Description
Space Radiocommunication Stations (SRS) are a foundational element in 3GPP's standardization of Non-Terrestrial Networks (NTN). An SRS can be a satellite payload (e.g., a bent-pipe transponder or a regenerative processor) or a ground-based gateway station that communicates with satellites. In the architecture, the SRS forms the space-borne or ground-based radio interface for user equipment (UE) or for network nodes like gNBs. For a transparent payload (bent-pipe), the SRS receives, amplifies, frequency-converts, and retransmits the signal between the UE and a gateway on Earth. For a regenerative payload, the SRS includes onboard processing to demodulate/decode and then re-modulate/re-encode the signal, effectively acting as a base station in space.
The operation of an SRS is defined by stringent radio transmission and reception parameters to cope with the unique challenges of satellite links. These include very long propagation delays (up to hundreds of milliseconds), high Doppler shifts due to satellite motion, and significant path loss. The 3GPP specifications detail the required performance for SRS in terms of maximum output power, frequency stability, spurious emissions, and receiver sensitivity. The SRS must support specific 3GPP-defined waveforms and channel bandwidths, adapting terrestrial NR or LTE air interfaces for space-based propagation.
Key components of an SRS system include the antenna subsystem (often with steerable or multi-beam antennas for coverage area shaping), the radio frequency (RF) front-end for amplification and conversion, and the digital processing unit. For regenerative payloads, this includes baseband processing modules equivalent to a gNB's functions. The SRS's role is to extend the 3GPP radio access network (RAN) into space, providing service continuity, ubiquitous coverage, and backhaul connectivity in remote areas, over oceans, and for aerial vehicles. It is a critical node enabling direct communication between standard 3GPP UEs and satellites, as standardized from Release 15 onwards for 5G NTN.
Purpose & Motivation
The standardization of Space Radiocommunication Stations (SRS) within 3GPP was motivated by the growing need to integrate satellite networks with terrestrial mobile networks seamlessly. Historically, satellite communication operated in proprietary silos, using non-3GPP technologies that prevented interoperability with the billions of existing cellular devices. This created coverage gaps in rural, maritime, and aeronautical scenarios where terrestrial infrastructure is economically unviable. The purpose of defining SRS is to bring satellites into the 3GPP ecosystem as standardized radio nodes, enabling global and seamless service coverage.
By creating technical specifications for SRS, 3GPP addresses the limitations of previous fragmented approaches. It allows mobile network operators to incorporate satellite assets into their networks, using standardized interfaces and protocols. This solves critical problems such as providing disaster resilience when terrestrial networks fail, enabling Internet of Things (IoT) services over vast geographical areas, and supporting connectivity for moving platforms like ships and airplanes. The SRS definitions ensure that satellite networks can meet the same service quality, security, and mobility management expectations as terrestrial 5G networks, facilitating the vision of truly ubiquitous connectivity.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (158 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, new signalling was introduced for SRS antenna switching and SRS carrier switching capabilities, alongside clarifications and corrections for SRS resource mapping and the SRS-TPC-CommandConfig. The release also specifically addressed the signalling for SRS switching capability and provided a correction to the SRS-Config parameters.
- Correction to frequency-domain starting position for SRS resource mapping TS 38.211CR0009
- Correction on PDSCH resource allocation scheduled by PDCCH in Type 0 common search space TS 38.211CR0018
- Clarification on UL_SUL indicator field and SRS request field TS 38.212CR0013
- Correction on search space sharing TS 38.213CR0009
- Correction on SRS-TPC-CommandConfig TS 38.331CR0299
- Correction to 38331 in SRS-Config TS 38.331CR0388
+ 5 more changes
In Release 16, key enhancements for SRS included the introduction of power headroom reporting for Additional SRS and defined UE behaviour for SRS measurements for Cross-Link Interference (CLI). The release also introduced downgraded configurations for SRS antenna switching and provided corrections and clarifications for SRS resource set configurations, SRS carrier switching, and the configuration of SRS for positioning. Furthermore, it specified the use of DL-PRS as a spatial relation for positioning SRS and addressed the configuration of semi-persistent SRS for positioning.
- Introduction of Power headroom reporting for Additional SRS TS 36.321CR1461
- Introduction of UE behaviour for SRS measurements for CLI TS 38.214CR0043
- Introduction of downgraded configurations for SRS antenna switching TS 38.214CR0062
- Introduction of downgraded configuration for SRS antenna switching TS 38.331CR1433
- CR to 38.211 to correct CP extension for SRS TS 38.211CR0063
- Correction on SRS resource set configuration in TS 38.212 TS 38.212CR0070
+ 34 more changes
In Release 17, enhancements for SRS focused on improving carrier aggregation operations and transmission flexibility. Key introductions included enabling parallel transmissions of SRS with PRACH, PUCCH, and PUSCH across component carriers in intra-band non-contiguous CA, and refining procedures for SRS carrier switching. Corrections and updates were also made to power control parameters, slot offsets for multiple aperiodic SRS resource sets, and the SRS switching time for positioning.
