Advanced RAIM Architecture Design and User Algorithm Performance in a real GPS, GLONASS and Galileo scenario

In the past years the scientific community is investigating with increasing interest innovative techniques to provide vertical guidance to aviation users up to precision approach and even autonomous guidance on ground. Next to SBAS and GBAS systems other novel architectures have been under investigated. In particular the ARAIM concept is based on the fact that the future of multiconstellation and multifrequency signals will offer the possibility to reduce the dependency from the ground infrastructure and consequently reduce further the deployment and operation costs. The user will be provided with an augmentation signal (Integrity Support Message) updated and transmitted with a long latency. This is the idea of the Advanced Receiver Autonomous Monitoring. This paper proposes an architecture which aims on one hand to maximize the reuse of existing infrastructure and on the other to provide the user with the necessary robustness required mostly in the early next years by new constellations. The differentiating factor among the different alternatives is the so called Time to ISM Alarm, the update frequency and dissemination of the ISM information. The proposed architecture foresees the provision of two different type of messages: a long term one addressing nominal conditions and a short term one to detect anomaly conditions. The paper presents also the user algorithms suitable for this architecture which optimizes the user availability by reducing the protection level with respect to existing solutions. The performance of the user algorithm has been analysed in a real scenario: a receiver in front of an airport hangar disturbed by a GNSS repeater. The paper shows how the user algorithm can detect the disturbance and reject it. Furthermore the protection level performances is also shown, and in particular its improvement with respect to existing ARAIM algorithm [1].