Description
L1-RSRP (Layer 1 Reference Signal Received Power) is a fundamental radio measurement defined in 3GPP for 5G New Radio (NR) and evolved in later releases. It represents the linear average over the power contributions of the resource elements that carry cell-specific reference signals within a specified measurement bandwidth. Unlike higher-layer filtered measurements, L1-RSRP is a physical layer measurement, meaning it is performed directly on the received symbols before extensive layer 2 processing and filtering. The UE measures L1-RSRP on reference signals such as the Synchronization Signal Block (SSB) for initial cell selection and mobility, or the Channel State Information Reference Signal (CSI-RS) for more precise beam-level measurements and channel state reporting.
The measurement procedure involves the UE's physical layer processing chain. After synchronization and OFDM demodulation, the receiver identifies the resource elements allocated to the specific reference signal sequences. It then calculates the received power for these elements, typically averaging the results over multiple symbols and subcarriers to mitigate the effects of fast fading and noise. The result is reported internally to higher layers (e.g., the RRC layer) as a raw measurement, which may then be filtered (becoming L3-RSRP) for use in events like handover triggering. In the context of beam management, the UE can measure L1-RSRP on multiple CSI-RS beams transmitted by the gNB and report the best beams, enabling the network to select the optimal transmission/reception beam pair.
L1-RSRP is specified with strict accuracy requirements in conformance test specifications (e.g., 38.133). Its value is reported in dBm and is crucial for several network functions. It serves as the primary metric for cell selection and reselection in idle/inactive states. During connected mode, it is used for handover evaluation and radio link monitoring (to detect radio link failure). In 5G's beam-centric operation, L1-RSRP measurements on CSI-RS resources are the basis for beam failure detection and recovery procedures, as well as for determining the best beam for PDCCH and PDSCH transmission.
Purpose & Motivation
L1-RSRP was introduced to provide a fast, accurate, and granular measurement of signal strength specifically tailored for the advanced features of 5G NR. Previous technologies like LTE used RSRP, but the 5G L1-RSRP is designed to address the challenges of higher frequencies (including mmWave), massive MIMO, and beamforming. The problem it solves is the need for timely and precise signal quality assessment for beam management, which is critical for maintaining reliable connectivity in environments with high path loss and dynamic blockages.
The motivation for specifying L1-RSRP separately stems from the need for low-latency measurements to support fast beam switching and mobility in 5G. Beamforming, especially at millimeter-wave frequencies, creates narrow, directional beams that can change rapidly as a user moves. The network requires frequent and accurate power measurements on these individual beams to make swift beam management decisions. L1-RSRP provides this raw, unfiltered data point directly from the physical layer, enabling faster reaction times compared to more heavily filtered Layer 3 measurements. It is a foundational enabler for the reliability and high throughput promised by 5G NR.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (85 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the specification introduced detailed scheduling availability requirements for the UE performing L1-RSRP measurements. These requirements were specifically defined for scenarios where the measurement subcarrier spacing was either the same as or different from that of the PDSCH/PDCCH on FR1, and separately for operations on FR2.
In Release 16, key enhancements for L1-RSRP introduced new scheduling availability requirements and measurement restrictions, particularly for scenarios involving different subcarrier spacings and carrier aggregation. Specifically, the release defined separate scheduling availability rules for UEs performing L1-RSRP measurements when the subcarrier spacing matched or differed from that of PDSCH/PDCCH on FR1, and for measurements on FR2. Furthermore, it introduced explicit measurement restrictions for L1-RSRP, refining its operation during active time and in relation to cross-slot scheduling.
- Aperiodic CSI-RS Triggering for UE reporting beamSwitchTiming values of 224 and 336 TS 38.214CR0060
- Corrections of cross-slot scheduling restriction and CSI/L1-RSRP measurement outside active time TS 38.214CR0074
- Correction on SRS-RSRP reception procedure for CLI TS 38.214CR0094
- Correction on aperiodic CSI-RS triggering with beam switching timing of 224 and 336 and on CSI reporting TS 38.214CR0107
- Correction on aperiodic CSI-RS triggering with beam switching timing of 224 and 336 TS 38.214CR0121
- Corrections for default TCI state of AP CSI-RS in multi-TRP TS 38.214CR0131
+ 14 more changes
In Release 17, new scheduling availability requirements were defined for a UE performing L1-RSRP measurement. These requirements specify the UE's availability when the measurement uses the same or a different subcarrier spacing as the PDSCH/PDCCH on FR1, and for measurements on FR2, including specific cases for FR1-FR2 inter-band Carrier Aggregation and NR-Dual Connectivity.
- Introduction of NR UE Power Saving Enhancements TS 38.214CR0236
- Correction to IAB-MT timing reference point in TS 38.174 TS 38.174CR0042
- Corrections on NR UE Power Saving Enhancements TS 38.214CR0258
- CR on the positioning frequency layer within a PPW and UE capability for the PPW TS 38.214CR0304
- Correction on CQI derivation accounting for provided DL Tx power adjustment for IAB-MT TS 38.214CR0308
- CR for CSI-RS power for inter-cell mTRP TS 38.214CR0313
+ 18 more changes
In Release 18, the L1-RSRP function was updated with new scheduling availability requirements for UEs performing these measurements, particularly in complex carrier aggregation and dual-connectivity scenarios like FR1-FR2 inter-band CA and NR-DC. The release also introduced specific applicability for inter-cell SSB based L1-RSRP measurements, expanding its use cases. Furthermore, corrections and clarifications were made to ensure power consistency and phase continuity during cell DRX operation, which impacts the measurement conditions.
- Corrections on RRC parameters for R18 NES spatial/power domain adaptation TS 38.214CR0544
- Correction on modulation order of Msg3 when higher layer parameter tp-pi2BPSK is configured TS 38.214CR0551
- Correction of power consistency and phase continuity during cell DRX operation TS 38.214CR0554
- Correction of physical channels and signals during cell DTX/DRX operation TS 38.214CR0566
- Correction on CSI processing criteria for new NES capability signaling TS 38.214CR0584
- Correction on threshold for A-CSI-RS reception for Rel-18 TCI framework TS 38.214CR0613
+ 20 more changes
In Release 19, the L1-RSRP function saw clarifications and corrections to procedures for counting simultaneous NZP-CSI-RS resources and to the association between NZP CSI-RS and CSI-IM. The release also added specific applicability for L1-RSRP test cases in Non-Terrestrial Networks (NTN) and introduced new scheduling availability requirements for UEs performing these measurements, particularly in FR1-NTN scenarios.
- TEI19 Counting of CSI-RS resource referred by N CSI reporting settings [SimCSI_count] TS 38.214CR0681
- TEI19 Simultaneous NZP-CSI-RS resource counting with NES [SimCSI_countNES] TS 38.214CR0689
- Correction on Semi-persistent CSI/Semi-persistent CSI-RS for LTM TS 38.214CR0733
- Correction on association between NZP CSI-RS and CSI-IM TS 38.214CR0744
- Clarification on the number of simultaneous L1 CLI-RSSI and simultaneous L1 SRS-RSRP measurement resources TS 38.214CR0745
- Correction on the maximum number of SRS-RSRP measurement resource sets and CLI-RSSI measurement resource sets TS 38.214CR0746
+ 6 more changes
Explore further
Broader topics and technologies where L1-RSRP plays a role.
Defining Specifications
3GPP specifications that define or reference L1-RSRP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.174 vj10 | NR Integrated Access and Backhaul Radio Spec | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |
| TS 38.843 vj00 | Study on AI/ML for NR Air Interface | Rel-19 |