Description
Received Signal Strength Indication (RSSI) is a fundamental, wideband power measurement performed by a User Equipment (UE) or a base station (e.g., NodeB, eNB, gNB). It quantifies the total received power within the specified channel bandwidth of the receiver. This measurement encompasses all contributing sources: the desired serving cell signal, co-channel interference from other cells, adjacent channel interference, and thermal noise. The measurement is typically performed on the receiver's intermediate frequency (IF) or baseband signal after analog-to-digital conversion but before any despreading or channel decoding. In 3GPP specifications, RSSI is defined for various radio access technologies (RATs) including UMTS (UTRA), LTE (E-UTRA), and NR. The specific measurement bandwidth, reference point, and averaging methods are detailed in the physical layer specifications for each RAT (e.g., TS 25.215 for UTRA, TS 36.214 for E-UTRA, TS 38.215 for NR). RSSI is a key input for calculating other derived metrics. Most notably, the Reference Signal Received Power (RSRP) measurement, which is a narrowband power measurement of specific reference symbols, is often considered in the context of the total RSSI to calculate the Signal-to-Interference-plus-Noise Ratio (SINR) or Reference Signal Received Quality (RSRQ). RSRQ is defined as (N * RSRP) / RSSI, where N is the number of resource blocks, linking the quality of the reference signal to the total received power. The network uses RSSI and its derived metrics for critical Radio Resource Management (RRM) functions. During initial cell selection and reselection, the UE measures the RSSI/RSRP of neighboring cells to identify the best candidate. For mobility management, RSSI trends trigger measurement reports that enable the network to make handover decisions. Furthermore, RSSI is used in uplink power control algorithms to help the UE adjust its transmit power to compensate for path loss and interference, ensuring reliable uplink communication while minimizing interference to other users.
Purpose & Motivation
RSSI exists as a fundamental, technology-agnostic metric for assessing the raw radio frequency (RF) conditions at a receiver. Its primary purpose is to provide a coarse, immediate indication of the overall signal strength in an operating channel, which is essential for basic radio functionality. Before more sophisticated, signal-specific measurements like RSRP were standardized for LTE and NR, RSSI (and its UMTS counterpart, Received Signal Code Power - RSCP) served as the primary metric for cell quality evaluation. It solves the fundamental problem of determining whether a receiver is in a viable coverage area. Without an RSSI measurement, a device cannot know if there is sufficient RF energy to even attempt synchronization or decoding of broadcast channels. Historically, RSSI has been a cornerstone of cellular systems since early GSM, providing the essential input for algorithms controlling cell selection, handover, and link adaptation. While modern systems rely more heavily on cleaner metrics like RSRP for precision, RSSI remains indispensable for calculating the interference-plus-noise floor (via metrics like RSRQ) and for operations in scenarios where specific reference signals may not be reliably detectable, offering a robust fallback measurement of the RF environment.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (59 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, specific corrections were introduced for the configuration of SS-RSSI measurements in System Information Block 24. Furthermore, the release added signalling for the RSRP result within the SFTD measurement report and introduced the new NR-SS-SINR measurement capability for LTE.
- Introduction of NR-SS-SINR TS 36.214CR0051
- Signalling for euCA (Enhancing LTE CA Utilization) TS 36.331CR3391
- Additional capability signalling for 1024QAM support TS 36.331CR4031
- Correction of CN type indication for RRC Redirection from E-UTRA/5GC to E-UTRA/5GC or E-UTRAN TS 36.331CR3601
- RSRP result in SFTD measurement report TS 36.331CR3602
- CR on carrier frequency indication in SidelinkUEInformation TS 36.331CR3700
+ 19 more changes
In Release 16, the primary update to the RSSI function was the removal of RSS-based RSRQ measurements, as indicated in the CR titles. This change refined the measurement framework by deprecating a specific method of deriving RSRQ (Reference Signal Received Quality). Furthermore, the release introduced signalling support for new scenarios and indications, such as for high-speed trains and SCG overheating termination.
