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83
Performance of a distributed robotic system using shared communications channels
 IEEE Trans. on Robotics and Automation
, 2002
"... Abstract—We have designed and built a set of miniature robots, called Scouts, and have developed a distributed software system to control them. This paper addresses the fundamental choices we made in the design of the control software, describes experimental results in a surveillance task, and analy ..."
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Cited by 29 (15 self)
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Abstract—We have designed and built a set of miniature robots, called Scouts, and have developed a distributed software system to control them. This paper addresses the fundamental choices we made in the design of the control software, describes experimental results in a surveillance task, and analyzes the factors that affect robot performance. Space and power limitations on the Scouts severely restrict the computational power of their onboard computers, requiring a proxyprocessing scheme in which the robots depend on remote computers for their computing needs. While this allows the robots to be autonomous, the fact that robots ’ behaviors are executed remotely introduces an additional complication – sensor data and motion commands have to be exchanged using wireless communications channels. Communications channels cannot always be shared, thus requiring the robots to obtain exclusive access to them. We present experimental results on a surveillance task in which multiple robots patrol an area and watch for motion. We discuss how the limited communications bandwidth affects robot performance in accomplishing the task and analyze how performance depends on the number of robots that share the bandwidth. Index Terms—Multiple robots, Mobile robots, Distributed software architecture, Resource allocation.
A Regionbased Approach for Cooperative MultiTarget Tracking in a Structured Environment
, 2002
"... This paper addresses the problem of tracking multiple anonymous targets using a network of communicating robots and stationary sensors. We introduce a regionbased approach which controls robot deployment at two levels. A coarse deployment controller distributes robots across regions using a topologi ..."
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Cited by 26 (3 self)
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This paper addresses the problem of tracking multiple anonymous targets using a network of communicating robots and stationary sensors. We introduce a regionbased approach which controls robot deployment at two levels. A coarse deployment controller distributes robots across regions using a topological map and density estimates, and a targetfollowing controller attempts to maximize the number of tracked targets within a region. A behaviorbased system is presented implementing the regionbased approach. Intensive simulations were performed to investigate the correlation between our approach and the degree of occlusion in the environment. The regionbased approach shows better performance than a `naive' localfollowing strategy when the environment has significant occlusion. We performed realrobot experiments to validate the system. These experiments open up a new line of research, which suggests that an optimal ratio of robots to stationary sensors may exist for a given environment with certain occlusion characteristics. 1
A pointbased POMDP planner for target tracking
 in Proc. ICRA
, 2008
"... AbstractTarget tracking has two variants that are often studied independently with different approaches: target searching requires a robot to find a target initially not visible, and target following requires a robot to maintain visibility on a target initially visible. In this work, we use a part ..."
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Cited by 25 (7 self)
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AbstractTarget tracking has two variants that are often studied independently with different approaches: target searching requires a robot to find a target initially not visible, and target following requires a robot to maintain visibility on a target initially visible. In this work, we use a partially observable Markov decision process (POMDP) to build a single model that unifies target searching and target following. The POMDP solution exhibits interesting tracking behaviors, such as anticipatory moves that exploit target dynamics, informationgathering moves that reduce target position uncertainty, and energyconserving actions that allow the target to get out of sight, but do not compromise longterm tracking performance. To overcome the high computational complexity of solving POMDPs, we have developed SARSOP, a new pointbased POMDP algorithm based on successively approximating the space reachable under optimal policies. Experimental results show that SARSOP is competitive with the fastest existing pointbased algorithm on many standard test problems and faster by many times on some.
PursuitEvasion on Trees by Robot Teams
, 2010
"... We present GraphClear, a novel pursuitevasion problem on graphs which models the detection of intruders in complex indoor environments by robot teams. The environment is represented by a graph, and a robot team can execute sweep and block actions on vertices and edges respectively. A sweep action ..."
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Cited by 25 (4 self)
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We present GraphClear, a novel pursuitevasion problem on graphs which models the detection of intruders in complex indoor environments by robot teams. The environment is represented by a graph, and a robot team can execute sweep and block actions on vertices and edges respectively. A sweep action detects intruders in a vertex and represents the capability of the robot team to detect intruders in the region associated to the vertex. Similarly, a block action prevents intruders from crossing an edge and represents the capability to detect intruders as they move between regions. Both actions may require multiple robots to be executed. A strategy is a sequence of block and sweep actions detecting all intruders. When solving instances of GraphClear the goal is to determine optimal strategies, i.e. strategies using the least number of robots. We prove that for the general case of graphs the problem of computing optimal strategies is NPhard. Next, for the special case of trees we provide a polynomial time algorithm. The algorithm ensures that throughout the execution of the strategy all cleared vertices form a connected subtree, and we show it produces optimal strategies.
Locating and Capturing an Evader in a Polygonal Environment
, 2003
"... This paper contains two main results: First, we revisit the wellknown visibility based pursuitevasion problem and show that, in contrast to deterministic strategies, a single pursuer can locate an unpredictable evader in any simplyconnected polygonal environment using a randomized strategy. The e ..."
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Cited by 23 (4 self)
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This paper contains two main results: First, we revisit the wellknown visibility based pursuitevasion problem and show that, in contrast to deterministic strategies, a single pursuer can locate an unpredictable evader in any simplyconnected polygonal environment using a randomized strategy. The evader can be arbitrarily faster than the pursuer and it may know the position of the pursuer at all times but it does not have prior knowledge of the random decisions made by the pursuer. Second, using the randomized algorithm together with the solution of a known lion and man problem [1] as subroutines, we present a strategy for two pursuers (one of which is at least as fast as the evader) to quickly capture an evader in a simplyconnected polygonal environment. We show how this strategy can be extended to obtain a strategy for (i) capturing the evader in a polygonal room with a door, (ii) two pursuers who have only lineofsight communication, and (iii) a single pursuer (at the expense of increased capture time).
