DARP

EGNSS plays a key role in Safety of Life (SoL) applications providing precise, reliable, and robust services. In this setting, integrity is one of the essential qualities of service to be provided to the users of SoL applications. 

The Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is a concept to which much effort is being devoted: the intention is to provide a global integrity service based on multiple satellite constellations, including Galileo which, with its features, can substantially contribute to ARAIM.

In this context, the DARP project comes into play, in the attempt of improving the achievable performance and of extending the application domain of the legacy RAIM concept, a technique extensively used in aviation to determine the integrity of GNSS position solutions. 

The ambition of the DARP project is to enable a double constellation for worldwide air navigation, able to support en-route and terminal-area flight, and lateral and vertical guidance during airport approach operations.

The DARP project developed a GNSS receiver prototype that integrates the ARAIM algorithm.

In order to achieve this result, three main tasks were performed. 

• Definition of requirements and specifications, targeting the design, implementation, and test of an ARAIM prototype
• Assessment of the performance that can be achieved with the prototype, taking into account the error model defining both laboratory and real scenarios in which the ARAIM prototype will be tested
• Standardisation, dissemination, and support to EUSPA/EC 

Challenges and technical solution

The prototype is composed by a core GNSS Receiver and a Navigation Processing Unit, enabling a suite of  functionalities: searching visible Galileo/GPS/SBAS Space Vehicles (SVs), allocating HW Channels on the basis of predefined strategies; acquiring and tracking Galileo/GPS/SBAS signals; maintaining Code Lock and Carrier Lock, demodulating and decoding data messages, and recovering navigation data from connected GNSS satellites; performing position, time, and velocity calculation with GPS and Galileo SVs in view; performing ARAIM/RAIM and integrity related calculations to alert the user in case of integrity risks; providing raw measurements data for GNSS satellites in lock; monitoring receiver status; allowing receiver control by the user through its Command and Control interface.