Description
CSI-RSRP is a Layer 1 measurement defined in 3GPP specifications 38.214 and 38.215 for New Radio (NR). It represents the linear average over the power contributions of the resource elements that carry CSI reference signals within the considered measurement frequency bandwidth. Unlike SS-RSRP which measures synchronization signal blocks, CSI-RSRP specifically measures reference signals that are configured for channel state information acquisition, enabling more precise beam-specific measurements.
The measurement procedure involves the UE measuring the received power of configured CSI-RS resources, which can be transmitted in different spatial directions (beams) from the gNB. The UE performs power measurement on the designated CSI-RS resource elements, applying appropriate filtering and averaging as specified. The measurement bandwidth can be configured per CSI-RS resource, allowing flexible measurement granularity. CSI-RSRP measurements are reported to the network through Layer 1 or Layer 3 reporting mechanisms, supporting both periodic and event-triggered reporting.
Architecturally, CSI-RSRP operates within the physical layer measurement framework where the UE's physical layer processes the received CSI-RS symbols, extracts the reference signal sequences, and computes the received power. The measurement accounts for antenna port-specific configurations, supporting measurements from multiple transmit antenna ports. Key components include the CSI-RS resource configuration (defining time-frequency patterns), measurement timing configuration, and reporting configurations that determine when and how measurements are reported to higher layers.
In the network operation, CSI-RSRP serves multiple critical functions. For beam management, it enables the gNB to determine the best transmit/receive beam pairs by comparing CSI-RSRP measurements from different CSI-RS resources transmitted on different beams. For mobility, it provides beam-specific signal quality measurements that complement cell-level measurements, enabling more accurate handover decisions in beamformed networks. For link adaptation, it helps estimate the channel quality for specific transmission configurations, supporting MIMO layer selection and modulation and coding scheme (MCS) adaptation.
Purpose & Motivation
CSI-RSRP was introduced in 5G NR Release 15 to address the limitations of existing reference signal measurements in beamformed systems. Previous LTE systems primarily used CRS (Cell-specific Reference Signal) based RSRP measurements, which were broadcast over the entire cell coverage area. However, in 5G's massive MIMO deployments with beamforming, broadcast reference signals cannot provide accurate beam-specific channel quality information needed for optimal beam management and mobility.
The technology solves the problem of accurately measuring signal strength for specific beamformed transmissions. In beamforming scenarios, different beams have different coverage patterns and signal qualities, requiring beam-specific measurements for effective beam selection and handover. CSI-RSRP enables precise measurement of the channel quality experienced by UE-specific or beam-specific reference signals, which is essential for beam management procedures including beam sweeping, beam measurement, and beam reporting.
Historical context shows that earlier systems lacked beam-specific measurement capabilities. LTE's RSRP measurements were cell-wide and didn't support beam-level granularity. The introduction of CSI-RSRP in 5G NR was motivated by the need to support advanced beam management features, massive MIMO operations, and millimeter wave deployments where beamforming is essential for coverage and capacity. It addresses the limitation of SS-RSRP which, while useful for initial access, doesn't provide the beam-specific accuracy needed for ongoing beam management and mobility in dense beamformed networks.
Key Features
- Beam-specific power measurement for CSI-RS resources
- Configurable measurement bandwidth per CSI-RS resource
- Support for multiple antenna port measurements
- Layer 1 and Layer 3 reporting mechanisms
- Flexible time-domain measurement occasions
- Integration with beam management procedures
Evolution Across Releases
Introduced CSI-RSRP as a new physical layer measurement for 5G NR, defining the basic measurement procedure for CSI reference signals. Established the framework for beam-specific measurements supporting beam management, with configuration through RRC signaling and reporting via MAC CE or RRC. Enabled measurement of configured CSI-RS resources for both periodic and aperiodic reporting.
Defining Specifications
| Specification | Title |
|---|---|
| TS 38.214 | 3GPP TR 38.214 |
| TS 38.215 | 3GPP TR 38.215 |