Figure 6.1.1-1 illustrates the general network positioning for the LCS clients external to the PLMN for the regulatory location service for non-roaming scenario. In this scenario, it is assumed that the target UE is identified using an SUPI or GPSI.
This procedure is applicable to a request from an LCS client for a current location of the target UE, and it is assumed that the LCS client is authorised to use the location service and no privacy verification is required.
The external location services client sends a request to the GMLC for a location for the target UE identified by an GPSI or an SUPI. The request may include the required QoS, UE unaware indication and Supported GAD shapes. If location is required for more than one UE, the steps following below may be repeated and in that case the GMLC shall verify whether the number of Target UEs in the LCS request is equal to or less than the Maximum Target UE Number of the LCS client. If Maximum Target UE Number is exceeded, the GMLC shall reject the LCS request, the step 2-10 are skipped, and then GMLC respond to the client with proper error cause in the step 11.
The GMLC invokes the Namf_Location_ProvidePositioningInfo service operation towards the AMF to request the current location of the UE. The service operation includes the SUPI, and client type and may include the required QoS, UE unaware indication and Supported GAD shapes.
If the UE is in CM IDLE state and UE unaware indication is not included, the AMF initiates a network triggered Service Request procedure as defined in clause 126.96.36.199 of TS 23.502 to establish a signalling connection with the UE.
If UE unaware indication is received by AMF, and the UE is in CM_IDLE state or in RRC_INACTIVE state (if known by AMF by requesting the NG-RAN to report RRC state information), the steps 6 - 9 are skipped.
The AMF selects an LMF based on the available information as defined in clause 5.1 or based on AMF local configuration. The LMF selection takes the 5G-AN currently serving the UE into account. The selection may use a NRF query.
The AMF invokes the Nlmf_Location_DetermineLocation service operation towards the LMF to request the current location of the UE. The service operation includes a LCS Correlation identifier, the serving cell identity of the Primary Cell in the Master RAN node and the Primary Cell in the Secondary RAN node when available based on Dual Connectivity scenarios, and the client type and may include an indication if UE supports LPP, the required QoS, UE Positioning Capability if available, UE unaware indication and Supported GAD shapes. If any of the procedures in clause 6.11.1 or clause 6.11.2 are used the service operation includes the AMF identity.
The LMF performs one or more of the positioning procedures described in clauses 6.11.1, 6.11.2 and 6.11.3. During this step the LMF may use the Namf_Communication_N1N2MessageTransfer service operation to request the transfer of a Positioning related N1 message to the UE or the transfer of a Network Positioning message to the serving NG-RAN node (gNB or NG-eNB) for the UE. The LMF shall determine a geographical location and optionally a location in local coordinates.
If UE unaware indication is received from AMF in step 7, the LMF selects Uplink Positioning method to obtain UE location and performs the positioning procedure described in clause 6.11.2.
The LMF returns the Nlmf_Location_DetermineLocation Response towards the AMF to return the current location of the UE and UE Positioning Capability if the UE Positioning Capability is received in step 8 including an indication that the capabilities are non-variable and not received from AMF in step 7. The service operation includes the LCS Correlation identifier, the location estimate, its age and accuracy and may include information about the positioning method and the timestamp of the location estimate.
If UE unaware indication is received from AMF in step 7 and the NG-RAN rejects the Network Positioning message as described in clause 6.11.2 with appropriate rejection cause (e.g. UE cannot be paged) in step 8, the LMF rejects the Nlmf_Location_DetermineLocation Request with appropriate rejection cause (e.g. UE cannot be paged).
The AMF returns the Namf_Location_ProvidePositioningInfo Response towards the GMLC/LRF to return the current location of the UE. The service operation includes the location estimate, its age and accuracy and may include information about the positioning method and the timestamp of the location estimate. The AMF stores the UE Positioning Capability in UE context when received from LMF.
If the AMF decides to skip steps 5 - 9 in step 5 based on the UE unaware indication and the UE state or the LMF rejects the Nlmf_Location_DetermineLocation Request with appropriate rejection cause (e.g. UE cannot be paged), the AMF may convert any last known location in the form of a cell ID or TAI into geographical information based on TS 23.032 and as defined in clause 188.8.131.52.5 of TS 29.518 and clauses 184.108.40.206, 220.127.116.11 and 18.104.22.168 of TS 29.571 and answer to the GMLC with the geographical information together with the age of this location.