5G NR - System Information Block 23 (SIB23)

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	5.2.2.4.24, 6.3.1
Direction	gNB -> UE	Message Type	Broadcast System Information

Full message name	5G NR - System Information Block 23 (SIB23)
Protocol	RRC
Technology	5G
Direction	gNB -> UE
Interface	Uu
Signaling bearer / channel	Broadcast transport / BCCH-DL-SCH
Typical trigger	Broadcast when the cell supports ranging or sidelink positioning.
Main purpose	Provides broadcast configuration for ranging and sidelink positioning so the UE can apply the correct positioning-related behavior.
Main specification	3GPP TS 38.331, 5.2.2.4.24, 6.3.1
Release added	Release 18
Procedures where used	System Information Acquisition, Ranging and Sidelink Positioning
Related timers	SIB23 does not use a dedicated UE-specific transaction timer
Related cause values	SIB23 does not carry reject causes

What is System Information Block 23 (SIB23) in simple terms?

System Information Block 23 (SIB23) is an NR broadcast system information block used to provide ranging and sidelink positioning information.

Provides broadcast configuration for ranging and sidelink positioning so the UE can apply the correct positioning-related behavior.

Why this message matters

SIB23 gives the UE the broadcast information needed for ranging and sidelink positioning behavior.

Where this message appears in the call flow

System Information Acquisition

Call flow position: Read as additional SI after the basic broadcast context is available.

Typical state: UE is camped and expanding broadcast context for ranging or sidelink positioning.

Preconditions:

MIB and SIB1 have been acquired.

Next likely message: UE applies the ranging or sidelink positioning configuration locally

Call flow position

Previous message(s): MIB, System Information Block 1 (SIB1), System Information Block 12 (SIB12)

Next message(s): Ranging or sidelink positioning preparation

Message direction and transport

Sender and receiver: gNB -> UE

Interface: Uu

Domain: Access-side radio control and sidelink positioning information

Signaling bearer: Broadcast transport

Logical channel: BCCH-DL-SCH

Transport / encapsulation: RRC system information carried on BCCH-DL-SCH after MIB and SIB1 acquisition.

Security context: Broadcast information. It is cell-common and not protected by dedicated AS security.

Message Structure Overview

SIB23 is the broadcast SI block for ranging and sidelink positioning.
Its practical value is explaining why positioning-related sidelink behavior starts, fails, or uses the wrong configuration.

ASN.1 for 5G NR - System Information Block 23 (SIB23)

SystemInformation-IEs ::= SEQUENCE {
  sib-TypeAndInfo SEQUENCE (SIZE (1..maxSIB)) OF CHOICE {
    sib23-v1800 SIB23-r18,
    ...
  },
  ...
}

SIB23-r18 ::= SEQUENCE {
  ... -- ranging and sidelink positioning parameters
}

How to read this ASN.1

SIB23 is release-18 broadcast information for ranging and sidelink positioning. Engineers usually care whether the positioning-related block is present and matches the expected sidelink scenario.

Decoded Message Dump

BCCH-DL-SCH-Message
  message: c1
    systemInformation
      criticalExtensions
        systemInformation
          sib-TypeAndInfo
            sib23
              sl-PosConfig-r18: present

How to read this dump

The practical question is whether the ranging or positioning configuration is present and valid for the target scenario.

Important Information Elements

IE	Required	Description
`ranging and sidelink positioning configuration`	Yes	Broadcast configuration block used for ranging and sidelink positioning behavior.

Detailed field explanation

`ranging and sidelink positioning configuration`

Broadcast configuration block used for ranging and sidelink positioning behavior.

Presence: Required

In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.

What to check in logs and traces

Confirm SIB23 was acquired when debugging ranging or sidelink positioning issues.
Compare SIB23 with SIB12 if the scenario also depends on general sidelink configuration.

Common Issues and Troubleshooting

Sidelink positioning or ranging does not start correctly.

Likely cause: SIB23 may be missing or its ranging/positioning configuration may not match the deployment.

What to inspect: Check the relevant positioning-related SIB23 block.

Next step: Compare SIB23 with the general sidelink broadcast context in SIB12.

LTE / 5G / Variant Comparison

SIB23 versus SIB12

SIB12 covers general sidelink configuration, while SIB23 focuses on ranging and sidelink positioning.

FAQ

What is SIB23 in 5G NR?

SIB23 is System Information Block 23, used for ranging and sidelink positioning information.

Related message pages

Related Procedures

Related Tools

Use This Reference in Practice

Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.