Content for  TS 23.273  Word version:  18.5.0

The procedures and signalling specified in clause 6.2 of TS 23.586 are used to provision the Ranging/Sidelink positioning service authorization and policy/parameter provisioning to UEs 1 to n.

Based on a trigger of service request (e.g. received from the application layer), which includes UE1/.../UEn, UE discovery is performed for Ranging/Sidelink positioning as specified in clause 6.4 of TS 23.586:

• If UE1 is the target UE, UE1 discovers UEs 2 to n.

Secure groupcast and/or unicast links are established between UEs 1 to n to enable UE1 to exchange Ranging and Sidelink Positioning Protocol (RSPP) messages over PC5-U reference point with each of UEs 2 to n and possibly enabling UEs 2 to n to exchange RSPP over PC5-U between each other as defined in clause 5.3 of TS 23.586. Groupcast and/or unicast links are only established between UEs 1 to n that are registered in the same PLMN. Security mechanisms defined for V2X unicast mode communication in TS 33.536 and for 5G ProSe unicast mode Direct Communication in TS 33.503 are reused. The Security procedures for RSPP signalling using groupcast mode is specified in TS 33.533.

UE1 and UEs 2 to n may communicate over PC5 for authorization of Ranging/Sidelink positioning. Each UE verifies that Ranging/Sidelink positioning is permitted, including whether Ranging/SL positioning results may be transferred to an LCS Client or AF if this is used, according to any service authorization and policy/parameter provisioning received at step 1. This step is specified in TS 33.533.

The Ranging/Sidelink positioning capabilities exchange between UE-1 and UEs 2 to n is performed using SLPP message(s) as specified in TS 38.355 via the groupcast and/or unicast links established in step 3.

Based on the Ranging/Sidelink positioning capabilities of UE1/.../UEn, the target UE determines SL-MO-LR is to be performed.

If UE1 is in CM-IDLE state, UE1 instigates a UE triggered Service Request in order to establish a signalling connection with the serving AMF of UE1.

UE1 sends a supplementary services SL-MO-LR request message to the serving AMF in an UL NAS TRANSPORT message. The SL-MO-LR request indicates the other UEs 2 to n (using Application Layer ID), indicates any assistance data needed, indicates whether location calculation assistance is needed, and indicates whether location results should be transferred to an LCS client or AF. The message may include the identity of the LCS client or the AF and may include the address of the GMLC through which the LCS client or AF (via NEF) should be accessed. In addition, a Service Type indicating which MO-LR service of the LCS Client is requested by the UE may be included. For location calculation assistance from the LMF, the preferred type of Ranging/Sidelink positioning location results (e.g. absolute locations, relative locations or distances and directions between pairs of UEs, velocities and relative velocities) and the required QoS are included.

The serving AMF selects an LMF serving UE1 (e.g. an LMF that supports Ranging/Sidelink positioning) and sends an Nlmf_Location_DetermineLocation service operation towards the LMF with the information from the SL-MO-LR Request. The service operation includes a LCS Correlation identifier. AMF may include its stored information from step 21, the sidelink positioning capabilities of UE1 in the service operation.

The LMF may send a request to UE1 for the required capabilities of UEs 2 to n using supplementary service message with embedded SLPP message(s) as specified in TS 38.355 and the correlated application layer ID(s) for SLPP message(s) for UEs 2 to n. The LMF requests for the capabilities of UE1 by SLPP message. LMF may also provide the list of candidate Located UE(s), identified by the Application Layer ID by supplementary service message to UE1, if absolute location is requested at step 8. LMF also includes capabilities of each candidate Located UE in the request, if available, when Target UE selecting Located UE is indicated.

UE 1 returns its capabilities to the LMF using SLPP message as specified in TS 38.355 if requested by the LMF at step 10. UE1 may additionally return the capabilities of the other UEs if requested by the LMF at step 10 using supplementary service message(s) with embedded SLPP message(s) and the correlated Application Layer ID(s). UE1 requests the capabilities of UE2 to n separately using SLPP message over PC5 if step 5 is not performed. After checking the capabilities of the UEs, LMF may downselect the UEs (so called, down-selected list of UEs) for SL positioning operation. UE 1 also indicates the selected Located UE(s) to the LMF in the response.

