Universal Geographical Area Description

Description

Universal Geographical Area Description (GAD) is a fundamental concept within 3GPP specifications that provides a standardized method for describing geographical areas. It is not a single protocol but a set of definitions and encodings used across various network interfaces and applications. GAD defines how geographical information—such as points, ellipsoid points, polygons, and ellipsoid arcs—is structured and communicated. This structured description allows network entities and user equipment to unambiguously interpret location-related data.

The architecture of GAD is embedded within the broader location services (LCS) framework of 3GPP. It is utilized in signaling messages between core network nodes, such as the Gateway Mobile Location Centre (GMLC) and the Mobile Switching Centre (MSC), as well as in protocols like the Mobile Application Part (MAP) and Diameter. The GAD format includes parameters for shape, coordinates, and uncertainty, enabling precise or approximate area definitions depending on the service requirement. For instance, it can describe a cell coverage area, a predefined geofence, or a target region for location-based alerts.

Key components of GAD include the shape type (e.g., ellipsoid point, polygon), the geographical coordinates (typically using the World Geodetic System 1984, WGS84), and associated uncertainty or confidence levels. These components are encoded according to ASN.1 rules specified in 3GPP technical specifications. The role of GAD is critical for enabling services like emergency caller location, location-based charging, fleet management, and enhanced 911 (E911). By providing a universal format, it ensures interoperability between different network elements and across different generations of mobile networks, from GSM to 5G.

Purpose & Motivation

GAD was created to solve the problem of inconsistent and proprietary geographical descriptions in early mobile networks. Before standardization, vendors and operators used ad-hoc methods to define areas, leading to interoperability issues and hindering the rollout of location-based services. The need for a universal format became pressing with regulatory requirements for emergency services (e.g., E112 in Europe) and the commercial potential of location-aware applications.

The historical context lies in the evolution of GSM into 3G, where location services became a mandated feature. GAD, introduced in Release 4, provided a common language that allowed network equipment from different manufacturers to exchange geographical information seamlessly. It addressed limitations such as the inability to precisely define complex geographical zones or to convey uncertainty in location estimates. By standardizing the description, GAD enabled the development of a wide range of services that rely on accurate and interpretable area definitions, from navigation aids to geofencing for IoT devices.

Key Features

• Standardized encoding for geographical shapes (point, ellipse, polygon, arc)
• Uses WGS84 coordinate reference system for global consistency
• Includes uncertainty and confidence parameters for location accuracy
• Embedded in multiple 3GPP protocols (MAP, Diameter) for wide applicability
• Supports both 2D and 3D geographical descriptions
• Enables interoperability across different network generations and vendor equipment

Evolution Across Releases

Defining Specifications