LTE小区选择和小区重选(3
本节主要介绍小区重选过程，再次强调 重选过程发生在IDLE状态下
LTE小区重选分为同系统内的同频、异频重选以及异系统重选。
LTE小区同频重选没有优先级的概念。异频和异系统重选有高优先级的小区重选和低优先级的小区重选
向高优先级的小区重选时，只要高优先级的小区门限超过一定门限，不管本小区信号如何，终端都要向高优先小区进行重选
向低优先级的小区重选时，需要本小区的信号低于一定门限值，低优先级的小区高于一定门限值才能发生重选。
小区重选的步骤：启动测量->计算、评估->排序->重选
同频小区重选：
对于同频测量：主要参数在SIB1和SIB3中
启动测量：
如果满足Srxlev > SIntraSearchP 且Squal >SIntraSearchQ时，UE可以选择不进行intra_freq测量
否则开始进行测量同频小区
相关的参数有：
TreselectionRAT 测量时间
SIntraSearchP 用于启动同频测量的RSRP信号电平门限值
SIntraSearchQ 用于启动同频测量的RSRQ信号质量门限值
2011 Jul 22 14:27:32.497 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
Pkt Version = 2
RRC Release Number.Major.minor = 9.3.0
Radio Bearer ID = 0, Physical Cell ID = 11
Freq = 5230
SysFrameNum = 990, SubFrameNum = 5
PDU Number = BCCH_DL_SCHMessage, MsgLength = 22
Interpreted PDU:
value BCCH-DL-SCH-Message ::=
{
message c1 : systemInformationBlockType1 :
============================================
cellSelectionInfo
{
q-RxLevMin -60, //最小接入电平值-60*2=-120dBm
q-RxLevMinOffset 4 //q-RxLevMinOffset=4*2=8dB
},
{
si-Periodicity rf8,
sib-MappingInfo
{
sibType3//--->SIB3消息
}
}
},
2011 Jul 22 14:27:32.533 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
Pkt Version = 2
RRC Release Number.Major.minor = 9.3.0
Radio Bearer ID = 0, Physical Cell ID = 11
Freq = 5230
SysFrameNum = 994, SubFrameNum = 1
PDU Number = BCCH_DL_SCHMessage, MsgLength = 7
Interpreted PDU:
value BCCH-DL-SCH-Message ::=
{
message c1 : systemInformation:
{
criticalExtensions systemInformation-r8 :
{
sib-TypeAndInfo
{
sib3 :
{
cellReselectionInfoCommon
{
q-Hyst dB2------------->=2dB
},
cellReselectionServingFreqInfo
{
s-NonIntraSearch 7,====SnonIntraSearchP”
threshServingLow 5,
cellReselectionPriority 5
},
intraFreqCellReselectionInfo ==同频测量信息
{
q-RxLevMin -60,
s-IntraSearch 31,//同频测量门限，SIntraSearchP
presenceAntennaPort1 TRUE,
neighCellConfig '01'B,
t-ReselectionEUTRA 2==时间 2s
}
}
从LOG中可以看到：
同频小区的测量：
Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset)– Pcompensation
= Qrxlevmeas-(-60*2+4*2)-0= Qrxlevmeas+112< SintraSearchP=31
Qrxlevmeas<31-112=-81dBm时，启动测量
当邻区的Rn 大于服务小区的Rs时，即可进行小区重选。
异频/异系统重选
高优先级：
EUTRAN or UTRAN RAT/ frequency ： Squal > ThreshX, HighQ
GERAN or CDMA2000 RAT/ frequency ： Srxlev > ThreshX, HighP
也就是说，只要邻小区高于一个门限值，不论当前小区门限值是多少，则都执行重选
ThreshX, HighQ---在SIB5~SIB8中
低优先级：
EUTRAN or UTRAN RAT/ frequency ：
Squal-serving < ThreshServing, LowQ 且Squal-neighbor > ThreshX, LowQ
ThreshServing, LowQ---在SIB3中
ThreshX, LowQ---在SIB5~SIB8中
GERAN or CDMA2000 RAT/ frequency ：
Squal-serving < ThreshServing, LowQ and Srxlev-neighbor >ThreshX, LowP
也就是说，当前小区低于一个门限值，邻小区高于一个门限值，则进行重选
若没有提供threshServingLowQ则所有的都是用Srxlev来进行判别
小区使用R准则进行排序：
Rs = Qmeas,s +QHyst
Rn = Qmeas,n - Qoffset
LOG=====
2013 Aug 14 02:59:42.869 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
cellSelectionInfo
{
q-RxLevMin -53
},
SIB3:
cellReselectionServingFreqInfo
{
threshServingLow 0,
cellReselectionPriority 4—当前小区优先级=4
},
2013 Aug 14 02:59:42.966 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
Pkt Version = 2
RRC Release Number.Major.minor = 9.10.0
Radio Bearer ID = 0, Physical Cell ID = 0
Freq = 900
SysFrameNum = 132, SubFrameNum = 3
PDU Number = BCCH_DL_SCHMessage, MsgLength = 17
Interpreted PDU:
value BCCH-DL-SCH-Message ::=
{
message c1 : systemInformation:
{
criticalExtensions systemInformation-r8 :
{
sib-TypeAndInfo
{
sib5 :
{
interFreqCarrierFreqList //异频小区信息
{
{
dl-CarrierFreq 650,
q-RxLevMin -53,
t-ReselectionEUTRA 0,
threshX-High 10,
threshX-Low 1,
allowedMeasBandwidth mbw50,
presenceAntennaPort1 FALSE,
cellReselectionPriority 5,
neighCellConfig '01'B,
q-OffsetFreq dB0
},
{
dl-CarrierFreq 1150,
