Content for  TS 23.273  Word version:  18.5.0

The Access Network is involved in the handling of various positioning procedures including positioning of a target UE, provision of location related information not associated with a particular target UE and transfer of positioning messages between an AMF or LMF and a target UE. The Access Network shall support determination of location estimates in geographical and/or local co-ordinates as defined in TS 23.032. In this version of the specification, location services are supported for NG-RAN and non-3GPP access. The LCS specific functionalities of the radio access network elements are specified in TS 38.305 for NG-RAN.

AFs and NFs may access LCS services from a GMLC in the same trust domain (e.g. in the same PLMN) using the Ngmlc interface or Event Exposure with location information from an AMF in the same trust domain using the Namf interface. The NWDAF collects UE location information by accessing GMLC directly. LCS Clients may access LCS services from a GMLC (e.g. HGMLC) using the Le reference point. External AFs may access LCS services from an NEF using Nnef interface or CAPIF API. The CAPIF and associated API provider domain functions are specified in TS 23.222. An LCS Client or AF may access LCS services from a UE over a user plane connection for reporting of location events by the UE for a periodic or triggered 5GC-MT-LR when the UE is able to determine location estimates.

The Gateway Mobile Location Centre (GMLC) contains functionality required to support LCS. In one PLMN, there may be more than one GMLC. A GMLC is the first node an external LCS client accesses in a PLMN (i.e. the Le reference point is supported by the GMLC). AFs and NFs may access GMLC directly or via NEF. The GMLC may request routing information and/or target UE privacy information from the UDM via the Nudm interface. After performing authorization of an external LCS Client or AF and verifying target UE privacy, a GMLC forwards a location request to either a serving AMF using Namf interface or to a GMLC in another PLMN using the Ngmlc interface in the case of a roaming UE. The target UE's privacy profile settings shall always be checked in the UE's home PLMN prior to delivering a location estimate. The "Visited GMLC" (VGMLC) is the GMLC, which is associated with the serving node of the target UE. The "Home GMLC" (HGMLC) is the GMLC residing in the target UE's home PLMN, which is responsible for the control of privacy checking of the target UE. Additional functions which may be performed by a GMLC to support location services include the following:

• At an HGMLC, determine the serving AMF for a target UE when there is more than one serving AMF.
• At an HGMLC, determine whether to attempt a second location request for a target UE from a different AMF when location information returned by a first AMF does not meet QoS requirements and there is more than one serving AMF.
• At an HGMLC, support location requests from an external LCS client or NEF for a 5GC-MT-LR and deferred 5GC-MT-LR for periodic, triggered and UE available location events.
• At an HGMLC, support additional check of whether the UE is located within the requested target area for deferred 5GC-MT-LR for periodic, triggered and UE available location events.
• At an HGMLC, forward location requests for a roaming UE to a VGMLC or serving AMF in the VPLMN based on deployment configurations.
• At an HGMLC, receive event reports from a VGMLC or LMF for a deferred 5GC-MT-LR for periodic or triggered location and return to an external LCS Client or NEF.
• At an HGMLC, support cancelation of a periodic or triggered location.
• At an HGMLC, receive location information from an VGMLC for a 5GC-MO-LR and forwards to an LCS Client or an AF (via NEF) if requested by the UE.
• At a VGMLC, receive location requests from an HGMLC for a roaming UE and forward to a serving AMF.
• At a VGMLC, receive event reports from an LMF for a deferred 5GC-MT-LR for periodic or triggered location for a roaming UE and forward to an HGMLC.
• At a VGMLC, receive location information from an AMF for a 5GC-MO-LR and forwards to an HGMLC.
• At an HGMLC, reject the LCS request coming from a LCS client, e.g. when the number of Target UEs in the LCS request exceeds the Maximum Target UE Number of such client.
• At an HGMLC, allocate the reference number for each location request from an external LCS client for LDR.
• At an HGMLC, assign the pseudonym if pseudonym indicator is received in the service request and transfer it to external LCS client, e.g. when core network provides the UE's location information to LCS client. Resolve the verinym from the pseudonym, if it is received from the LCS client.
• At an HGMLC, resolve group identifier to identifier of individual UEs and aggregate responses to LCS Client or NEF during bulk operation procedure.
• At an HGMLC, verify a request for user plane reporting by an LCS Client or AF for a periodic or triggered 5GC-MT-LR and verify or assign parameters to the request to enable the target UE to establish a secure user plane connection to the LCS Client or AF. Subsequently, support the transfer of cumulative event reports from the target UE via control plane back to the LCS Client or AF.
• During UE mobility between 5GS and EPS, the GMLC transfers the LCS request between 5GS and EPS, may map the LCS QoS and (re-)initiate the LCS sessions towards the 5GS to/from EPS.
• At an HGMLC, determine a reporting indication on how a target UE sends event reports when the UE is outside the event report allowed area based on LCS privacy profile data, LCS Client type, the type of periodic or triggered location reporting and associated parameters.
• Support aggregation of a single UE's location estimates over a period of time for a periodic or triggered 5GC-MT-LR event.
• At an HGMLC or a VGMLC, for a regulatory location service, support multiple location reports if requested by the LCS client.
• At an HGMLC, transform the universal location co-ordinates provided by the AMF into some local geographic reference system.

