5G NR Channel State Reporting: SSBRI and CRI
This page describes the 5G NR channel state reporting fields, specifically SSBRI and CRI, used in Layer 1 RSRP measurements.
Introduction
- SSBRI is short for SS/PBCH Block Resource Indicator.
- CRI is short for CSI Reference Signal Resource Indicator.
Both terms are used in 5G NR (New Radio) Layer-1 RSRP measurement. They play a crucial role during beam management procedures to identify the best downlink beam.
5G NR SSBRI
- SSBRI is reported when the
"reportQuantity"
field within the"CSI-reportConfig"
is configured with the value'sub-index-RSRP'
. - It’s reported in conjunction with the Layer 1 RSRP measurement recorded from the SSS (Secondary Synchronization Signal).
- It’s used to identify the best downlink beam(s). Think of it as helping the UE quickly find the strongest signal from the available beams.
- CSI (Channel State Information) allows for rapid and responsive beam switching. This allows the network to adapt to changing conditions and ensure optimal data rates.
- The base station (BS) can enable or disable the use of Group-based Beam Reporting while the UE is configured to provide SSBRI reports. This configuration is managed using the
"groupBasedBeamReporting"
Information Element (IE) within"CSI-reportConfig"
. This gives the network flexibility in how it handles beam reporting.
5G NR CRI
- CRI is reported in combination with the Layer 1 RSRP measurement when the
"reportQuantity"
within"CSI-reportConfig"
is configured with the value'cri-RSRP'
. The RSRP measurement in this case is recorded from the CSI reference signal. - CRI is also reported along with other channel state information when
"reportQuantity"
is configured with values such as'cri-RI-PMI-CQI'
,'cri-RI-i1'
,'cri-RI-i1-CQI'
,'cri-RI-CQI'
, or'cri-RI-LI-PMI-CQI'
. This allows the network to gather a more comprehensive picture of the channel conditions. - CRI enables the base station to switch between CSI Reference Signal Beams, which are typically more directional than SS/PBCH beams. This allows for more precise targeting of the UE and improved signal quality.
References
- 3GPP TS 38.214
- 3GPP TS 38.212
- 3GPP TS 38.133