Description
A Search Space Set Group (SSSG) is a feature in 5G New Radio (NR) that logically groups multiple PDCCH (Physical Downlink Control Channel) search space sets configured for a User Equipment (UE). A search space set defines where in time and frequency (in terms of Control Resource Sets - CORESETs) a UE should attempt to blindly decode potential PDCCH transmissions carrying Downlink Control Information (DCI). Prior to Release 17, a UE with multiple active search space sets might need to monitor PDCCH candidates across all of them in every monitoring occasion, leading to high computational complexity and power consumption.
The SSSG mechanism allows the network (gNB) to configure one or more SSSGs for a UE via RRC signaling. Each SSSG contains a subset of the UE's total configured search space sets. Crucially, the network can then dynamically activate or deactivate a specific SSSG using a MAC Control Element (MAC CE) command. When an SSSG is activated, the UE is only required to monitor PDCCH candidates within the search space sets belonging to that active group. It can ignore search space sets not in the active group. The network can switch the UE between different SSSGs based on traffic activity, enabling a form of dynamic power saving. For example, one SSSG might contain search space sets for scheduling grants (requiring more frequent monitoring), while another might contain only a minimal set for paging or pre-emption indication.
Architecturally, SSSG configuration is part of the PDCCH-Config information element. A UE can be configured with multiple SSSGs, each with an identifier. The activation/deactivation is handled by the MAC layer, providing fast reconfiguration without RRC signaling overhead. This grouping is particularly beneficial for advanced features introduced in later releases, such as multi-beam operation and multi-TRP (Transmission Reception Point) transmission, where a UE might be configured with a large number of search space sets associated with different beams or TRPs. Instead of monitoring all possibilities, the network can guide the UE to monitor only the relevant group for its current conditions, significantly reducing the number of blind decodes attempted per slot and thus saving UE battery life.
Purpose & Motivation
SSSG was introduced in 3GPP Release 17 primarily to address the growing complexity and power consumption associated with PDCCH monitoring in advanced 5G NR deployments. As NR evolved to support features like carrier aggregation, multi-beam operation, multi-TRP, and diverse services (eMBB, URLLC, mMTC), the number of search space sets a UE needed to be configured with increased substantially. Blindly decoding all possible PDCCH candidates across all these sets in every monitoring occasion became a significant drain on UE battery life and increased processing complexity.
The purpose of SSSG is to provide the network with a fine-grained tool to manage UE monitoring behavior dynamically. It solves the problem of static, always-on monitoring mandates. By grouping search spaces and allowing rapid switching between groups, the network can align the UE's monitoring activity with its actual traffic pattern and operational state. For instance, during periods of high activity, an SSSG with frequent monitoring opportunities can be activated. During periods of inactivity or low-power states (like connected-mode DRX), the UE can be switched to an SSSG containing only essential search spaces (e.g., for wake-up signals or pre-emption), drastically reducing power consumption.
This addresses a key limitation of the pre-Rel-17 approach, where power saving was coarser (e.g., relying mainly on DRX cycles). SSSG enables more intelligent, traffic-adaptive power saving without compromising scheduling flexibility for the network. It was motivated by the industry's focus on enhanced power saving features for 5G, especially for power-constrained devices and to improve overall user experience through longer battery life.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (61 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SSSG function was introduced to manage PDCCH monitoring across multiple CORESETs, particularly addressing scenarios with overlapped CORESETs and dedicated DL BWPs. It defined procedures for search space sharing and established specific QCL assumptions for receiving PDCCH, including for RAR and for CORESETs other than CORESET#0. The framework also clarified monitoring behaviors for NR-DC (NR Dual Connectivity) and the use of CORESET#0 within a dedicated downlink bandwidth part.
- Correction on search space sharing TS 38.213CR0009
- CR on using CORESET#0 in dedicated DL BWP TS 38.213CR0017
- PDCCH monitoring for overlapped CORESETs TS 38.213CR0018
- CR on QCL assumption for receiving PDCCH for RAR TS 38.213CR0026
- CR on QCL assumption for a CORESET other than 0 TS 38.213CR0030
- Correction on PDCCH monitoring TS 38.213CR0040
+ 2 more changes
In Release 16, the SSSG function was enhanced with specific corrections and clarifications for new capabilities and scenarios introduced in that release. This included corrections for search space set group switching without a channel occupancy duration field and for PDCCH monitoring procedures when a UE is configured with the Rel-16 PDCCH monitoring capability. Furthermore, the specification provided corrections for search space configurations related to DCI formats 3_0 and 3_1 and for the UE procedure to determine PDCCH assignments when using that new capability.
