Description
The Physical Sidelink Broadcast Channel (PSBCH) is a fundamental channel within the 3GPP sidelink (SL) interface, which facilitates direct Device-to-Device (D2D) and Vehicle-to-Everything (V2X) communication. It operates in the physical layer (Layer 1) and is primarily responsible for broadcasting sidelink-specific Master Information Block (SL-MIB) information. This information is crucial for UEs to discover each other and establish a common timing reference for subsequent sidelink communication. The PSBCH is transmitted by a UE acting as a synchronization source, which could be an eNodeB/gNodeB (in-coverage), another UE (out-of-coverage), or a Global Navigation Satellite System (GNSS). The channel carries parameters such as the in-coverage indicator, direct frame number, and sidelink system bandwidth, enabling receiving UEs to synchronize in time and frequency and to correctly decode other sidelink channels.
Architecturally, the PSBCH is mapped to specific resource elements within the sidelink resource grid. In LTE-based sidelink (often referred to as PC5 interface in the context of ProSe), the PSBCH is transmitted in subframes configured for sidelink communication, specifically within the Sidelink Broadcast Control Channel (SBCCH) period. The channel structure involves specific modulation (QPSK) and coding schemes defined in the relevant 3GPP specifications (e.g., TS 36.211). The information carried by the PSBCH is used by receiving UEs to acquire the sidelink radio frame timing and to understand the basic configuration of the sidelink carrier, which is a prerequisite for decoding the Physical Sidelink Control Channel (PSCCH) and Physical Sidelink Shared Channel (PSSCH).
In NR sidelink (introduced in Release 16 and enhanced in later releases), the PSBCH continues to play a vital role, though its structure and the details of the carried information (now termed NR Sidelink Synchronization Signal Block, NR S-SSB) are adapted to the more flexible NR numerology and frame structure. The NR PSBCH is part of the S-SSB, which also includes the Primary Sidelink Synchronization Signal (PSSS) and Secondary Sidelink Synchronization Signal (SSSS). This block is transmitted periodically, and its content includes essential information for initial access and resource pool configuration. The PSBCH is a cornerstone for enabling autonomous sidelink operation, especially in scenarios where UEs are outside network coverage, such as public safety communications or platooning in V2X.
Purpose & Motivation
The PSBCH was introduced to solve the fundamental problem of synchronization and system information distribution in direct device-to-device communications standardized by 3GPP. Prior to its introduction, cellular communication was strictly network-centric, requiring all communication to pass through the base station (eNodeB). This architecture was insufficient for use cases like public safety, where first responders need to communicate directly when infrastructure is damaged, or for vehicular networks requiring ultra-low latency communication between nearby vehicles. The PSBCH provides the necessary mechanism for UEs to establish a common 'sidelink network' by broadcasting the minimal set of information needed for other devices to find and synchronize with a potential transmitter.
Its creation was motivated by the need for efficient, infrastructure-independent communication. In the absence of PSBCH, devices would have no standardized way to discover each other's timing or understand the basic configuration of the direct communication link. This would lead to inefficient, ad-hoc communication prone to interference and high power consumption. The PSBCH, as part of the broader sidelink framework, enables controlled, scheduled, and efficient direct communication. It addresses the limitations of previous non-3GPP D2D solutions (like Wi-Fi Direct) which lacked the tight integration, quality of service, and scalability required for large-scale, mission-critical cellular off-network services.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (93 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-12, normative work from Rel-15.
In Release 15, the PSBCH was enhanced as part of corrections and specifications for V2X sidelink communication, specifically addressing the physical layer procedures and modulation and coding scheme (MCS). This introduction included the definition of specific UE maximum output power requirements for the modulation and channel bandwidth used for V2X Communication. Furthermore, the release established applicable channel bandwidths per operating band explicitly for V2X sidelink operations.
- Clarification on CRC attachment for DL-SCH and PCH transport channels in NB-IoT TS 36.212CR0285
- Correction on V2X sidelink communication in TS 36.300 TS 36.300CR1199
- 36.300 CR on Correction of Physical Layer Resource to Cell Resource TS 36.300CR1211
- RAN sharing with multiple Cell ID broadcast TS 36.300CR1239
- Minor corrections to services provided by physical layer TS 36.302CR1195
- Correction on MCS for V2X sidelink communication in TS 36.302 TS 36.302CR1196
+ 3 more changes
In Release 16, the PSBCH function was enhanced as part of the introduction of 5G V2X sidelink features, with specific corrections made to the sidelink broadcast channel. These updates were integrated into the physical layer specifications, alongside other corrections and clarifications for NR sidelink communication procedures.
