Description
Channel State Information (CSI) is a collective term for metrics that describe the signal propagation conditions between a transmitter (e.g., a gNB) and a receiver (e.g., a UE). It is crucial for adaptive transmission techniques in OFDMA-based systems like LTE and NR. CSI is primarily acquired through reference signals (e.g., CSI-RS in NR, CRS/CSI-RS in LTE) transmitted by the base station. The UE performs measurements on these signals to estimate key parameters. The core components of CSI typically include the Channel Quality Indicator (CQI), which recommends a modulation and coding scheme; the Precoding Matrix Indicator (PMI), which suggests a precoding matrix for multi-antenna (MIMO) beamforming; and the Rank Indicator (RI), which indicates the number of useful transmission layers. In advanced systems, CSI can also encompass more detailed feedback like CSI-RS Resource Indicators (CRI) or Layer 1 Reference Signal Received Power (L1-RSRP). The UE reports this information back to the gNB via uplink control channels (PUCCH) or shared channels (PUSCH) in a process called CSI reporting. The network scheduler then uses this feedback to select the most efficient transmission parameters for the next downlink transmission, adapting to rapid changes in the radio environment. This closed-loop process is fundamental for achieving high spectral efficiency and link reliability.
Purpose & Motivation
CSI exists to enable intelligent, adaptive radio resource management in fading wireless channels. Early cellular systems used fixed modulation or simplistic feedback, leading to either conservative (low throughput) or aggressive (high error rate) transmissions. CSI solves this by providing the transmitter with near-real-time knowledge of the channel, allowing it to 'match' the transmission to current conditions. This was motivated by the need to maximize data rates and system capacity in bandwidth-limited spectrum. In MIMO and beamforming systems, accurate CSI is especially critical as it informs the precoder, directing energy towards the intended user and minimizing interference to others. Its evolution from simple CQI in HSDPA to complex multi-beam, multi-panel CSI in 5G NR addresses the challenges of higher frequencies (mmWave) and massive MIMO, where channel properties are more directional and susceptible to blockage.
What changed in its specifications
The latest release-to-release comparison of specifications that define CSI. Each summary describes the whole specification, not only this term.
Rel-18 brings only minor changes to TS 21.905: 0 clauses changed, with no change attributed to a release feature.
Full comparison in TR 21.905 →Rel-18 added 3D scenes and assets support, updated video, speech, and audio capabilities, and relaxed several media format requirements for 5G-Advanced messaging media profiles.
Full comparison in TS 26.141 →Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (201 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
- Introduction of advanced CSI CBSR in TS 36.213 TS 36.213CR1097
- Advanced CSI CBSR CBSR related capability for FD-MIMO TS 36.306CR1593
- Advanced CSI CBSR CBSR parameter and related capability for FD-MIMO TS 36.331CR3397
- Correction on aperiodic CSI triggering for feCoMP in 36.213 TS 36.213CR1144
- Removal of R_CSI from 1024QAM CQI table TS 36.213CR1147
- Corrections related to CSI update capability for sTTI TS 36.213CR1184
+ 38 more changes
- Aperiodic CSI-RS Triggering for UE reporting beamSwitchTiming values of 224 and 336 TS 38.214CR0060
- Behaviour for triggered with a CSI report for non-active BWP TS 38.214CR0061
- Aperiodic CSI-RS triggering with beam switching timing of 224 and 336 TS 38.331CR1716
- CR to 38.331 on CSI-RS inter-node message TS 38.331CR1354
- 38331 CR for CSI-RS-ResourceConfigMobility TS 38.331CR2250
- Clarification on KNZ to codepoint mapping for eType II CSI TS 38.212CR0081
+ 46 more changes
- Adding UE capability of CSI reporting cross PUCCH SCell group TS 38.331CR3144
- Support of Multiple CSI Subframe Sets on CQI-ReportPeriodicScell TS 36.306CR1866
- Support of Multiple CSI Subframe Sets on CQI-ReportPeriodicScell TS 36.331CR4899
- CR on CSI reporting TS 38.212CR0134
- Correction for the mapping of rank combination value for Rel-17 NCJT CSI TS 38.212CR0142
- Correction of CSI assumptions over multiplexing NCJT CSI reports in PUCCH TS 38.213CR0354
+ 40 more changes
- Introduction of specification support for MIMO enhancements on CSI TS 38.214CR0437
- Correction on priority for LTM CSI report TS 38.213CR0643