q-RxLevMin -53,===最小接入电平-106
t-ReselectionEUTRA 0,时间为0
threshX-High 10,
threshX-Low 1,
allowedMeasBandwidth mbw50,
presenceAntennaPort1 FALSE,
cellReselectionPriority4,
neighCellConfig '01'B,
q-OffsetFreq dB0
}
同频同优先级重选，使用R准则：
Rs = Qmeas,s + Qhyst=-90+0=-90
Rn = Qmeas,n - Qoffset =-85-0=-85
所以选择到邻小区PCI=3的小区上！
2013 Aug 14 03:00:06.289 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
Pkt Version = 2
RRC Release Number.Major.minor = 9.10.0
Radio Bearer ID = 0, PhysicalCell ID = 3
Freq = 1150
SysFrameNum = 674, SubFrameNum = 1
PDU Number = BCCH_DL_SCHMessage, MsgLength = 7
Interpreted PDU:
value BCCH-DL-SCH-Message ::=
{
message c1 : systemInformation:
{
criticalExtensions systemInformation-r8 :
{
sib-TypeAndInfo
{
sib3 :
{
cellReselectionInfoCommon
{
q-Hyst dB0====0
},
cellReselectionServingFreqInfo
{
threshServingLow 0,
cellReselectionPriority 4
},
intraFreqCellReselectionInfo
{
q-RxLevMin -53,
presenceAntennaPort1 FALSE,
neighCellConfig '01'B,
t-ReselectionEUTRA 0
}
}
}
}
}
}
2013 Aug 14 03:00:06.630 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
Pkt Version = 2
RRC Release Number.Major.minor = 9.10.0
Radio Bearer ID = 0, Physical Cell ID = 3
Freq = 1150
SysFrameNum = 708, SubFrameNum = 3
PDU Number = BCCH_DL_SCHMessage, MsgLength = 17
Interpreted PDU:
value BCCH-DL-SCH-Message ::=
{
message c1 : systemInformation:
{
criticalExtensions systemInformation-r8 :
{
sib-TypeAndInfo
{
sib5 :
{
interFreqCarrierFreqList
{
{
dl-CarrierFreq 900,
q-RxLevMin -53,
t-ReselectionEUTRA 0,
threshX-High 2,
threshX-Low 1,
allowedMeasBandwidth mbw50,
presenceAntennaPort1 FALSE,
cellReselectionPriority 4,
neighCellConfig '01'B,
q-OffsetFreq dB0
},
{
dl-CarrierFreq 650,
q-RxLevMin -53,==最小接入点评-106
t-ReselectionEUTRA 0,==重选时间0秒
threshX-High 10,
threshX-Low 1,
allowedMeasBandwidth mbw50,
presenceAntennaPort1 FALSE,
cellReselectionPriority 5,
neighCellConfig '01'B,
q-OffsetFreq dB0
}
从优先级=4重选到优先级=5的高优先级小区上时，只需要邻小区的信号
EUTRAN or UTRAN RAT/ frequency ： Squal> ThreshX, HighQ
也就是Squal = Qqualmeas – (Qqualmin +Qqualminoffset)= Qqualmeas-（-53*2+0）>10*2
Qqualmeas>-86dBm就会重选过去
sib3 :
{
cellReselectionInfoCommon
{
q-Hyst dB0
},
cellReselectionServingFreqInfo
{
threshServingLow 10,====== ThreshServing, LowQ
cellReselectionPriority 5
},
intraFreqCellReselectionInfo
{
q-RxLevMin -53,
presenceAntennaPort1 FALSE,
neighCellConfig '01'B,
t-ReselectionEUTRA 0
}
}
2013 Aug 14 03:00:10.315 [00] 0xB0C0 LTE RRC OTA Packet -- BCCH_DL_SCH
Pkt Version = 2
RRC Release Number.Major.minor = 9.10.0
Radio Bearer ID = 0, Physical Cell ID = 6
Freq = 650
SysFrameNum = 452, SubFrameNum = 3
PDU Number = BCCH_DL_SCHMessage, MsgLength = 17
Interpreted PDU:
value BCCH-DL-SCH-Message ::=
{
message c1 : systemInformation:
{
criticalExtensions systemInformation-r8 :
{
sib-TypeAndInfo
{
sib5 :
{
interFreqCarrierFreqList
{
{
dl-CarrierFreq 900,
q-RxLevMin -53,
t-ReselectionEUTRA 0,
threshX-High2,
threshX-Low 1,
allowedMeasBandwidth mbw50,
presenceAntennaPort1 FALSE,
cellReselectionPriority 4,
neighCellConfig '01'B,
q-OffsetFreq dB0
},
{
dl-CarrierFreq 1150,
q-RxLevMin -53,
t-ReselectionEUTRA 0,
threshX-High 2,
threshX-Low 1,
allowedMeasBandwidth mbw50,
presenceAntennaPort1 FALSE,
cellReselectionPriority 4,
neighCellConfig '01'B,
q-OffsetFreq dB0
}
从优先级=5重选到优先级=4的低优先级小区上时，需要本小区信号质量：
低优先级：
EUTRAN or UTRAN RAT/ frequency ：
Squal-serving < ThreshServing, LowQ and Squal-neighbor >ThreshX, LowQ
也就是：
Squal = Qqualmeas – (Qqualmin + Qqualminoffset)=Qqualmeas-(-106+0)<10*2
Qqualmeas<-86dBm
临小区小区质量：Squal-neighbor > ThreshX, LowQ=Qqualmeas-(-106+0)>1*2
Qqualmeas>-104dBm