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Content for  TS 38.304  Word version:  16.2.0

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5.2.4  Cell Reselection evaluation process

5.2.4.1  Reselection priorities handling

Absolute priorities of different NR frequencies or inter-RAT frequencies may be provided to the UE in the system information, in the RRCRelease message, or by inheriting from another RAT at inter-RAT cell (re)selection. In the case of system information, an NR frequency or inter-RAT frequency may be listed without providing a priority (i.e. the field cellReselectionPriority is absent for that frequency). If priorities are provided in dedicated signalling, the UE shall ignore all the priorities provided in system information. If UE is in camped on any cell state, UE shall only apply the priorities provided by system information from current cell, and the UE preserves priorities provided by dedicated signalling and deprioritisationReq received in RRCRelease unless specified otherwise. When the UE in camped normally state, has only dedicated priorities other than for the current frequency, the UE shall consider the current frequency to be the lowest priority frequency (i.e. lower than any of the network configured values). If the UE is configured to perform both NR sidelink communication and V2X sidelink communication, the UE may consider the frequency providing both NR sidelink communication configuration and V2X sidelink communication configuration to be the highest priority. If the UE is configured to perform NR sidelink communication and not perform V2X communication, the UE may consider the frequency providing NR sidelink communication configuration to be the highest priority. If the UE is configured to perform V2X sidelink communication and not perform NR sidelink communication, the UE may consider the frequency providing V2X sidelink communication configuration to be the highest priority.
The UE shall only perform cell reselection evaluation for NR frequencies and inter-RAT frequencies that are given in system information and for which the UE has a priority provided.
In case UE receives RRCRelease with deprioritisationReq, UE shall consider current frequency and stored frequencies due to the previously received RRCRelease with deprioritisationReq or all the frequencies of NR to be the lowest priority frequency (i.e. lower than any of the network configured values) while T325 is running irrespective of camped RAT. The UE shall delete the stored deprioritisation request(s) when a PLMN selection or SNPN selection is performed on request by NAS (TS 23.122).
The UE shall delete priorities provided by dedicated signalling when:
  • the UE enters a different RRC state; or
  • the optional validity time of dedicated priorities (T320) expires; or
  • the UE receives an RRCRelease message with the field cellReselectionPriorities absent; or
  • a PLMN selection or SNPN selection is performed on request by NAS (TS 23.122).
The UE shall not consider any black listed cells as candidate for cell reselection.
The UE shall consider only the white listed cells, if configured, as candidates for cell reselection.
The UE in RRC_IDLE state shall inherit the priorities provided by dedicated signalling and the remaining validity time (i.e. T320 in NR and E-UTRA), if configured, at inter-RAT cell (re)selection.
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5.2.4.2  Measurement rules for cell re-selectionWord‑p. 22
Following rules are used by the UE to limit needed measurements:
  • If the serving cell fulfils Srxlev > SIntraSearchP and Squal > SIntraSearchQ, the UE may choose not to perform intra-frequency measurements.
  • Otherwise, the UE shall perform intra-frequency measurements.
  • The UE shall apply the following rules for NR inter-frequencies and inter-RAT frequencies which are indicated in system information and for which the UE has priority provided as defined in 5.2.4.1:
    • For a NR inter-frequency or inter-RAT frequency with a reselection priority higher than the reselection priority of the current NR frequency, the UE shall perform measurements of higher priority NR inter-frequency or inter-RAT frequencies according to TS 38.133.
    • For a NR inter-frequency with an equal or lower reselection priority than the reselection priority of the current NR frequency and for inter-RAT frequency with lower reselection priority than the reselection priority of the current NR frequency:
      • If the serving cell fulfils Srxlev > SnonIntraSearchP and Squal > SnonIntraSearchQ, the UE may choose not to perform measurements of NR inter-frequencies or inter-RAT frequency cells of equal or lower priority;
      • Otherwise, the UE shall perform measurements of NR inter-frequencies or inter-RAT frequency cells of equal or lower priority according to TS 38.133.
  • If the UE supports relaxed measurement and relaxedMeasurement is present in SIB2, the UE may further relax the needed measurements, as specified in clause 5.2.4.9.
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5.2.4.3  Mobility states of a UE

