Description
The Positioning Calculation Function (PCF) is a critical component of the 3GPP Location Services (LCS) architecture, responsible for the computational aspect of determining a mobile device's location. It acts as the 'engine' of the positioning system. The PCF receives raw measurement data and requests from the Gateway Mobile Location Center (GMLC) or other Location Management Functions (LMF in 5GC). Its primary task is to select an appropriate positioning method, retrieve the necessary measurements, perform the location calculation, and return an estimated position (latitude, longitude, altitude) with an associated accuracy and confidence level.
The PCF supports multiple standardized positioning methods, each with its own calculation algorithm. For Observed Time Difference of Arrival (OTDOA), the PCF receives measurements from the UE of observed time differences between reference signals from neighboring cells. It uses a database of known cell transmitter locations and timing relationships to solve hyperbolic equations for the UE's position. For Uplink Time Difference of Arrival (UTDOA), the PCF processes time-of-arrival measurements of the UE's uplink signal taken by multiple Location Measurement Units (LMUs) in the network. For Assisted GNSS (A-GNSS), the PCF may assist by providing satellite ephemeris and almanac data to the UE and then calculating a position based on pseudo-range measurements sent by the UE. For Enhanced Cell ID (E-CID), the PCF combines the serving cell identity with additional measurements like Round Trip Time (RTT), Angle of Arrival (AoA), or received signal levels to refine the location estimate.
Architecturally, the PCF interfaces with several network elements. It communicates with the Radio Access Network (RAN) via the Serving Mobile Location Center (SMLC) in UMTS/GSM or the LMF in 5GC to obtain network-based measurements or to instruct the RAN/UE to perform measurements. It may also access external data sources, such as GNSS reference networks for A-GNSS assistance data or geographic information systems. The PCF's role is purely computational and logical; it does not directly interact with the UE or perform radio measurements itself. Its output is delivered to the requesting entity (e.g., GMLC), which then formats and provides the location to the final LCS client, which could be an emergency service, a commercial application, or a network operator's own service.
Purpose & Motivation
The PCF was developed to provide a standardized, network-based capability for determining the location of mobile devices, driven primarily by regulatory requirements for emergency caller location (e.g., E911 in the US, E112 in Europe) and the growing commercial demand for Location-Based Services (LBS). Early mobile networks had very crude location capabilities, often limited to identifying the serving cell, which could cover a radius of several kilometers, making it useless for emergencies or precise services.
The creation of a dedicated calculation function separated the complex, mathematical task of location computation from the management and client-handling functions (GMLC). This modular architecture allowed for the independent evolution and optimization of positioning technologies. The PCF enabled the introduction of more accurate methods like OTDOA and A-GNSS, which required sophisticated signal processing and calculation algorithms that were not feasible to implement in a distributed manner across other network nodes.
By centralizing the calculation logic, the PCF provides a consistent interface for location requests regardless of the underlying positioning method used. This abstraction allows the network to select the best available method (e.g., A-GNSS outdoors, OTDOA indoors) based on capability, accuracy requirements, and UE/network conditions, without the requesting client needing to understand the technical details. The PCF's evolution reflects the continuous push for higher accuracy, lower latency, and support for new use cases, from emergency services to IoT asset tracking and vehicular positioning in 5G.
Architecture
In the Network Map
- Mobile Network → 5G Core → PCF (Policy & Charging)
Evolution Lineage
- Evolved from: PCRF (4G→5G)
- Network evolution overview →
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (222 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the PCF (Positioning Calculation Function) saw its role in the 5G system architecture formalized with new service-based interfaces, specifically the Npcf_UEPolicyControl and Npcf_EventExposure services. The release introduced updates for PCF discovery and selection procedures, now considering network slice information, and provided clarifications on its interactions within the reference architecture, including with the SMF. Additionally, procedures for PCF-initiated policy association termination and resource cleanup were corrected and specified.
- Clarification on PCF selection TS 23.501CR0015
- Alignment of PCF selection description TS 23.501CR0435
- Update to PCF discovery and selection TS 23.501CR0597
- Interactions with PCF - Updates to reference architecure for interworking TS 23.501CR0639
- Clarification on DN authorization data between PCF and SMF TS 23.501CR0726
- Addition of PCF services Npcf_UEPolicyControl and Npcf_EventExposure TS 23.501CR0904
+ 23 more changes
In Release 16, the PCF (Positioning Calculation Function) saw no new functional updates; the provided Change Requests and grounding context exclusively pertain to the Policy Control Function, which shares the same PCF acronym. The listed CRs describe enhancements for the Policy Control Function, such as integration with IMS over the N5 interface, support for TSN/TSC assistance information transport, and refined selection procedures for ATSSS and eSBA.
