Description
Flächenkorrekturparameter (FKP), or Area Correction Parameters, are a crucial component of the Observed Time Difference of Arrival (OTDOA) positioning method defined in 3GPP for LTE (E-UTRA) and NR (5G). OTDOA is a network-based positioning technique where the UE measures the time difference of arrival of reference signals from multiple neighboring cells (eNodeBs/gNBs) relative to a reference cell. These measured Reference Signal Time Differences (RSTDs) are used to calculate hyperbolas, whose intersection estimates the UE's location. However, the raw RSTD measurements contain errors due to non-ideal factors like timing synchronization inaccuracies between base stations and signal propagation delays not accounted for in the basic model.
FKPs work by providing correction values that are broadcast by the positioning server, typically the Enhanced Serving Mobile Location Centre (E-SMLC) or Location Management Function (LMF), to the UE via the LTE Positioning Protocol (LPP). These parameters are associated with specific geographic areas, known as FKP areas. The UE receives the FKP values applicable to its current or expected area. The core technical function of an FKP is to represent the relative timing offset of a neighbor cell's positioning reference signal (PRS) transmission compared to the ideal synchronized timing assumed for the reference cell. By applying this correction to its raw RSTD measurement for that neighbor cell, the UE can compensate for the base station's real transmission timing error.
Architecturally, the generation of FKPs is a network management task. The network operator or a dedicated positioning server must calculate these parameters based on known, precise locations of the base stations and potentially calibration measurements. The parameters are then configured into the network's positioning infrastructure. Key components involved are the UE (which applies the correction), the base stations (eNodeB/gNB whose timing errors are corrected), and the positioning server (E-SMLC/LMF) which provisions the FKP data. The role of FKPs is to enhance the accuracy of OTDOA positioning without requiring perfect and costly time synchronization across all base stations in the network, making mass-market, regulatory-grade location services (e.g., for emergency calls) more feasible and accurate.
Purpose & Motivation
FKP technology exists to solve the fundamental accuracy problem in OTDOA positioning caused by timing synchronization errors between base stations. The theoretical OTDOA method assumes all base stations transmit their positioning reference signals in perfect synchronization. In practical deployments, achieving and maintaining nanosecond-level synchronization across a large network is extremely challenging and expensive, even with technologies like GPS/GNSS or IEEE 1588 Precision Time Protocol. Without correction, these timing errors translate directly into large geographic positioning errors, rendering OTDOA unusable for applications like emergency location (E911/112) or location-based services.
The creation and standardization of FKP were motivated by the need for a cost-effective, deployable OTDOA solution. It addresses the limitation of requiring perfect network synchronization by introducing a software-based correction layer. Instead of investing in ultra-precise hardware synchronization for every cell site, operators can characterize the existing timing errors (which are relatively stable over time) and broadcast correction parameters. This approach decouples positioning accuracy from absolute network sync quality, allowing operators to meet regulatory location accuracy mandates using their existing network infrastructure with manageable calibration efforts. It was a key enabler for the commercial viability of network-based positioning in LTE and its continuation into 5G NR.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (45 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the FKP (Flächenkorrekturparameter) function was newly introduced through the capability to provide "RTK FKP Gradients," which delivers horizontal gradients for geometric and ionospheric signal components to the GNSS receiver. This enables network-based RTK positioning by supplying area correction parameters, contrasting with the user-specific state parameters used in SSR corrections. The gradients are typically transmitted every 10-60 seconds to support precise positioning.
In Release 16, the FKP (Flächenkorrekturparameter) function was enhanced as part of the broader NR positioning framework, with specific new support defined for **RTK FKP Gradients**. This assistance data provides the GNSS receiver with horizontal gradients for geometric and ionospheric signal components in the observation space, which are typically transmitted every 10-60 seconds. These corrections are part of the suite of SSR (State Space Representation) and network RTK corrections standardized in Release 16 to improve positioning accuracy.
- Correction to LTE stage2 spec for MO-LR TS 36.305CR0104
- Correction on user-plane positioning support by SUPL TS 36.305CR0105
- Corrections to NR Positioning TS 38.305CR0025
- Correction to SUPL support for NR positioning methods TS 38.305CR0028
- Correction on Stage-2 for gNB and LMF information transfer TS 38.305CR0029
- Miscellaneous correction to stage2 spec TS 38.305CR0032
+ 12 more changes
In Release 17, enhancements for the FKP function were introduced through corrections and clarifications to the underlying NR positioning stage 2 descriptions and NRPPa procedures. Specifically, the release provided a clearer technical definition for **RTK FKP Gradients**, which deliver horizontal gradients for geometric and ionospheric components in the observation space. These updates also included integrity-related improvements, such as the formal provision of **Integrity Bounds** to statistically bound residual errors after applying positioning corrections.
- Correction on the mean orbit error projection in TS 36.305 TS 36.305CR0110
- Stage 2 corrections for NR Positioning Enhancements TS 38.305CR0100
- Mscellaneous corrections for TS38.305 TS 38.305CR0105
- Corrections on NRPPa functions and procedures TS 38.305CR0117
- Corrections to stage 2 descriptions for NR positioning TS 38.305CR0118
- Miscellaneous corrections for Positioning Stage2 TS 38.305CR0119
+ 5 more changes
In Release 18, the FKP (Flächenkorrekturparameter) function was enhanced through corrections to the SLPP assistance data transfer procedures and the provision of RTK FKP Gradients, which deliver horizontal gradients for geometric and ionospheric components in the observation space. These updates specifically refined the transfer of area correction parameters and the associated network error models for interpolated corrections. The changes aimed to improve the integrity and accuracy of Network RTK positioning techniques.
- Correction on support of Bluetooth positioning mode [BT-AoA-AoD] TS 38.305CR0157
- Miscellaneous Stage 2 Corrections and Alignments TS 38.305CR0158
- Miscellaneous Stage 2 Corrections TS 38.305CR0163
- Correction to OAM requirement for UE location verification TS 38.305CR0171
- Correction to LPP Measurement Time Windows and SLPP Assistance Data Transfer procedures TS 38.305CR0172
- Correction on assistance data transfer in SL positioning for stage-2 TS 38.305CR0175
+ 3 more changes
In Release 19, the FKP (Flächenkorrekturparameter) function was enhanced through corrections to the overall data collection report procedure and to specific positioning techniques, including LPHAP and carrier phase-based positioning. These updates aimed to improve the generation and delivery of RTK FKP Gradients, which provide horizontal gradients for geometric and ionospheric components in the observation space. The corrections also addressed the positioning activation and deactivation procedure to ensure more reliable operation.
- Corrections on AIML Positioning TS 38.305CR0197
- Correction of Data Collection Report procedure and others TS 38.305CR0201
- Corrections on LPHAP, carrier phase, bandwidth aggregation and frequency hopping for positioning (R19 Cat. A CR) TS 38.305CR0198
- Correction to Positioning activation and deactivation procedure TS 38.305CR0200
Explore further
Broader topics and technologies where FKP plays a role.
Defining Specifications
3GPP specifications that define or reference FKP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |