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5G NR Channel State Reporting: SSBRI and CRI

5g nr channel state information beam management rsrp measurement layer 1

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