The NAS is informed if the cell selection and reselection results in changes in the received NAS system information.
The UE shall monitor the Paging Occasions (POs) as described in clause 7.1 to receive System Information change notifications in RRC_IDLE and RRC_INACTIVE. The changes in the system information are notified by the network using a Short Message as specified in TS 38.331. When the Short Message notifies system information changes, then the UE shall acquire or re-acquire the concerned system information as specified in TS 38.331.
The UE may use Discontinuous Reception (DRX) in RRC_IDLE and RRC_INACTIVE state in order to reduce power consumption. The UE monitors one paging occasion (PO) per DRX cycle. A PO is a set of PDCCH monitoring occasions and can consist of multiple time slots (e.g. subframe or OFDM symbol) where paging DCI can be sent (TS 38.213). One Paging Frame (PF) is one Radio Frame and may contain one or multiple PO(s) or starting point of a PO.
In multi-beam operations, the UE assumes that the same paging message and the same Short Message are repeated in all transmitted beams and thus the selection of the beam(s) for the reception of the paging message and Short Message is up to UE implementation. The paging message is same for both RAN initiated paging and CN initiated paging.
The UE initiates RRC Connection Resume procedure upon receiving RAN initiated paging. If the UE receives a CN initiated paging in RRC_INACTIVE state, the UE moves to RRC_IDLE and informs NAS.
The PF and PO for paging are determined by the following formulae:
SFN for the PF is determined by:
(SFN + PF_offset) mod T = (T div N)*(UE_ID mod N)
Index (i_s), indicating the index of the PO is determined by:
i_s = floor (UE_ID/N) mod Ns
The PDCCH monitoring occasions for paging are determined according to pagingSearchSpace as specified in TS 38.213 and firstPDCCH-MonitoringOccasionOfPO and nrofPDCCH-MonitoringOccasionPerSSB-InPO if configured as specified in TS 38.331. When SearchSpaceId = 0 is configured for pagingSearchSpace, the PDCCH monitoring occasions for paging are same as for RMSI as defined in clause 13 in TS 38.213.
When SearchSpaceId = 0 is configured for pagingSearchSpace, Ns is either 1 or 2. For Ns = 1, there is only one PO which starts from the first PDCCH monitoring occasion for paging in the PF. For Ns = 2, PO is either in the first half frame (i_s = 0) or the second half frame (i_s = 1) of the PF.
When SearchSpaceId other than 0 is configured for pagingSearchSpace, the UE monitors the (i_s + 1)th PO. A PO is a set of 'S*X ' consecutive PDCCH monitoring occasions where 'S' is the number of actual transmitted SSBs determined according to ssb-PositionsInBurst in SIB1 and X is the nrofPDCCH-MonitoringOccasionPerSSB-InPO if configured or is equal to 1 otherwise. The [x*S+K]th PDCCH monitoring occasion for paging in the PO corresponds to the Kth transmitted SSB, where x=0,1,…,X-1, K=1,2,…,S. The PDCCH monitoring occasions for paging which do not overlap with UL symbols (determined according to tdd-UL-DL-ConfigurationCommon) are sequentially numbered from zero starting from the first PDCCH monitoring occasion for paging in the PF. When firstPDCCH-MonitoringOccasionOfPO is present, the starting PDCCH monitoring occasion number of (i_s + 1)th PO is the (i_s + 1)th value of the firstPDCCH-MonitoringOccasionOfPO parameter; otherwise, it is equal to i_s * S*X. If X > 1, when the UE detects a PDCCH transmission addressed to P-RNTI within its PO, the UE is not required to monitor the subsequent PDCCH monitoring occasions for this PO.
