Section: 5.8.6.2 Selection and reselection of synchronisation reference
Content: The UE shall for frequency(ies) which have been selected for NR sidelink communication/discovery as specified in TS 38.321[ NR; Medium Access Control (MAC) protocol specification ]  [3]: 1> if one frequency is selected for NR sidelink communication/discovery: 2> if sl-SyncFreqList is not included in RRCReconfiguration nor in SIB12; or 2> if sl-SyncFreqList is included in RRCReconfiguration or in SIB12, and none of the frequency(ies) selected as specified in TS 38.321[ NR; Medium Access Control (MAC) protocol specification ]  [3] is included in the syncFreqList: 3> if the frequency used for NR sidelink communication/discovery is included in sl-FreqInfoToAddModList in sl-ConfigDedicatedNR within RRCReconfiguration message or included in sl-ConfigCommonNR within SIB12, and sl-SyncPriority is configured for the concerned frequency and set to gnbEnb: 4> select a cell as the synchronization reference source as defined in 5.8.6.3: NOTE 1: When an out of coverage L2 U2N Remote UE receives SIB12 with sl-SyncPriority set to gnbEnb, the L2 U2N Remote UE continues using the current synchronization source until higher priority synchronization source is found or the current synchronization source becomes unreliable. 3> else if the frequency used for NR sidelink communication/discovery is included in sl-FreqInfoToAddModList in sl-ConfigDedicatedNR within RRCReconfiguration message or included in sl-ConfigCommonNR within SIB12, and sl-SyncPriority for the concerned frequency is not configured or is set to gnss, and GNSS is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 4> select GNSS as the synchronization reference source; 3> else if the frequency used for NR sidelink communication/discovery is included in SL-PreconfigurationNR, and sl-SyncPriority in SidelinkPreconfigNR is set to gnss and GNSS is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 4> select GNSS as the synchronization reference source; 3> else: 4> perform a full search (i.e. covering all subframes and all possible SLSSIDs) to detect candidate SLSS, in accordance with TS 38.133[ NR; Requirements for support of radio resource management ]  [14] 4> when evaluating the one or more detected SLSSIDs, apply layer 3 filtering as specified in 5.5.3.2 using the preconfigured sl-filterCoefficient in SL-SyncConfig, before using the PSBCH-RSRP measurement results; 4> if the UE has selected a SyncRef UE: 5> if the PSBCH-RSRP of the strongest candidate SyncRef UE exceeds the minimum requirement TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the strongest candidate SyncRef UE belongs to the same priority group as the current SyncRef UE and the PSBCH-RSRP of the strongest candidate SyncRef UE exceeds the PSBCH-RSRP of the current SyncRef UE by syncRefDiffHyst; or 5> if the PSBCH-RSRP of the candidate SyncRef UE exceeds the minimum requirement TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the candidate SyncRef UE belongs to a higher priority group than the current SyncRef UE; or 5> if GNSS becomes reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14], and GNSS belongs to a higher priority group than the current SyncRef UE; or 5> if a cell is detected and gNB/eNB (if sl-NbAsSync is set to true) belongs to a higher priority group than the current SyncRef UE; or 5> if the PSBCH-RSRP of the current SyncRef UE is less than the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 6> consider no SyncRef UE to be selected; 4> if the UE has selected GNSS as the synchronization reference for NR sidelink communication/discovery: 5> if the PSBCH-RSRP of the candidate SyncRef UE exceeds the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the candidate SyncRef UE belongs to a higher priority group than GNSS; or 5> if GNSS becomes not reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 6> consider GNSS not to be selected; 4> if the UE has selected cell as the synchronization reference for NR sidelink communication/discovery: 5> if the PSBCH-RSRP of the candidate SyncRef UE exceeds the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the candidate SyncRef UE belongs to a higher priority group than gNB/eNB; or 5> if the selected cell is not detected: 6> consider the cell not to be selected; 4> if the UE has not selected any synchronization reference: 5> if the UE detects one or more SLSSIDs for which the PSBCH-RSRP exceeds the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and for which the UE received the corresponding MasterInformationBlockSidelink message (candidate SyncRef UEs), or if the UE detects GNSS that is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14], or if the UE detects a cell, select a synchronization reference according to the following priority group order: 6> if sl-SyncPriority corresponding to the concerned frequency is set to gnbEnb: 7> UEs of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, starting with the UE with the highest PSBCH-RSRP result (priority group 1); 7> UE of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 2); 7> GNSS that