Fountain codes for GNSS I. Fernández-Hernández; European Commission; Belgium

The dissemination of large messages in a fast and robust way through the GNSS signal in space is relevant for new services such as high-accuracy and authentication, as well as for existing services. Large messages cannot be enclosed into a single word or page, hence without an appropriate strategy of dissemination, losing one portion of the message can imply losing the full message till it is rebroadcast again. Fountain codes are ideal for erasure channels, providing high-robustness against chunk losses. They allow encoding a message into small packets so that the original message can be reconstructed when receiving any subset of the packets when this subset is slightly higher than the size of the original message. This paper analyses the applicability of fountain codes to the GNSS domain and its singularities and explores different implementations described in the literature. A simple implementation based on Random Linear Fountain Codes has been developed and evaluated, including transmission performance and computational resources. A comparison against traditional strategies based on offsetting and rebroadcasting is also presented for different messages such as ECDSA signature dissemination, almanac broadcasting and post-quantum signatures, in different reception conditions.