If Target UE's absolute location information is required at step 8, LMF can either retrieved the location of the Located UE(s) locally if available or triggers 5GC-MT-LR procedure to the (V)GMLC to acquire the absolute location of the Located UE(s) using Application Layer ID of the Located UE(s). LMF may use the QoS requirement for Target UE's positioning received at step 8 to derive the required QoS for Located UE(s) positioning and includes the required QoS for Located UE positioning in the request to GMLC. If scheduled location time is used in step 15, LMF includes the same scheduled location time in the request to GMLC. (V)GMLC requests to retrieve the mapping of Application Layer ID to GPSI as specified in clause 4.3.9 of TS 23.586. If mapping of Application Layer ID to GPSI is not available for any of these Located UE(s), the UE(s) is considered as roaming UE. The (V)GMLC uses local configuration to get home PLMN ID. The (V)GMLC triggers 5GC-MT-LR procedure to the home GMLC of each of these roaming Located UE(s) to acquire the absolute location of the UE(s).

UE1 may send a request for specific assistance data to the LMF, if not requested in step 8.

• For the specific assistance data used by UE1, the request is transmitted by SLPP message.
• For the specific assistance data used by UE2/…/UEn, the request is transmitted by supplementary service message with embedded SLPP messages and correlated Application Layer IDs.

LMF sends the requested assistance data to UE1 and optionally a down-selected list of UEs using an SLPP message for UE1 assistance data and using supplementary service message(s) with embedded SLPP message(s) for UE 2 to n assistance data as specified in TS 38.355 and the correlated Application Layer ID(s). UE1 forwards the assistance data received from LMF to UE2/.../UEn (or the indicated downselection thereof) using SLPP messages as specified in TS 38.355. The assistance data may assist UEs 1 to n (or the indicated downselection thereof) to obtain Sidelink location measurements at step 16 and/or may assist UE1 to calculate Ranging/Sidelink positioning location results at step 18 and may include the absolute location(s) of Located UE(s) in case the LMF determines to use Network-assisted SL Positioning and if absolute location information is requested in step 8 and if sharing the location is allowed by the Located UE(s) privacy profile.

If the SL-MO-LR request at step 8 indicated location calculation assistance is needed and/or indicated transfer of Ranging/Sidelink positioning location results to an LCS Client or AF, the LMF sends a request for location information of UE1 by SLPP message and location information of UE2-UEn by supplementary service message. If LMF determines to apply Network-assisted Sidelink Positioning, LMF includes in the request the indication of Network-assisted Sidelink Positioning. If scheduled location time is not received at step 9. LMF may generate a scheduled location time, e.g. based on response time, and include the scheduled location time in the request.

UE1 performs a Ranging/Sidelink positioning procedure among UEs 1 to n (or the indicated downselection thereof) in which UEs obtain Sidelink location measurements and UEs 2 to n (or the indicated downselection thereof) transfer their Sidelink location measurements to UE1. If scheduled location time is received at step 15, Sidelink positioning/ranging is performed at the scheduled location time. This procedure is specified in TS 38.355.

For the case of Network-assisted SL Positioning (i.e., the indication of Network-assisted SL Positioning is received in step 15), if Target UE's absolute location information is required at step 8 and if absolute location of Located UE(s) is not available, the Target UE may send a supplementary services request to the Located UE(s) to request their locations. The Located UEs may already know their locations or may trigger 5GC-MO-LR procedure to acquire their own absolute location, after which a Located UE may provide the location of the Located UE to the Target UE if allowed by its privacy profile. The QoS requirement for Target UE's positioning, is used by the Target UE to derive the required QoS for Located UE(s) positioning. The required QoS for Located UE(s) positioning is included in the request.

If LMF determined in step 15 to use Network-assisted Sidelink Positioning, at least one of UE1/.../UEn calculates Ranging/Sidelink positioning location results based on the Sidelink location measurements obtained at step 16 and possibly using assistance data received at step 14 as specified in TS 38.355. The Ranging/Sidelink positioning location results can include absolute locations, relative locations i.e. distance and/or directions related to the UEs.

If UE1 received a request for location information at step 15, UE1 sends a response using supplementary service message with embedded SLPP message(s) as specified in TS 38.355 and the correlated Application Layer ID(s) for SLPP message(s) for UEs 2 to n to the LMF to include the Sidelink location measurements obtained at step 16 or the Ranging/Sidelink positioning location results obtained at step 18 if step 18 was performed. In the response message, UEs 2 to n (or the indicated downselection thereof) are identified by its Application Layer ID. If only UE1's location information is sent, UE1 sends a response using SLPP message for UE1 to LMF.

If the LMF will calculate location results, the LMF calculates Ranging/Sidelink positioning location results for the target UE based on the Sidelink location measurements received at step 19 and absolute location of Located UE(s) at step 12 or step 17. The Ranging/Sidelink positioning location results can include absolute locations, relative locations i.e. distance and/or directions related to the UEs, depending on the location request received in step 8.

