5G学习笔记之系统消息

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参考资料：3GPP 38.300、3GPP 38.331

SI：System Information
MIB：Master Information Block
SIB：SystemInformation Block
SSB：Synchronization Signal Block
RMSI：Remaining Minimum SI，剩余最小SI，即除MIB外的最小SI。
PSCell：Primary SCG Cell
BWP：Bandwidth Part
1. 系统消息

SI包括一个MIB和多个SIB。SI分为最小SI 和其它SI。

（1）最小SI ：包括了初始接入和如何获取其它SI的基本信息。

  • MIB：包含了如何获取SIB1的信息，以及其它。
    携带的消息：systemFrameNumber、subCarrierSpacingCommon、 ssb-SubcarrierOffset、dmrs-TypeA-Position、pdcch-ConfigSIB1、cellBarred 、 intraFreqReselection（是否允许同频重选）。
    MIB消息在BCH上周期性重复广播，周期为80ms。重复次数由SSB的周期决定。
  • SIB1：包括了初始接入需要的信息以及其它SI的调度信息。
    携带的消息： cellSelectionInfo 、cellAccessRelatedInfo 、connEstFailureControl、si-SchedulingInfo、 servingCellConfigCommon、ims-EmergencySupport、eCallOverIMS-Support 、ue-TimersAndConstants 、uac-BarringInfo、useFullResumeID。
    SIB1也叫RMSI，剩余最小SI，即除MIB外的最小SI。
    SIB1在DL-SCH上周期性重复广播，周期为160ms。在每个周期内重复广播的次数是不固定的，其取决于具体实现。默认是8次。
    当UE处于RRC_CONNECTED态时，可通过周期广播，或者通过RRCReconfiguration消息获取SIB1。
    SIB1指示其它SI是周期性广播，还是按需提供。若按需提供其它SI，则SIB1还需包括UE执行SI请求的信息。

（2）其它SI：不包括在最小SI的其余所有系统消息。

  • 获取其它SI的方式：
    ① 周期性广播，其广播信息由SIB1中携带的si-SchedulingInfo决定；
    ② 按需广播（ RRC_IDLE、RRC_INACTIVE），或者通过RRCReconfiguration发送给特定UE（ RRC_CONNECTED）；
  • SIB2：包括了小区重选公共信息（同频、异频、RAT间），服务小区小区重选信息、同频小区重选信息。
SIB2 ::=                            SEQUENCE {
    cellReselectionInfoCommon           SEQUENCE {
        nrofSS-BlocksToAverage              INTEGER (2..maxNrofSS-BlocksToAverage)          OPTIONAL,       -- Need R
        absThreshSS-BlocksConsolidation     ThresholdNR                                     OPTIONAL,       -- Need R
        rangeToBestCell                     RangeToBestCell                                 OPTIONAL,       -- Need R
        q-Hyst                              ENUMERATED {
                                                dB0, dB1, dB2, dB3, dB4, dB5, dB6, dB8, dB10,
                                                dB12, dB14, dB16, dB18, dB20, dB22, dB24},
        speedStateReselectionPars           SEQUENCE {
            mobilityStateParameters             MobilityStateParameters,
            q-HystSF                        SEQUENCE {
                sf-Medium                       ENUMERATED {dB-6, dB-4, dB-2, dB0},
                sf-High                         ENUMERATED {dB-6, dB-4, dB-2, dB0}
            }
        }                                                                                   OPTIONAL,       -- Need R
    ...
    },
    cellReselectionServingFreqInfo      SEQUENCE {
        s-NonIntraSearchP                   ReselectionThreshold                            OPTIONAL,       -- Need R
        s-NonIntraSearchQ                   ReselectionThresholdQ                           OPTIONAL,       -- Need R
        threshServingLowP                   ReselectionThreshold,
        threshServingLowQ                   ReselectionThresholdQ                           OPTIONAL,       -- Need R
        cellReselectionPriority             CellReselectionPriority,
        cellReselectionSubPriority          CellReselectionSubPriority                      OPTIONAL,       -- Need R
        ...
    },
    intraFreqCellReselectionInfo        SEQUENCE {
        q-RxLevMin                          Q-RxLevMin,
        q-RxLevMinSUL                       Q-RxLevMin                                      OPTIONAL,       -- Need R
        q-QualMin                           Q-QualMin                                       OPTIONAL,       -- Need S
        s-IntraSearchP                      ReselectionThreshold,
        s-IntraSearchQ                      ReselectionThresholdQ                           OPTIONAL,       -- Cond RSRQ
        t-ReselectionNR                     T-Reselection,
        frequencyBandList                   MultiFrequencyBandListNR-SIB                    OPTIONAL,       -- Need S
        frequencyBandListSUL                MultiFrequencyBandListNR-SIB                    OPTIONAL,       -- Need R
        p-Max                               P-Max                                           OPTIONAL,       -- Need R
        smtc                                SSB-MTC                                         OPTIONAL,       -- Need R
        ss-RSSI-Measurement                 SS-RSSI-Measurement                             OPTIONAL,       -- Need R
        ssb-ToMeasure                       SSB-ToMeasure                                   OPTIONAL,       -- Need R
        deriveSSB-IndexFromCell             BOOLEAN,
        ...,
        [[
        t-ReselectionNR-SF                  SpeedStateScaleFactors                          OPTIONAL        -- Need N
        ]]
    },
    ...
}