- Corrections to LTE-based 5G terrestrial broadcast TS 36.201CR0031
- Introduction of 5G V2X with NR Sidelink TS 36.300CR1271
- Introduction of 5G V2X sidelink features into TS 38.212 TS 38.212CR0025
- Introduction of Physical Layer Enhancements for NR URLLC TS 38.212CR0026
- Introduction of shared spectrum channel access TS 38.213CR0071
- Correction for NR sidelink communication TS 36.300CR1287
+ 29 more changes
In Release 17, the PSBCH function was enhanced as part of the broader NR sidelink enhancements. These enhancements included corrections and refinements to the technical specifications, such as those documented in 38.212 for NR sidelink and multicast-broadcast services. The updates aimed to improve the reliability and performance of sidelink broadcast communications for use cases like V2X.
- Introduction of new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.300CR1360
- Introduction of Rel-17 sidelink enhancements TS 37.985CR0001
- Introduction of NR Multicast and Broadcast Services TS 38.212CR0088
- Introduction of NR sidelink enhancement TS 38.212CR0094
- Introduction of multicast-broadcast services in NR TS 38.213CR0273
- Introduction of sidelink enhancements in NR TS 38.213CR0279
+ 20 more changes
In Release 18, the PSBCH saw specific enhancements as part of the broader NR sidelink evolution, including a correction to the sidelink starting symbol index for indications of uplink slots in PSBCH when operating in unlicensed spectrum (SL-U). This release also introduced new sidelink channel access procedures for operation in shared and unlicensed bands.
- Introduction of sidelink CA and dynamic resource pool sharing for NR V2X TS 37.985CR0007
- Introduction of sidelink channel access procedures for Rel-18 NR sidelink evolution TS 38.201CR0003
- Introduction of Rel-18 NR sidelink evolution TS 38.212CR0149
- Introduction of Rel-18 enhancements of NR Multicast and Broadcast Services TS 38.212CR0173
- Introduction of NR sidelink evolution TS 38.213CR0509
- Introduction of Rel-18 enhancements of NR Multicast and Broadcast Services TS 38.213CR0584
+ 11 more changes
In Release 19, the PSBCH function was enhanced as part of the introduction of LTE-based 5G Broadcast Phase 2. This included the definition of new minimum requirements for LTE-based 5G terrestrial broadcast, as detailed in multiple new specification sections. Furthermore, the release introduced specific operating bands and channel bandwidth parameters, such as the PMCH bandwidth, for this broadcast system.
- Introduction of Rel-19 LTE-based 5G Broadcast Phase 2 TS 36.212CR0376
- Introduction of LTE-based 5G Broadcast Phase 2 TS 36.300CR1428
- Corrections for Rel-19 LTE-based 5G Broadcast Phase 2 TS 36.212CR0379
- RRC parameter name alignment for Rel-19 LTE-based 5G Broadcast Phase 2 TS 36.212CR0381
- Corrections on R19 NES adaptation of common channel/signals TS 38.212CR0243
- Corrections on R19 NES adaptation of common channel/signals TS 38.213CR0753
Explore further
Broader topics and technologies where PSBCH plays a role.
Defining Specifications
3GPP specifications that define or reference PSBCH, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.101 vj30 | LTE UE Radio Transmission & Reception Requirements | Rel-19 |
| TS 36.201 vj00 | LTE Physical Layer General Description | Rel-19 |
| TS 36.211 vj10 | LTE Physical Layer Specification | Rel-19 |
| TS 36.212 vj10 | LTE Multiplexing and Channel Coding | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 |
| TS 36.785 ve00 | LTE Sidelink V2V Services Study | Rel-14 |
| TS 36.786 ve00 | TR on V2X Services based on LTE sidelink | Rel-14 |
| TS 36.787 vf00 | V2X New Band Combinations for LTE | Rel-15 |
| TS 36.788 vf00 | V2X Phase 2 Technical Report for LTE | Rel-15 |
| TS 36.877 vc00 | LTE Device to Device Proximity Services | Rel-12 |
| TR 37.985 vj00 | Overview of V2X features in LTE and NR | Rel-19 |
| TS 38.201 vj00 | NR Physical Layer General Description | Rel-19 |
| TS 38.212 vj10 | NR Multiplexing and Channel Coding | Rel-19 |
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TR 38.786 vi20 | Technical Report for NR Sidelink Evolution | Rel-18 |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 |