Description
Sub-Band non-overlapping Full Duplex (SBFD) is an advanced duplexing scheme introduced in 3GPP Release 18 for NR (New Radio). It operates on a single carrier frequency but partitions the available bandwidth into distinct, non-overlapping sub-bands dedicated to uplink (UL) and downlink (DL) transmissions. This allows a base station (gNB) or user equipment (UE) to transmit and receive simultaneously within the same carrier, unlike Time Division Duplex (TDD) which alternates in time or Frequency Division Duplex (FDD) which requires paired spectrum with a guard band. The architecture involves sophisticated RF front-end design, digital signal processing, and interference cancellation algorithms to manage self-interference between the transmitter and receiver chains. Key components include SBFD-aware scheduling in the Medium Access Control (MAC) layer, physical layer procedures defined for channel state information (CSI) reporting and sounding reference signals (SRS) in SBFD slots, and resource allocation mechanisms that coordinate UL and DL resources within the sub-bands. Its role in the network is to significantly boost spectral efficiency, reduce latency for applications like XR and industrial IoT, and provide more flexible resource utilization compared to conventional duplexing, forming a foundational technology for 5G-Advanced evolution towards 6G.
Purpose & Motivation
SBFD was created to address the growing demand for higher spectral efficiency and lower latency in 5G-Advanced networks, overcoming limitations of existing duplexing methods. Traditional FDD requires paired spectrum, which is scarce and expensive, while TDD introduces latency due to switching gaps and requires strict synchronization across the network. SBFD solves these by enabling full-duplex operation on a single carrier, effectively doubling the utilization of available spectrum and enabling instantaneous bidirectional communication. The historical context stems from research in in-band full-duplex, which faced challenges with self-interference cancellation. SBFD's sub-band non-overlapping approach provides a more practical implementation by separating TX and RX frequencies, reducing interference complexity and making it feasible for commercial deployment. It addresses the need for enhanced capacity for dense urban deployments, ultra-reliable low-latency communication (URLLC), and support for asymmetric traffic patterns efficiently.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (45 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the foundational framework for Sub-Band non-overlapping Full Duplex (SBFD) was introduced, defining an SBFD-capable base station and the key concept of an SBFD symbol for simultaneous uplink and downlink transmission on separate, non-overlapping subbands of the same carrier. The specification established core parameters for SBFD operation, including transmission bandwidth configurations for UL and DL subbands (N_RB,SBFD,UL, N_RB,SBFD,DL) and the required guardband between them, while also specifying applicable frequency ranges and minimum channel bandwidths. Furthermore, this release included clarifications and corrections for handling overlapping grants and channels, such as for PUSCH with SP-CSI overlapping with PUSCH with data and for Msg3 grant overlapping with another UL grant, within this new SBFD context.
In Release 16, the SBFD (Sub-Band non-overlapping Full Duplex) function was newly introduced, defining the capability for a base station to transmit and receive simultaneously on separate, non-overlapping frequency subbands within the same carrier. The specification established key configurations for SBFD operation, including transmission bandwidth parameters for uplink and downlink subbands and a necessary guardband, applicable to specific FR1 and FR2-1 TDD bands. It also formalized different SBFD operational cases such as SBFD UD, where the uplink subband is configured at a lower frequency than the downlink subband.
- Configuration for directional collision handling between reference cell and other cell for half-duplex operation in CA TS 38.331CR2017
- Introduction of half-duplex operation in CA with unpaired spectrum TS 38.213CR0097
- Corrections on half-duplex operation in CA with unpaired spectrum TS 38.213CR0113
- CR on handling overlapping PUCCH/PUSCH transmissions with repetitions and with different priorities TS 38.213CR0178
- Correction on half-duplex operation in CA with unpaired spectrum TS 38.213CR0215
- Correction on half-duplex operation in CA with unpaired spectrum TS 38.213CR0240
+ 2 more changes
In Release 17, the SBFD (Sub-Band non-overlapping Full Duplex) function introduced new operational modes and configurations for base stations capable of simultaneous uplink and downlink transmission in separate subbands. The release defined specific transmission bandwidth configurations for SBFD UL and DL subbands, along with guardbands, for operations like SBFD DU, UD, and DUD. It also established minimum channel bandwidth requirements and specified which TDD bands are applicable for SBFD deployment.
- CR on PDCCH monitoring when overlapping with the rate matching pattern to TS 38.213 TS 38.213CR0383
- CR on UE procedure for overlapping CG PUSCH and DG PUSCH TS 38.214CR0322
- Clarification for half-duplex consideration in partial sensing based re-evaluation/pre-emption checking TS 38.214CR0423
- Correction on overlapping PUCCHs with repetitions of a same priority TS 38.213CR0406
- Clarification of PUSCH with SP-CSI overlapping with PUSCH with data TS 38.214CR0273
In Release 18, the new SBFD (Sub-Band non-overlapping Full Duplex) function introduced the capability for a base station to operate with simultaneous uplink and downlink transmissions on separate, non-overlapping frequency subbands within the same TDD carrier. This release specifically defined the operational configurations (DUD, DU, and UD), the associated transmission bandwidth parameters for the subbands and guardbands, and the applicable frequency ranges for FR1 and FR2-1. It also established minimum channel bandwidth requirements for SBFD operation, such as no less than 40MHz for most applicable FR1 bands.
- Introduction of QCL-TypeD priorities for overlapping CORESETs in M-DCI/M-TRP operation [QCL-TypeD CORESET priority for M-TRP] TS 38.213CR0569
- Introduction of QCL-TypeD priorities for overlapping CORESETs in M-DCI/M-TRP operation [QCL-TypeD CORESET priority for M-TRP] TS 38.331CR4512
- Big CR for 38.858 on SBFD TS 38.858CR0001
- CR for TR 38.858 on regulatory aspects for deploying SBFD in TDD unpaired spectrum TS 38.858CR0004
- CR on overlapping SRS resources TS 38.214CR0523
In Release 19, the new SBFD (Sub-Band non-overlapping Full Duplex) function introduced the capability for a base station to simultaneously transmit and receive on separate, non-overlapping frequency subbands within the same carrier during configured SBFD symbols. The release specified detailed RF requirements for SBFD-capable base stations, including configurations for SBFD DU, UD, and DUD operations with defined transmission bandwidths and guardbands. It also extended support to various FR1 and FR2-1 TDD bands while excluding specific ones like n34 and n46, and introduced clarifications for operation with Carrier Aggregation and UE-to-UE cross-link interference mitigation.
- CR to TS38.104 to introduce BS RF requirement for SBFD-capable BS TS 38.104CR0729
- Big CR on PUSCH requirement for SBFD-capable BS in 38.104 TS 38.104CR0768
- Introduction of Rel-19 evolution of NR duplex operation TS 38.212CR0218
- Introduction of evolution of NR duplex operation: Sub-band full duplex (SBFD) TS 38.213CR0707
- Introduction of evolution of NR duplex operation: Sub-band full duplex (SBFD) TS 38.214CR0673
- Introduction of Rel-19 Evolution of NR duplex operation (SBFD) TS 38.300CR1008
+ 17 more changes
Explore further
Broader topics and technologies where SBFD plays a role.
Defining Specifications
3GPP specifications that define or reference SBFD, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.104 vj20 | NR Base Station RF Requirements | 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 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TR 38.858 vi20 | Technical Report on Evolution of NR Duplex Operation | Rel-18 |
| TR 38.922 vj20 | Study on IMT Parameters for NR in Higher Bands | Rel-19 |