RangeToBestCell    ::= Q-OffsetRange
  • SIB3：包括了同频邻区信息和同频黑名单小区信息，用于同频小区重选。
SIB3 ::=                            SEQUENCE {
    intraFreqNeighCellList              IntraFreqNeighCellList      OPTIONAL,   -- Need R
    intraFreqBlackCellList              IntraFreqBlackCellList      OPTIONAL,   -- Need R
    lateNonCriticalExtension            OCTET STRING                OPTIONAL,
    ...
}

IntraFreqNeighCellList ::=          SEQUENCE (SIZE (1..maxCellIntra)) OF IntraFreqNeighCellInfo

IntraFreqNeighCellInfo ::=          SEQUENCE {
    physCellId                          PhysCellId,
    q-OffsetCell                        Q-OffsetRange,
    q-RxLevMinOffsetCell                INTEGER (1..8)              OPTIONAL,   -- Need R
    q-RxLevMinOffsetCellSUL             INTEGER (1..8)              OPTIONAL,   -- Need R
    q-QualMinOffsetCell                 INTEGER (1..8)              OPTIONAL,   -- Need R
    ...
}

IntraFreqBlackCellList ::=          SEQUENCE (SIZE (1..maxCellBlack)) OF PCI-Range
  • SIB4：包括了异频小区重选信息，异频邻区信息，以及异频黑名单小区信息，用于异频小区重选。
SIB4 ::=                            SEQUENCE {
    interFreqCarrierFreqList            InterFreqCarrierFreqList,
    lateNonCriticalExtension            OCTET STRING                                OPTIONAL,
    ...
}

InterFreqCarrierFreqList ::=        SEQUENCE (SIZE (1..maxFreq)) OF InterFreqCarrierFreqInfo

InterFreqCarrierFreqInfo ::=        SEQUENCE {
    dl-CarrierFreq                      ARFCN-ValueNR,
    frequencyBandList                   MultiFrequencyBandListNR-SIB                OPTIONAL,   -- Cond Mandatory
    frequencyBandListSUL                MultiFrequencyBandListNR-SIB                OPTIONAL,   -- Need R
    nrofSS-BlocksToAverage              INTEGER (2..maxNrofSS-BlocksToAverage)      OPTIONAL,   -- Need R
    absThreshSS-BlocksConsolidation     ThresholdNR                                 OPTIONAL,   -- Need R
    smtc                                SSB-MTC                                     OPTIONAL,   -- Need R
    ssbSubcarrierSpacing                SubcarrierSpacing,
    ssb-ToMeasure                       SSB-ToMeasure                               OPTIONAL,   -- Need R
    deriveSSB-IndexFromCell             BOOLEAN,
    ss-RSSI-Measurement                 SS-RSSI-Measurement                         OPTIONAL,
    q-RxLevMin                          Q-RxLevMin,
    q-RxLevMinSUL                       Q-RxLevMin                                  OPTIONAL,   -- Need R
    q-QualMin                           Q-QualMin                                   OPTIONAL,   -- Need S,
    p-Max                               P-Max                                       OPTIONAL,   -- Need R
    t-ReselectionNR                     T-Reselection,
    t-ReselectionNR-SF                  SpeedStateScaleFactors                      OPTIONAL,    -- Need S
    threshX-HighP                       ReselectionThreshold,
    threshX-LowP                        ReselectionThreshold,
    threshX-Q                           SEQUENCE {
        threshX-HighQ                       ReselectionThresholdQ,
        threshX-LowQ                        ReselectionThresholdQ
    }                                                                               OPTIONAL,   -- Cond RSRQ
    cellReselectionPriority             CellReselectionPriority                     OPTIONAL,   -- Need R
    cellReselectionSubPriority          CellReselectionSubPriority                  OPTIONAL,   -- Need R
    q-OffsetFreq                        Q-OffsetRange                               DEFAULT dB0,
    interFreqNeighCellList              InterFreqNeighCellList                      OPTIONAL,   -- Need R
    interFreqBlackCellList              InterFreqBlackCellList                      OPTIONAL,   -- Need R
    ...
}

InterFreqNeighCellList ::=          SEQUENCE (SIZE (1..maxCellInter)) OF InterFreqNeighCellInfo

InterFreqNeighCellInfo ::=          SEQUENCE {
    physCellId                          PhysCellId,
    q-OffsetCell                        Q-OffsetRange,
    q-RxLevMinOffsetCell                INTEGER (1..8)                              OPTIONAL,   -- Need R
    q-RxLevMinOffsetCellSUL             INTEGER (1..8)                              OPTIONAL,   -- Need R
    q-QualMinOffsetCell                 INTEGER (1..8)                              OPTIONAL,   -- Need R
    ...