is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14] (priority group 3); 7> UEs of which SLSSID is 0, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, or of which SLSSID is 0 and SLSS is transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, starting with the UE with the highest PSBCH-RSRP result (priority group 4); 7> UEs of which SLSSID is 0 and SLSS is not transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 5); 7> UEs of which SLSSID is 337 and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 5); 7> Other UEs, starting with the UE with the highest PSBCH-RSRP result (priority group 6); 6> if sl-SyncPriority corresponding to the concerned frequency is set to gnss, and sl-NbAsSync is set to true: 7> UEs of which SLSSID is 0, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, or of which SLSSID is 0 and SLSS is transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, starting with the UE with the highest PSBCH-RSRP result (priority group 1); 7> UEs of which SLSSID is 0 and SLSS is not transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCHS-RSRP result (priority group 2); 7> UEs of which SLSSID is 337 and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 2); 7> the cell detected by the UE as defined in 5.8.6.3 (priority group 3); 7> UEs of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, starting with the UE with the highest PSBCH-RSRP result (priority group 4); 7> UE of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 5); 7> Other UEs, starting with the UE with the highest S-RSRP result (priority group 6); 6> if sl-SyncPriority corresponding to the concerned frequency is set to gnss, and sl-NbAsSync is set to false: 7> UEs of which SLSSID is 0, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, or of which SLSSID is 0 and SLSS is transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, starting with the UE with the highest PSBCH-RSRP result (priority group 1); 7> UEs of which SLSSID is 0 and SLSS is not transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCHS-RSRP result (priority group 2); 7> UEs of which SLSSID is 337 and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 2); 7> Other UEs, starting with the UE with the highest PSBCH-RSRP result (priority group 3); 1> else if more than one frequency is selected for NR sidelink communication: 2> if sl-SyncFreqList is included in RRCReconfiguration or in SIB12, and includes at least one of the concerned frequency(ies) 3> if the concerned frequency(ies) are included in sl-FreqInfoToAddModList/sl-FreqInfoToAddModListExt in sl-ConfigDedicatedNR within RRCReconfiguration message or included in sl-ConfigCommonNR within SIB12, and sl-SyncPriority is configured for the concerned frequency(ies) and set to gnbEnb: 4> select one frequency from the concerned frequency(ies) which are included in sl-SyncFreqList as the synchronisation carrier frequency; 4> select a cell in accordance with the synchronisation carrier frequency as the synchronization reference source as defined in 5.8.6.3: 3> else if the concerned frequency(ies) are included in sl-FreqInfoToAddModList/sl-FreqInfoToAddModListExt in sl-ConfigDedicatedNR within RRCReconfiguration message or included in sl-ConfigCommonNR within SIB12, and sl-SyncPriority for concerned frequency(ies) are not configured or are set to gnss, and GNSS is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14]; or if the concerned frequency(ies) are included in SL-PreconfigurationNR, and sl-SyncPriority in SidelinkPreconfigNR is set to gnss and GNSS is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 4> select one frequency from the concerned frequency(ies) which are included in sl-SyncFreqList as the synchronisation carrier frequency; 4> select GNSS in accordance with the synchronisation carrier frequency as the synchronization reference source; 3> else: 4> perform a full search (i.e. covering all subframes and all possible SLSSIDs) to detect candidate SLSS, in accordance with TS 38.133[ NR; Requirements for support of radio resource management ]  [14] 4> when evaluating the one or more detected SLSSIDs, apply layer 3 filtering as specified in 5.5.3.2 using the preconfigured sl-filterCoefficient, before using the PSBCH-RSRP measurement results; 4> if the UE has selected a SyncRef UE: 5> if the PSBCH-RSRP of the strongest candidate SyncRef UE exceeds the minimum requirement TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the strongest candidate SyncRef UE belongs to the same priority group as the current SyncRef UE and the PSBCH-RSRP of the strongest candidate SyncRef UE exceeds the PSBCH-RSRP of the current SyncRef UE by syncRefDiffHyst; or 5> if the PSBCH-RSRP of the candidate SyncRef UE exceeds the minimum requirement TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the candidate SyncRef UE belongs to a higher priority group than the current SyncRef UE; or 5> if GNSS becomes reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14], and GNSS belongs to a higher priority group than the current SyncRef UE; or 5> if a cell is detected and gNB/eNB (if sl-NbAsSync is set to true) belongs to a higher priority group than