## Materials and Methods  
### Background and Motivations  
In the last few decades, CIRA has gained relevant expertise in the design of DAA systems thanks to activities that have been carried out in both nationally-funded Italian projects and in internationally-funded European projects. The integrated ADS-B-based automatic separation assurance collision avoidance system, whose real-time simulation campaign is the subject of this paper, is indeed the result of many years of incremental research on this topic. The main motivation that led the design of such a system was the capitalization and extension of previous experience related to single baseline systems for collision avoidance (radar-based) and self-separation in order to achieve the design of a unique, integrated system managing all functions at the same time according to properly designed overall system automation logic and the implementation of the above-mentioned functions in the most appropriate way while considering the requirements of compliance with the rules of the air [15] and self-compatibility. Here, the evolutionary approach that led to the ASACAS design is outlined. A baseline version of an autonomous collision avoidance radar-based system was developed in the framework of the nationally-funded Italian project TECVOL (Technologies for Autonomous Flight), reaching TRL (Technology Readiness Level) 6 as an individual technology [16; 17; 18; 19]. The baseline version of an ADS-B-based separation assurance system was developed in the framework of the Italian project SEPARA (System for General Aviation Separation Support), reaching TRL 5 as an individual technology [20; 21]. Starting from these baseline individual systems, in the nationally-funded Italian project MISE (Applications for Unmanned Aircraft Avionics), the first and baseline version of the ADS-B-based integrated ASACAS was developed. The first version of the ASACAS then evolved in the nationally-funded Italian project EATS (Efficient Air Transport System). The second (evolved) version of the system was then demonstrated, both in real-time and real live flight trials, in the SJU-funded project RAID, which was completed in 2016 and achieved TRL 6. In more detail, ASACAS development was implemented through the incremental steps described as follows. The first version of the ASACAS (version 1p0) was designed in order to update the former autonomous collision avoidance (ACA) system developed in the framework of the project TECVOL. The rationale of this update was the need to adapt the collision avoidance functionality to the use of the ADS-B IN cooperative surveillance sensor as unique sensor for obstacle detection purposes, thus replacing the radar-based non-cooperative sensor suite used in the application developed in TECVOL. This represented the first step towards the development of a fully integrated automatic separation assurance and collision avoidance system (ASACAS version 2p0), including both separation assurance and collision avoidance functionalities based on the ADS-B IN surveillance sensor, as well as the integration of a dedicated situational awareness functionality and overall ASACAS logic. The ADS-B IN-provided surveillance data are used as input for conflict and collision detection algorithms in order to support the collision avoidance and the separation assurance functionalities. In ASACAS 1p0, the collision detection system for collision avoidance was specifically modified with respect to the former TECVOL application [16; 17; 18; 19] and designed in order to allow it to use ADS-B IN-provided data that are broadcast by all ADS-B OUT-equipped surrounding aircraft. The overall collision detection system architecture designed in ASACAS 1p0 aimed to manage the ADS-B data in order to provide the collision avoidance resolution algorithm (which has not been changed from the baseline version) with proper information about surrounding traffic [22; 23].