- Add Space Division Multiplexing PRB Usage for MIMO cell TS 28.552CR0341
- Parallel PRACH and SRS/PUCCH/PUSCH transmissions across CCs in intra-band non-contiguous CA [NC-PRACH-SimulTx] TS 38.331CR3577
- CR on the description of the SRS resource set indication for PUSCH repetition TS 38.212CR0117
- Correction of BWP for SRS TS 38.213CR0336
- Correction on parallel transmission of PRACH and SRS/PUCCH/PUSCH TS 38.213CR0386
- CR on broadcast search space monitoring occasion determination TS 38.213CR0429
+ 33 more changes
In Release 18, enhancements to the SRS (Sounding Reference Signal) function focused on refining procedures for positioning and improving reliability. Key updates included corrections and clarifications for SRS frequency hopping patterns, bandwidth aggregation, and transmission rules specific to positioning operations. The release also introduced specific handling for SRS in RRC_INACTIVE mode, adjustments for multi-port SRS power scaling, and defined activation procedures for pre-configured and area-specific SRS resources.
- Correction for hop counting in SRS for positioning with tx hopping TS 38.211CR0127
- Correction on bandwidth part for SRS frequency hopping for positioning TS 38.211CR0135
- Correction on staircase pattern for SRS frequency hopping for positioning TS 38.211CR0136
- CR on SRS hopping for positioning in TS 38.211 TS 38.211CR0150
- Correction on Multi-Resource SRS Port Power Scaling TS 38.213CR0676
- CR for dropping rule on SRS bandwidth aggregation TS 38.214CR0569
+ 48 more changes
In Release 19, key enhancements for the SRS function included the introduction and extension of SRS frequency hopping for positioning to include non-RedCap UEs, as well as new support for combining carrier-switching SRS with UL carrier aggregation and UL Tx Switching. Several corrections and clarifications were also made, focusing on UE capabilities for these features, aperiodic SRS with frequency hopping, and parameters for SRS-RSRP and CLI-RSSI measurement resource sets.
- Introduction of UE capability for SRS frequency hopping for non-RedCap UE in 37355 [Pos_SRSHop] TS 37.355CR0553
- TEI19 Combination of carrier-switching SRS and UL carrier aggregation [Simul_SRSCS] TS 38.214CR0682
- TEI19 Extension of SRS frequency hopping for positioning to non-RedCap UEs [Pos_SRSHop] TS 38.214CR0683
- TEI19 Carrier-Switching SRS with UL Tx Switching [SRSCS_ULTxSwitch] TS 38.214CR0684
- Introduction on the SRS frequency hopping for non-RedCap UE in 38331 [Pos_SRSHop] TS 38.331CR5290
- Correction on UE capability for UTW in positioning SRS frequency hopping for nonRedCap UE [Pos_SRSHop] TS 37.355CR0565
+ 8 more changes
Explore further
Broader topics and technologies where SRS plays a role.
Defining Specifications
3GPP specifications that define or reference SRS, 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 26.522 vj30 | RTP for XR in 5G Systems | Rel-19 |
| TS 26.565 vj00 | Split Rendering Media Service Enabler | Rel-19 |
| TS 26.854 vj00 | Study on Haptics in 5G Media Services | Rel-19 |
| TS 28.552 vk10 | 5G Performance Management Measurements | Rel-20 |
| TS 36.111 vj00 | LMU Requirements for UTDOA Positioning | Rel-19 |
| TS 36.112 vj00 | E-UTRAN LMU Conformance Requirements | Rel-19 |
| TS 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 36.211 vj10 | LTE Physical Layer Specification | Rel-19 |
| TS 36.212 vj10 | LTE Multiplexing and Channel Coding | Rel-19 |
| TS 36.213 vj10 | LTE Physical Layer Procedures | Rel-19 |
| TS 36.214 vj00 | E-UTRA Physical Layer Measurements | Rel-19 |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 |
| TS 36.321 vj00 | E-UTRA MAC Protocol Specification | Rel-19 |
| TS 36.455 vj00 | LTE Positioning Protocol Annex (LPPa) | Rel-19 |
| TS 36.459 vj00 | SLmAP for E-UTRAN Positioning | Rel-19 |
| TS 36.855 vd00 | E-UTRA Positioning Enhancements Study | Rel-13 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.857 vd10 | Study on Indoor Positioning Enhancements | Rel-13 |
| TR 37.910 vj00 | 5G SRIT and NR RIT Self-Evaluation Report | Rel-19 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| 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 38.201 vj00 | NR Physical Layer General Description | Rel-19 |
| TS 38.202 vj00 | 5G NR Physical Layer Services | Rel-19 |
| TS 38.211 vj10 | NR Physical Channels and Modulation | Rel-19 |
| TS 38.212 vj10 | NR Multiplexing and Channel Coding | Rel-19 |
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |
| TS 38.215 vj10 | NR Physical Layer Measurements | 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 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |
| TS 38.523 vj20 | 5G NR UE Conformance Testing: Idle/Inactive | Rel-19 |
| TS 38.807 vg10 | NR beyond 52.6 GHz Study | Rel-16 |
| TR 38.820 vg10 | NR; 7-24 GHz Frequency Range Study | Rel-16 |
| TS 38.843 vj00 | Study on AI/ML for NR Air Interface | Rel-19 |
| TR 38.857 vh00 | Study on NR Positioning Enhancements | Rel-17 |
| TR 38.859 vi10 | Technical Report | Rel-18 |
| TS 38.863 vj10 | NR NTN RF and Co-existence Spec | Rel-19 |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 |
| TR 38.912 vj00 | Study on New Radio Access Technology | Rel-19 |