the current SyncRef UE; or 5> if the PSBCH-RSRP of the current SyncRef UE is less than the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 6> consider no SyncRef UE to be selected; 4> if the UE has selected GNSS as the synchronization reference for NR sidelink communication/discovery: 5> if the PSBCH-RSRP of the candidate SyncRef UE exceeds the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the candidate SyncRef UE belongs to a higher priority group than GNSS; or 5> if GNSS becomes not reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14]: 6> consider GNSS not to be selected; 4> if the UE has selected cell as the synchronization reference for NR sidelink communication/discovery: 5> if the PSBCH-RSRP of the candidate SyncRef UE exceeds the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and the candidate SyncRef UE belongs to a higher priority group than gNB/eNB; or 5> if the selected cell is not detected: 6> consider the cell not to be selected; 4> if the UE has not selected any synchronization reference: 5> if the UE detects one or more SLSSIDs for which the PSBCH-RSRP exceeds the minimum requirement defined in TS 38.133[ NR; Requirements for support of radio resource management ]  [14] by sl-SyncRefMinHyst and for which the UE received the corresponding MasterInformationBlockSidelink message (candidate SyncRef UEs), or if the UE detects GNSS that is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14], or if the UE detects a cell, 6> select the synchronisation reference source(s) on each concerned frequency which is included in sl-SyncFreqList according to the following priority group order; 6> select the frequency with the highest synchronisation reference source priority as the synchronisation carrier frequency, according to the following priority group order, and consider the synchornization reference source (i.e. eNB/gNB, GNSS or SyncRef UE) that selected on the synchronisation carrier frequency as the synchronization reference: 7> if sl-SyncPriority corresponding to the concerned frequency is set to gnbEnb: 8> UEs of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, starting with the UE with the highest PSBCH-RSRP result (priority group 1); 8> UE of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 2); 8> GNSS that is reliable in accordance with TS 38.101[ None ] -1 [15] and TS 38.133[ NR; Requirements for support of radio resource management ]  [14] (priority group 3); 8> UEs of which SLSSID is 0, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, or of which SLSSID is 0 and SLSS is transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, starting with the UE with the highest PSBCH-RSRP result (priority group 4); 8> UEs of which SLSSID is 0 and SLSS is not transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 5); 8> UEs of which SLSSID is 337 and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 5); 8> Other UEs, starting with the UE with the highest PSBCH-RSRP result (priority group 6); 7> if sl-SyncPriority corresponding to the concerned frequency is set to gnss, and sl-NbAsSync is set to true: 8> UEs of which SLSSID is 0, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, or of which SLSSID is 0 and SLSS is transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, starting with the UE with the highest PSBCH-RSRP result (priority group 1); 8> UEs of which SLSSID is 0 and SLSS is not transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCHS-RSRP result (priority group 2); 8> UEs of which SLSSID is 337 and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 2); 8> the cell detected by the UE as defined in 5.8.6.3 (priority group 3); 8> UEs of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, starting with the UE with the highest PSBCH-RSRP result (priority group 4); 8> UE of which SLSSID is part of the set defined for in coverage, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 5); 8> Other UEs, starting with the UE with the highest S-RSRP result (priority group 6); 7> if sl-SyncPriority corresponding to the concerned frequency is set to gnss, and sl-NbAsSync is set to false: 8> UEs of which SLSSID is 0, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to true, or of which SLSSID is 0 and SLSS is transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, starting with the UE with the highest PSBCH-RSRP result (priority group 1); 8> UEs of which SLSSID is 0 and SLSS is not transmitted on slot(s) indicated by sl-SSB-TimeAllocation3, and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCHS-RSRP result (priority group 2); 8> UEs of which SLSSID is 337 and inCoverage, included in the MasterInformationBlockSidelink message received from this UE, is set to false, starting with the UE with the highest PSBCH-RSRP result (priority group 2); 8> Other UEs, starting with the UE with the highest PSBCH-RSRP result (priority group 3); NOTE 2: How the UE achieves subframe boundary alignment between V2X sidelink communication and NR sidelink communication/discovery (if both are performed by the UE) is as specified in TS 38.213[ NR; Physical layer procedures for control ] , clause 16.7.