Introduction:
When a device (UE) powers on and searches for a 5G network, it needs essential system information before establishing a connection. This information is broadcast by the gNB in the form of System Information Blocks (SIBs). Among these, SIB1 plays a critical role in enabling the UE to access the network.
What is SIB1?
SIB1 stands for System Information Block Type 1. It is part of the Radio Resource Control (RRC) layer and is transmitted on the BCCH over DL-SCH channel. After decoding the Master Information Block (MIB) from PBCH, the UE reads SIB1 to learn how to proceed with cell selection and request additional system information.
Why is SIB1 Important below are the some Key pointer?
- Provides cell access parameters such as PLMN identity, Tracking Area Code, and Cell Identity.
- Informs the UE about access restrictions (e.g., cell barred, access barring for certain categories).
- Contains serving cell configuration for initial access.
- Specifies how other SIBs are scheduled (periodic or on-demand).
- Includes connection failure control and system information versioning.
High level Contents of SIB1:
Here’s a simplified breakdown of what SIB1 includes:
1. Cell Access Related Info
- PLMN Identity List
- Tracking Area Code (TAC)
- Cell Identity
- Access barring parameters
2. Serving Cell Configuration
- Common configuration for initial access
- Frequency and bandwidth info
- Subcarrier spacing and timing parameters
3. SI Scheduling Info
- How and when other SIBs (SIB2, SIB3, etc.) are broadcast
4. Connection Establishment Failure Control
- Rules for handling repeated RRC failures
5. System Info Value Tag
- Helps UE detect changes in system information
