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Adaptive Beacon Placement
, 2001
"... Beacon placement strongly affects the quality of spatial localization, a critical service for contextaware applications in wireless sensor networks; yet this aspect of localization has received little attention. Fixed beacon placement approaches such as uniform and very dense placement are not alwa ..."
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Cited by 119 (6 self)
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Beacon placement strongly affects the quality of spatial localization, a critical service for contextaware applications in wireless sensor networks; yet this aspect of localization has received little attention. Fixed beacon placement approaches such as uniform and very dense placement are not always viable and will be inadequate in very noisy environments in which sensor networks may be expected to operate (with high terrain and propagation uncertainties). In this paper, we motivate the need for empirically adaptive beacon placement and outline a general approach based on exploration and instrumentation of the terrain conditions by a mobile human or robot agent. We design, evaluate and analyze three novel adaptive beacon placement algorithms using this approach for localization based on RFproximity. In our evaluation, we find that beacon density rather than noise level has a more significant impact on beacon placement algorithms. Our beacon placement algorithms are applicable to a low (beacon) density regime of operation. Noise makes moderate density regimes more improvable.
Visibilitybased pursuitevasion with limited field of view.
 The International Journal of Robotics Research,
, 2006
"... Abstract We study a form of the pursuitevasion problem, in which one or more searchers must move through a given environment so as to guarantee detection of any and all evaders, which can move arbitrarily fast. Our goal is to develop techniques for coordinating teams of robots to execute this task ..."
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Cited by 93 (1 self)
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Abstract We study a form of the pursuitevasion problem, in which one or more searchers must move through a given environment so as to guarantee detection of any and all evaders, which can move arbitrarily fast. Our goal is to develop techniques for coordinating teams of robots to execute this task in application domains such as clearing a building, for reasons of security or safety. To this end, we introduce a new class of searcher, the φsearcher, which can be readily instantiated as a physical mobile robot. We present a detailed analysis of the pursuitevasion problem using φsearchers. We show that computing the minimum number of φsearchers required to search a given environment is NPhard, and present the first complete search algorithm for a single φsearcher. We show how this algorithm can be extended to handle multiple searchers, and give examples of computed trajectories.
Randomized PursuitEvasion in a Polygonal Environment
, 2004
"... 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 ..."
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Cited by 91 (12 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 to a problem called the "lion and man problem" [2] 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) 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).
Finding an Unpredictable Target in a Workspace with Obstacles
, 1997
"... This paper introduces a visibilitybased motion planning problem in which the task is to coordinate the motions of one or more robots that have omnidirectional vision sensors, to eventually "see" a target that is unpredictable, has unknown initial position, and is capable of moving arbitra ..."
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Cited by 79 (13 self)
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This paper introduces a visibilitybased motion planning problem in which the task is to coordinate the motions of one or more robots that have omnidirectional vision sensors, to eventually "see" a target that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. A visibility region is associated with each robot, and the goal is to guarantee that the target will ultimately lie in at least one visibility region. Both a formal characterization of the general problem and several interesting problem instances are presented. A complete algorithm for computing the motion strategy of the robots is also presented, and is based on searching a finite cell complex that is constructed on the basis of critical information changes. A few computed solution strategies are shown. Several bounds on the minimum number of needed robots are also discussed. 1 Introduction Have you ever searched for someone in a building, possibly exploring the same places multiple time...
Tracking Targets using Multiple Robots: The Effect of Environment Occlusion
 Autonomous Robots
, 2002
"... This paper addresses the problem of tracking multiple 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 w ..."
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Cited by 72 (3 self)
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This paper addresses the problem of tracking multiple 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 which maintains urgency estimates for each region, and a targetfollowing controller attempts to maximize the number of tracked targets within a region. A behaviorbased system is presented implementing the RegionBased Approach, which is fully distributed and scalable. We compared the Regionbased Approach to a ‘naive ’ localfollowing strategy in three environments with varying degree of occlusion. The experimental results showed that the Regionbased Approach performs better than the naive strategy when the environment has significant occlusion. Second, we performed experiments (the environment was held constant) in which two techniques for computing urgency estimates were compared. Last, different combinations of mobile sensors and stationary sensors were compared in a given environment. Keywords: Multitarget tracking, mobile robotics, embedded sensors
Automated camera layout to satisfy taskspecific and floorplanspecific coverage requirements
 COMPUT. VIS. IMAGE UNDERST
, 2004
"... In many multicamera vision systems the effect of camera locations on the taskspecific quality of service is ignored. Researchers in Computational Geometry have proposed elegant solutions for some sensor location problem classes. Unfortunately, these solutions utilize unrealistic assumptions about t ..."
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Cited by 52 (1 self)
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In many multicamera vision systems the effect of camera locations on the taskspecific quality of service is ignored. Researchers in Computational Geometry have proposed elegant solutions for some sensor location problem classes. Unfortunately, these solutions utilize unrealistic assumptions about the cameras’ capabilities that make these algorithms unsuitable for many realworld computer vision applications: unlimited field of view, infinite depth of field, and/or infinite servo precision and speed. In this paper, the general camera placement problem is first defined with assumptions that are more consistent with the capabilities of realworld cameras. The region to be observed by cameras may be volumetric, static or dynamic, and may include holes that are caused, for instance, by columns or furniture in a room that can occlude potential camera views. A subclass of this general problem can be formulated in terms of planar regions that are typical of building floorplans. Given a floorplan to be observed, the problem is then to efficiently compute a camera layout such that certain taskspecific constraints are met. A solution to this problem is obtained via binary optimization over a discrete problem space. In experiments the performance of the resulting system is demonstrated with different real floorplans.