- Allowing IMS to use N5 interface to interact with PCF TS 23.228CR1203
- Additional corrections for allowing IMS to use N5 interface to interact with PCF TS 23.228CR1204
- eSBA communication schemas related to PCF discovery and selection TS 23.501CR0802
- Allowing IMS to use N5 interface to interact with PCF TS 23.501CR1134
- 23.501 part of PCF selection for PDU sessions with same DNN and S-NSSAI TS 23.501CR1375
- Transport of TSN information and containers between SMF and PCF TS 29.512CR0368
+ 48 more changes
In Release 17, the PCF (Policy Control Function) saw enhancements focused on its discovery mechanisms and its integration with analytics and new services. Key developments included the completion of PCF discovery procedures, support for PCF discovery in MBS (Multicast Broadcast Service) PCC deployments, and enabling the PCF to act as a consumer of network analytics from the NWDAF. Furthermore, the PCF was extended to support service experience analytics and control for Data Collection, Analytics, and Modeling for Performance (DCAMP).
- Selecting the same PCF for AMF and SMF TS 23.501CR2644
- PCF impacts of 5MBS TS 23.501CR2880
- NWDAF instance provisioning to the PCF TS 29.507CR0181
- NWDAF instance provisioning to the PCF TS 29.512CR0849
- PCF control of MPS for DTS TS 29.513CR0257
- Selecting the same PCF for AMF and SMF TS 29.513CR0263
+ 63 more changes
In Release 18, the PCF (Positioning Calculation Function) saw enhancements to its services and event exposure, including support for 5GS Packet Delay Variation monitoring exposed to an Application Function. Key new capabilities included the PCF providing periodicity to the SMF via PCC rules, triggering UE mobility from 5GS to EPS, and completing support for provisioning slice-related inactivity timers. The release also clarified PCF authorization procedures and added support for PCF binding information and URSP delivery over EPS capability in the PCF profile.
- Enhancements of PCF Services and NEF Services TS 23.501CR3796
- PCF support of 5GS Packet Delay Variation monitoring based on QoS monitoring mechanism and exposed to AF TS 23.501CR3792
- PCF provides the Periodicity to SMF via PCC rules for resolving the EN for KI#8 TS 23.501CR4529
- PCF triggered UE mobility from 5GS to EPS TS 29.507CR0242
- Completing the support of slice deregistration inactivity timer provisioning by the PCF TS 29.507CR0258
- PCF Function Clarification TS 29.512CR1064
+ 25 more changes
In Release 19, the PCF (Positioning Calculation Function) saw enhancements focused on improving network reliability and service integration. Key additions included a new PCF-based restoration solution for core network function failures and procedures for IMS restoration following a PCF failure. The release also expanded the PCF's role by enabling its awareness of I-SMF insertion for local traffic management and introducing support for handling non-3GPP device information.
- Add the PCRF/PCF-based restoration solution for EPC/5GC NF failure TS 23.380CR0128
- IMS restoration procedure after PCRF/PCF failure TS 23.380CR0130
- PCF's awareness of I-SMF insertion for Local Offloading Management TS 23.501CR5833
- Passing non-3gpp device information to the PCF TS 29.512CR1292
- Support of UP path event reporting to AF via PCF TS 29.512CR1327
- Handling of Non-3GPP device information in the PCF TS 29.512CR1338
+ 32 more changes
In Release 20, the PCF (Positioning Calculation Function) saw enhancements in its integration and selection procedures, specifically regarding the SMF and PCF Selection for UIA_ARC. This builds upon the PCF's core role of calculating a mobile's position using methods like TA, TOA, or GPS, and its existing interfaces with functions like the PSMF.
- SMF and PCF Selection for UIA_ARC TS 23.501CR6504
Explore further
Broader topics and technologies where PCF plays a role.
