  This paper presents a time-coordination algorithm for multiple UAVs executing
cooperative missions. Unlike previous algorithms, it does not rely on the
assumption that the communication between UAVs is bidirectional. Thus, the
topology of the inter-UAV information flow can be characterized by digraphs. To
achieve coordination with weak connectivity, we design a switching law that
orchestrates switching between jointly connected digraph topologies. In
accordance with the law, the UAVs with a transmitter switch the topology of
their coordination information flow. A Lyapunov analysis shows that a
decentralized coordination controller steers coordination errors to a
neighborhood of zero. Simulation results illustrate that the algorithm attains
coordination objectives with significantly reduced inter-UAV communication
compared to previous work.