The LMF returns an Nlmf_Location_DetermineLocation service operation response to the AMF and includes the Ranging/Sidelink positioning location results received at step 19 or calculated at step 20. The service operation may also contain the UE1's sidelink positioning capabilities if the capabilities are received in step 11 including an indication that the capabilities are non-variable and not received from AMF in step 9.

If Ranging/Sidelink positioning location results were received at step 21, the AMF performs steps 7-12 of clause 6.2 to send the Ranging/Sidelink positioning location results to the GMLC and to an AF or LCS Client if this was requested at step 8. The Ranging/Sidelink positioning location results include the identities for the respective UEs received at step 8. The AMF may store the UE1's sidelink positioning capabilities from step 21.

The AMF returns a supplementary services SL-MO-LR response to UE1 in a DL NAS TRANSPORT message and includes any Ranging/Sidelink positioning location results received at step 21 if the SL-MO-LR request at step 8 indicated location calculation assistance is needed.

The LCS Client or the AF (via NEF) sends an LCS service request to the (H)GMLC for Ranging/Sidelink Positioning location results for the n UEs which may each be identified by an Application Layer ID and/or a GPSI and/or a SUPI. The request may include the required QoS, the required location results (e.g. absolute locations, relative locations or distances and/or directions related to the UEs, velocities and relative velocities), the SL reference UE(s) in case of relative locations, distance, or direction, Located UE(s) and Coordinate ID defined in TS 38.455 representing a local coordinate in case of absolute locations. The information of UE initiating the Ranging/SL Positioning may be included to help (H)GMLC select the corresponding UE in step 3. The (H)GMLC or NEF authorizes the LCS Client or the AF for the usage of the LCS service. If the authorization fails, the remaining steps are skipped and the (H)GMLC or NEF responds to the LCS Client or the AF with the failure of the service authorization. In addition, an Application Layer ID shall be used for each of the n UEs to enable discovery of the UEs at step 12. If any of the UEs belongs to another PLMN, then (H)GMLC requests the Home GMLC of each of those UEs to retrieve the mapping information between Application Layer ID and GPSI. The Home GMLC of each of those UEs queries the NEF in its own PLMN for the mapping Application Layer ID as specified in clause 4.3.9 of TS 23.586.

The (H)GMLC invokes a Nudm_SDM_Get service operation towards the UDM of each of the n UEs to get the privacy settings of the UE identified by its GPSI or SUPI. The UDM returns the UE Privacy setting of the UE. The (H)GMLC checks the UE LCS privacy profile. If only the UE's SUPI is provided to the (H)GMLC, (H)GMLC can get the UE's GPSI along with the privacy settings. If Application layer IDs of the UEs are not provided to the (H)GMLC, the (H)GMLC can query the NEF for the mapping Application Layer ID as specified in clause 4.3.9 of TS 23.586. If any of UEs belong to another PLMN, then (H)GMLC sends a request to the Home GMLC of each of those UEs to check the Ranging/SL positioning privacy information of those UE(s) identified by GPSI or SUPI. The Home GMLC of each of those UEs queries the UDM in its own PLMN via Nudm_SDM_Get service operation to get the privacy settings of the UE and sends back the privacy check result to the (H)GMLC.

The (H)GMLC invokes a Nudm_UECM_Get service operation towards the UDM of each of the n UEs (for which GPSI or SUPI is available), one at a time, using the GPSI or SUPI of each UE. The (H)GMLC selects the UE (e.g. which is treated as UE1 in following steps) that initiates the Ranging/SL Positioning and selects the corresponding serving AMF, based on UE subscription and UE reachability. If the UE is not reachable, the (H)GMLC does not select such UE to initiate the Ranging/SL Positioning.

For a non-roaming case, this step is skipped. In the case of roaming, the (H)GMLC may receive an address of a (V)GMLC (together with the network address of the current serving AMF) from the UDM in step 3, otherwise, the (H)GMLC may use the NRF service in the (H)PLMN to select an available (V)GMLC in the (V)PLMN, based on the (V)PLMN identification contained in the AMF address received in step 3. The (H)GMLC then sends the location request to the (V)GMLC by invoking the Ngmlc_Location_ProvideLocation service operation towards the (V)GMLC. In the cases when the (H)GMLC did not receive the address of the (V)GMLC, or when the (V)GMLC address is the same as the (H)GMLC address, or when both PLMN operators agree, the (H)GMLC sends the location service request message to the serving AMF. In this case, step 4 is skipped. The (H)-GMLC also provides the LCS client type of AF, if received in step 1, or LCS client type of LCS client and other attributes to be sent to AMF in step 5.

