4.3.21 Core Network assisted eNodeB parameters tuning

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

4.3.21.1 CN Assistance Information

Core Network assisted eNodeB parameters tuning aids the eNodeB to minimize the UE state transitions and achieve optimum network behaviour. How the eNodeB uses the Core Network assistance information is not in scope of this specification and is implementation specific.

Core Network assistance information may be derived by the MME per UE in the MME based on collection of UE behaviour statistics or other available information about the expected UE behaviour (such as subscribed APN, IMSI ranges or other subscription information). If the HSS provides the Communication Pattern (CP) parameters (see TS 23.682 [74]) within the subscription profile information, then the MME may use the CP parameters for selecting the CN assisted eNodeB parameters. The CP parameters received from the HSS are used by the MME as input to derive the CN assisted eNodeB parameter values. For the case of statistics-based Core Network assistance information collection, this may be enabled based on local configuration (e.g. subscribed APN, IMSI ranges or other subscription information). This information provides the eNodeB with a way to understand the UE behaviour for these aspects:

– "Expected UE activity behaviour", i.e. the expected pattern of the UE’s changes between ECM-CONNECTED and ECM-IDLE states. This may be derived e.g. from statistical information or from subscription information.

– "Expected HO interval", i.e. the expected time interval between inter-eNodeB handovers. This may be derived e.g. from statistical information or from subscription information. The "Expected HO interval" parameter is not based on subscription information. Highly mobile UEs may have the ECM-CONNECTED state reduced to reduce handover signalling, unless the activity data do not justify that, as reduced handover signalling would be outweighed by more Service Request signalling).

– "UE Differentiation Information" including the Communication Pattern parameters (see TS 23.682 [74]) to support Uu operation optimisation for NB-IoT UE differentiation.

The respective signalling to support this feature is specified in TS 36.413 [36]. The cases where the Traffic Profile (see see TS 23.682 [74]) is not used are described in clauses 5.3.4B.2 and 5.3.4B.3.

The MME decides when to send this information to the eNodeB as "Expected UE behaviour" carried in S1-AP signalling over the S1-MME interface as per procedure documented in clause 4.3.21.3.

NOTE 1: The calculation of the Core Network assistance information, i.e. the algorithms used and related criteria, and the decision when it is considered suitable and stable to send to the eNodeB are vendor specific. Unreliable information should not be provided to the eNodeB as it may drive undesirable system effects.

NOTE 2: It is recommended the MME or, depending on where this assessment is performed, the eNodeB, can consider the average times in the ECM-CONNECTED and ECM-IDLE states an accurate representation of the traffic patterns if the average time in ECM-CONNECTED mode is short enough to assume the UE is generally actively transmitting and/or receiving data while in ECM-CONNECTED state.

NOTE 3: When there are multiple overlapping CP parameter sets received from the HSS for one UE, then the MME considers a merge per CP parameter when deriving the CN assisted eNodeB parameters, e.g. based on the Scheduled communication time and/or Communication duration time parameters. A conflict on the Stationary Indication parameter can be resolved by considering the UE as "mobile".

4.3.21.2 Void

4.3.21.3 Core Network Assistance Procedures

The MME provides CN assistance information to the eNodeB if available, during the setup of the S1 signalling connection (e.g., Attach, Service Request).

The following figure is a high level description of the transfer of information from an MME to eNodeB during a service request procedure.

Figure 4.3.21.3-1: Core Network assisted eNodeB parameters tuning

4.3.21.4 Wake Up Signal Assistance

4.3.21.4.1 General

The RAN and UE may use a Wake Up Signal (WUS) to reduce the UE’s idle mode power consumption. The RAN sends the WUS shortly before the UE’s paging occasion. The WUS feature enables UEs to determine that in the paging occasions immediately following their WUS occasion they will not be paged if their WUS is not transmitted, or that they might be paged if their WUS is transmitted (see TS 36.304 [34]).

To avoid waking up UEs due to an MME paging other UEs across multiple cells (e.g. due to frequent UE mobility and/or for low paging latency services such as VoLTE), the use of WUS by the eNodeB and the UE is restricted to the last used cell, i.e. the cell in which the UE’s RRC connection was last released. To support this:

a) WUS-capable eNodeBs should provide the Recommended Cells for Paging IE in the Information On Recommended Cells And eNodeBs For Paging IE (see TS 36.413 [36]) to the MME in the S1 UE Context Release Complete or UE Context Suspend Request messages;

b) if received during the last S1 UE Context Release Complete or UE Context Suspend Request message, the MME provides (without modification) the Recommended Cells for Paging as Assistance Data for Recommended Cells IE in the S1-AP Paging message to the RAN (see also TS 36.413 [36]); and

c) the MME shall delete (or mark as invalid) the Information On Recommended Cells And eNodeBs For Paging when a new S1-AP association is established for the UE.

In the S1-AP Paging message, the last used cell ID is sent in the Assistance Data for Recommended Cells IE in the Assistance Data for Paging IE (see TS 36.413 [36]). When receiving an S1-AP Paging message for a WUS-capable UE that also includes the Assistance Data for Recommended Cells IE then a WUS-capable eNodeB shall only broadcast the WUS on the cell that matches the last used cell ID.

4.3.21.4.2 Group Wake Up Signal

To support the Group Wake Up Signal feature, the WUS Assistance Information is used by the eNodeB to help determine the WUS group used when paging the UE (see TS 36.300 [5]).

The content of the WUS Assistance Information consists of the paging probability information. The paging probability information provides a metric on the probability of a UE receiving a paging message based on, e.g., statistical information.

The UE may in the Attach Request message provide its capability to support WUS Assistance Information. If WUS Assistance Information is supported, then the UE in the Attach Request or Tracking Area Update message may provide the additional UE paging probability information. The MME may use the UE provided paging probability, local configuration and/or previous statistical information for the UE, when determining the WUS Assistance Information. If the UE supports WUS Assistance Information, the MME may assign WUS Assistance Information to the UE, even when the UE has not provided the additional UE paging probability information.

If the MME has determined WUS Assistance Information for the UE, the MME provides it to the UE in every Attach Accept and/or Tracking Area Update message. The MME stores the WUS Assistance Information parameter in the MM context and provides it to the eNodeB when paging the UE.

UE and MME shall not include WUS Assistance Information in Emergency Attach Request/Attach Accept and in Tracking Area Update/Tracking Area Update Accept messages if the UE has an active emergency PDN connection.