Air-To-Ground

Description

Air-To-Ground (ATG) communications in 3GPP refer to the system that provides direct wireless connectivity between commercial aircraft and a ground-based network. Unlike satellite-based in-flight connectivity, ATG uses terrestrial base stations with antennas specifically designed to project coverage upward into aerial corridors. The aircraft is equipped with an ATG modem and an external antenna, functioning as user equipment (UE) within a modified cellular network.

The architecture involves a network of ground-based 'aerial cells' deployed along common flight paths. These cells have specialized antennas with broad vertical beamwidths and downtilt adjustments to cover altitudes typically up to 12-15 km. The ground stations connect to a dedicated ATG core network, which then aggregates traffic to/from the public internet or an airline's private network. Key technical adaptations for ATG include handling extreme Doppler shifts due to high aircraft speeds (up to 1000 km/h), managing extended cell ranges (tens of kilometers), and supporting rapid handovers between ground cells as the aircraft traverses them.

From a 3GPP standards perspective, work on ATG, notably from Release 18, focuses on adapting 5G NR for aerial vehicles. This involves enhancements to the Uu interface for the aerial environment. Key areas include defining new UE radio capabilities for high-speed scenarios, modifying channel estimation and compensation algorithms for severe Doppler effects, optimizing mobility procedures (like handover and cell reselection) for predictable aerial trajectories, and potentially utilizing specific frequency bands allocated for aviation broadband. The system must also support both passenger communications (CPE onboard providing Wi-Fi) and critical operational communications for the airline, potentially requiring differentiated QoS via network slicing.

Purpose & Motivation

ATG technology exists to provide a cost-effective, high-bandwidth, low-latency alternative to satellite connectivity for in-flight services. It addresses the growing passenger demand for seamless internet access during flights and the airline industry's need for real-time operational data (e.g., engine telemetry, cabin systems monitoring) to improve efficiency and safety. Satellite solutions often have higher latency and cost per bit.

The motivation for 3GPP standardization of ATG is to leverage the economies of scale and continuous innovation of the global cellular ecosystem for the aviation market. Prior to standardization, proprietary ATG systems existed, but they lacked interoperability and the performance roadmap of 3GPP technologies. By adapting 5G NR, ATG can benefit from massive MIMO, network slicing, and edge computing. Standardization solves the problem of fragmented solutions, enables global roaming for airlines, and ensures that aircraft can connect to ground networks worldwide using a common technology framework, ultimately driving down costs and accelerating deployment.