VisibilityBased PursuitEvasion in a Polygonal Region by a Searcher
 Proceedings of the International Colloquium on Automata, Languages and Programming (ICALP
, 2001
"... We consider the most basic visibilitybased pursuitevasion problem defined as follows: Given a polygonal region, a searcher with 360 # vision, and an unpredictable intruder that is arbitrarily faster than the searcher, plan the motion of the searcher so as to see the intruder. In this paper, we ..."
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Cited by 48 (1 self)
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We consider the most basic visibilitybased pursuitevasion problem defined as follows: Given a polygonal region, a searcher with 360 # vision, and an unpredictable intruder that is arbitrarily faster than the searcher, plan the motion of the searcher so as to see the intruder. In this paper, we present simple necessary and su#cient conditions for a polygon to be searchable, which settles a decadeold open problem raised in [15]. We also show that every searchable polygon is also searchable by a searcher with two flashlights (that is, ray visions). This implies, combined with the previous work, that there is an O(n 2 )time algorithm for constructing a search path for an nsided polygon. 1 Introduction The visibilitybased pursuitevasion problem is that of planning the motion of one or more searchers in a polygonal environment to eventually see an intruder that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. This problem can mode...
Tracking and coordination of multiple agents using sensor networks: system design, algorithms and experiments
"... This paper considers the problem of pursuit evasion games (PEGs), where a group of pursuers is required to chase and capture a group of evaders in minimum time with the aid of a sensor network. We assume that a sensor network is previously deployed and provides global observability of the surveilla ..."
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Cited by 43 (13 self)
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This paper considers the problem of pursuit evasion games (PEGs), where a group of pursuers is required to chase and capture a group of evaders in minimum time with the aid of a sensor network. We assume that a sensor network is previously deployed and provides global observability of the surveillance region, allowing an optimal pursuit policy. While sensor networks provide global observability, they cannot provide high quality measurements in a timely manner due to packet losses, communication delays, and false detections. This has been the main challenge in developing a realtime control system using sensor networks. We address this challenge by developing a realtime hierarchical control system which decouples the estimation of evader states from the control of pursuers via multiple layers of data fusion. While a sensor network generates noisy, inconsistent, and bursty measurements, the multiple layers of data fusion convert them into consistent and high quality measurements and forward them to the controllers of pursuers in a timely manner. For this control system, three new algorithms are developed: multisensor fusion, multitarget tracking and multiagent coordination algorithms. The multisensor fusion algorithm converts correlated sensor measurements into position estimates, the multitarget tracking algorithm tracks an unknown number of targets, and the multiagent coordination algorithm coordinates pursuers to capture all evaders in minimum time using a robust minimumtime feedback controller. The combined system is evaluated in simulation and tested in a sensor network deployment. To our knowledge, this paper presents the first demonstration of multitarget tracking using a sensor network without relying on classification.
Randomized PursuitEvasion with Local Visibility
 SIAM Journal on Discrete Mathematics
, 2006
"... 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 su#ce ..."
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Cited by 41 (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 su#ce 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.
Randomized pursuitevasion in graphs
 Proceedings of the International Colloquium on Automata, Languages and Programming (ICALP
, 2002
"... We analyze a randomized pursuitevasion game on graphs. This game is played by two players, a hunter and a rabbit. Let G be any connected, undirected graph with n nodes. The game is played in rounds and in each round both the hunter and the rabbit are located at a node of the graph. Between rounds b ..."
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Cited by 37 (0 self)
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We analyze a randomized pursuitevasion game on graphs. This game is played by two players, a hunter and a rabbit. Let G be any connected, undirected graph with n nodes. The game is played in rounds and in each round both the hunter and the rabbit are located at a node of the graph. Between rounds both the hunter and the rabbit can stay at the current node or move to another node. The hunter is assumed to be restricted to the graph G: in every round, the hunter can move using at most one edge. For the rabbit we investigate two models: in one model the rabbit is restricted to the same graph as the hunter, and in the other model the rabbit is unrestricted, i.e., it can jump to an arbitrary node in every round. We say that the rabbit is caught as soon as hunter and rabbit are located at the same node in a round. The goal of the hunter is to catch the rabbit in as few rounds as possible, whereas the rabbit aims to maximize the number of rounds until it is caught. Given a randomized hunter strategy for G, the escape length for that strategy is the worst case expected number of rounds it takes the hunter to catch the rabbit, where the worst case is with regards to all (possibly randomized) rabbit strategies. Our main result is a hunter strategy for general graphs with an escape length of only O(n log(diam(G))) against restricted as well as unrestricted rabbits. This bound is close to optimal since Ω(n) is a trivial lower bound on the escape length in both models. Furthermore, we prove that our upper bound is optimal up to constant factors against unrestricted rabbits. 1