European Geostationary Navigation Overlay Service

Description

The European Geostationary Navigation Overlay Service (EGNOS) is a Satellite-Based Augmentation System (SBAS) developed by the European Space Agency, the European Commission, and Eurocontrol. While not a 3GPP-created technology, its support and integration are specified within 3GPP standards to enable location-based services in mobile networks. EGNOS enhances the performance of core Global Navigation Satellite Systems (GNSS) like GPS by providing correction data and integrity information.

Architecturally, EGNOS consists of a network of precisely surveyed ground reference stations (RIMS - Ranging and Integrity Monitoring Stations) spread across Europe. These stations continuously monitor the signals from GPS satellites. The collected data is sent to master control centers (MCCs) where errors (such as those caused by ionospheric delays, satellite clock drift, and ephemeris inaccuracies) are computed. These computed correction and integrity messages are then uploaded to geostationary satellites (GEO satellites) that broadcast them over the EGNOS service area.

A User Equipment (UE) with an EGNOS-enabled GNSS receiver receives both the standard GPS signals and the EGNOS augmentation signals from the GEO satellites. The receiver applies the correction data to the raw GPS measurements, significantly improving positional accuracy from about 10 meters (standalone GPS) to better than 1-2 meters horizontally. Crucially, EGNOS also provides integrity information, alerting the user within seconds if the GPS signal is unreliable or contains errors beyond safe limits for applications like aviation navigation. In the 3GPP context, this enhanced positioning data can be used by the UE or provided to the network via control plane or user plane location protocols (e.g., LPP, SUPL) to support advanced Location-Based Services (LBS).

Purpose & Motivation

EGNOS was created to address the limitations of standalone GPS for safety-of-life and other high-precision commercial applications in Europe. While GPS provides global coverage, its signals are susceptible to errors that degrade accuracy and, more importantly, lack a guaranteed integrity monitoring system. This made it unsuitable for critical phases of flight in aviation or for other applications where liability and safety are paramount.

The purpose of integrating EGNOS support into 3GPP standards (starting from Release 8) was to leverage this high-quality, certified positioning service for mobile applications. It enables network operators and service providers to offer more accurate and reliable location services. This solves problems such as providing enhanced 911 (E112) emergency caller location with better precision, enabling road tolling systems, precision agriculture, and supporting the evolving needs of intelligent transportation systems and IoT applications that depend on trustworthy positional data.

By specifying how UEs and networks can utilize EGNOS data, 3GPP allowed the mobile ecosystem to benefit from a publicly funded infrastructure that provides open, free, and certified augmentation signals, moving beyond the limitations of basic cell-ID or standalone GPS positioning available in earlier releases.