- Introduction of RSRP measurement based on RSS TS 36.214CR0055
- Introduction of B1C signal in BDS system in A-GNSS TS 36.305CR0083
- Introduction of signalling for high-speed train scenarios TS 36.331CR4326
- Introduction of B1C signal in BDS system in A-GNSS TS 38.305CR0013
- Introduction of voice fallback indication TS 36.331CR4136
- Redirection with MPS Indication [Redirect_MPS_I] TS 36.331CR4579
+ 10 more changes
In Release 17, the key development for RSSI was the addition of a UE capability for NR-U RSSI/CO measurement, specifically for New Radio in Unlicensed spectrum operations. This enhancement introduced a new UE capability signaling mechanism to support these measurements in the NR-U context. The release did not introduce changes to the fundamental definition or calculation of RSSI itself, but rather expanded the framework for its application in unlicensed frequency bands.
- Introduction of B2a and B3I signal in BDS system and GNSS Positioning Integrity TS 36.305CR0107
- UE Security Capabilities signaling in NG-RAN [UE_Sec_Caps] TS 38.300CR0427
- Addition of NR-U RSSI/CO measurement UE capability TS 36.331CR4729
- Correction on UE behavior for NAS-based busy indication in RRC_INACTIVE TS 36.331CR4822
- Correction on SIB31 signalling only in NTN cell TS 36.331CR4972
In Release 18, specific corrections were made to the RSSI-related measurement of UL-RSCP (Uplink Received Signal Code Power). Furthermore, enhancements for Small Data Transmission (SDT) included corrections and the introduction of a resume indication in the RRCRelease procedure.
- Correction on SDT RRC Release with resume indication [SDT_ReleaseEnh] TS 38.300CR0872
- Clarification on the mapping of RSRP thresholds to CE levels TS 36.331CR5100
- Correction on MBMS Interest Indication TS 36.331CR5125
- Correction of availability indication of logged MDT report for SNPN TS 37.320CR0132
- Resume indication in RRCRelease [SDT_ReleaseEnh] TS 38.300CR0807
- Correction on UL-RSCP TS 38.455CR0153
+ 3 more changes
In Release 19, the primary update related to RSSI functionality was the introduction of the Low-Power Wake-Up Signal and Receiver for NR, which includes mechanisms for its control such as an LP-WUS disabling indication. This new signal operates alongside existing receiver measurements to improve power efficiency. The change involves specific signalling procedures for enabling and disabling this wake-up functionality.
Explore further
Broader topics and technologies where RSSI plays a role.
Defining Specifications
3GPP specifications that define or reference RSSI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.402 vj00 | EPC for Non-3GPP Access (PMIP) | Rel-19 |
| TS 24.312 vj00 | ANDSF Management Objects Specification | Rel-19 |
| TS 25.101 vj00 | UTRA FDD UE RF Requirements | Rel-19 |
| TS 25.102 vj00 | UTRA TDD RF Characteristics | Rel-19 |
| TS 25.103 v1100 | RF Requirements for RRM | R99 |
| TS 25.104 vj00 | UTRA FDD Base Station RF Characteristics | Rel-19 |
| TS 25.105 vj00 | UTRA TDD Base Station RF Requirements | Rel-19 |
| TS 25.123 vj00 | Radio Resource Management for TDD | Rel-19 |
| TS 25.133 vj00 | UTRAN RRM Requirements for FDD | Rel-19 |
| TS 25.141 vj00 | UTRA FDD Base Station RF Conformance Testing | Rel-19 |
| TS 25.215 vj00 | UTRA FDD Measurement Definitions | Rel-19 |
| TS 25.225 vj00 | UTRA TDD Physical Layer Measurements | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TR 26.969 vj00 | eCall In-band Modem Performance Characterization | Rel-19 |
| TS 33.814 vg01 | Security aspects of enhanced Location Services (eLCS) | Rel-16 |
| TS 36.133 vj20 | E-UTRA RRM Requirements | Rel-19 |
| TS 36.201 vj00 | LTE Physical Layer General Description | Rel-19 |
| TS 36.214 vj00 | E-UTRA Physical Layer Measurements | Rel-19 |
| TS 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.455 vj00 | LTE Positioning Protocol Annex (LPPa) | Rel-19 |
| TR 36.791 vg00 | E-UTRA 2.4 GHz TDD Band for US | Rel-16 |
| TS 37.171 vj00 | UE Positioning Performance Requirements | Rel-19 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |