5G/NR - MIB / SIB                                           Home : www.sharetechnote.com

 

 

 

 

MIB / SIB

 

Overall functionality and structure of MIB / SIB  of NR is almost same as LTE, but there is one major differeces between NR and LTE. In LTE (actually all other techology except NR), all the SIBs are broadcast periodically regardless of whether UE want it or not. However, in NR there are two different types of SIBs. One type is the one being transmitted periodically like SIBs in LTE and the other type is the one being transmitted only when there is the request from UE.  

 

 

 

Overall MIB/SIB Transmission Flow

 

Overall MIB / SIB transmission and relationships among SIBs is illustrated as below (38.331 - 5.2 System information)  

 

 

 

 

MIB/SIB Aquisition Process

 

MIB / SIB acquisition process would vary depending on cases. I will describe the overall MIB/SIB acquisition process with various cases.

 

 

< Case 1 : Upon Power On and No Stored SIB in UE, No-OnDemand SI indication >

    i) Power On

    ii) Search Cell and Decode MIB

    iii) Store the decoded MIB

    iv) Check if CellBarred = barred, stop there and if not, move to next step.

    v) Using the parameters in MIB, try decoding SIB1.

    vi) [if SIB1 decoding is successful] store the infromation and then move to next step.

    vii) [assuming that SIB1 indicate No On-Demand SI] Decode Other SIBs (SI)

 

 

< Case 2 : Upon Power On and No Stored SIB in UE, OnDemand SI indication >

    i) Power On

    ii) Search Cell and Decode MIB

    iii) Store the decoded MIB

    iv) Check if CellBarred = barred, stop there and if not, move to next step.

    v) Using the parameters in MIB, try decoding SIB1.

    vi) [if SIB1 decoding is successful] store the infromation and then move to next step.

    vii) [assuming that SIB1 indicate On-Demand SI] Check the RRC Status (NOTE : Based on 38.331-5.2.2.3.3]

      a) if RRC Status is in RRC_IDLE or RRC_INACTIVE

      • Trigger lower layer to initiate preamble transmission procedure
      • Aquire the requiested SI messages when Acknowledgement for SI request is received

      b) if RRC Status is in RRC_CONNECTED

      • [Process is not defined yet.]

 

 

 

MasterInformationBlock

 

Followings are the overall characteristics of MIB (MasterInformationBlock)

  • Transmitted over BCH
  • Transmitted with the periodicity of 80 ms and within this 80 ms repeatative transmission happens
  • Includes the parameters that are required to decode SIB1 (SystemInformationType1)

 

MIB ::= SEQUENCE {

    ssb-IndexExplicit           INTEGER (1..7)  OPTIONAL, -- Cond Above6Ghz

    halfFrameIndex              ENUMERATED {firstHalf,secondHalf},

    systemFrameNumber           BIT STRING (SIZE (10)),

    subCarrierSpacingCommon     SubcarrierSpacing,

    ssb-subcarrierOffset        INTEGER (0..11),

    dmrs-TypeA-Position         ENUMERATED {pos2, pos3},

    pdcchConfigSIB1             INTEGER(0..255),

    cellBarred                  ENUMERATED {barred, notBarred},

    intraFreqReselection        ENUMERATED {allowed, notAllowed},

    spare                       BIT STRING (SIZE (ffsValue))

}

 

 

ssb-IndexExpliciit : identifies the time domain location of SSB in the SS-Burst-Set as described in  SSB Time Domain Location (based on 38.213 4.1 Cell search). The field is only present for carrier frequencies > 6 GHz.

 

halfFrameIndex : Indicates  whether the SS block is in the first or second 5 ms of a radio frame

 

subCarrierSpacingCommon : Indicates the Subcarrier spacing for SIB1, Msg.2/4 for initial access and SI-messages. Values 15 and 30 kHz are applicable for carrier frequencies < 6GHz; Values 60 and 120 kHz are applicable for carrier frequencies > 6GHz

 

ssb-subcarrierOffset : Indicates the frequency domain offset between SSB and the overall resource block grid in number of subcarriers.

 

dmrs-TypeA-Position : Indicates Position of (first) DL DM-RS.

 

pdcchConfigSIB1 : Determines a bandwidth for PDCCH/SIB, a common ControlResourceSet (CORESET), a common search space and necessary PDCCH parameters

 

 

 

SystemInformationBlockType1

 

Followings are the overall characteristics of SIB1 (SystemInformationBlockType1)

  • Transmitted over DL-SCH
  • Transmitted with the periodicity of [X] ms and within this [X] ms repeatative transmission happens
  • Includes information regarding the availability and scheduling (e.g. periodcity, SI-window size) of other SIB
  • Indicates whether they (i.e. other SIBs) are provided via periodic broadcast basis or only on-demand basis
  • (If other SIBs are provided on-demand then SIB1) Includes information for the UE to perform SI request   

 

 

SIB1 ::= SEQUENCE {

    ssb-PositionsInBurst           SEQUENCE {

        inOneGroup                 BIT STRING (SIZE (8)),

        groupPresence              BIT STRING (SIZE (8))   OPTIONAL, -- Cond above6GHzOnly

    },

 

    ssb-periodicityServingCell     ENUMERATED { ms5,ms10,ms20,ms40,ms80,ms160,spare1,spare2 },

    ss-PBCH-BlockPower             INTEGER (-60..50),

 

    frequencyInfoUL                FrequencyInfoUL         OPTIONAL -- Cond FDD

 

    supplementaryUplink            SEQUENCE {

        frequencyInfoUL                FrequencyInfoUL

    }                              OPTIONAL, -- Cond SUL

 

    tdd-UL DLconfiguration         TYPE_FFS!     OPTIONAL -- Cond TDD

 

    pucch-Format0-BaseSequenceHopping           ENUMERATED {true}       OPTIONAL,

    PUCCH-Format1-BaseSequenceHopping           ENUMERATED {true}       OPTIONAL,

}

 

 

 

Other SIBs (Periodic SIBs)

 

Followings are the overall characteristics of other SIBs (i.e, SIBs other than SIB1) that are transmitted by periodic broadcast

  • Transmitted over DL-SCH
  • Transmitted within periodically occurring time-domain window called SI-Window

 

 

Reference

 

[1]