ProDeveloperTutorial.com

Tutorials and Programming Solutions
Menu
  • Shell Scripting
  • System Design
  • Linux System Programming
  • 4g LTE
  • Coding questions
  • C
  • C++
  • DSA
  • GIT
  • 450 DSA Cracker
  • 5G NR
  • O-RAN

5G NR System Information Acquisition and On Demand SIB

prodevelopertutorial February 8, 2022

When UE is switched on it will acquire system information for cell selection, cell-reselection.

MIB and SIB1 are 2 important SI that UE requires to select and latch on to a cell.

MIB and SIB1 are called as “MSI” “Minimum System Information”.
Standalone SIB1 is called as “RMSI” “Remaining Minimum System Information”.

All other SI fro SIB2 to SIB9 is called as OSI “Other System Information”

MIB is periodically broadcasted on BCH.

SIB1 is periodically broadcasted on DL-SCH or unicast on DL-SCH.

Other SI:

SIB2 through SIB9 can be periodically broadcast on DL-SCH or Broadcast on-demand on DL-SCH or unicast on DL-SCH.

SIB1 contains the scheduling information for all SI messages.

The SIB that have the same periodicity can be mapped to the same SI message.

SI_window is the time domain window that each SI message is send and only one window length is defined for all SI messages.

Scheduling Other SI:

OSI can be sent in below ways and we shall look at the ways in details:

1. Periodically broadcasted on DL-SCH or

2. Broadcasted on-demand on DL-SCH or

3. Sent in dedicated manner on DL-SCH to UEs in RRC-CONNECTED mode.

1. Broadcasted on-demand by UE on DL-SCH

When UE is in RRC_IDLE or RRC_INACTIVE, request for OSI will trigger a random access procedure.

UE will read SI scheduling information from SIB1 and UE will determine the broadcast status from “si-BroadcastStatus” for an SI message.

If “si-BroadcastStatus” is “broadcasting”, the UE would acquire the required SIB normally.

If “si-BroadcastStatus” is “notbroadcasting”, then UE would proceed with RA procedure to acquire required SIB.

If network configures UE with PRACH resource for SI request, then CFRA is used else CBRA will be used.

On Demand SI request using CBRA procedure:

If “SI-RequestConfig” is not present in SIB1, then CBRA is used to request SI using RRCSystemInfoRequest message in Msg3.

gNB will respond using MSG4.

After that gNB will broadcast the required SI.

5G NR System Information Acquisition and On Demand SIB

 

–RRCSystemInfoRequest
The RRCSystemInfoRequest message is used to request SI message(s) required by the UE as specified in clause 5.2.2.3.3.

It is transmitted using SRB0 -> TM mode -> CCCH logical channel on MSG3.

Below are the contents of “RRCSystemInfoRequest”

“requested-SI-List” it contains the list of requested SI messages.

According to the order of entry in the list of SI messages configured by schedulingInfoList in si-SchedulingInfo in SIB1, first bit corresponds to first/leftmost listed SI message, second bit corresponds to second listed SI message, and so on.

After gNB acknowledge this in MSG2 in CFRA and MSG4 in CBRA, it will broadcast the required SI messages.

 -- ASN1START
 -- TAG-RRCSYSTEMINFOREQUEST-START

RRCSystemInfoRequest-IEs ::=    SEQUENCE { 
    requested-SI-List
                   BIT STRING (SIZE (maxSI-Message)),   --32bits
    spare                               BIT STRING (SIZE (12)) 
} 
RRC-PosSystemInfoRequest-r16-IEs ::=  SEQUENCE { 
    requestedPosSI-List
                   BIT STRING (SIZE (maxSI-Message)),   --32bits
    spare                                 BIT STRING (SIZE (11)) 
} 
 -- TAG-RRCSYSTEMINFOREQUEST-STOP
 -- ASN1STOP

On Demand SI request using CFRA procedure:

gNB may configure the UE with dedicated RA resources for SI in SI-RequestConfig within SI-SchedulingInfo IE in SIB1.

5G NR System Information Acquisition and On Demand SIB

–SI-RequestConfig
The IE SI-RequestConfig contains configuration for Msg1 based SI request.

 

 -- ASN1START
 -- TAG–SI-REQUESTCONFIG-START
SI-RequestConfig::=                 SEQUENCE { 
    rach-OccasionsSI
                    SEQUENCE { 
        rach-ConfigSI                       RACH-ConfigGeneric, 
        ssb-perRACH-Occasion                ENUMERATED {oneEighth, oneFourth, oneHalf, one, two, four, eight, sixteen} 
    }                                                                                                       OPTIONAL,   -- Need R
    si-RequestPeriod
                    ENUMERATED {one, two, four, six, eight, ten, twelve, sixteen}       OPTIONAL,   -- Need R
    si-RequestResources
                 SEQUENCE (SIZE (1..maxSI-Message)) OF SI-RequestResources 
} 
SI-RequestResources ::=             SEQUENCE { 
    ra-PreambleStartIndex               INTEGER (0..63), 
    ra-AssociationPeriodIndex           INTEGER (0..15)                                                     OPTIONAL,   -- Need R
    ra-ssb-OccasionMaskIndex            INTEGER (0..15)                                                     OPTIONAL  -- Need R
} 
 -- ASN1STOP
 -- TAG–SI-REQUESTCONFIG-STOP

“SI-RequestConfig” can be used to configure for each SI-message.

UE selects appropriate RA preamble and transmits MSG1.

gNB acknowledges the SI request in MSG2.

Then gNB wil transmits the required SI message.

 

Acquisition of an SI messages

Below steps are followed for an UE to acquire an SI message:

1. UE shall determine the start of SI window that includes radio frame and slot number.

2. for the concerned SI message, determine the number n which corresponds to the order of entry in the list of SI messages configured by schedulingInfoList in si-SchedulingInfo in SIB1;

3. determine the integer value x = (n – 1) × w, where w is the si-WindowLength

4. the SI-window starts at the slot #a, where a = x mod N, in the radio frame for which SFN mod T = FLOOR(x/N), where T is the si-Periodicity of the concerned SI message and N is the number of slots in a radio frame

Example:

Consider below scenario:

1. There is one SIB in each SI message.
2. The first entry in schedulingInfoList of SIB1 is SIB2, the second entry is SIB3 and so on up to SIB5.
3. Sub carrier spacing of 30KHz and the number of slots is 20.
4. Different periodicity for different SI is given in 2nd column. For example, SIB2 periodicity is 8 in radio frame. It will be transmitted in 8 radio frame.

5G NR System Information Acquisition and On Demand SIB

5G NR System Information Acquisition and On Demand SIB

TS 38.300 and 38.331

 

 

Share
Email
Tweet
Linkedin
Reddit
Stumble
Pinterest
Prev Article
Next Article

About The Author

prodevelopertutorial

Follow this blog to learn more about C, C++, Linux, Competitive Programming concepts, Data Structures.

Leave a Reply Cancel Reply

You must be logged in to post a comment.

ProDeveloperTutorial.com

Tutorials and Programming Solutions
Copyright © 2023 ProDeveloperTutorial.com
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies.
Do not sell my personal information.
Cookie SettingsAccept
Manage consent

Privacy Overview

This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary
Always Enabled
Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
CookieDurationDescription
cookielawinfo-checkbox-analytics11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checkbox-functional11 monthsThe cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checkbox-necessary11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-others11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-performance11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy11 monthsThe cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
Functional
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytics
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
Others
Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
SAVE & ACCEPT