Defining Specifications
3GPP specifications that define or reference PCF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 03.071 v7b0 | Location Services (LCS) Stage 2 Description | Rel-7 |
| TS 23.171 v1300 | LCS Stage 2 Specification for UMTS | Rel-4 |
| TS 23.207 vj00 | End-to-End QoS Framework for GPRS | Rel-19 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.271 vj00 | LCS Stage 2 Specification | Rel-19 |
| TS 23.380 vj10 | IMS Restoration Procedures | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.558 vk00 | Architecture for Edge Applications | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.745 vh00 | Study on App Layer Support for Factories of the Future in 5G | Rel-17 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TR 23.764 vh10 | Study on V2X Application Layer Enhancements | Rel-17 |
| TS 23.795 vg10 | V2X Application Architecture Study | Rel-16 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.502 vj20 | 5G Core Access via Non-3GPP Networks; Stage 3 | Rel-19 |
| TS 24.526 vj30 | UE Policies for 5GS; Stage 3 | Rel-19 |
| TS 24.548 vj10 | SEAL Network Resource Management Protocol | Rel-19 |
| TS 24.549 vj10 | SEAL Network Slice Capability Enablement Protocol | Rel-19 |
| TS 25.305 vj00 | UTRAN UE Positioning Stage 2 | Rel-19 |
| TS 26.501 vj30 | 5G Media Streaming (5GMS) Architecture | Rel-19 |
| TS 26.502 vj30 | 5G Multicast-Broadcast User Services Architecture | Rel-19 |
| TS 26.510 vj10 | Media Delivery APIs for 5GMS and RTC Systems | Rel-19 |
| TS 26.512 vj10 | 5G Media Streaming Protocols & APIs | Rel-19 |
| TS 26.517 vj10 | 5G MBS User Service Protocols and Formats | Rel-19 |
| TS 26.802 vj20 | Multicast Enhancements for 5G Media Streaming | Rel-19 |
| TR 26.803 vh00 | 5G Media Streaming Extensions for Edge Processing | Rel-17 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TR 26.806 vi00 | Technical Report on Smartly Tethering AR Glasses | Rel-18 |
| TS 26.891 vg00 | Media Distribution Services in 5G System | Rel-16 |
| TR 26.919 vj00 | Study on 5G Conversational Media Handling | Rel-19 |
| TR 26.928 vj00 | Study on eXtended Reality (XR) in 5G | Rel-19 |
| TR 26.942 vj00 | Study on Media Energy Consumption Exposure & Evaluation | Rel-19 |
| TR 26.998 vj00 | 5G AR/MR Glasses Integration Study | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 28.802 vf00 | Management Study for 5G Network Architecture | Rel-15 |
| TR 28.840 vi10 | Technical Report | Rel-18 |
| TS 29.165 vj10 | Inter-IMS Network to Network Interface (NNI) | Rel-19 |
| TS 29.214 vj20 | Policy and Charging Control over Rx | Rel-19 |
| TS 29.276 vj00 | EPS S101/S121/S103 Interfaces Stage 3 | Rel-19 |
| TS 29.504 vj50 | Nudr Service Based Interface Stage 3 Protocol | Rel-19 |
| TS 29.507 vj40 | 5G Access & Mobility Policy Control Service | Rel-19 |
| TS 29.508 vj40 | 5G Session Management Event Exposure Service | Rel-19 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.519 vj40 | UDR Usage for Policy & Exposure Data | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.521 vj40 | 5G Binding Support Management Service Stage 3 | Rel-19 |
| TS 29.522 vj40 | 5G NEF Northbound APIs Stage 3 | Rel-19 |
| TS 29.523 vj20 | 5G Policy Control Event Exposure Service | Rel-19 |
| TS 29.524 vj00 | 5G Cause Code Mapping Specification | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.534 vj20 | 5G Access & Mobility Policy Authorization Service | Rel-19 |
| TS 29.543 vj20 | 5G Data Transfer Policy Control Services Stage 3 | Rel-19 |
| TS 29.552 vj40 | 5G Network Data Analytics Signalling Flows | Rel-19 |
| TS 29.554 vj10 | 5G Background Data Transfer Policy Control Service | Rel-19 |
| TS 29.558 vj40 | Enabling Edge Applications | 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 29.594 vj20 | 5G Spending Limit Control Service Stage 3 | Rel-19 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.260 vj10 | IMS Charging Management | Rel-19 |
| TS 32.290 vj50 | 5G Charging for Service Based Interface | Rel-19 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | Rel-19 |
| TS 33.528 vj00 | Security Assurance for Policy Control Function (PCF) | Rel-19 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TS 33.794 vj10 | Study on Zero Trust Security Enablers for 5G | Rel-19 |
| TS 33.836 vg10 | Security Study for Advanced V2X Services | Rel-16 |
| TR 33.847 vh10 | 5G Proximity Services Security Study | Rel-17 |
| TS 43.059 vj00 | GERAN LCS Stage 2 Specification | Rel-19 |