}

InterFreqBlackCellList ::=          SEQUENCE (SIZE (1..maxCellBlack)) OF PCI-Range
  • SIB5：包括了E-UTRA小区重选信息、E-UTRA小区信息，E-UTRA黑名单小区信息，用于RAT间小区重选。 
SIB5 ::=                            SEQUENCE {
    carrierFreqListEUTRA                CarrierFreqListEUTRA                        OPTIONAL,       -- Need R
    t-ReselectionEUTRA                  T-Reselection,
    t-ReselectionEUTRA-SF               SpeedStateScaleFactors                      OPTIONAL,       -- Need S
    lateNonCriticalExtension            OCTET STRING                                OPTIONAL,
    ...
}

CarrierFreqListEUTRA ::=            SEQUENCE (SIZE (1..maxEUTRA-Carrier)) OF CarrierFreqEUTRA

CarrierFreqEUTRA ::=                SEQUENCE {
    carrierFreq                         ARFCN-ValueEUTRA,
    eutra-multiBandInfoList             EUTRA-MultiBandInfoList                     OPTIONAL,       -- Need R
    eutra-FreqNeighCellList             EUTRA-FreqNeighCellList                     OPTIONAL,       -- Need R
    eutra-BlackCellList                 EUTRA-FreqBlackCellList                     OPTIONAL,       -- Need R
    allowedMeasBandwidth                EUTRA-AllowedMeasBandwidth,
    presenceAntennaPort1                EUTRA-PresenceAntennaPort1,
    cellReselectionPriority             CellReselectionPriority                     OPTIONAL,       -- Need R
    cellReselectionSubPriority          CellReselectionSubPriority                  OPTIONAL,       -- Need R
    threshX-High                        ReselectionThreshold,
    threshX-Low                         ReselectionThreshold,
    q-RxLevMin                          INTEGER (-70..-22),
    q-QualMin                           INTEGER (-34..-3),
    p-MaxEUTRA                          INTEGER (-30..33),
    threshX-Q                           SEQUENCE {
        threshX-HighQ                       ReselectionThresholdQ,
        threshX-LowQ                        ReselectionThresholdQ
    }                                                                               OPTIONAL        -- Cond RSRQ
}

EUTRA-FreqBlackCellList ::=         SEQUENCE (SIZE (1..maxEUTRA-CellBlack)) OF EUTRA-PhysCellIdRange

EUTRA-FreqNeighCellList ::=         SEQUENCE (SIZE (1..maxCellEUTRA)) OF EUTRA-FreqNeighCellInfo

EUTRA-FreqNeighCellInfo ::=         SEQUENCE {
    physCellId                          EUTRA-PhysCellId,
    q-OffsetCell                        EUTRA-Q-OffsetRange,
    q-RxLevMinOffsetCell                INTEGER (1..8)                              OPTIONAL,       -- Need R
    q-QualMinOffsetCell                 INTEGER (1..8)                              OPTIONAL        -- Need R
}
  • SIB6：ETWS主通知。
  • SIB7：ETWS辅通知
  • SIB8：CMAS告警通知
  • SIB9：GPS和UTC相关信息。UE可根据SIB9获取GPS、UTC以及本地时间。
     
2. UE获取系统消息

（1）UE何时需要获取系统消息？

  • 小区选择（刚开机）、小区重选、从未覆盖的区域到有覆盖的区域、从其它RAT进入到当前RAT、收到系统消息变更的指示、收到PWS通知、存储的SI已过期、after reconfiguration with sync completion。

（2）UE如何获取系统消息？

  • 获取MIB和SIB1：
    当UE获取MIB和SIB1消息失败时，则认为该小区禁止接入。
    处于RRC_IDLE或 RRC_INACTIVE的UE，根据38.213协议所述，在BCCH信道上获取MIB消息；
    处于RRC_IDLE、 RRC_INACTIVE，或已激活BWP，searchSpaceSIB1 和pagingSearchSpace配置了公共搜索空间且被指示系统消息已变更RRC_CONNECTED的UE，根据MIB消息，在DL-SCH信道上获取SIB1。

  • 获取其它SI：

（3）UE存储系统消息


  •  
3. 系统消息的有效性


 

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