Description
The Location Management Function (LMF) is a critical component of the 5G Core Network's location service architecture, defined as a Network Function (NF) within the Service-Based Architecture (SBA). It is the primary entity responsible for orchestrating all positioning-related activities to determine the geographical location of a User Equipment (UE). The LMF receives location service requests from other network functions, such as the Gateway Mobile Location Centre (GMLC) for external applications or the Access and Mobility Management Function (AMF) for network-initiated requests. Upon receiving a request, the LMF initiates a positioning session with the target UE and the Radio Access Network (RAN).
The LMF's operation involves several key steps. First, it selects the appropriate positioning method based on the requested Quality of Service (QoS), UE capabilities, and network conditions. Supported methods include LTE/5G NR downlink and uplink techniques like Observed Time Difference of Arrival (OTDOA), Uplink Time Difference of Arrival (UTDOA), Multi-Cell Round Trip Time (Multi-RTT), and Assisted Global Navigation Satellite System (A-GNSS). The LMF coordinates with the NG-RAN (Next Generation RAN) via the AMF using the NLs interface to instruct gNBs to perform necessary measurements (e.g., timing measurements for OTDOA) or to configure positioning reference signals. For UE-based methods, the LMF may provide assistance data (e.g., satellite ephemeris, base station almanac) to the UE to facilitate its own position calculation.
Architecturally, the LMF exposes service-based interfaces, primarily Nlmf_Location, to other NFs. It interacts with the AMF (Nlmf_Location service) to reach the UE and RAN, and with the GMLC (Ngl interface) for external location requests. The LMF also interfaces with the Unified Data Management (UDM) for subscriber data and policy retrieval. It performs the location calculation by processing measurement reports received from the RAN (e.g., gNB measurements) and/or the UE. The final location estimate, which can be in the form of geographical coordinates (latitude, longitude) with an uncertainty ellipse, is then returned to the requesting entity.
Beyond basic positioning, the LMF supports advanced features such as periodic and triggered location reporting, velocity estimation, and barometric sensor data fusion for vertical positioning. It also handles error cases, fallback procedures, and QoS negotiation. In a network slicing context, the LMF can be instantiated as part of a slice to provide dedicated location services for specific verticals (e.g., high-accuracy positioning for factory automation). Its design emphasizes scalability, low latency, and support for diverse use cases from mass-market consumer services to mission-critical industrial applications.
Purpose & Motivation
The LMF was introduced in 3GPP Release 15 as part of the new 5G System (5GS) to provide a unified, flexible, and enhanced location management capability. It addresses the limitations of previous generations (e.g., 4G E-SMLC) by being natively integrated into the 5G Service-Based Architecture, offering improved scalability, lower latency, and support for new radio technologies like 5G NR. The shift to a cloud-native, microservices-based design allows the LMF to be deployed dynamically to meet varying service demands.
Its creation was driven by the need for more accurate and reliable location services to support emerging 5G use cases. These include Vehicle-to-Everything (V2X) communication for autonomous driving, which requires cm-level accuracy; Industrial IoT for asset tracking and automation; and enhanced emergency services (e.g., Advanced Mobile Location) mandated by regulators. The LMF provides the core intelligence to coordinate multiple positioning sources and methods to meet these stringent requirements.
Furthermore, the LMF enables network operators to offer location as a service to third-party application providers in a standardized and secure manner. By centralizing positioning coordination, it reduces complexity in the RAN and UE, allows for optimized resource usage, and facilitates the introduction of new positioning technologies (like sidelink positioning) in future releases. It is a foundational element for realizing 5G's vision of pervasive, high-precision location awareness.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (498 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the LMF (Location Management Function) was newly introduced as the core network function for 5G location services, supporting procedures like Network Induced, Mobile Terminated, and Mobile Originated Location Requests. It was defined with specific services such as ProvideLocationInfo and ProvidePositioningInfo, and it manages deferred location requests including area event and periodic location reporting. The release also established the LMF's role in privacy verification and its interaction with the AMF for network-initiated localization, such as for emergency calls.
- Network Provided Location for non-3GPP access TS 23.501CR0078
- User Plane management to support interworking with EPS TS 23.501CR0122
- Clarification on location reporting for LADN in RRC Inactive clause 5.3.3.2.5 - TS 23.501 TS 23.501CR0136
- Management of service area restriction information TS 23.501CR0144
- Corrections to PFD management TS 23.501CR0210
- SMF getting UE location from the AMF for NPLI when no QoS Flow to create/Update/modify TS 23.501CR0266
+ 31 more changes
In Release 16, the LMF saw significant enhancements for commercial and deferred Mobile Terminated Location Requests (5GC-MT-LR), with new, dedicated LMF service operations defined for these request types. The release also introduced a specific Location Privacy Setting operation and expanded location information support for trusted non-3GPP access. Furthermore, procedures were added for LMF identification during an LMF change and for the AMF to forward location services messages between the UE and LMF.