In the case of roaming, the (V)GMLC first authorizes that the location request is allowed from this (H)GMLC, PLMN or from this country. If not, an error response is returned. The (H)GMLC or (V)GMLC invokes the Namf_Location_ProvidePositioningInfo service operation towards the AMF serving UE1 to request Ranging/Sidelink positioning location results of the n UEs. The service operation includes the SUPI of UE1, Application layer IDs of the UEs, the client type and may include the required LCS QoS, the required location results (e.g. relative locations i.e. distances and directions between pairs of UEs, velocities and relative velocities) and other attributes as received or determined in step 1.

If UE1 is in CM-IDLE state, the AMF initiates a network triggered Service Request procedure to establish a signalling connection with UE1. If signalling connection establishment fails, steps 7-17 are skipped.

If the indicator of privacy check indicates an action is needed, then same operation as that of step 7-8 of clause 6.1.2 is carried out.

The serving AMF selects an LMF serving UE1 (e.g. an LMF that supports Ranging/Sidelink Positioning) and sends an Nlmf_Location_DetermineLocation service operation towards the LMF with the information received at step 5 e.g. required location results (e.g. relative locations i.e. distances and directions between pairs of UEs velocities and relative velocities), SL reference UE(s) in case of relative locations, Located UE(s) in the case of absolute location, Application layer IDs of the UEs if received in step 5 and whether UE1 supports RSPP. The service operation includes a LCS Correlation identifier. The AMF may include its stored sidelink positioning capabilities of UE1 provided in step 17.

The LMF sends an SL-MT-LR request to the serving AMF as a supplementary services message, using the Namf_Communication_N1N2MessageTransfer service operation, and the session ID parameter is set to the LCS Correlation identifier. The SL-MT-LR request may include the Application Layer IDs of the other UEs 2 to n, the types of required location results (e.g. relative locations or distances and/or directions) and SL reference UE(s) in the case of relative locations. The SL-MT-LR request may include the Application Layer IDs of the other UEs 2 to n, the types of required location results (absolute location), Located UE(s) and Coordinate ID in the case of absolute locations.

The serving AMF forwards the SL-MT-LR request and a Routing identifier equal to the LCS Correlation identifier to UE1 using a DL NAS TRANSPORT message.

UE1 attempts to discover the other UE 2 to n using their Application Layer IDs, if not already discovered using procedure defined in clause 6.4 of TS 23.586.

UE1 obtains the required sidelink positioning capabilities of the discovered UEs via SLPP if not already obtained.

UE1 returns a supplementary services SL-MT-LR response to the serving AMF in an UL NAS TRANSPORT message and includes the Routing identifier received in step 11. Supplementary services message may include embedded SLPP message(s) which contain UEs' Ranging capabilities and the correlated Application Layer ID(s). The SL-MT-LR response indicates which of UEs 2 to n have been discovered and the sidelink positioning capabilities of the discovered UEs.

The serving AMF forwards the SL-MT-LR response to the LMF indicated by the Routing identifier received at step 14 and includes a LCS Correlation identifier equal to the Routing identifier.

Ranging/Sidelink Positioning of UE1 and the other discovered UEs occurs as for an SL-MO-LR as described for steps 12-20 of clause 6.20.1 with the difference that Ranging/Sidelink Positioning location measurement data or results are always returned to the LMF and the LMF indicates to UE1 at step 15 of clause 6.20.1 whether the Ranging/Sidelink Positioning location results will be calculated by the LMF (at step 20) or by UE1 (at step 18). For the undiscovered UEs or UEs for which the Ranging/Sidelink Positioning location measurements cannot be obtained based on their sidelink positioning capabilities among the other UEs 2 to n, the LMF may interact with GMLC to initiate the 5GC-MT-LR procedure using Application Layer ID for UE2 to n to get their absolute locations. In order to calculate the relative locations or distances and/or directions between UE1 and these UEs, if the absolute location of UE1 is not known yet, the LMF will trigger the 5GC-MT-LR procedure to derive the location of UE1. The LMF uses the absolute locations of all the UEs to calculate the relative locations or distances and/or directions between the pairs of these UEs. LMF may determine the Ranging/Sidelink Positioning location results in local coordinate if Coordinate ID is received in step 9. To fulfil the required QoS, the LMF may determine to use both Ranging/SL Positioning and Uu absolute Positioning to obtain the location results.

The LMF returns the Ranging/Sidelink positioning location results via AMF and GMLC to the LCS Client or AF as in steps 13-15 and step 24 of clause 6.1.2. The LMF result may also include the UE1's sidelink positioning capabilities if the capabilities are received in step 15 including an indication that the capabilities are non-variable and not received from the AMF in step 9. The results also include failure information of the UE(s) that was not discovered or the requested information was not possible to derive.