5G学习笔记之系统消息 - HelloWorld开发者社区

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 ::= cellReselectionInfoCommon nrofSS-BlocksToAverage absThreshSS-BlocksConsolidation rangeToBestCell q-Hyst speedStateReselectionPars mobilityStateParameters q-HystSF sf-Medium sf-High } } ... }, cellReselectionServingFreqInfo s-NonIntraSearchP s-NonIntraSearchQ threshServingLowP threshServingLowQ cellReselectionPriority cellReselectionSubPriority ... }, intraFreqCellReselectionInfo q-RxLevMin q-RxLevMinSUL q-QualMin s-IntraSearchP s-IntraSearchQ t-ReselectionNR frequencyBandList frequencyBandListSUL p-Max smtc ss-RSSI-Measurement ssb-ToMeasure deriveSSB-IndexFromCell ..., [[ t-ReselectionNR-SF ]] }, ... } SEQUENCE { SEQUENCE { INTEGER (2..maxNrofSS-BlocksToAverage) OPTIONAL, -- Need R ThresholdNR OPTIONAL, -- Need R RangeToBestCell OPTIONAL, -- Need R ENUMERATED { dB0, dB1, dB2, dB3, dB4, dB5, dB6, dB8, dB10, dB12, dB14, dB16, dB18, dB20, dB22, dB24}, SEQUENCE { MobilityStateParameters, SEQUENCE { ENUMERATED {dB-6, dB-4, dB-2, dB0}, ENUMERATED {dB-6, dB-4, dB-2, dB0} OPTIONAL, -- Need R SEQUENCE { ReselectionThreshold OPTIONAL, -- Need R ReselectionThresholdQ OPTIONAL, -- Need R ReselectionThreshold, ReselectionThresholdQ OPTIONAL, -- Need R CellReselectionPriority, CellReselectionSubPriority OPTIONAL, -- Need R SEQUENCE { Q-RxLevMin, Q-RxLevMin OPTIONAL, -- Need R Q-QualMin OPTIONAL, -- Need S ReselectionThreshold, ReselectionThresholdQ OPTIONAL, -- Cond RSRQ T-Reselection, MultiFrequencyBandListNR-SIB OPTIONAL, -- Need S MultiFrequencyBandListNR-SIB OPTIONAL, -- Need R P-Max OPTIONAL, -- Need R SSB-MTC OPTIONAL, -- Need R SS-RSSI-Measurement OPTIONAL, -- Need R SSB-ToMeasure OPTIONAL, -- Need R BOOLEAN, 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