- Correction of specification support for MIMO enhancements on CSI TS 38.214CR0483
- Correction on Rel-18 Type II Doppler codebook based CSI enhancement TS 38.214CR0567
- Correction on CSI processing criteria for new NES capability signaling TS 38.214CR0584
- Clarification on SL CSI request in TS 38.214 TS 38.214CR0588
+ 23 more changes
- Introduction of Rel-19 early CSI acquisition for L3 handover to TS 38.212 [EarlyCSI_L3HO] TS 38.212CR0236
- Introduction of CSI enhancements for NR MIMO Phase 5 TS 38.214CR0677
- 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
- Introduction of Rel-19 early CSI acquisition for L3 handover to TS 38.214 [EarlyCSI_L3HO] TS 38.214CR0722
- Introduction of early CSI acquisition for L3 handover [EarlyCSI_L3HO] TS 38.331CR5587
+ 22 more changes
Defining Specifications
3GPP specifications that define or reference CSI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj20 | 3GPP Terminology and Definitions | Rel-19 read |
| TR 21.978 v300 | CAMEL Control of VoIP Services Feasibility Study | R99 read |
| TS 23.279 vj00 | Combined CS and IMS Services (CSI) Architecture | Rel-19 read |
| TS 23.806 v700 | Voice Call Continuity between CS and IMS | Rel-7 read |
| TS 26.141 vj00 | IMS Messaging & Presence Media Formats | Rel-19 read |
| TS 26.235 vc00 | Default Codecs for 3GPP IP Multimedia Subsystem | Rel-12 read |
| TS 28.882 vk00 | AI/ML Management Enhancements for 5G-Advanced | Rel-20 read |
| TS 29.078 vj00 | CAMEL Phase 4 CAP Specification | Rel-19 read |
| TS 29.163 vj00 | Interworking between 3GPP IM CN and CS networks | Rel-19 read |
| TS 29.278 vj00 | CAMEL Application Part (CAP) for IMS Phase 4 | Rel-19 read |
| TS 33.126 vj30 | Lawful Interception Requirements | Rel-19 read |
| TS 33.127 vj80 | Lawful Interception Architecture | Rel-19 read |
| TS 33.727 vj00 | Lawful Interception with End-to-End Encryption in 5G | Rel-19 read |
| TS 36.201 vj00 | LTE Physical Layer General Description | Rel-19 read |
| TS 36.211 vj30 | E-UTRA Physical Layer Specifications | Rel-19 read |
| TS 36.212 vj30 | E-UTRA Physical Layer Procedures | Rel-19 read |
| TS 36.213 vj50 | LTE Physical Layer Procedures | Rel-19 read |
| TS 36.300 vj20 | E-UTRAN Radio Interface Protocol Architecture | Rel-19 read |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 read |
| TS 36.306 vj30 | E-UTRA UE Radio Access Capability Parameters | Rel-19 read |
| TS 36.307 vk00 | Release Independent UE Requirements for E-UTRA | Rel-20 read |
| TS 36.321 vj30 | E-UTRA MAC Protocol Specification | Rel-19 read |
| TS 36.331 vj40 | E-UTRA Radio Resource Control (RRC) Protocol | Rel-19 read |
| TS 36.521 vj11 | E-UTRA UE Conformance Testing for Satellite Access | Rel-19 read |
| TS 36.741 ve00 | Enhancements to Coordinated Multi-Point Operation | Rel-14 read |
| TS 36.825 vd00 | Study on Additional LTE TDD Configurations | Rel-13 read |
| TS 36.855 vd00 | E-UTRA Positioning Enhancements Study | Rel-13 read |
| TS 36.867 vd00 | LTE DL 4 Rx Antenna Port Study TR | Rel-13 read |
| TS 36.871 vb00 | Downlink MIMO Enhancement for LTE-Advanced | Rel-11 read |
| TS 36.878 vd00 | LTE Performance Enhancements for High Speed Scenarios | Rel-13 read |
| TS 38.133 vk10 | NR Radio Resource Management Requirements | Rel-20 read |
| TS 38.174 vk00 | NR Integrated Access and Backhaul Requirements | Rel-20 read |
| TS 38.176 vj40 | IAB Conformance Testing | Rel-19 read |
| TS 38.211 vj50 | NR Physical Channels and Signals | Rel-19 read |
| TS 38.212 vj40 | NR Multiplexing and Channel Coding | Rel-19 read |
| TS 38.213 vj50 | NR Physical Layer Control Procedures | Rel-19 read |
| TS 38.214 vj50 | NR Physical Layer Data Channel Procedures | Rel-19 read |
| TS 38.321 vj40 | NR MAC Protocol Specification | Rel-19 read |
| TS 38.331 vj40 | NR Radio Resource Control (RRC) | Rel-19 read |
| TS 38.522 vk00 | NR UE Conformance Test Applicability | Rel-20 read |
| TS 38.551 vj10 | NR MIMO OTA Performance Requirements | Rel-19 read |
| TR 38.808 vh00 | Study on NR above 52.6 GHz to 71 GHz | Rel-17 read |
| TR 38.810 vg70 | NR OTA Test Methods Study | Rel-16 read |
| TS 38.824 vg00 | NR URLLC Physical Layer Enhancements Study | Rel-16 read |
| TR 38.825 vg00 | Study on NR Industrial IoT | Rel-16 read |
| TR 38.830 vh00 | NR Coverage Enhancements Study | Rel-17 read |
| TR 38.838 vh00 | Study on XR Evaluations for NR | Rel-17 read |
| TS 38.843 vj00 | Study on AI/ML for NR Air Interface | Rel-19 read |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 read |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 read |
| TR 38.903 vj40 | NR UE Test Tolerances and Uncertainties | Rel-19 read |