In the context of 5G, 3GPP introduced New Radio vehicle to everything (NR-V2X) for direct vehicle-to-vehicle communication. However, starting from Release 18 the focus of the standard has been expanded from vehicles to any device and use case that can benefit from direct communication. In 3GPP terminology, the standard is now referred to simply as Sidelink communication. This standard allows direct communication between devices based on synchronous resource scheduling. Users can rely on controlled scheduling when in network coverage or, in the absence of coverage, autonomously select resources for transmission via a distributed resource allocation mechanism. Focusing on the autonomous resource allocation, this paper investigates the possibility of applying Release 18 Sidelink communication to Air-to-Air (A2A) links between airborne entities. The paper outlines the main challenges and required modifications to adapt the current standard for longer links in the order of kilometres. The analysis identifies the propagation delay as a critical limitation. Communications at distances over 42.4 km require a restriction of the user's transmitting opportunities. However, sidelink communication remains feasible for distances below this threshold without modifications to the standard.

翻译：在5G背景下，3GPP引入了用于车对车直接通信的新空口车联网（NR-V2X）技术。然而，自第18版本起，该标准关注范围已从车辆扩展至任何可从直接通信中受益的设备与应用场景。按照3GPP术语，该标准现简称为Sidelink通信。此标准支持设备间基于同步资源调度的直接通信。用户可在网络覆盖范围内依赖受控调度，或在无覆盖时通过分布式资源分配机制自主选择传输资源。本文聚焦自主资源分配，探究将第18版本Sidelink通信应用于空中实体间空对空（A2A）链路的可能性。文章概述了为适配千米级更长链路而需解决的主要挑战与必要修改。分析表明，传播延迟是关键限制因素：当通信距离超过42.4千米时，需限制用户的传输机会；然而，在该阈值以下，无需修改标准即可实现Sidelink通信。