Multirobot surveillance: an improved algorithm for the graphclear problem
 In Proc. IEEE Intl. Conf. on Robotics and Automation
, 2008
"... Abstract—The main contribution of this paper is an improved algorithm for the GRAPHCLEAR problem, a novel NPcomplete graph theoretic problem we recently introduced as a tool to model multirobot surveillance tasks. The proposed algorithm combines two previously developed solving techniques and p ..."
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Cited by 20 (6 self)
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Abstract—The main contribution of this paper is an improved algorithm for the GRAPHCLEAR problem, a novel NPcomplete graph theoretic problem we recently introduced as a tool to model multirobot surveillance tasks. The proposed algorithm combines two previously developed solving techniques and produces strategies that require less robots to be executed. We provide a theoretical framework useful to identify the conditions for the existence of an optimal solution under special circumstances, and a set of mathematical tools characterizing the problem being studied. Finally we also identify a set of open questions deserving more investigations. I.
Capturing an evader in a polygonal environment with obstacles
 22nd International Joint Conference on Artificial Intelligence
"... We study a pursuitevasion game in which one or more cops try to capture a robber by moving onto the robber’s current location. All players have equal maximum velocities. They can observe each other at all times. We show that three cops can capture the robber in any polygonal environment (which can ..."
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Cited by 20 (8 self)
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We study a pursuitevasion game in which one or more cops try to capture a robber by moving onto the robber’s current location. All players have equal maximum velocities. They can observe each other at all times. We show that three cops can capture the robber in any polygonal environment (which can contain any finite number of holes). 1
Counting targets with mobile sensors in an unknown environment
 In Proceedings of the 3rd International Workshop in Algorithmic Aspects of Wireless Sensor Networks (ALGOSENSORS), Revised Selected Papers
, 2007
"... Abstract. We consider the problem of counting the number of indistinguishable targets using a simple binary sensing model. Our setting includes an unknown number of point targets in a (simple or multiplyconnected) polygonal workspace, and a moving pointrobot whose sensory input at any location is a ..."
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Cited by 19 (3 self)
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Abstract. We consider the problem of counting the number of indistinguishable targets using a simple binary sensing model. Our setting includes an unknown number of point targets in a (simple or multiplyconnected) polygonal workspace, and a moving pointrobot whose sensory input at any location is a binary vector representing the cyclic order of the polygon vertices and targets visible to the robot. In particular, the sensing model provides no coordinates, distance or angle measurements. We investigate this problem under two natural models of environment, friendly and hostile, which differ only in whether the robot can walk up to them or not, and under three different models of motion capability. In the friendly scenario we show that the robots can count the targets, whereas in the hostile scenario no (2 − ε)approximation is possible, for any ε> 0. Next we consider two, possibly minimally more powerful robots that can count the targets exactly. 1 The Problem and the Model
Randomized pursuitevasion with limited visibility
, 2003
"... We study the following pursuitevasion game: One or more hunters are seeking to capture an evading rabbit on a graph. At each round, the rabbit tries to gather information about the location of the hunters but it can see them only if they are located on adjacent nodes. We show that two hunters suffi ..."
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Cited by 19 (2 self)
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We study the following pursuitevasion game: One or more hunters are seeking to capture an evading rabbit on a graph. At each round, the rabbit tries to gather information about the location of the hunters but it can see them only if they are located on adjacent nodes. We show that two hunters suffice for catching rabbits with such local visibility with high probability. We distinguish between reactive rabbits who move only when a hunter is visible and general rabbits who can employ more sophisticated strategies. We present polynomial time algorithms that decide whether a graph G is hunterwin, that is, if a single hunter can capture a rabbit of either kind on G.
Parallel stochastic hillclimbing with small teams, in L.E.Parker et al., eds
 MultiRobot Systems: From Swarms to Intelligent Automata, Volume III’, Springer, the Netherlands
, 2005
"... Abstract We address the basic problem of coordinating the actions of multiple robots that are working toward a common goal. This kind of problem is NPhard, because in order to coordinate a system of n robots, it is in principle necessary to generate and evaluate a number of actions or plans that is ..."
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Cited by 18 (1 self)
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Abstract We address the basic problem of coordinating the actions of multiple robots that are working toward a common goal. This kind of problem is NPhard, because in order to coordinate a system of n robots, it is in principle necessary to generate and evaluate a number of actions or plans that is exponential in n (assuming P � = NP). However, we suggest that many instances of coordination problems, despite the NPhardness of the overall class of problems, do not in practice require exponential computation in order to arrive at good solutions. In such problems, it is not necessary to consider all possible actions of the n robots; instead an algorithm may restrict its attention to interactions within small teams, and still produce highquality solutions. We use this insight in the development of a novel coordination algorithm that we call parallel stochastic hillclimbing with small teams, or Parish. This algorithm is designed specifically for use in multirobot systems: it can run offline or online, is easily distributed across multiple machines, and is efficient with regard to communication. We state and analyze the Parish algorithm present results from the implementation and application of the algorithm for a concrete problem: multirobot pursuitevasion. In this demanding domain, a team of robots must coordinate their actions so as to guarantee location of a skilled evader. 1 2