The periodic and triggered SL-MT-LR procedure is based on SL-MT-LR procedure in clause 6.20.3, and used to estimate the relative locations or distances and/or directions between the UEs periodically or following certain trigger events. LCS Client or AF to obtain Ranging/Sidelink Positioning location results for a group of n UEs (n ≥ 2), i.e. UE1, UE2, ..., UEn either periodically or when certain trigger events occur.
Besides relative locations, ranges, directions as defined in clause 6.20.3, for periodic and triggered SL-MT-LR procedure, and the Ranging/Sidelink Positioning location results may additionally include velocities and relative velocities related to the UEs based on the service request. Figure 6.20.4-1 illustrates the procedure.
The LCS service request further includes periodic or trigger event parameters. For periodic location, the LCS Service Request includes the time interval between successive location reports and the total number of reports. For triggered location. the LCS Service Request includes details of the trigger event, the duration of event reporting, the minimum and maximum time intervals between successive event reports, the maximum event sampling interval, whether location estimates shall be included in event reports, and whether only one location report is required or more than one. Trigger events can be one of the following;
ranging event with range threshold and threshold type (a, b, c or d): a trigger event occurs if the ranges between at least one UE of the n UEs and each of the other UEs are such that any range for the one UE is less than the threshold (type a), any range for the one UE exceeds the threshold (type b), all ranges for the one UE are less than the threshold (type c), or all ranges for the one UE exceed the threshold (type d).
In the message sent by (H)GMLC, the (H)GMLC also includes a contact address for the (H)GMLC (Notification Target Address, e.g. a URI) and an LDR reference number (Notification correlation ID) to be used for event reporting at steps 24-31 defined for periodic and triggered SL-MT-LR procedure only. The LDR reference number is either allocated by (H-)GMLC based on predefined rule or allocated by NEF, if the location request is sent by an NEF at step 1.
The message Namf_Location_ProvidePositioningInfo service operation towards the AMF is to request periodic or triggered Sidelink positioning/ranging location results of the n UEs. The service operation further includes the periodic or trigger event parameters and other attributes as received or determined in steps 1 and 4.
The LMF sends a Periodic-Triggered SL-MT-LR request to the serving AMF. The LCS Periodic-Triggered SL-MT-LR request further includes a deferred routing identifier, which can be the identification of the LMF when the LMF will act as a serving LMF or a default LMF identification otherwise. The LCS Periodic-Triggered SL-MT-LR request may include the QoS and allowed or required location results at step 24 for each location event reported. The LCS Periodic-Triggered SL-MT-LR request also includes the application IDs of UEs 1 to m, the address for the (H)GMLC and LDR reference number. The LCS Periodic-Triggered SL-MT-LR request also includes the identities of the target UEs. The requested location results (e.g. absolute locations, relative locations, ranges, directions, velocities and relative velocities) for the target UEs and QoS.
The SL-MT-LR response from UE1 is Periodic-Triggered, and Routing identifier is immediate Routing identifier. The supplementary services Periodic-Triggered SL-MT-LR response indicates whether UE1 and other UEs 2 to m accept the periodic or triggered location request and which of UEs 2 to m were discovered by UE1 at step 12.
The Sidelink positioning/ranging location results returned by LMF to LCS Client is initial one.
The following additional steps are dedicated for Periodic and Triggered SL-MT-LR Procedure:
21. The UEs 1 to m periodically perform Sidelink positioning/ranging in order to support steps 22 and 24.
UE1 monitors for occurrence of the trigger or periodic event requested in step 11. For a trigger event, UE1 monitors the requested event at intervals equal to or less than the maximum event sampling interval. An event trigger is detected by UE1 when any of the following occur: (i) a requested non-periodic trigger event has been detected and the minimum reporting time interval has elapsed since the last report (if this is not the first event report); (ii) a requested periodic location event has occurred; or (iii) the maximum reporting time for a non-periodic trigger event has expired.
UE1 sends a supplementary services event report message to the serving AMF using the Namf_Communication_N1N2MessageTransfer service operation, and includes the deferred Routing ID received in step 11. The event report indicates the type of event being reported (e.g. whether a normal event or expiration of the maximum reporting interval) and may include location results obtained at step 21. UE1 also includes the (H)GMLC contact address, the LDR reference number, whether location results are to be reported and if so the location QoS in the event report.
When the LMF receives the event report and if it can handle this event report, the LMF updates the status of event reporting (e.g. the number of event reports so far received from UE1 and/or the duration of event reporting so far) and returns a supplementary services acknowledgment for the event report to the serving AMF using the Namf_Communication_N1N2MessageTransfer service operation, and a Correlation ID identifying the LMF. The acknowledgment may optionally include a new deferred routing identifier indicating a new serving LMF or a default (any) LMF.
The serving AMF forwards the event report Ack and an immediate Routing ID equal to the Correlation ID to UE1 using a DL NAS TRANSPORT message. If UE1 does not receive any response from the LMF after a predefined time, i.e. the current LMF does not support the deferred location request (for temporary or permanent reasons) or due to some radio access failures, UE1 may re-send the report one or more times.
The procedure is used to estimate the location of a UE by using the location of one or more Located UEs and the distance and/or direction between the UE and the Located UE(s).
Procedure of Figure 6.1.2-1 can be reused, with step 12 of Figure 6.1.2-1 replaced by the step 10-16 of Figure 6.20.3-1 with the following adaptations:
UE1 is the target UE, and UEs 2 to n are Located UEs.
In step 10, the types of required location results is absolute solution, and the other UEs 2 to n are the candidate Located UE(s) if included. SL-MT-LR request also includes the indication of Target UE/LMF selecting Located UE.
In step 14, if UE1 receives the indication of LMF selecting Located UE in step 11, step 14 includes the obtained information of all the discovered Located UEs. If UE1 receives the indication of Target UE selecting Located UE in SL-MT-LR request, UE1 performs the Located UE selection, and SL-MT-LR response includes the selected Located UEs ID.