Towards Modern Air-to-Air Communications: the LDACS A2A Mode

The increasing air traffic foreseen for the next decades has triggered an extensive modernization of the air traffic management. Specifically, new air traffic services and operational concepts have been defined and shall be supported during all phases of flight by a set of modern digital data links integrated into a single communications network named the Future Communications Infrastructure (FCI). The air-to-air (A2A) component of the FCI, the L-band Digital Aeronautical Communications System (LDACS) A2A mode, is currently in the initial stages of its development. Given that the LDACS A2A mode must be able to operate without any ground or satellite support, the data link must provide means for the aircraft to establish and organize an independent communications ad-hoc network, which imposes a great challenge for the design of the data link and specially for its medium-access control. In this paper, we contribute to the development of the LDACS A2A mode by assessing the performance of an A2A data link based on two different medium-access protocols; ALOHA with and without diversity, and a self-organizing time-division multiple-access (STDMA) scheme. The performance is obtained by simulating the implemented models of both the ALOHA-based and the STDMA-based A2A data link for different design parameters, requirements, and air traffic conditions. The obtained results show that the STDMA-based A2A data link performs better than the ALOHA-based A2A data link in most considered cases, given than the former requires a lower bandwidth than the latter to achieve the desired performance. Based on our analysis, we conclude that STDMA is a better candidate than ALOHA with or without diversity for the medium-access control of the LDACS A2A mode.