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Content for  TS 38.304  Word version:  16.2.0

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5.2  Cell selection and reselection

5.2.1  Introduction

UE shall perform measurements for cell selection and reselection purposes as specified in TS 38.133.
When evaluating Srxlev and Squal of non-serving cells for reselection evaluation purposes, the UE shall use parameters provided by the serving cell and for the final check on cell selection criterion, the UE shall use parameters provided by the target cell for cell reselection.
The NAS can control the RAT(s) in which the cell selection should be performed, for instance by indicating RAT(s) associated with the selected PLMN, and by maintaining a list of forbidden registration area(s) and a list of equivalent PLMNs. The UE shall select a suitable cell based on RRC_IDLE or RRC_INACTIVE state measurements and cell selection criteria.
In order to expedite the cell selection process, stored information for several RATs, if available, may be used by the UE.
When camped on a cell, the UE shall regularly search for a better cell according to the cell reselection criteria. If a better cell is found, that cell is selected. The change of cell may imply a change of RAT. Details on performance requirements for cell reselection can be found in TS 38.133.
The NAS is informed if the cell selection and reselection result in changes in the received system information relevant for NAS.
For normal service, the UE shall camp on a suitable cell, monitor control channel(s) of that cell so that the UE can:
  • receive system information from the PLMN or SNPN; and
    • receive registration area information from the PLMN or SNPN, e.g., tracking area information; and
    • receive other AS and NAS Information; and
  • if registered:
    • receive paging and notification messages from the PLMN or SNPN; and
    • initiate transfer to Connected mode.
For cell selection in multi-beam operations, measurement quantity of a cell is up to UE implementation.
For cell reselection in multi-beam operations, including inter-RAT reselection from E-UTRA to NR, the measurement quantity of this cell is derived amongst the beams corresponding to the same cell based on SS/PBCH block as follows:
  • if nrofSS-BlocksToAverage (maxRS-IndexCellQual in E-UTRA) is not configured in SIB2/SIB4 (SIB24 in E-UTRA); or
  • if absThreshSS-BlocksConsolidation (threshRS-Index in E-UTRA) is not configured in SIB2/SIB4 (SIB24 in E-UTRA); or
  • if the highest beam measurement quantity value is below or equal to absThreshSS-BlocksConsolidation (threshRS-Index in E-UTRA):
    • derive a cell measurement quantity as the highest beam measurement quantity value, where each beam measurement quantity is described in TS 38.215.
  • else:
    • derive a cell measurement quantity as the linear average of the power values of up to nrofSS-BlocksToAverage (maxRS-IndexCellQual in E-UTRA) of highest beam measurement quantity values above absThreshSS-BlocksConsolidation (threshRS-Index in E-UTRA).
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5.2.2  States and state transitions in RRC_IDLE state and RRC_INACTIVE stateWord‑p. 17
Figure 5.2.2-1 shows the states and state transitions and procedures in RRC_IDLE and RRC_INACTIVE. Whenever a new PLMN selection or new SNPN selection is performed, it causes an exit to number 1.
Reproduction of 3GPP TS 38.304, Figure 5.2.2-1: RRC_IDLE and RRC_INACTIVE Cell Selection and Reselection
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5.2.3  Cell Selection processWord‑p. 18

5.2.3.1  Description

Cell selection is performed by one of the following two procedures:
  1. Initial cell selection (no prior knowledge of which RF channels are NR frequencies):
    1. The UE shall scan all RF channels in the NR bands according to its capabilities to find a suitable cell.
    2. On each frequency, the UE need only search for the strongest cell, except for operation with shared spectrum channel access where the UE may search for the next strongest cell(s).
    3. Once a suitable cell is found, this cell shall be selected.
  2. Cell selection by leveraging stored information:
    1. This procedure requires stored information of frequencies and optionally also information on cell parameters from previously received measurement control information elements or from previously detected cells.
    2. Once the UE has found a suitable cell, the UE shall select it.
    3. If no suitable cell is found, the initial cell selection procedure in a) shall be started.
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5.2.3.2  Cell Selection CriterionWord‑p. 19
The cell selection criterion S is fulfilled when:
Srxlev > 0 AND Squal > 0
where:
Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset )- Pcompensation - Qoffsettemp
Squal = Qqualmeas - (Qqualmin + Qqualminoffset) - Qoffsettemp
where:
Srxlev
Cell selection RX level value (dB)
Squal
Cell selection quality value (dB)
Qoffsettemp
Offset temporarily applied to a cell as specified in TS 38.331 (dB)
Qrxlevmeas
Measured cell RX level value (RSRP)
Qqualmeas
Measured cell quality value (RSRQ)
Qrxlevmin
Minimum required RX level in the cell (dBm). If the UE supports SUL frequency for this cell, Qrxlevmin is obtained from q-RxLevMinSUL, if present, in SIB1, SIB2 and SIB4, additionally, if QrxlevminoffsetcellSUL is present in SIB3 and SIB4 for the concerned cell, this cell specific offset is added to the corresponding Qrxlevmin to achieve the required minimum RX level in the concerned cell;
else Qrxlevmin is obtained from q-RxLevMin in SIB1, SIB2 and SIB4, additionally, if Qrxlevminoffsetcell is present in SIB3 and SIB4 for the concerned cell, this cell specific offset is added to the corresponding Qrxlevmin to achieve the required minimum RX level in the concerned cell.
Qqualmin
Minimum required quality level in the cell (dB). Additionally, if Qqualminoffsetcell is signalled for the concerned cell, this cell specific offset is added to achieve the required minimum quality level in the concerned cell.
Qrxlevminoffset
Offset to the signalled Qrxlevmin taken into account in the Srxlev evaluation as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN, as specified in TS 23.122.
Qqualminoffset
Offset to the signalled Qqualmin taken into account in the Squal evaluation as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN, as specified in TS 23.122.
Pcompensation
For FR1, if the UE supports the additionalPmax in the NR-NS-PmaxList, if present, in SIB1, SIB2 and SIB4:
max(PEMAX1 -PPowerClass, 0) - (min(PEMAX2, PPowerClass) - min(PEMAX1, PPowerClass)) (dB);
else:
max(PEMAX1 -PPowerClass, 0) (dB)
For FR2, Pcompensation is set to 0.
PEMAX1, PEMAX2
Maximum TX power level of a UE may use when transmitting on the uplink in the cell (dBm) defined as PEMAX in TS 38.101-1. If UE supports SUL frequency for this cell, PEMAX1 and PEMAX2 are obtained from the p-Max for SUL in SIB1 and NR-NS-PmaxList for SUL respectively in SIB1, SIB2 and SIB4 as specified in TS 38.331, else PEMAX1 and PEMAX2 are obtained from the p-Max and NR-NS-PmaxList respectively in SIB1, SIB2 and SIB4 for normal UL as specified in TS 38.331.
PPowerClass
Maximum RF output power of the UE (dBm) according to the UE power class as defined in TS 38.101-1.
The signalled values Qrxlevminoffset and Qqualminoffset are only applied when a cell is evaluated for cell selection as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN (TS 23.122). During this periodic search for higher priority PLMN, the UE may check the S criteria of a cell using parameter values stored from a different cell of this higher priority PLMN.
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5.2.3.3  E-UTRAN case in Cell SelectionWord‑p. 20
The cell selection criteria and procedures in E-UTRAN are specified in TS 36.304.


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