The Location Retrieval Function (LRF) may be collocated with a GMLC or separate and is responsible for retrieving or validating location information, providing routing and/or correlation information for a UE which has initiated an IMS emergency session. The information is provided by an LRF to an E-CSCF. For more details, refer to TS 23.167.

A target UE may support positioning according to four different modes:

• UE assisted mode (the UE obtains location measurements and sends the measurements to another entity (e.g. an LMF) to compute a location);
• UE based mode (the UE obtains location measurements and computes a location estimate making use of assistance data provided by serving PLMN);
• standalone mode (the UE obtains location measurements and computes a location estimate without making use of assistance data provided by serving PLMN);
• network based mode (a serving PLMN obtains location measurements of signals transmitted by a target UE and computes a location estimate).

Positioning procedures used by a UE for NG-RAN access are described in TS 38.305. A limited set of UE positioning capabilities and UE user plane positioning capabilities can be transferred to the 5GCN in the 5GMM capability during registration of the UE as described in TS 24.501. Some of these positioning capabilities may be transferred subsequently to an LMF as described in TS 29.572. UE positioning capabilities may also be transferred directly to a location server (e.g. LMF). Additional functions which may be supported by a UE to support location services include the following.

• Support location requests received from a network for 5GC-MT-LR, 5GC-NI-LR or a deferred 5GC-MT-LR for periodic or triggered location.
• Support location requests to a network for a 5GC-MO-LR.
• Support privacy notification and verification for a 5GC-MT-LR or deferred 5GC-MT-LR for periodic or triggered location.
• Send updated privacy requirements to a serving AMF (for transfer to a UDR via UDM).
• Support periodic or triggered location reporting to an LMF.
• Support change of a serving LMF for periodic or triggered location reporting.
• Support cancelation of periodic or triggered location reporting.
• Support multiple simultaneous location sessions.
• Support the reception of unciphered and/or ciphered assistance data broadcast by NG-RAN.
• Support the reception of ciphering keys for the assistance data from the AMF.
• Support handling of 5GC-MT-LR, 5GC-NI-LR, 5GC-MO-LR and deferred 5GC-MT-LR for periodic or triggered location over a user plane connection between UE and LMF.
• Support reporting of location events for a periodic or triggered 5GC-MT-LR over a user plane connection to an LCS Client or AF with periodic cumulative event reports being sent over control plane to the LMF, H-GMLC and LCS Client or AF.

The UDM contains LCS subscriber LCS privacy profile and routing information. The UDM is accessible from an AMF, GMLC or NEF via the Nudm interface. The UDM may also contain an indication whether a UE is allowed to serve as a PRU and indication whether PRU is stationary PRU as part of the UE subscription data. The UDM may also contain LMF identifier(s) and indication of user plane positioning between UE and LMF in UE LCS subscription data.

