PBCH

Physical Broadcast Channel

Physical Layer →
Introduced in Rel-8

PBCH is the Physical Broadcast Channel, a downlink channel that transmits essential system information like the Master Information Block to enable initial cell access and synchronization.

Category
Physical Layer
Introduced
Rel-8
Where
Radio Access Network › NG-RAN (5G)
Specifications
29 specs
PBCH Description Purpose Related Classification Detected Changes Specifications

Description

The Physical Broadcast Channel (PBCH) is a fundamental downlink physical channel in both LTE (E-UTRA) and NR (New Radio) technologies. Its primary function is to broadcast a minimal set of essential system information, known as the Master Information Block (MIB), to all user equipment (UE) within a cell. The PBCH is transmitted with a fixed, robust coding scheme and is always located in the central 72 subcarriers (6 resource blocks) around the DC carrier, regardless of the system's total bandwidth. This ensures that a UE performing initial cell search can find and decode the PBCH without prior knowledge of the system bandwidth.

In LTE, the PBCH is transmitted in the first 4 OFDM symbols of slot 1 in subframe 0 of every radio frame (every 10 ms). The MIB payload is small (24 bits) and includes the most crucial information: the downlink system bandwidth, the Physical Hybrid-ARQ Indicator Channel (PHICH) configuration, and the 8 most significant bits of the System Frame Number (SFN). The full SFN is encoded across four consecutive PBCH transmissions (over 40 ms) using a specific coding scheme. The UE must successfully decode the PBCH to obtain the system bandwidth, which then allows it to properly receive the rest of the carrier and proceed to decode the Physical Downlink Shared Channel (PDSCH) carrying the System Information Blocks (SIBs). The PBCH uses a transmit diversity scheme (e.g., Space Frequency Block Coding) to improve reception reliability at cell edges.

In NR, the PBCH concept is evolved but retains its core purpose. The NR PBCH is part of the SS/PBCH block (Synchronization Signal/PBCH block), which is a burst of signals transmitted periodically. The MIB in NR contains information necessary for initial access, including the subcarrier spacing, the SSB index (for beamforming), the system frame number, and an indication for the SIB1 scheduling. A key enhancement in NR is that the PBCH payload includes additional bits that, combined with the Demodulation Reference Signals (DM-RS) within the PBCH, help the UE determine the half-radio frame timing and the SSB index within a burst, which is vital for operation in beamformed mmWave environments. The robust design of the PBCH in both LTE and NR ensures that UEs can reliably achieve initial synchronization and acquire the mandatory information needed to camp on a cell, forming the very first step in the network access procedure.

Purpose & Motivation

The PBCH was created to solve the fundamental bootstrap problem in OFDM-based cellular systems: a UE powering on has no knowledge of the cell's configuration. Before decoding any user data or detailed system information, the UE needs a minimal set of parameters to configure its receiver. The PBCH provides this absolutely critical information in a highly robust and predictable manner. It addresses the limitations of earlier systems where such information might be scattered or required multi-step blind detection procedures.

In LTE and NR, the design philosophy emphasizes a clear and efficient initial access sequence. The UE first detects the Primary and Secondary Synchronization Signals (PSS/SSS) to achieve time and frequency synchronization and identify the physical cell ID. The next immediate step is to decode the PBCH to get the MIB. The information in the MIB, especially the system bandwidth, is a prerequisite for the UE to properly tune its receiver to the full carrier bandwidth and locate the control region to receive the PDCCH, which then schedules the SIB1. Without the PBCH, the UE would be unable to proceed beyond coarse synchronization. Its fixed location and robust coding ensure that even UEs at the cell edge with low signal-to-noise ratio can successfully decode it, guaranteeing reliable cell coverage for initial access, which is paramount for network usability and mobility.

Classification

Part ofPDCCH
Specific typesSCH
Related approachesPSSSSS

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (107 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.

Rel-15 22 changes

In Release 15, the PBCH was enhanced to support a maximum of eight SS/PBCH blocks for operation in unpaired spectrum at carrier frequencies beyond 2.4 GHz. This change increased the number of synchronization signal blocks that could be transmitted, improving beamforming and initial access capabilities in higher frequency bands. The update specifically addressed the needs of new radio deployments requiring more robust broadcast signaling.

  • Support maximum 8 SS/PBCH blocks for unpaired spectrum beyond 2.4GHz TS 38.213CR0006
  • Clarification on CRC attachment for DL-SCH and PCH transport channels in NB-IoT TS 36.212CR0285
  • 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
  • Number of PDCCH/EPDCCH/SPDCCH received parallel TS 36.302CR1198

+ 16 more changes

Rel-16 26 changes

In Release 16, the PBCH-related enhancements were primarily focused on supporting LTE-based 5G terrestrial broadcast, as indicated by the introduction of new broadcast numerologies. Furthermore, the release added the capability for the broadcast channel to carry new types of assistance data, specifically barometric pressure and TBS (Transport Block Size) assistance data. These updates expanded the PBCH's role in supporting enhanced broadcast services and providing additional system information to user equipment.

