Complexity of planning for connected agents

International audience; We study a variant of the Multi-Agent Path Finding (MAPF) problem in which the group of agents are required to stay connected with a supervising base station throughout the execution. In addition, we consider the problem of covering an area with the same connectivity constraint. We show that both problems are PSPACE-complete on directed and undirected topological graphs while checking the existence of a bounded plan is NP-complete when the bound is given in unary (and PSPACE-hard when the encoding is in binary). Moreover, we identify a realistic class of topo-logical graphs on which the decision problem falls in NLOGSPACE although the bounded versions remain NP-complete for unary encoding.