The AMF contains functionality responsible for managing positioning for a target UE for all types of location request. The AMF is accessible to the GMLC and NEF via the Namf interface, to the RAN via the N2 reference point and to the UE via the N1 reference point. Functions which may be performed by an AMF to support location services include the following.

• Initiate an NI-LR location request for a UE with an IMS emergency call or to know a UE geographical area with NR satellite access for PLMN selection verification.
• Receive and manage location requests from a GMLC for a 5GC-MT-LR and deferred 5GC-MT-LR for periodic, triggered and UE available location events.
• Receive and manage location requests from a UE for a 5GC-MO-LR.
• Receive and manage Event Exposure request for location information from an NEF.
• Select an LMF.
• Receive updated privacy requirements from a UE and transfer to a UDR via UDM.
• Support cancelation of periodic or triggered location reporting for a target UE.
• Support change of a serving LMF for periodic or triggered location reporting for a target UE.
• When assistance data is broadcast by 5GS in ciphered form, the AMF receives ciphering keys from the LMF and forwards to suitably subscribed UEs using mobility management procedures.
• Store UE Positioning Capability received from an LMF and send the UE Positioning Capability along with the received location request to an LMF.
• Receive and store UE user plane positioning capabilities (the user plane positioning using LCS-UPP and/or the user plane positioning using SUPL [49]) as part of the "5GMM capability" from UE.
• Receive UL NAS Transport including a PRU Association, Association Update, or Disassociation Request (contained in an LCS supplementary service message) from a UE.
• AMF may verify whether a UE can serve as a PRU based on UE subscription data after receiving the PRU Association Request, Association Update, or Disassociation. AMF may also use local policy to determine if UEs are allowed to serve as a PRU. AMF may verify based on subscription information or local policy if PRU can work as stationary PRU.
• Sends the PRU Association Request or PRU Disassociation Request to LMF and may include a UE verification indication indicating whether this UE is authorized to serve as a PRU.
• Support verifying whether UE is subscribed with user plane positioning between UE and LMF and triggering LMF to establish a User Plane Connection to UE if UE requested that.
• Support subscribing from LMF status of LCS user plane connection between a UE and the LMF.
• Store in UE context that UE has a maintained User Plane connection with certain LMFs.
• Support of local configuration of a mapping table of UE identifier ranges and LMF identifier(s) or querying the UDM the LMF identifier for a UE for a 5GC-MO-LR.
• Support the 5G to EPS Handover by providing the target MME ID to GMLC as part of the LCS Service response.
• Support interaction with NWDAF to obtain UE related analytics to assist with UE location verification for NR satellite access.

The LMF manages the overall co-ordination and scheduling of resources required for the location of a UE that is registered with or accessing 5GCN. It also calculates or verifies a final location and any velocity estimate and may estimate the achieved accuracy. The LMF receives location requests for a target UE from the serving AMF using the Nlmf interface. The LMF interacts with the UE in order to exchange location information applicable to UE assisted and UE based position methods and interacts with the NG-RAN, N3IWF or TNAN in order to obtain location information. The LMF shall determine the result of the positioning in geographical co-ordinates as defined in TS 23.032 and/or in local co-ordinates as defined in TS 23.032. If requested and if available, the positioning result may also include the velocity of the UE. The coordinate type(s) is determined by LMF when receiving a location request, based on LCS Client type and supported GAD shapes. If the location request indicates regulatory LCS Client type the LMF shall determine a geographical location and optionally a location in local coordinates. For location request indicates a value added LCS Client type, the LMF may determine the UE location in local coordinates or geographical co-ordinates or both. If the supported GAD shapes is not received or Local Co-ordinates is not included in the supported GAD shapes, the LMF shall determine a geographical location. Additional functions which may be performed by an LMF to support location services include the following.

