Connecting soldiers with relay robots in challenging environments

Real-time exchange of information amongst a team of soldiers is critical to the success of their mission in a battle field environment. The soldiers may not have a direct Line-of-Sight (LoS) between them in places with geographical separations and obstacles. A team of robots can be readily used in these scenarios to act as relays and facilitate real-time exchange of information between the soldiers. If there is no direct LoS between a pair of soldiers, the robots can be strategically placed and moved to act as a communication gateway between the soldiers. This article addresses the problem of placing a minimum number of robots in the environment such that any pair of soldiers can exchange information between each other either through direct LoS or through a series of relay robots. This problem is challenging, even in known environments, as the shape of the obstacles could be non-convex. We first show that this optimization problem is closely related to several NP-Hard problems. We then present fast heuristics that can find good feasible solutions to the problem. The heuristics sample the environment for potential robot locations and solve a connected set-cover problem to find a subset of locations that can provide the desired connectivity. The performance of the proposed heuristics is tested on a large number of problem instances generated by varying the number and placement of soldiers, and the shapes of the obstacles.