The following parameters are used for the calculation of PF and i_s above:
DRX cycle of the UE (T is determined by the shortest of the UE specific DRX value(s), if configured by RRC and/or upper layers, and a default DRX value broadcast in system information. In RRC_IDLE state, if UE specific DRX is not configured by upper layers, the default value is applied).
number of total paging frames in T
number of paging occasions for a PF
offset used for PF determination
5G-S-TMSI mod 1024
Parameters Ns, nAndPagingFrameOffset, nrofPDCCH-MonitoringOccasionPerSSB-InPO, and the length of default DRX Cycle are signaled in SIB1. The values of N and PF_offset are derived from the parameter nAndPagingFrameOffset as defined in TS 38.331. The parameter first-PDCCH-MonitoringOccasionOfPO is signalled in SIB1 for paging in initial DL BWP. For paging in a DL BWP other than the initial DL BWP, the parameter first-PDCCH-MonitoringOccasionOfPO is signaled in the corresponding BWP configuration.
If the UE has no 5G-S-TMSI, for instance when the UE has not yet registered onto the network, the UE shall use as default identity UE_ID = 0 in the PF and i_s formulas above.
5G-S-TMSI is a 48 bit long bit string as defined in TS 23.501. 5G-S-TMSI shall in the formulae above be interpreted as a binary number where the left most bit represents the most significant bit.
The UE may transmit or receive NR sidelink communication if it fulfils the condition(s) defined in TS 38.331, clause 5.8.2. When UE is in-coverage for sidelink operation as defined in clause 8.2, the UE may perform NR sidelink communication according to SystemInformationBlockType12, and when out-of-coverage for sidelink, the UE may perform NR sidelink communication according to SL-V2X-PreconfigurationNR or according to SystemInformationBlockType12 of the cell on the frequency which provides inter-carrier NR sidelink configuration, as specified in TS 38.331. The UE shall not perform NR sidelink communication according to SL-V2X-PreconfigurationNR if the UE detects a cell providing NR sidelink configuration or inter-carrier NR sidelink configuration for the frequency UE is interested to perform NR sidelink communication on.
The UE may transmit or receive V2X sidelink communication if it fulfills the condition(s) defined in TS 36.331, clause 5.10.1d. When UE is in-coverage for sidelink operation as defined in clause 8.2, the UE may perform V2X sidelink communication according to SystemInformationBlockType13/SystemInformationBlockType14 of the cell on an NR frequency.
The requirements defined in this clause for sidelink operation apply for UEs in RRC_IDLE, RRC_INACTIVE and in RRC_CONNECTED.
When UE is interested to perform NR sidelink communication on non-serving frequency, it may perform measurements on that frequency or the frequencies which can provide inter carrier NR sidelink configuration for that frequency for cell selection and intra-frequency reselection purpose in accordance with TS 38.133. When UE is interested to perform V2X sidelink communication on non-serving frequency, it may perform measurements on that frequency or the frequencies which can provide inter carrier V2X sidelink configuration for that frequency for cell selection and intra-frequency reselection purpose in accordance with TS 38.133.
If the UE detects at least one cell on the frequency which UE is configured to perform NR sidelink communication on fulfilling the S criterion in accordance with clause 8.2.1, it shall consider itself to be in-coverage for NR sidelink communication on that frequency. If the UE cannot detect any cell on that frequency meeting the S criterion, it shall consider itself to be out-of-coverage for NR sidelink communication on that frequency.
If the UE detects at least one cell on the frequency which UE is configured to perform V2X sidelink communication on fulfilling the S criterion in accordance with clause 8.2.1, it shall consider itself to be in-coverage for V2X sidelink communication on that frequency. If the UE cannot detect any cell on that frequency meeting the S criterion, it shall consider itself to be out-of-coverage for V2X sidelink communication on that frequency.
If the UE has selected a cell on a non-serving frequency for NR sidelink communication or V2X sidelink communication, it shall perform additional intra-frequency reselection process to select a better cell for sidelink operation on that frequency in accordance with clause 8.2.1.
When evaluating S criterion or R criterion (ranking), as defined in clause 220.127.116.11 and clause 18.104.22.168 respectively, for cell selection/reselection triggered for NR sidelink communication or V2X sidelink communication on a non-serving frequency, UE shall perform the evaluation as follows:
The UE shall use cell selection/reselection parameters broadcast by the concerned cell (i.e. selected cell for the sidelink operation) for the evaluation.