- CR on correction on PDCCH monitoring for DAPS HO TS 38.213CR0132
- Clarify DCI Format 2_5 search space sets TS 38.213CR0146
- 38.213 CR Correction on HARQ-ACK codebook for secondary PUCCH group TS 38.213CR0167
- Correction on UL grant Type 2 PUSCH release for search space sharing TS 38.213CR0169
- Correction on PDCCH monitoring on cell(s) configured with Rel-15 PDCCH monitoring capability TS 38.213CR0170
- Correction on search space set group switching without channel occupancy duration field TS 38.213CR0191
+ 7 more changes
In Release 17, the SSSG function was enhanced to support PDCCH repetition with SSSG switching and its operation in FR2-2 scenarios with multiple cells. The release also included corrections and alignment for SSSG switching procedures, alongside broader corrections for PDCCH monitoring adaptation and multi-slot monitoring in carrier aggregation and dual connectivity scenarios.
- CR on PDCCH repetition with SSSG switching TS 38.213CR0332
- Correction on the tables for determining Type0 PDCCH monitoring occasions TS 38.213CR0337
- Correction on multi-slot PDCCH monitoring in NR-DC and CA scenarios with mixed capability types TS 38.213CR0342
- Corrections on PDCCH monitoring enhancement for 52-71GHz spectrum TS 38.213CR0346
- Correction for multi-slot PDCCH monitoring in FR2-2 TS 38.213CR0372
- Correction for SSSG switching with multiple cells in FR2-2 TS 38.213CR0374
+ 17 more changes
In Release 18, the enhancements for Search Space Set Group (SSSG) operation included a clarification on the reset behavior of SSSG during a BWP switch triggered by a Random Access procedure. Furthermore, corrections were made to the PDCCH monitoring adaptation behavior for DRX groups to ensure proper operation. These changes refined the SSSG framework to improve reliability during state transitions and discontinuous reception scenarios.
- Introduction of QCL-TypeD priorities for overlapping CORESETs in M-DCI/M-TRP operation [QCL-TypeD CORESET priority for M-TRP] TS 38.213CR0569
- CR on PDCCH monitoring for dedicated spectrum less than 5 MHz TS 38.213CR0596
- Correction on TCI state applied for CORESET 0 in LTM TS 38.213CR0621
- Correction on TCI state applied for CORESETs other than CORESET 0 in LTM TS 38.213CR0645
- Clarification of PDCCH ordered CFRA for 2TA TS 38.300CR0868
- Correction on Type1A search space for SDT TS 38.213CR0520
+ 3 more changes
In Release 19, the key new feature for Search Space Set Group (SSSG) functionality is the introduction of SR-triggered SSSG switching, allowing a UE to autonomously switch its active SSSG based on Scheduling Request transmission. This enhancement provides more dynamic and UE-initiated control over PDCCH monitoring behavior. Additionally, the release introduced PDCCH repetitions for the Type0-PDCCH CSS set in Terrestrial Networks (TNs), improving reliability for common control channel reception.
- Introduction of SR triggered SSSG switching [SRTrig_SSSGSwitch] TS 38.213CR0713
- Introduction of PDCCH repetitions for Type0-PDCCH CSS set in TNs [Common_PDCCH_Rep_TN] TS 38.213CR0748
- Introduction of common PDCCH repetition (Rel-19 NTN) for TN [Common_PDCCH_rep_TN] TS 38.300CR1058
- Corrections on SR triggered SSSG switching [SRTrig_SSSGSwitch] TS 38.213CR0747
- Correction on PDCCH candidates skipping for receiving RAR when overlapping with candidate SSB TS 38.213CR0755
- Alignment on parameter for intra-slot PDCCH repetition TS 38.213CR0761
+ 2 more changes
Explore further
Broader topics and technologies where SSSG plays a role.
Defining Specifications
3GPP specifications that define or reference SSSG, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |