Improving Usable LDACS Data Rate via Certificate Validity Optimization

Since the beginning of the century, an increasing amount of air traffic has pushed current aeronautical communication systems to their limits. Therefore, a modernization process is ongoing, envisioning to digitalize previously analog systems and prepare them for future requirements. Among these efforts is the L-Band Digital Aeronautical Communications System (LDACS), which is a cellular broadband digital data link system, foreseen for regularity-of-flight and safety-communications. Any newly developed system must provide strong cybersecurity, especially when deployed within critical infrastructures. Similar to other communication systems, LDACS will utilize digital certificates within its Public Key Infrastructure (PKI). Such certificates must be available to the respective communication partner, and therefore might have to be transmitted via the radio link upon first contact. With bandwidth generally being a restricting factor in wireless communication, especially in the spectrum-scarce Lband different certificate lifetimes have varying impacts on the amount of security data. In previous research work, reduction of the LDACS security overhead has already been considered in e.g., the secure cell-attachment procedure between ground and aircraft stations or within a proposal for the utilization of group key distribution procedures in LDACS. However, the effect of different certificate lifetimes on the amount of security data and therefore the available user data rate has not been investigated so far. The objective of this paper is to compare different approaches for certificate validity periods in respect to the additional network overheads being created. Computer simulations using historical flight data from the OpenSky Network and a dedicated LDACS simulator help identifying the most effective solution.