5G学习笔记之系统消息

参考资料：3GPP 38.300、3GPP 38.331

1. 名词缩写

缩写	全称	描述
SI	System Information	系统信息
MIB	Master Information Block	主信息块
SIB	System Information Block	系统信息块
RMSI	Remaining Minimum SI	剩余最小SI，即除MIB外的最小SI
SSB	Synchronization Signal Block	同步信息块
PSCell	Primary SCG Cell
BWP	Bandwidth Part

2. 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 RabsThreshSS-BlocksConsolidation     ThresholdNR                                     OPTIONAL,       -- Need RrangeToBestCell                     RangeToBestCell                                 OPTIONAL,       -- Need Rq-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 Rs-NonIntraSearchQ                   ReselectionThresholdQ                           OPTIONAL,       -- Need RthreshServingLowP                   ReselectionThreshold,threshServingLowQ                   ReselectionThresholdQ                           OPTIONAL,       -- Need RcellReselectionPriority             CellReselectionPriority,cellReselectionSubPriority          CellReselectionSubPriority                      OPTIONAL,       -- Need R...},intraFreqCellReselectionInfo        SEQUENCE {q-RxLevMin                          Q-RxLevMin,q-RxLevMinSUL                       Q-RxLevMin                                      OPTIONAL,       -- Need Rq-QualMin                           Q-QualMin                                       OPTIONAL,       -- Need Ss-IntraSearchP                      ReselectionThreshold,s-IntraSearchQ                      ReselectionThresholdQ                           OPTIONAL,       -- Cond RSRQt-ReselectionNR                     T-Reselection,frequencyBandList                   MultiFrequencyBandListNR-SIB                    OPTIONAL,       -- Need SfrequencyBandListSUL                MultiFrequencyBandListNR-SIB                    OPTIONAL,       -- Need Rp-Max                               P-Max                                           OPTIONAL,       -- Need Rsmtc                                SSB-MTC                                         OPTIONAL,       -- Need Rss-RSSI-Measurement                 SS-RSSI-Measurement                             OPTIONAL,       -- Need Rssb-ToMeasure                       SSB-ToMeasure                                   OPTIONAL,       -- Need RderiveSSB-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 RintraFreqBlackCellList              IntraFreqBlackCellList      OPTIONAL,   -- Need RlateNonCriticalExtension            OCTET STRING                OPTIONAL,...
}IntraFreqNeighCellList ::=          SEQUENCE (SIZE (1..maxCellIntra)) OF IntraFreqNeighCellInfoIntraFreqNeighCellInfo ::=          SEQUENCE {physCellId                          PhysCellId,q-OffsetCell                        Q-OffsetRange,q-RxLevMinOffsetCell                INTEGER (1..8)              OPTIONAL,   -- Need Rq-RxLevMinOffsetCellSUL             INTEGER (1..8)              OPTIONAL,   -- Need Rq-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 InterFreqCarrierFreqInfoInterFreqCarrierFreqInfo ::=        SEQUENCE {dl-CarrierFreq                      ARFCN-ValueNR,frequencyBandList                   MultiFrequencyBandListNR-SIB                OPTIONAL,   -- Cond MandatoryfrequencyBandListSUL                MultiFrequencyBandListNR-SIB                OPTIONAL,   -- Need RnrofSS-BlocksToAverage              INTEGER (2..maxNrofSS-BlocksToAverage)      OPTIONAL,   -- Need RabsThreshSS-BlocksConsolidation     ThresholdNR                                 OPTIONAL,   -- Need Rsmtc                                SSB-MTC                                     OPTIONAL,   -- Need RssbSubcarrierSpacing                SubcarrierSpacing,ssb-ToMeasure                       SSB-ToMeasure                               OPTIONAL,   -- Need RderiveSSB-IndexFromCell             BOOLEAN,ss-RSSI-Measurement                 SS-RSSI-Measurement                         OPTIONAL,q-RxLevMin                          Q-RxLevMin,q-RxLevMinSUL                       Q-RxLevMin                                  OPTIONAL,   -- Need Rq-QualMin                           Q-QualMin                                   OPTIONAL,   -- Need S,p-Max                               P-Max                                       OPTIONAL,   -- Need Rt-ReselectionNR                     T-Reselection,t-ReselectionNR-SF                  SpeedStateScaleFactors                      OPTIONAL,    -- Need SthreshX-HighP                       ReselectionThreshold,threshX-LowP                        ReselectionThreshold,threshX-Q                           SEQUENCE {threshX-HighQ                       ReselectionThresholdQ,threshX-LowQ                        ReselectionThresholdQ}                                                                               OPTIONAL,   -- Cond RSRQcellReselectionPriority             CellReselectionPriority                     OPTIONAL,   -- Need RcellReselectionSubPriority          CellReselectionSubPriority                  OPTIONAL,   -- Need Rq-OffsetFreq                        Q-OffsetRange                               DEFAULT dB0,interFreqNeighCellList              InterFreqNeighCellList                      OPTIONAL,   -- Need RinterFreqBlackCellList              InterFreqBlackCellList                      OPTIONAL,   -- Need R...
}InterFreqNeighCellList ::=          SEQUENCE (SIZE (1..maxCellInter)) OF InterFreqNeighCellInfoInterFreqNeighCellInfo ::=          SEQUENCE {physCellId                          PhysCellId,q-OffsetCell                        Q-OffsetRange,q-RxLevMinOffsetCell                INTEGER (1..8)                              OPTIONAL,   -- Need Rq-RxLevMinOffsetCellSUL             INTEGER (1..8)                              OPTIONAL,   -- Need Rq-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 Rt-ReselectionEUTRA                  T-Reselection,t-ReselectionEUTRA-SF               SpeedStateScaleFactors                      OPTIONAL,       -- Need SlateNonCriticalExtension            OCTET STRING                                OPTIONAL,...
}CarrierFreqListEUTRA ::=            SEQUENCE (SIZE (1..maxEUTRA-Carrier)) OF CarrierFreqEUTRACarrierFreqEUTRA ::=                SEQUENCE {carrierFreq                         ARFCN-ValueEUTRA,eutra-multiBandInfoList             EUTRA-MultiBandInfoList                     OPTIONAL,       -- Need Reutra-FreqNeighCellList             EUTRA-FreqNeighCellList                     OPTIONAL,       -- Need Reutra-BlackCellList                 EUTRA-FreqBlackCellList                     OPTIONAL,       -- Need RallowedMeasBandwidth                EUTRA-AllowedMeasBandwidth,presenceAntennaPort1                EUTRA-PresenceAntennaPort1,cellReselectionPriority             CellReselectionPriority                     OPTIONAL,       -- Need RcellReselectionSubPriority          CellReselectionSubPriority                  OPTIONAL,       -- Need RthreshX-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-PhysCellIdRangeEUTRA-FreqNeighCellList ::=         SEQUENCE (SIZE (1..maxCellEUTRA)) OF EUTRA-FreqNeighCellInfoEUTRA-FreqNeighCellInfo ::=         SEQUENCE {physCellId                          EUTRA-PhysCellId,q-OffsetCell                        EUTRA-Q-OffsetRange,q-RxLevMinOffsetCell                INTEGER (1..8)                              OPTIONAL,       -- Need Rq-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。

3. 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