This activity will firstly identify the user requirements and the operational use cases in cooperation with the rail, road and UAV stakeholders. In this sense, the presence of the advisory board is a key element and its deep involvement since the project beginning. After that, the system requirements (functional, performance, security and RAMS) and their harmonisation will be defined, and they will be the drivers for the architecture design (WP3), including both AIMN and MOBU platform (in particular focusing on data-fusion and multi-sensor FDE ARAIM algorithms). The design phase will be split into two phases: preliminary design and detailed design. In the preliminary design, the functional architecture and the interfaces will be defined in order to map the system requirements into design requirements for the two HELMET main subsystems. In the second design phase, the functional architecture will be mapped into the physical architecture with the detailed definition of all building blocks. The third stage is represented by the system development and testing (WP4).