In order to enable passengers to access the Internet in the cabin of an aircraft through the use of a wireless LAN, in December 2020 3GPP RAN4 discusses the following definitions in R17 regarding ATG (Air-to-ground) network technology;
I. Application Scenario ATG (Air to Ground) network refers to in-flight connectivity technology, where signals are sent to the aircraft antenna of the airborne ATG terminal through the use of a ground base station. When the aircraft flies into different airspace, the airborne ATG terminal will automatically connect to the base station with the strongest received signal power; this is just like a cell phone on the ground.
Figure 1. Schematic diagram of the ATG communication system
II.3GPP discussion The new WID (RP-193234) solution for 5G (NR) to support NTN (Non-Terrestrial Networks) was approved at RAN#86.The NTN work item specifies enhancements identified for NR NTN (Non-Terrestrial Networks) based on the following principles, in particular LEO and GEO with implicit compatibility to support HAPS (High Altitude Platform Station) and ATG (Air to Ground) scenarios; among others. Station) and ATG (Air to Ground) scenarios;
* NR-NTN core specification working assumptions for FDD.
* Assumption that the Earth Fixed Tracking Area (EFTA) has both Earth Fixed and Mobile units
* UEs are assumed to have GNSS capability.
III.ATG characteristics Base stations and terminals (UEs) are unique types, and ATG will operate in existing frequency bands without the need to identify new frequency bands and band attributes.
IV. Some characteristics of ATG deployment scenarios can be considered
* Extremely large Inter-Site Distance (ISD) and large coverage area:In order to control the network deployment cost and considering the limited number of flights, it is preferable to use a large ISD, e.g., about 100 km to 200 km. The distance between the aircraft and the nearest base station may be more than 200 km or even up to 300 km when the aircraft is over the sea. Therefore the ATG network should be able to provide cell coverage of up to 300 km.
* Deploying ATG and terrestrial networks using non-separated operators' proprietary frequencies:Operators want to deploy ATG and terrestrial networks using the same frequencies in order to save the cost of frequency resources, while the interference between ATG and terrestrial networks becomes non-negligible and should be addressed. From China Mobile's point of view, 4.8GHz is an optimal frequency for deploying ATG and terrestrial NR networks.
* More Powerful Airborne ATG Terminal Capacity:Airborne ATG terminals are more powerful than normal terrestrial UEs, e.g., higher EIRP through higher transmission power and/or larger onboard antenna gain.
V. Challenges to ATG Deployment Considering the network deployment specificities, the following issues will be addressed in the ATG project:
* Extremely large cell coverage (up to 300 km) and flight speed (up to 1200 km/h);
* Coexistence requirements between ATG and terrestrial networks;
* ATG BS/UE core and performance requirements.
VI. ATG Objectives RAN4 discusses RF requirements for coexistence between ATG and IMT terrestrial networks Core specification designation functions include.
* Determine the absolute need to differentiate ATG BS and UE from terrestrial BS and UE key characteristics - Reuse existing BS and UE requirements wherever possible.
* Study and specify the framework for defining the ATG core requirements.
6.1 Determine if these requirements are included in existing specifications or if new specifications are created; Determine if both BS and UE require conduction, OTA, or both types of requirements; In addition
* Determine the potential FR1 frequency bands to be used as ATG examples
* Perform FR1 coexistence assessment for ATG networks (e.g. ACLR, ACS)
* Assign new UE/BS types for ATG networks if necessary
6.2 Consider identified differences between ATG and terrestrial systems
- Specify RF requirements for the ATG UE/BS
6.3 Consider the impact of coexistence simulation results on transmit and RX requirements, cell size and link budgets, technical capabilities, possible BS and UE architectures, and other relevant aspects.
* Specify test procedures for ATG BS conformance testing
6.4 Determine at an early stage whether conduction, OTA or both types of testing are required
