ETSI TS 125 171 V18.0.0 (2024-05)-2024 - Universal Mobile Telecommunications System (UMTS); Requirements for support of Assisted Global Positioning System (A-GPS); Frequency Division Duplex (FDD) (3GPP TS 25.171 version 18.0.0 Release 18)

Standard No.: ETSI TS 125 171 V18.0.0 (2024-05)-2024
Release Date: 2024
Published By: European Telecommunications Standards Institute (ETSI) IX / ETSI

Introduction

Standard Overview and Technical Background

ETSI TS 125 171 V18.0.0 is a key technical specification in 3GPP Release 18 regarding the technical requirements for the Assisted Global Positioning System (A-GPS) in UMTS networks. This standard defines the minimum performance requirements for user equipment (UE) to support A-GPS functionality in frequency division duplex (FDD) mode.

With the rapid development of mobile positioning services, A-GPS technology plays a key role in UMTS networks. This standard specifies the positioning performance of user equipment to ensure reliable positioning services in different network environments and application scenarios. The latest version of the standard, released in May 2024, reflects 3GPP's continuous optimization of positioning technology.

Detailed explanation of core performance requirements

Chapter 5 of the standard specifies in detail the five key performance requirements of A-GPS, which form the technical basis for evaluating the positioning capabilities of user equipment.

Performance Indicators	Test Scenario	Success Rate	2D Position Error	Maximum Response Time
Sensitivity	Coarse Time Assistance	95%	100 meters	20 seconds
Sensitivity	Fine Time Assistance	95%	100 meters	20 seconds
Nominal Accuracy	Ideal Conditions	95%	30 meters	20 seconds
Dynamic Range	Signal Strength Difference	95%	100 meters	20 seconds
Multipath Scenario	Multipath Interference	95%	100 meters	20 seconds

Sensitivity Requirements Analysis

Sensitivity testing verifies the performance of the A-GPS receiver under weak satellite signal conditions. The standard defines two time assistance modes:

Coarse Time Assistance: The network provides the current GPS time with an accuracy of ±2 seconds.
Fine Time Assistance: An optional function that provides the relationship between GPS system time and UTRAN time with an accuracy of ±10 microseconds.

In the sensitivity test, an 8-satellite configuration was used, with one satellite at -142dBm signal strength and the remaining at -147dBm. The first-time positioning performance of the user equipment was verified under an AWGN channel model.

Test Environment and Conditions Specification

Annex B of the standard specifies the test conditions in detail to ensure the comparability and repeatability of the test results.

Test parameters	Technical requirements	Application scenarios
Satellite constellation	24 satellites, at least 9 visible	All test scenarios
Reference position	Semi-major axis uncertainty 3km, elevation uncertainty 500m	Position accuracy test
Atmospheric delay	Typical ionospheric and tropospheric delay simulation	Real environment simulation
UTRA frequency	Mid-band frequency, +0.025 PPM offset relative to the GPS carrier frequency	Frequency synchronization test

Mobile scenario test requirements

The mobile scenario test verifies the tracking capability of the user equipment in a dynamic environment. The test uses a rectangular track to simulate an urban street environment:

Trajectory size: 940m × 1440m
Maximum speed: 100km/h
Turn radius: 20m
Reporting interval: 2 seconds

This test requires the user equipment to maintain a position accuracy of 100 meters in 95% of cases, reflecting the standard's full consideration of real-world application scenarios.

Technological Evolution and Standard Development

From the historical versions of the standard, 3GPP TS 25.171 has gone through multiple stages of technological evolution:

Release version	Major improvements	Release time
Release 6	Basic A-GPS performance requirements	2004
Release 7	Horizontal Accuracy IE changes	2007
Release 15	Technical maintenance and update	2018
Release 18	Current latest version	2024

The technical evolution of the standard reflects the continuous development of mobile positioning technology from basic positioning services to high-precision and high-reliability positioning services, laying the foundation for positioning technology in 5G and future mobile communication systems.

Implementation Recommendations and Best Practices

Based on the standard requirements, the following implementation recommendations are provided for device manufacturers and network operators:

Device Design Recommendations

Adopt advanced signal processing algorithms to cope with multipath interference
Optimize power consumption management to ensure positioning performance while extending battery life
Implement optional support for fine time assistance to improve performance in weak signal environments

Test and Verification Recommendations

Perform conformance testing strictly in accordance with the test conditions in Annex B
Focus on continuous positioning performance in mobile scenarios
Verify positioning capabilities in different RRC states (Cell_DCH, Cell_FACH)

Network Deployment Recommendations

Ensure that the network side can provide accurate time assistance information
Optimize the transmission efficiency and accuracy of assistance data
Consider the differences in positioning performance in different geographical environments

By following these implementation recommendations, relevant parties can ensure that their products and services comply with the requirements of the 3GPP TS 25.171 standard and provide users with a high-quality location service experience.

Universal Mobile Telecommunications System (UMTS); Requirements for support of Assisted Global Positioning System (A-GPS); Frequency Division Duplex (FDD) (3GPP TS 25.171 version 18.0.0 Release 18)

ETSI TS 125 171 V18.0.0 (2024-05)-2024Universal Mobile Telecommunications System (UMTS); Requirements for support of Assisted Global Positioning System (A-GPS); Frequency Division Duplex (FDD) (3GPP TS 25.171 version 18.0.0 Release 18)