• Support a request for a single location received from a serving AMF for a target UE.
• Support a request for periodic or triggered location received from a serving AMF for a target UE.
• Determine type and number of position methods and procedures based on UE and PLMN capabilities, QoS, UE connectivity state per access type, LCS Client type, co-ordinate type and optionally service type and indication of requiring reliable UE location information.
• Report UE location estimates directly to a GMLC for periodic or triggered location of a target UE.
• Support cancelation of periodic or triggered location for a target UE.
• Support the provision of broadcast assistance data to UEs via NG-RAN in ciphered or unciphered form and forward any ciphering keys to subscribed UEs via the AMF.
• Support change of a serving LMF for periodic or triggered location reporting for a target UE.
• Support of receiving stored UE Positioning Capability from AMF and support of providing updated UE Positioning Capability to AMF.
• Map the UE location to a geographical area where the PLMN is or is not allowed to operate based on the request from AMF.
• Support determination of a UE location at a scheduled location time.
• Support determination of indoor or outdoor for a location estimate.
• Determine whether to use user plane or control plane for positioning.
• Support handling of 5GC-MT-LR, 5GC-NI-LR, 5GC-MO-LR and deferred 5GC-MT-LR for periodic or triggered location over a user plane connection between UE and LMF over TLS.
• Support collection of GNSS assistance data from AFs.
• Support service level PRU Association, PRU Association update or PRU Disassociation.
  • LMF supports verification of a PRU initiated Association or Disassociation by checking whether there is an PRU verified indication from AMF.
  • LMF stores the received PRU information contained in service level PRU Association message and removes the PRU information after PRU Disassociation.
  • LMF keeps PRU information for PRUs which are in OFF state.
  • LMF may indicate support of PRU function to NRF via NF profile and may further send the PRU indication via NF profile update if PRU is stationary PRU.
  • LMF may request a PRU to associate to a new LMF by returning a Routing ID of the new LMF.
  • PRU ON/OFF states indicate temporarily availability of the PRU functionality of a UE at the serving LMF (e.g. PRU OFF due to other high priority tasks/energy saving at the UE, or the UE temporarily loses network coverage).
• Support selection of a PRU based on stored PRU information if the LMF needs to obtain the location measurements from the PRU to assist positioning of a target UE.
• Support to obtain PRU location measurements as described in clause 5.4.5 of TS 38.305 by triggering the procedure in clause 6.11.
• Support to obtain PRU location measurements from other PRU serving LMF(s).
  • As a serving LMF of target UE(s), support discovery and selection of other PRU serving LMF(s) by querying the NRF and support to request PRU location measurements from the selected LMF(s).
  • As a serving LMF of PRU(s), support to provide PRU location measurements to other LMF(s) after receiving a request from other LMF(s).
• Support to determine UE location by considering obtained PRU location measurements.
• Support a request for user plane reporting from a UE to an LCS Client or AF for a periodic or triggered 5GC-MT-LR. Subsequently, support the transfer of cumulative event reports from the target UE via control plane back to the H-GMLC and LCS Client or AF. Also support any request for assistance data received in a cumulative event report.
• Determine UE location for a UE connecting to a MBSR based on location and velocity of the MBSR and the timing of the location estimations for the target UE and MBSR.
• For a regulatory location service, support reporting of multiple INTERMEDIATE location estimates to GMLC.

An NEF provides a means of accessing location services by an external AF or internal AF. AFs access location services from an NEF using an API. Depending on QoS requirements, an NEF can forward a location request to a GMLC or request an event exposure for location information from serving AMF (optionally via a UDM). When event exposure via AMF is used, an NEF may request routing information and/or target UE privacy information from the UDM via the Nudm interface. Additional functions which may be performed by an NEF to support location services include the following.

• Support location requests from an AF for immediate location and for deferred periodic and triggered location events.
• Support location information exposure to an AF based on the location request.
• Support determination of GMLC or AMF based on e.g. the QoS requirements from AF, type of the location request.
• Select the serving AMF for a target UE when there is more than one serving AMF.
• Determine whether to attempt a second location request for a target UE from a different AMF when location information returned by a first AMF does not meet QoS requirements and there is more than one serving AMF.
• Support UE LCS privacy profile provision from the AF.
• Support suspending and cancellation of a periodic or triggered location request.
• Support authorization of LCS request from the AF.
• Support rejecting the LCS request coming from an AF, e.g. when the number of Target UEs in the LCS request exceeds the Maximum Target UE Number of such client.
• Support allocating the reference number for each location request from an AF for LDR.

