Assisted - Galileo and Additional Navigation Satellite Systems

Description

A-GANSS is a standardized positioning technology within the 3GPP framework that extends Assisted-GPS (A-GPS) to incorporate assistance data for the European Galileo system and other global navigation satellite systems (GNSS) such as GLONASS, BeiDou, and QZSS. It operates as part of the control plane or user plane location services architecture, where a Secure User Plane Location (SUPL) enabled Location Server (e.g., SLP) or a control plane Mobile Location Center (MLC) delivers assistance data to the User Equipment (UE). This assistance data includes real-time or predicted satellite orbital information (ephemeris), coarse satellite almanac data, ionospheric correction parameters, UTC model data, and acquisition assistance parameters tailored for the specific GNSS constellations. The UE uses this pre-delivered data to drastically reduce the Time To First Fix (TTFF) and improve sensitivity, as it does not need to decode this slow-changing information directly from the satellite signals, which can be weak indoors or in urban canyons.

The architecture involves several key network elements: the UE with a multi-GNSS capable receiver, the Radio Access Network (RAN) which transports the assistance data, and the core network location server. The location server, such as an Evolved Serving Mobile Location Center (E-SMLC) in LTE or a Location Management Function (LMF) in 5G, generates or retrieves the GNSS assistance data. This data is formatted according to 3GPP protocols (e.g., RRC or LPP/LPPa messages) and delivered to the UE upon request or proactively. The UE performs the satellite signal measurements (pseudoranges, Doppler) using the assistance data to narrow the search window. These raw measurements or the computed position fix can then be sent back to the network for further processing or verification in hybrid positioning methods.

A-GANSS supports multiple operational modes: UE-based, where the UE computes its own position; UE-assisted, where the UE sends measurements to the network for calculation; and standalone, though the primary value is in the assisted modes. The assistance data is standardized in binary formats within 3GPP TS 25.453 and 25.173, ensuring interoperability between network equipment and handsets from different vendors. By leveraging multiple constellations, A-GANSS enhances availability, accuracy, and integrity of the position solution. More satellites are visible in challenging environments, allowing for better geometric dilution of precision (GDOP). This multi-constellation support is a foundational capability for modern high-accuracy positioning services, including those required for automotive, logistics, and public safety applications.

Purpose & Motivation

A-GANSS was created to address the limitations of relying solely on the United States' Global Positioning System (GPS) for cellular network-assisted positioning. Prior to its introduction, 3GPP standards primarily supported A-GPS (Assisted GPS). However, dependence on a single satellite constellation presented risks related to service availability, geopolitical control, and performance in obstructed environments where GPS signals alone might be insufficient. The development of Galileo, Europe's independent global satellite navigation system, along with the modernization of other systems like Russia's GLONASS and China's BeiDou, motivated 3GPP to standardize a generic framework for assisting any current or future GNSS.

The core problem A-GANSS solves is improving the performance, reliability, and universality of mobile device positioning. By incorporating assistance for multiple constellations, it ensures faster and more robust location fixes, which is paramount for regulatory emergency services like E911 in the US and E112 in Europe. These mandates require carriers to provide accurate caller location, often within tens of meters, and A-GANSS helps meet these requirements in urban and indoor scenarios where GPS-only solutions may fail or be too slow. Furthermore, it reduces the power consumption on the UE by shortening the active search time for satellites, extending battery life for location-based applications.

Historically, the introduction of A-GANSS in 3GPP Release 8 coincided with the initial deployment phase of the Galileo system and growing industry recognition of multi-GNSS benefits. It future-proofed the 3GPP positioning standards, allowing seamless integration of new satellite systems without requiring entirely new protocol designs. This extensibility addressed the limitation of the earlier A-GPS framework, which was hard-coded for a specific constellation, thereby enabling global interoperability and fostering innovation in the location services ecosystem.

Key Features

• Provides network-generated assistance data for Galileo, GLONASS, BeiDou, QZSS, and other GNSS constellations
• Significantly reduces Time To First Fix (TTFF) and improves acquisition sensitivity compared to standalone GNSS
• Supports both UE-based and UE-assisted positioning modes for flexibility
• Enables operation in challenging signal environments (urban canyons, indoors) through multi-constellation visibility
• Standardized assistance data formats (e.g., in RRC and LPP) ensure multi-vendor interoperability
• Reduces UE power consumption by providing pre-cached satellite orbital and timing data

Evolution Across Releases

Defining Specifications