Dispatch-and-Search: Hierarchical Multi-Ferry Control with Local Cooperation

We consider the problem of disseminating data from a base station to a sparse, partitioned mobile network by controllable data ferries with limited ferry-node and ferry-ferry communication ranges. Existing solutions to data ferry control mostly assume the nodes to be stationary, which reduces the problem to designing fixed ferry routes. In the more challenging scenario of mobile networks, existing solutions have focused on single-ferry control and left out an important issue of ferry cooperation in the presence of multiple ferries. In this paper, we jointly address the issues of ferry navigation and cooperation using the approach of stochastic control. Under the assumption that ferries can communicate within each partition, we propose a hierarchical control system called Dispatch-and-Search (DAS), consisting of a global controller that dispatches ferries to individual partitions and local controllers that coordinate the search for nodes within each partition. Formulating the global and the local control as Partially Observable Markov Decision Processes (POMDPs), we develop efficient control policies to optimize the (discounted) total throughput, which significantly improve the performance of their predetermined counterparts in cases of limited prior knowledge.