Yes agree, for open loop case Cqi config IE can be check.
My question is even RI report is setup.
Does UE in connected mode, no data, send RI?
Yes as it will be in connected mode then cqi reporting will be there in case of periodic cqi so need to indicate RI as well.
CQI is based on SINR measurement from CRS, even no data UE still can measure.
But RI is based on SVD, I think UE should already have data so UE can recommend rank.
@RFSpecialist, could you talk again about SVD, how UE recommend the rank?
Rank is calculated based on SVD of air interface matrix.
Idea is that we cannot force a higher rank, other than what air interface allows.
But a UE with more receiving antenna, that has a smart algo for antenna selection mechanism, can report a higher rank than a regular UE.
UE receive TB data first, then UE estimate how mane layers are prefered, right?
From what I’ve seen in logs UE is scheduled with 4 layers even if it has low data to transmit.
I ask about: if UE no data received, does it report RI?
I think it does, otherwise how can it be scheduled with data in next TTI if data comes in the buffer?
If no data, UE just receive CRS, no PDSCH.
How UE know how many layers?
UE measures CRS, so based on this it estimates air interface matrix.
From air interface matrix with SVD technique it gets the RI.
Then it reports RI to gnodeB together with PMI.
RI means how many clean and uncorrrlated multipath signals UE is receiving.
Doesn’t mattter data is transmitted to UE or not.
But we have csi-rs so air interface matrix can be calculated.
And so SVD and so rank.
Csi-rs is in 5G, here is 4G.
In Huawei system counters, I see counter CQI report is much more than RI report.
ENB with 4 antenna will send 4 different CRS that UE can decode. This will give the RI.
For more than 4 , it is csi-rs that will help to calculate RI.