Content for  TS 38.304  Word version:  18.0.0

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 any fields with cellReselectionPriority or nsag-CellReselectionPriority are provided in dedicated signalling, the UE shall ignore any fields with cellReselectionPriority and nsag-CellReselectionPriority provided in system information. When UE is in camped normally state, if it supports slice-based cell reselection and has received the network slice(s) and NSAG information from NAS to be used for cell reselection, UE shall derive reselection priorities according to clause 5.2.4.11. 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). When the HSDN capable UE is in High-mobility state, the UE shall always consider the HSDN cells to be the highest priority (i.e., higher than any other network configured priorities). When the HSDN capable UE is not in High-mobility state, the UE shall always consider HSDN cells to be the lowest priority (i.e., lower than any other network configured priorities). 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. If the UE is configured to perform ranging/sidelink positioning, the UE may consider the frequency providing ranging/sidelink positioning configuration to be the highest priority. A UE on a vehicle with a mobile-IAB cell may consider the frequency for which a mobile-IAB cell is the best cell to be the highest priority. The UE identifies a mobile-IAB cell by mobileIAB-Cell in SIB1 (see TS 38.331). The UE may narrow its search scope for mobile-IAB cell(s) by mobileIAB-InfoList-r18 if broadcasted in SIB4 (see TS 38.331). A non-mobile-IAB cell may be excluded from this mobile IAB frequency prioritization for up to 300 seconds. 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. If the MBS broadcast capable UE is receiving or interested to receive an MBS broadcast service(s) and can only receive this MBS broadcast service(s) by camping on a frequency on which it is provided, the UE may consider that frequency to be the highest priority during the MBS broadcast session as specified in TS 38.300 as long as the two following conditions are fulfilled:

1. SIB1 scheduling information of the cell reselected by the UE due to frequency prioritization for MBS contains SIB20;
2. Either:
   • One or more MBS FSAI(s) of that frequency is indicated in SIB21 of the serving cell and the same MBS FSAI(s) is also indicated for this MBS broadcast service in MBS User Service Description (USD) as specified in TS 26.346, or
   • SIB21 is not provided in the serving cell and that frequency is included in the USD of this service, or
   • SIB21 is provided in the serving cell but does not provide the frequency mapping for the concerned service, and that frequency is included in the USD of this service.

If the MBS broadcast capable UE is receiving or interested to receive an MBS broadcast service, the UE may consider cell reselection candidate frequencies at which it cannot receive the MBS broadcast service to be of the lowest priority during the MBS broadcast session as specified in TS 38.300, as long as SIB1 scheduling information of the cell contains SIB20 on the MBS frequency which the UE monitors and as long as the condition 2) above is fulfilled for the serving cell. 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 exclude-listed cells as candidate for cell reselection. The UE shall consider only the allow-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.

Following rules are used by the UE to limit needed measurements:

• If the serving cell fulfils Srxlev > S_IntraSearchP and Squal > S_IntraSearchQ:
  • If distanceThresh and referenceLocation are broadcasted in SIB19, and if UE supports location-based measurement initiation for NTN quasi-Earth-fixed system and has obtained its location information:
    • If the distance between UE and the serving cell reference location referenceLocation is shorter than distanceThresh, the UE may not perform intra-frequency measurements;
    • Else, the UE shall perform intra-frequency measurements;
  • else if distanceThresh and movingReferenceLocation are broadcasted in SIB19, and if UE supports location-based measurement initiation for NTN Earth-moving system and has obtained its location information:
    • if the distance between UE's location and the serving cell reference location determined based on movingReferenceLocation is shorter than distanceThresh, the UE may not perform intra-frequency measurements;
    • else, the UE shall perform intra-frequency measurements;
  • Else, the UE may not perform intra-frequency measurements;
• Else, 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 clause 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 > S_{nonIntraSearchP} and Squal > S_{nonIntraSearchQ}:
      • If distanceThresh and referenceLocation are broadcasted in SIB19, and if UE supports location-based measurement initiation for NTN quasi-Earth-fixed system and has obtained its UE location information:
        • If the distance between UE and the serving cell reference location referenceLocation is shorter than distanceThresh, the UE may choose not to perform measurements of NR inter-frequency cells of equal or lower priority, or inter-RAT frequency cells of lower priority;
        • Else, the UE shall perform measurements of NR inter-frequency cells of equal or lower priority, or inter-RAT frequency cells of lower priority according to TS 38.133;
      • else if distanceThresh and movingReferenceLocation are broadcasted in SIB19, and if UE supports location-based measurement initiation for NTN Earth-moving system and has obtained its location information:
        • if the distance between UE's location and the serving cell reference location determined based on movingReferenceLocation is shorter than distanceThresh, the UE may not perform measurements of NR inter-frequency cells of equal or lower priority, or inter-RAT frequency cells of lower priority;
        • else, the UE shall perform measurements of NR inter-frequency cells of equal or lower priority, or inter-RAT frequency cells of lower priority according to TS 38.133;
      • Else, the UE may choose not to perform measurements of NR inter-frequency cells of equal or lower priority, or inter-RAT frequency cells of lower priority;
    • Else, the UE shall perform measurements of NR inter-frequency cells of equal or lower priority, or inter-RAT frequency cells of 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.
• For UE camping on NTN cell, if the UE supports skipping TN measurement, and the UE has obtained its location information, and if coverageAreaInfoList and tn-AreaIdList are broadcast in system information, the UE may not perform measurements of a TN frequency when UE is not in the coverage of that frequency provided via tn-AreaIdList, regardless of the frequency priority.

If the t-Service of the serving cell is present in SIB19, and if UE supports time-based measurement initiation, the UE shall perform intra-frequency, inter-frequency or inter-RAT measurements before the t-Service, regardless of the distance between UE and the serving cell reference location or whether the serving cell fulfils Srxlev > S_IntraSearchP and Squal > S_IntraSearchQ, or Srxlev > S_{nonIntraSearchP} and Squal > S_{nonIntraSearchQ}, The exact time to start measurement before t-Service is up to UE implementation. UE shall perform measurements of higher priority NR inter-frequency or inter-RAT frequencies according to TS 38.133 regardless of the remaining service time of the serving cell (i.e. time remaining until t-Service).

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 or indicated as being equivalent 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 intra-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 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, the limitation(s) on that frequency shall be removed.

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 > Thresh_{X, HighQ} during a time interval Treselection_RAT

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 > Thresh_{X, HighP} during a time interval Treselection_RAT; 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 < Thresh_{Serving, LowQ} and a cell of a lower priority NR or E-UTRAN RAT/ frequency fulfils Squal > Thresh_{X, LowQ} during a time interval Treselection_RAT.

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 < Thresh_{Serving, LowP} and a cell of a lower priority RAT/ frequency fulfils Srxlev > Thresh_{X, LowP} during a time interval Treselection_RAT; 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.

The cell-ranking criterion R_s for serving cell and R_n for neighbouring cells is defined by: where:

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 Q_meas,n and Q_meas,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 Treselection_RAT;
• more than 1 second has elapsed since the UE camped on the current serving cell.