I read somewhere DCI with MAC-CE A-CSI Report Trigger would do the following: DCI with MAC-CE is sent to UE to measure and report L1-CSI RSRP and starts CSI-RS resources transmission.

Does that mean that the MAC-CE would trigger the CSI-RS resources and the DCI further triggers subset of them? which of the MAC-CE and DCI are used to indicate reporting and which is used to configure the resources?

Thank you


Hello there! Nice question indeed but let shed some light first to clarify whole procedure that is usually related to beam management.

  1. Through RRC:
    -gNB sends TCI states (up to 64 for PDCCH, 128 PDSCH)
    -It also configures an aperiodic (AP) CSI-RS (nzp/CSI-IM) with “reportquantity” configured to L1-RSRP (for instance).

  2. a “CSI Request” field is flagged in DCI to trigger AP CSI-RS.

  3. After that, the UE reports L1-RSRP based on aperiodic offset list (for instance), if there is only CSI on PUSCH it will follow another rule.

  4. the gNB sends a MAC-CE command to activate a specific TCI state or a down-select (8 out of 128 relation for PDSCH, for instance) from the the list of TCI state sent previously (step 1).

  5. A TCI field (3bits) could select one out of 8 TCI states sent by MAC-CE (step 4). This step requires that “tci-PrensentInDCI” to be sent previously (step1).

obs.: TCI state might be related to CSI-RS or SSB.

So MAC-CE activates(changes) CSI-RS/SSB, but do not trigger CSI-RS reporting for L1-RSRP.
DCI can trigger CSI-RS for L1-RSRP reporting. The resources available for L1-RSRP are configured through RRC and how they should be reported as well.

obs.: this procedure could also be periodic without need of DCI triggering.