5.2.4.3.0  Introduction
The UE mobility state is determined if the parameters (TCRmax, NCR_H, NCR_M and TCRmaxHyst) are broadcasted in system information for the serving cell.
State detection criteria:
Normal-mobility state criteria:
  • If number of cell reselections during time period TCRmax is less than NCR_M.
Medium-mobility state criteria:
  • If number of cell reselections during time period TCRmax is greater than or equal to NCR_M but less than or equal to NCR_H.
High-mobility state criteria:
  • If number of cell reselections during time period TCRmax is greater than NCR_H.
The UE shall not consider consecutive reselections where a cell is reselected again right after one reselection for mobility state detection criteria.
State transitions:
The UE shall:
  • if the criteria for High-mobility state is detected:
    • enter High-mobility state.
  • else if the criteria for Medium-mobility state is detected:
    • enter Medium-mobility state.
  • else if criteria for either Medium- or High-mobility state is not detected during time period TCRmaxHyst:
    • enter Normal-mobility state.
If the UE is in High- or Medium-mobility state, the UE shall apply the speed dependent scaling rules as defined in clause 5.2.4.3.1.
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5.2.4.3.1  Scaling rulesWord‑p. 23
UE shall apply the following scaling rules:
  • If neither Medium- nor High-mobility state is detected:
    • no scaling is applied.
  • If High-mobility state is detected:
    • Add the sf-High of "Speed dependent ScalingFactor for Qhyst" to Qhyst if broadcasted in system information;
    • For NR cells, multiply TreselectionNR by the sf-High of "Speed dependent ScalingFactor for TreselectionNR" if broadcasted in system information;
    • For EUTRA cells, multiply TreselectionEUTRA by the sf-High of "Speed dependent ScalingFactor for TreselectionEUTRA" if broadcasted in system information.
  • If Medium-mobility state is detected:
    • Add the sf-Medium of "Speed dependent ScalingFactor for Qhyst" to Qhyst if broadcasted in system information;
    • For NR cells, multiply TreselectionNR by the sf-Medium of "Speed dependent ScalingFactor for TreselectionNR" if broadcasted in system information;
    • For EUTRA cells, multiply TreselectionEUTRA by the sf-Medium of "Speed dependent ScalingFactor for TreselectionEUTRA" if broadcasted in system information.
In case scaling is applied to any TreselectionRAT parameter, the UE shall round up the result after all scalings to the nearest second.
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5.2.4.4  Cells with cell reservations, access restrictions or unsuitable for normal camping

