10.1.4 Paging and C-plane establishment

36.3003GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)Overall descriptionRelease 17Stage 2TS

Paging groups (where multiple UEs can be addressed) are used on PDCCH:

– Precise UE identity is found on PCH;

– DRX configurable via BCCH and NAS;

– Only one subframe allocated per paging interval per UE;

– The network may divide UEs to different paging occasions in time;

– There is no grouping within paging occasion;

– One paging RNTI for PCH.

When extended DRX (eDRX) is used in idle mode, the following are applicable:

– The DRX cycle is extended up to and beyond 10.24s in idle mode, with a maximum value of 2621.44 seconds (43.69 minutes); For NB-IoT, the maximum value of the DRX cycle is 10485.76 seconds (2.91 hours);

– The hyper SFN (H-SFN) is broadcast by the cell and increments by one when the SFN wraps around;

– Paging Hyperframe (PH) refers to the H-SFN in which the UE starts monitoring paging DRX during a Paging Time Window (PTW) used in ECM-IDLE. The PH is determined based on a formula that is known by the MME/AMF, UE and (ng-)eNB as a function of eDRX cycle and UE identity;

– During the PTW, the UE monitors paging for the duration of the PTW (as configured by NAS) or until a paging message is including the UE’s NAS identity received for the UE, whichever is earlier. The possible starting offsets for the PTW are uniformly distributed within the PH and defined in TS 36.304 [11];

– MME/AMF uses the formulas defined in TS 36.304 [11] to determine the PH as well as the beginning of the PTW and sends the S1 paging request just before the occurrence of the start of PTW or during PTW to avoid storing paging messages in the (ng-)eNB;

– ETWS, CMAS, PWS requirement may not be met when a UE is in eDRX. For EAB, if the UE supports SIB14, when in extended DRX, it acquires SIB14 before establishing the RRC connection;

– When the eDRX cycle is longer than the system information modification period, the UE verifies that stored system information remains valid before establishing an RRC connection. Paging message can be used for system information change notification, when including systemInfoModification-eDRX, for a UE configured with eDRX cycle longer than the system information modification period.

NB-IoT UEs, BL UEs or UEs in enhanced coverage can use (G)WUS, when configured in the cell, to reduce the power consumption related to paging monitoring. (G)WUS is only applicable in RRC_IDLE.

When GWUS is used in RRC_IDLE, the following are applicable:

– Multiple WUS groups, possibly distributed over multiple WUS resources, can be configured in the cell;

– If the UE supports WUS assistance information, the MME/AMF may provide the UE with UE paging probability information (see TS 24.301 [20] and TS 24.501 [91]);

– UE selects one WUS group based on its UE paging probability information and /or its UE NAS identity as defined in TS 36.304 [11];

– A common WUS group may be used to wake up all UEs monitoring the same WUS resource.

When (G)WUS is used in RRC_IDLE, the following are applicable:

– The UE monitors (G)WUS only in the last used cell as defined in TS 36.304 [11];

– The WUS or WUS group is used to indicate that the UE shall monitor MPDCCH or NPDCCH to receive paging in that cell;

– For a UE not configured with extended DRX, the WUS or WUS group is associated to one paging occasion (N = 1);

– For a UE configured with extended DRX, the WUS or WUS group can be associated to one or multiple paging occasion(s) (N ≥ 1) in a PTW;

– If UE detects the WUS or WUS group, the UE shall monitor the following N paging occasions unless it has received a paging message;

– The paging operation in the MME/AMF is not aware of the use of the WUS in the (ng-)eNB;

– To reduce WUS use in cells not monitored by the UE, WUS-capable (ng-)eNBs provide UE’s last used cell information to MME/AMF in the S1-AP/NG-AP UE Context Release Complete or UE Context Suspend Request messages for all UEs, as described in TS 23.401 [17] and TS 23.501 [82]. In case of immediate suspension of a UE, the WUS-capable ng-eNB also provides the UE’s last cell information to the AMF in the UE Context Resume Request message, as described in TS 23.501 [82].

The timing between WUS and the paging occasion (PO) is illustrated in Figure 10.1.4-1. The timing between GWUS and the paging occasion (PO) is illustrated in Figure 10.1.4-2 and Figure 10.1.4-3. The UE can expect WUS repetitions during "Configured maximum WUS duration" but the actual WUS transmission can be shorter, e.g. for UE in good coverage. The UE does not monitor WUS during the non-zero "Gap".

Figure 10.1.4-1: Illustration of WUS timing

Figure 10.1.4-2: Illustration of GWUS timing for NB-IoT UEs

Figure 10.1.4-3: Illustration of GWUS timing for BL UEs and UEs in enhanced coverage

NOTE: WUS1/WUS3 could be higher or lower frequency than WUS0/WUS2.

For NB-IoT, UE in RRC_IDLE receives paging on the anchor carrier or on a non-anchor carrier based on system information.

When coverage based paging is used in NB-IoT:

– Some paging carriers may be configured for lower levels of coverage enhancements;

– The eNB can configure a UE during RRC connection release to select one of these paging carriers according to coverage information provided by the eNB;

– If configured for coverage based paging, the UE only selects one of the coverage based paging carriers if its NRSRP is suitable according to the coverage based paging configuration;

– Coverage based paging is only applicable in the last cell where the coverage information was received;- The eNB includes the coverage based paging information provided to the UE within the information on the coverage enhancement (CE) level described in clause 23.13.2.