Keeping Mobile Robots Connected

Abstract

Designing robust algorithms for mobile agents with reliable communication is difficult due to the distributed nature of computation, in mobile ad hoc networks (MANETs) the matter is exacerbated by the need to ensure connectivity. Existing distributed algorithms provide coordination but typically assume connectivity is ensured by other means. We present a connectivity service that encapsulates an arbitrary motion planner and can refine any plan to preserve connectivity (the graph of agents remains connected) and ensure progress (the agents advance towards their goal). The service is realized by a distributed algorithm that is modular in that it makes no assumptions of the motion-planning mechanism except the ability for an agent to query its position and intended goal position, local in that it uses 1-hop broadcast to communicate with nearby agents but doesn't need any network routing infrastructure, and \emph{oblivious} in that it does not depend on previous computations. We prove the progress of the algorithm in one round is at least Omega(min(d,r)), where d is the minimum distance between an agent and its target and r is the communication radius. We characterize the worst case configuration and show that when d >= r this bound is tight and the algorithm is optimal, since no algorithm can guarantee greater progress. Finally we show all agents get epsilon-close to their targets within O(D_0/r+n^2/epsilon) rounds where n is the number of agents and D_0 is the initial distance to the targets.