Description
The Secondary stream ETFC Offset (SD) is a technical parameter within the 5G New Radio (NR) physical layer specifications for uplink power control. It is applicable when the UE is configured for uplink transmission using the CP-OFDM waveform without transform precoding (i.e., not using DFT-s-OFDM) and is operating in a multi-layer (MIMO) scenario. ETFC stands for 'Effective Target received power per FFT bin per Channel'. The SD parameter, signaled by the network via RRC or MAC CE, provides an offset value in decibels (dB). This offset is used in the uplink power control formula to calculate the transmit power for a secondary data stream relative to a primary stream. The primary stream's power is determined based on open-loop and closed-loop power control mechanisms involving pathloss estimates and TPC commands. For the secondary stream, its power is derived by applying the SD offset to the primary stream's calculated power. This approach allows the gNB to finely control the relative power levels between multiple spatial layers, which is crucial for optimizing uplink MIMO performance, managing inter-layer interference, and ensuring reliable demodulation at the receiver. The parameter is part of a suite of power control adjustments that enable efficient spectral utilization and link adaptation in advanced 5G NR deployments.
Purpose & Motivation
The SD parameter was introduced to address the specific needs of uplink Multi-User MIMO (MU-MIMO) and single-user MIMO (SU-MIMO) in 5G NR, particularly when using the high-spectral-efficiency CP-OFDM waveform. In LTE, uplink MIMO was more limited and often used DFT-s-OFDM (SC-FDMA), which has different power characteristics. With 5G's support for CP-OFDM in the uplink and more advanced multi-antenna techniques, a more granular power control mechanism was required. Different spatial streams may experience different effective channels or interference conditions. Applying the same transmit power to all streams is suboptimal. The SD offset allows the gNB to independently balance the power between the primary and secondary streams, optimizing the signal-to-interference-plus-noise ratio (SINR) for each layer. This solves problems like one stream overpowering another or insufficient power for a secondary stream in a rank-2 transmission, ultimately improving uplink throughput, cell-edge performance, and overall MIMO efficiency in diverse radio conditions.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (31 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, the specification introduced updates for secondary authentication and authorization procedures for PDU Session Establishment, correcting the related terms. This enhancement supports the concurrent delivery of streaming content, including SD, FHD, and UHD resolution programs, over LTE-based TV services. These improvements facilitate optimized streaming content delivery and enable third-party OTT providers to utilize MNO network policy information for efficient content scheduling and delivery.
In Release 16, the enhancements for the "SD" (Secondary stream ETFC Offset) function were part of broader improvements for Per-Stream Filtering and Policing (PSFP) and traffic handling. Specifically, this included corrections and clarifications for TSN stream identification within PSFP information and the definition of the stream filter instance. These updates refined the mechanisms for managing and delivering combinations of different resolution streams, such as SD, FHD, and UHD, within services like LTE-based broadcast TV.
- Access restrictions for primary and secondary RAT TS 23.501CR1847
- Support secondary RAT data usage report TS 29.561CR0028
- New 5QIs for Enhanced Framework for Uplink Streaming TS 23.501CR0704
- Clarification of terms in secondary authentication TS 23.501CR1734
- Applying Per-Stream Filtering and Policing TS 23.501CR1981
- Correction to TSN stream aggregation and QoS parameter mapping guidelines TS 23.501CR2085
+ 6 more changes
In Release 17, the new enhancements for secondary authentication and authorization (NSSAA) included the introduction of remote provisioning of credentials for secondary authentication and the specification of 5GS interworking with EPS for EAP-based secondary authentication across both RADIUS and Diameter message flows. Furthermore, the release defined the use of UE default credentials specifically for secondary authentication, building upon the framework for delivering multi-resolution streaming services. These updates provided a more robust and flexible credential management system for secondary authorization procedures.
- Remote provisioning of credentials for NSSAA or secondary authentication/authorisation TS 23.501CR2714
- 5GS interworking with EPS for EAP based secondary AUTH in RADIUS message flow TS 29.561CR0088
- 5GS interworking with EPS for EAP based secondary AUTH in Diameter message flow TS 29.561CR0089
- Correction on remote provisioning of credentials for NSSAA or secondary authentication/authorization TS 23.501CR3146
- Correction on remote provisioning of credentials for NSSAA or secondary authentication/authorization TS 23.501CR3277
- UE default credentials for primary and secondary authentication TS 29.561CR0138
+ 2 more changes
In Release 18, the new "SD" (Secondary stream ETFC Offset) function is not explicitly detailed in the provided grounding context or CR titles. The listed changes focus on secondary DN authentication and authorization for EPS interworking, secondary re-authentication for MAPDU sessions across 5GC and EPC, and UE capability indications for secondary auth over EPC, with no specific mention of SD or ETFC Offset procedures.
- Secondary DN authentication and authorization in EPS IWK case TS 23.501CR3701
- Secondary DN authentication and authorization in EPS interworking use case related updates. TS 29.561CR0147
- Secondary DN authentication and authorization in EPS interworking use case related updates. TS 29.561CR0148
- Secondary re-auth for MAPDU session when one access is in 5GC and other in EPC TS 29.561CR0157
- UE 5GSM capability indication for supporting secondary auth over EPC TS 23.501CR5185
- Clarification of the Unmarked PDUs with SN Offset and PSI Value TS 23.501CR5175
+ 1 more changes
In Release 19, the new Secondary Cell Measurement Skipping function for NR ATG was introduced to optimize performance. Furthermore, a new SST (Slice/Service Type) for Guaranteed Bit Rate Streaming Services was defined to enhance service delivery. These additions support the network's capability to handle combinations of SD, FHD, and UHD resolution programs efficiently.
Explore further
Broader topics and technologies where SD plays a role.
Defining Specifications
3GPP specifications that define or reference SD, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 22.816 ve10 | 3GPP TV Service Enhancement Technical Report | Rel-14 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 25.700 vc00 | Further Enhanced Uplink (EUL) Study | Rel-12 |
| TR 26.949 vj00 | TV Service Profiles for 3GPP Networks | Rel-19 |
| TR 26.975 vj00 | AMR Speech Codec Performance Background | Rel-19 |
| TR 26.978 vj00 | AMR Noise Suppression Selection Phase Technical Report | Rel-19 |
| TS 28.535 vj00 | Closed Control Loop Assurance Management | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 31.105 vj10 | Slice Subscriber Identity Module (SSIM) Application | Rel-19 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |
| TS 32.101 vj00 | Management principles and high-level requirements | Rel-19 |
| TS 32.818 v800 | SA5 MTOSI XML Harmonization Study | Rel-8 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TR 38.859 vi10 | Technical Report | Rel-18 |
| TS 46.055 vj00 | GSM Enhanced Full Rate Speech Codec Performance | Rel-19 |