Distributed Swarm Navigation with Factored Filters

This work introduces the PNT Chain, a fully distributed filtering solution to collaborative positioning with ranging radios in GNSS-degraded and denied environments. The PNT (Positioning, Navigation, and Timing) Chain uses an Undirected Acyclic Bayes Graph (UABG) to factor a Kalman filter on the poses of an entire swarm into tractable cliques. The cliques are distributed across the physical nodes, which in combination with the use of equivalent propagation and equivalent measurement messages, keeps network traffic to an absolute minimum. The distributed PNT Chain algorithm is compared with an idealized (and impractical) centralized filter, and a legacy relative navigation algorithm in two scenarios where only two UAVS in a swarm are receiving GNSS signals. In both cases, the distributed PNT Chain achieves a positional accuracy comparable with the completely centralized filter, and an order of magnitude better than the legacy approach, while only requiring 22% the computation cost of the centralized filter.