5G基站采用大规模天线阵列massive MIMO形成(发射)信号波束更窄,增益更高。无线网络中如基站和终端都采用波束,那就需要有一个让两端波束对准的机制,否则相互之间就不能通信,这种机制协议中称波束管理。 波束恢复是波束管理中的一个功能,就是原本互相对准的基站波束和终端波束之间被阻挡(如人体,车辆)时重新寻找一对新波束,通过其他路径反射互相对准,以保证通信可继续进行。kangguoying20210825 在5G网络中终端的波束检查和恢复是按照网络配置,由层一和层二共同来完成的;kangguoying20210825 波束故障恢复 5G网络中波束从故障到恢复如下图所示分为:探测,选择,接入和完成四部分。kangguoying20210825
波束故障(Beam Failure)检测是层一据MAC层的波束故障指示(BFI)来判定的;当BFI达到设定最大值时,就判定为波束故障(失败)。 波束恢复,终端(UE)根据网络下发的RRC消息中BeamFailureRecoveryConfig资源,在最佳候选波束上通过随机接入(RACH)来完成。波束恢复(RRC)参数如下:kangguoying20210825 BeamFailureRecoveryConfig ::= SEQUENCE {kangguoying20210825 rootSequenceIndex-BFR INTEGER (0..137) OPTIONAL, -- Need M rach-ConfigBFR RACH-ConfigGeneric OPTIONAL, -- Need M rsrp-ThresholdSSB RSRP-Range OPTIONAL, -- Need Mkangguoying20210825 candidateBeamRSList SEQUENCE (SIZE(1..maxNrofCandidateBeams)) OFPRACH-ResourceDedicatedBFR OPTIONAL, -- Need Mkangguoying20210825 ssb-perRACH-Occasion ENUMERATED {oneEighth, oneFourth, oneHalf, one, two,four, eight, sixteen} OPTIONAL, -- Need M ra-ssb-OccasionMaskIndex INTEGER (0..15) OPTIONAL, -- Need M recoverySearchSpaceId SearchSpaceId OPTIONAL, -- Need R ra-Prioritization RA-Prioritization OPTIONAL, -- Need R beamFailureRecoveryTimer ENUMERATED {ms10, ms20, ms40, ms60, ms80, ms100, ms150, ms200} OPTIONAL, -- Need M ..., [[msg1-SubcarrierSpacing SubcarrierSpacing OPTIONAL-- Need M ]], [[ra-PrioritizationTwoStep-r16 RA-Prioritization OPTIONAL,-- Need R candidateBeamRSListExt-v1610SetupRelease{CandidateBeamRSListExt-r16 }OPTIONAL-- Need M ]]}kangguoying20210825 PRACH-ResourceDedicatedBFR ::= CHOICE { ssb BFR-SSB-Resource,kangguoying20210825 csi-RS BFR-CSIRS-Resource} BFR-SSB-Resource ::= SEQUENCE { ssb SSB-Index,kakangguoying20210825ngguoying20210825 ra-PreambleIndex INTEGER (0..63), ... }BFR-CSIRS-Resource ::= SEQUENCE { csi-RS NZP-CSI-RS-ResourceId,kakangguoying20210825ngguoying20210825 ra-OccasionList SEQUENCE (SIZE(1..maxRA-OccasionsPerCSIRS)) OF INTEGER (0..maxRA-Occasions-1) OPTIONAL, -- Need R ra-PreambleIndex INTEGER (0..63) OPTIONAL, -- Need R ... }CandidateBeamRSListExt-r16::= SEQUENCE (SIZE(1.. maxNrofCandidateBeamsExt-r16)) OF PRACH-ResourceDedicatedBFRkangguoying20210825 波束恢复方法 终端波束恢复可通过两种接入(RACH)方式完成:
1).基于竞争波束恢复(CBRA场景:
因此当终端为波束恢复执行CBRA RACH时,它将作为基于正常竞争接入过程来进行。kangguoying20210825 2)基于非竞争(CFRA)波束恢复 在CFRA Beam故障恢复请求场景中终端(UE)将收到用C-RNTI加扰的RAR。gNB还将配置一个专用CORSET配置用于波束故障恢复,UE在传输RACH前导码后监控该配置。kangguoying20210825 波束恢复主要包括以下几步:
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