The UDR contains privacy data information for target UEs and may be updated by a serving AMF via UDM with new privacy information received from a UE.

A UE may support the functions of a PRU. The PRU supports the following functions including functions defined in TS 38.305:

• Support service level association, association update and disassociation with a serving LMF.
  • The PRU sends service level association, association update or disassociation to LMF via LCS supplementary service message.
  • Support association with multiple LMFs. e.g. for the case a PRU is in multiple LMF overlapped serving areas.
  • The PRU information included in a PRU association or PRU association update contains one or more than one of the following aspects:
    • PRU Positioning Capabilities.
    • Location information if known.
    • PRU ON/OFF state.
  PRU ON/OFF states indicate temporarily availability of the PRU functionality of a UE at the serving LMF.

A UE accesses 5G network via NR satellite shall not operate as a PRU.

In addition to the functions defined in TS 23.501, the NRF may perform the following functions:

• Support to store or update PRU existence indication in TAI level in LMF profile based on request from PRU serving LMF.
• Support LMF(s) with PRU function discovery by AMF.
• LMF discovery by considering user plane Positioning Capability.
• Support LMF(s) associated with PRUs discovery by other LMF(s), according to target area in the discovery request and the LMF profiles with PRU existence indication in TAI level.

The Le reference point supports location requests sent by an LCS Client to a GMLC or LRF. The Le reference point may be supported using the Mobile Location Protocol (MLP) defined by OMA [13].

The NL3 reference point supports location requests forwarded by an HGMLC to a VGMLC.

The N1 reference point supports transfer of supplementary services messages between a serving AMF and target UE to support privacy notification and verification and change of UE privacy preference. The N1 reference point also supports transfer of positioning protocol messages and location event reports between a target UE and an LMF via a serving AMF. The N1 reference point supports the transfer of ciphering keys from an AMF to a suitably subscribed UE to enable the UE to receive ciphered broadcast assistance data. All messages sent over the N1 reference point for support of location services are encapsulated in NAS Transport messages as defined in TS 24.501.

The N2 reference point supports transfer of positioning messages, via an AMF, between an LMF and a RAN node, or N3IWF in the case of untrusted non-3GPP access. The N2 reference point also supports transfer of messages, via an AMF, from an LMF to an NG-RAN node, which carry assistance data to be broadcast by the NG-RAN node. Positioning messages relevant to the N2 interface are defined in TS 38.455.

The NL5 reference point supports location requests sent by an NEF or other NF to a GMLC.

The NL2 reference point supports location requests sent by a GMLC to a serving AMF for a target UE. Messages for the NL2 reference point are defined in TS 29.518.

The NL6 reference point supports queries from an HGMLC to a UDM for privacy subscription information for a target UE and routing information for a target UE.

The N51 reference point supports queries from an NEF to a serving AMF for the location of a target UE. Messages for the N51 reference point are defined in TS 29.518.

The NL1 reference point supports location requests for a target UE sent from a serving AMF for the target UE to an LMF. Location requests are supported for immediate location and for deferred location for periodic or triggered location events. The NL1 reference point also supports the transfer from an LMF to an AMF of ciphering keys and associated data that enable deciphering by suitably subscribed UEs of ciphered broadcast assistance data. Messages for the NLI reference point are defined in in TS 29.518 and TS 29.572.

The N52 reference point supports queries from an NEF to a UDM for privacy subscription information for a target UE and routing information for a target UE. The N52 interface also supports a request from an NEF to a UDM to forward a location request from the NEF to a serving AMF for the target UE.

The NL7 reference point supports location context transfer between two LMFs.

The NL8 reference point supports LMF to receive location related analytics from NWDAF as defined in TS 23.288.

The NL9 reference point supports location requests sent by NWDAF to a GMLC.

The NL10 reference point supports LMF to send location requests to GMLC in case of 5GC-MT-LR involving MBSR. Additionally, this reference point is used by LMF to send location result directly to GMLC in case of Deferred Location or 5GC-MT-LR multiple location or in case of support for PNI-NPN architecture.