How CQI, PMI and RI reporting by UE in LTE?
The UE is requested to send either periodic or a periodic reports concerning
• Rank indication (RI)
Reports are applicable for closed- and open-loop spatial multiplexing. In case of open-loop TRI=1 corresponds to transmit diversity and TRI>1 to large delay CDD.
• Precoding matrix indicator (PMI)
PMI reporting is relevant for spatial multiplexing (open- and closed-loop), MU-MIMO, closed-loop RANK=1 precoding. PMI and RI are confined to a subset of the codebook which is created by means of a codebookSubsetRestriction parameter.
• Channel quality indication (CQI)
CQI may be wideband or may be related to subbands. Similar to HSPA the CQI definition is targeted at 10 % BLER whereby the overall energy per bit is nearly minimized.
For the purpose of periodic reporting the PUCCH is utilized, a periodic reports are sent on the PUSCH. The latter reports are explicitly requested by setting the CQI request field in connection with an uplink grant. In case of “collision” the aperiodic report will be transmitted.
Furthermore the scheduling mode can be frequency non-selective (periodic) or frequency selective (periodic and aperiodic).
The offset is signaled by nom PDSCH-RS-EPRE-Offset.
How CQI, PMI and RI Reporting by UE in LTE?
In LTE, the UE reports CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), and RI (Rank Indicator) to help the eNB optimize resource allocation. CQI indicates the channel’s quality for selecting the appropriate modulation scheme, PMI reports the preferred precoding matrix for MIMO transmission, and RI indicates the number of spatial layers the UE can support. These reports are sent periodically or when requested by the eNB to adjust transmission strategies for improved data rates and reliability.