  • CR to 36.104: Introduction of LTE based 5G terrestrial broadcast numerologies TS 36.104CR4907
  • Corrections to LTE-based 5G terrestrial broadcast TS 36.201CR0031
  • Introduction of Physical Layer Enhancements for URLLC TS 38.202CR0012
  • Introduction of Physical Layer Enhancements for NR URLLC TS 38.212CR0026
  • Introduction of shared spectrum channel access TS 38.213CR0071
  • Addition of broadcast of barometric pressure assistance data TS 37.355CR0001

+ 20 more changes

Rel-17 36 changes

In Release 17, the primary enhancement for the PBCH function was to support the introduction of Multicast and Broadcast Services (MBS) in NR. This required updates to the physical layer specifications, including corrections to channel coding and procedures in TS 38.212 to ensure proper system information broadcast and cell identification for these new services. These changes enabled the network to broadcast data unidirectionally to all users or specific groups on the downlink.

  • Introduction of new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.300CR1360
  • Introduction of multicast and broadcast services TS 38.202CR0021
  • Introduction of Multicast and Broadcast Services (MBS) support TS 38.211CR0084
  • Introduction of NR Multicast and Broadcast Services TS 38.212CR0088
  • Introduction of multicast-broadcast services in NR TS 38.213CR0273
  • Corrections to NR support of multicast and broadcast services TS 38.202CR0022

+ 30 more changes

Rel-18 12 changes

In Release 18, the enhancements to the Physical Broadcast Channel (PBCH) were made within the broader framework of Rel-18 enhancements for NR Multicast and Broadcast Services (MBS). These updates specifically supported the introduction of 5G broadcast in UHF bands, as detailed in the changes to the RF requirements for terrestrial broadcast. This involved defining new adjacent channel leakage power ratio (ACLR) requirements to ensure proper operation when broadcasting on these additional frequency bands.

  • Introduction of 5G broadcast UHF bands to 36.104 TS 36.104CR4979
  • Introduction of sidelink channel access procedures for Rel-18 NR sidelink evolution TS 38.201CR0003
  • Introduction of Rel-18 enhancements of NR Multicast and Broadcast Services TS 38.212CR0173
  • Introduction of Rel-18 enhancements of NR Multicast and Broadcast Services TS 38.213CR0584
  • [LTE_terr_bcast_bands_part2-Core] CR to TS 36.104: Separation of additional ACLR requirements for LTE based 5G terrestrial broadcast, Rel-18 TS 36.104CR4986
  • Correction on mapping PSFCH to physical resources TS 38.211CR0141

+ 6 more changes

Rel-19 11 changes

In Release 19, the primary evolution for the PBCH function was its adaptation to support LTE-based 5G terrestrial broadcast for new deployment bands, as part of the broader "LTE-based 5G Broadcast Phase 2" introduction. This involved specific corrections and parameter alignments for the network's common channels and signals, including the broadcast channel, to ensure proper system information delivery in these new broadcast scenarios. The changes focused on enabling the unidirectional distribution service in the defined carrier bandwidths for these early deployments.

  • CR to TS 36.104 : New bands for LTE based 5G terrestrial broadcast for early deployments, Rel-19 TS 36.104CR5006
  • Introduction of Rel-19 LTE-based 5G Broadcast Phase 2 TS 36.212CR0376
  • Introduction of LTE-based 5G Broadcast Phase 2 TS 36.300CR1428
  • Introduction of PDCCH repetitions for Type0-PDCCH CSS set in TNs [Common_PDCCH_Rep_TN] TS 38.213CR0748
  • 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

+ 5 more changes

Explore further

Broader topics and technologies where PBCH plays a role.

Topics
LTE / LTE-Advanced5G NR (New Radio)Lawful InterceptRadio Access NetworkCore Network
Technologies
LTE

Defining Specifications

3GPP specifications that define or reference PBCH, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
TR 21.905 vj00 3GPP Technical Terms and Definitions Rel-19
TS 25.133 vj00 UTRAN RRM Requirements for FDD Rel-19
TS 36.104 vj10 Base Station (BS) radio transmission and reception Rel-19
TS 36.116 vj00 E-UTRA Relay RF Requirements Rel-19
TS 36.117 vj00 E-UTRA Relay RF Test Methods & Requirements Rel-19
TS 36.133 vj20 E-UTRA RRM Requirements Rel-19
TS 36.141 vj00 E-UTRA BS Conformance Testing 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 36.213 vj10 LTE Physical Layer Procedures 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 36.863 vc00 CRS Interference Mitigation for Homogeneous Networks Rel-12
TS 36.867 vd00 LTE DL 4 Rx Antenna Port Study TR Rel-13
TS 36.878 vd00 LTE Performance Enhancements for High Speed Scenarios Rel-13
TR 36.976 vj00 LTE-based 5G Terrestrial Broadcast Overview Rel-19
TS 37.355 vj20 LTE Positioning Protocol (LPP) Rel-19
TR 37.911 vj00 3GPP 5G NTN Self-Evaluation Report Rel-19
TS 38.133 vj20 5G UE Radio Requirements for RRC_IDLE Mobility 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 38.521 vj20 NR Physical Layer UE Conformance Testing Rel-19
TS 38.831 vg10 UE RF Requirements for FR2 Enhancements Rel-16
TR 38.889 vg00 NR-based access to unlicensed spectrum study Rel-16
TS 45.820 vd10 CIoT for Internet of Things Rel-13