For the highest ranked cell (including serving cell) according to cell reselection criteria specified in clause 5.2.4.6, for the best cell according to absolute priority reselection criteria specified in clause 5.2.4.5, the UE shall check if the access is restricted according to the rules in clause 5.3.1.
If that cell and other cells have to be excluded from the candidate list, as stated in clause 5.3.1, the UE shall not consider these as candidates for cell reselection. This limitation shall be removed when the highest ranked cell changes.
If the highest ranked cell or best cell according to absolute priority reselection rules is an intra-frequency or inter-frequency cell which is not suitable due to one or more of the following reasons:
  • this cell belongs to a PLMN which is not indicated as being equivalent to the registered PLMN, or
  • this cell is a CAG cell that belongs to a PLMN which is equivalent to the registered PLMN but with no CAG-ID that is present in the UE's allowed CAG list being broadcasted, or
  • this cell is not a CAG cell and the CAG-only indication in the UE is set, or
  • this cell does not belong to a SNPN that is equal to the registered or selected SNPN of the UE in SNPN access mode,
the UE shall not consider this cell and, for operation in licensed spectrum, other cells on the same frequency as candidates for reselection for a maximum of 300 seconds.
For operation with shared spectrum channel access, when the highest ranked cell or best cell is not a candidate for reselection per the previous paragraph, the UE should continue to consider other cells on the same frequency for cell reselection, however if the second highest ranked cell on this frequency is also not suitable due to one or more of the above reasons, the UE may consider this frequency to be the lowest priority for a maximum of 300 seconds.
If the highest ranked cell or best cell according to absolute priority reselection rules is an inter-frequency or inter-frequency cell which is not suitable due to being part of the "list of 5GS forbidden TAs for roaming", the UE shall not consider this cell and other cells on the same frequency as candidates for reselection for a maximum of 300 seconds.
If the UE enters into state any cell selection, any limitation shall be removed.
If the highest ranked cell or best cell according to absolute priority reselection rules is an inter-RAT cell which is not suitable due to being part of the "list of forbidden TAs for roaming" or belonging to a PLMN which is not indicated as being equivalent to the registered PLMN, the UE shall not consider this cell and other cells on the same frequency, as candidates for reselection for a maximum of 300 seconds. If the UE enters into state any cell selection, any limitation shall be removed. If the UE is redirected under NR control to a frequency for which the timer is running, any limitation on that frequency shall be removed.
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5.2.4.5  NR Inter-frequency and inter-RAT Cell Reselection criteriaWord‑p. 24
If threshServingLowQ is broadcast in system information and more than 1 second has elapsed since the UE camped on the current serving cell, cell reselection to a cell on a higher priority NR frequency or inter-RAT frequency than the serving frequency shall be performed if:
  • A cell of a higher priority NR or EUTRAN RAT/frequency fulfils Squal > ThreshX, HighQ during a time interval TreselectionRAT
Otherwise, cell reselection to a cell on a higher priority NR frequency or inter-RAT frequency than the serving frequency shall be performed if:
  • A cell of a higher priority RAT/ frequency fulfils Srxlev > ThreshX, HighP during a time interval TreselectionRAT; and
  • More than 1 second has elapsed since the UE camped on the current serving cell.
Cell reselection to a cell on an equal priority NR frequency shall be based on ranking for intra-frequency cell reselection as defined in clause 5.2.4.6.
If threshServingLowQ is broadcast in system information and more than 1 second has elapsed since the UE camped on the current serving cell, cell reselection to a cell on a lower priority NR frequency or inter-RAT frequency than the serving frequency shall be performed if:
  • The serving cell fulfils Squal < ThreshServing, LowQ and a cell of a lower priority NR or E-UTRAN RAT/ frequency fulfils Squal > ThreshX, LowQ during a time interval TreselectionRAT.
Otherwise, cell reselection to a cell on a lower priority NR frequency or inter-RAT frequency than the serving frequency shall be performed if:
  • The serving cell fulfils Srxlev < ThreshServing, LowP and a cell of a lower priority RAT/ frequency fulfils Srxlev > ThreshX, LowP during a time interval TreselectionRAT; and
  • More than 1 second has elapsed since the UE camped on the current serving cell.
Cell reselection to a higher priority RAT/frequency shall take precedence over a lower priority RAT/frequency if multiple cells of different priorities fulfil the cell reselection criteria.
If more than one cell meets the above criteria, the UE shall reselect a cell as follows:
  • If the highest-priority frequency is an NR frequency, the highest ranked cell among the cells on the highest priority frequency(ies) meeting the criteria according to clause 5.2.4.6;
  • If the highest-priority frequency is from another RAT, the strongest cell among the cells on the highest priority frequency(ies) meeting the criteria of that RAT.
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5.2.4.6  Intra-frequency and equal priority inter-frequency Cell Reselection criteriaWord‑p. 25
The cell-ranking criterion Rs for serving cell and Rn for neighbouring cells is defined by:
Rs = Qmeas,s +Qhyst - Qoffsettemp
Rn = Qmeas,n -Qoffset - Qoffsettemp
where:
Qmeas
RSRP measurement quantity used in cell reselections.
Qoffset
For intra-frequency: Equals to Qoffsets,n, if Qoffsets,n is valid, otherwise this equals to zero.
For inter-frequency: Equals to Qoffsets,n plus Qoffsetfrequency, if Qoffsets,n is valid, otherwise this equals to Qoffsetfrequency.
Qoffsettemp
Offset temporarily applied to a cell as specified in TS 38.331.
The UE shall perform ranking of all cells that fulfil the cell selection criterion S, which is defined in clause 5.2.3.2.
The cells shall be ranked according to the R criteria specified above by deriving Qmeas,n and Qmeas,s and calculating the R values using averaged RSRP results.
If rangeToBestCell is not configured, the UE shall perform cell reselection to the highest ranked cell. If this cell is found to be not-suitable, the UE shall behave according to clause 5.2.4.4.
If rangeToBestCell is configured, then the UE shall perform cell reselection to the cell with the highest number of beams above the threshold (i.e. absThreshSS-BlocksConsolidation) among the cells whose R value is within rangeToBestCell of the R value of the highest ranked cell. If there are multiple such cells, the UE shall perform cell reselection to the highest ranked cell among them. If this cell is found to be not-suitable, the UE shall behave according to clause 5.2.4.4.
In all cases, the UE shall reselect the new cell, only if the following conditions are met:
  • the new cell is better than the serving cell according to the cell reselection criteria specified above during a time interval TreselectionRAT;
  • more than 1 second has elapsed since the UE camped on the current serving cell.
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