- Support of Concurrent Location Request TS 23.273CR0006
- 5GS Logical TSN bridge management TS 23.501CR1002
- Location information TS 23.501CR0941
- Further detailing of 5G LAN group management TS 23.501CR1052
- Location information for trusted N3GPP TS 23.501CR1420
- Addition of location service message condition to Additional informaton IE TS 24.501CR1336
+ 101 more changes
In Release 17, key enhancements for the LMF included the introduction of a **Scheduled Location Time** for deferred location requests and the support for **UE Location Trends** event monitoring. The release also added the capability for the **GMLC to use the AMF event exposure service** and introduced the concept of **Local Location** based on local coordinates. Furthermore, higher resolution timestamps for location estimates were standardized to improve accuracy.
- Introduction of the Scheduled Location Time TS 23.273CR0187
- Addition of a Scheduled Location Time TS 23.273CR0151
- Adding the usage of Session Management Congestion Control Experience analytics TS 23.501CR2708
- The impact on UE due to the introduction of Authentication and Key Management for Applications (AKMA) TS 24.501CR2794
- UE's handling of the indication of country of UE location TS 24.501CR3219
- Clarify mobility management based on NSAC per access type independently TS 24.501CR3516
+ 88 more changes
In Release 18, the LMF saw several key enhancements including the introduction of a local LMF and GMLC selection feature, procedures for positioning over the user plane connection between UE and LMF, and support for AMF reselection of LMF for user plane positioning. It also added verification of location for Non-Terrestrial Network (NTN) access and introduced enhancements for triggered location reporting for UE power saving. Furthermore, the release expanded LMF interactions by including NWDAF as a GMLC service and enabling NWDAF-assisted LMF positioning method determination.
- Multiple location report for MT-LR Immediate Location Request for the regulatory service TS 23.273CR0237
- Support of Mobile Base Station Relay for Location Service TS 23.273CR0240
- UE location reporting only when the UE locates in the target area defined with finer granularity TS 23.273CR0242
- Privacy Check for NWDAF requesting UE location from GMLC TS 23.273CR0249
- Introduce new feature: local LMF and GMLC selection TS 23.273CR0254
- Verification of location for NTN access TS 23.273CR0258
+ 182 more changes
In Release 19, the LMF was enhanced to support AI/ML-based positioning, including procedures for LMF-based AI/ML positioning, ML model retrieval, and ML model performance monitoring. New procedures were also introduced for deferred MT-LR based on NRPPa periodic measurement reports and for enhanced data collection by the LMF. Additionally, support was added for location services for UEs served by a Mobile Wireless Access Binder (MWAB) and for reporting UE location trends at RAN node granularity.
- KI#1 - LMF enhancements for UE positioning using a ML model TS 23.273CR0532
- Introduction of LMF enhancement for Direct AI/ML based Positioning TS 23.273CR0543
- LMF enhancements for LMF-based AI/ML Positioning TS 23.273CR0574
- Update on Data Collection by LMF procedure TS 23.273CR0584
- Adding Deferred 5GC-MT-LR Procedure for Periodic Location Events based NRPPa Periodic Measurement Reports TS 23.273CR0589
- Support AI/ML model performance monitoring by LMF TS 23.273CR0595
+ 66 more changes
Explore further
Broader topics and technologies where LMF plays a role.
Defining Specifications
3GPP specifications that define or reference LMF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.273 vj50 | 5G Location Services Stage 2 Architecture | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.571 vj20 | Control Plane LCS Procedures | Rel-19 |
| TS 24.572 vj50 | 5G LCS User Plane Protocol Specification | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 29.517 vj40 | 5G AF Event Exposure Service Stage 3 | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.552 vj40 | 5G Network Data Analytics Signalling Flows | Rel-19 |
| TS 29.572 vj50 | Nlmf Service Based Interface Stage 3 | Rel-19 |
| TS 29.574 vj40 | 5G Data Collection Coordination Services Stage 3 | Rel-19 |
| TS 29.576 vj40 | 5G Messaging Framework Adaptor Services Stage 3 | Rel-19 |
| TS 29.591 vj40 | 5G NEF Southbound Services Stage 3 | Rel-19 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | Rel-19 |
| TS 33.533 vj00 | Security for 5G Ranging & Sidelink Positioning | Rel-19 |
| TS 33.814 vg01 | Security aspects of enhanced Location Services (eLCS) | Rel-16 |
| TR 33.893 vi01 | Security and Privacy Aspects of Ranging and Sidelink Positioning | Rel-18 |
| TS 37.171 vj00 | UE Positioning Performance Requirements | Rel-19 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 38.171 vj10 | 5G A-GNSS UE Positioning Requirements | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.355 vj00 | Sidelink Positioning Protocol (SLPP) | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TS 38.843 vj00 | Study on AI/ML for NR Air Interface | Rel-19 |
| TS 38.856 vg00 | Study on local NR positioning in NG-RAN | Rel-16 |
| TR 38.857 vh00 | Study on NR Positioning Enhancements | Rel-17 |