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27
Lineofsight networks
 Proc. 18th ACMSIAM Symposium on Discrete Algorithms
, 2007
"... Random geometric graphs have been one of the fundamental models for reasoning about wireless networks: one places n points at random in a region of the plane (typically a square or circle), and then connects pairs of points by an edge if they are within a fixed distance of one another. In addition t ..."
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Cited by 12 (1 self)
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Random geometric graphs have been one of the fundamental models for reasoning about wireless networks: one places n points at random in a region of the plane (typically a square or circle), and then connects pairs of points by an edge if they are within a fixed distance of one another. In addition to giving rise to a range of basic theoretical questions, this class of random graphs has been a central analytical tool in the wireless networking community. For many of the primary applications of wireless networks, however, the underlying environment has a large number of obstacles, and communication can only take place among nodes when they are close in space and when they have lineofsight access to one another — consider, for example, urban settings or large indoor environments. In such domains, the standard model of random geometric graphs is not a good approximation of the true constraints, since it is not designed to capture the lineofsight restrictions. Here we propose a randomgraph model incorporating both range limitations and lineofsight constraints, and we prove asymptotically tight results for kconnectivity. Specifically, we consider points placed randomly on a grid (or torus), such that each node can see up to a fixed distance along the row and column it belongs to. (We think of the rows and columns as “streets ” and “avenues ” among a regularly spaced array of obstructions.) Further, we show that when the probability of node placement is a constant factor larger than the threshold for connectivity, nearshortest
COLA: A Coverage and Latency aware Actor Placement for Wireless Sensor and Actor Networks
 in the Proceedings of IEEE Vehicular Technology Conference (VTCFall’06
, 2006
"... Abstract: In addition to the miniaturized sensor nodes, Wireless Sensor and Actor Networks (WSANs) employ significantly more capable actor nodes that can perform application specific actions to deal with events detected and reported by the sensors. In such networks responsiveness to serious events i ..."
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Abstract: In addition to the miniaturized sensor nodes, Wireless Sensor and Actor Networks (WSANs) employ significantly more capable actor nodes that can perform application specific actions to deal with events detected and reported by the sensors. In such networks responsiveness to serious events is of utmost importance and thus minimal latency should be experienced in both data gathering and action completion. In addition, since these actions are often taken at or close to where events are detected, which can be any spot within the monitored area, the actors should strive to provide maximal coverage of the area. In this paper, we propose two actor placement mechanisms for WSANs, namely COLA and COCOLA that consider both the delay requirements of data collection and the coverage of the area. COLA first evenly distributes the actors in the region for maximized coverage. Actors then collaboratively partition the sensors among themselves, forming clusters. An actor plays the role of the clusterhead for the assigned set of sensors; receiving and processing the sensed data. Each individual actor then repositions itself at a location that enables minimal latency in collecting the sensor reports in its cluster. COCOLA is an extension to COLA which additionally enforces connectivity among the actors by assigning appropriate locations to each actor for improved coverage and reduced latency. The effectiveness of both approaches is evaluated through extensive simulation experiments.
Clustering of wireless sensor and actor networks based on sensor distribution and connectivity
 J. Parallel Distrib. Comput
, 2009
"... employ significantly more capable actor nodes that can collect data from sensors and perform application specific actions. To take these actions collaboratively at any spot in the monitored regions, maximal actor coverage along with interactor connectivity is desirable. In this paper, we propose a ..."
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Cited by 8 (1 self)
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employ significantly more capable actor nodes that can collect data from sensors and perform application specific actions. To take these actions collaboratively at any spot in the monitored regions, maximal actor coverage along with interactor connectivity is desirable. In this paper, we propose a distributed actor positioning and clustering algorithm which employs actors as clusterheads and places them in such a way that the coverage of actors is maximized and the data gathering and acting process times are minimized. Such placement of actors is done by determining the khop Independent Dominating Set (IDS) of the underlying sensor network. Basically, before the actors are placed, the sensors pick the clusterheads based on IDS. The actors are then placed to the locations of such clusterheads. We further derive conditions to guarantee interactor connectivity after the clustering is performed. If interconnectivity does not exist, the actors coordinate through the underlying sensors within their clusters to adjust their locations so that connectivity can be established. The performances of the proposed approaches are validated through simulations. I.
Efficient sensor placement for surveillance problems
"... Abstract. We study the problem of covering a twodimensional spatial region P, cluttered with occluders, by sensors. A sensor placed at a location p covers a point x in P if x lies within sensing radius r from p and x is visible from p, i.e., the segment px does not intersect any occluder. The goal ..."
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Abstract. We study the problem of covering a twodimensional spatial region P, cluttered with occluders, by sensors. A sensor placed at a location p covers a point x in P if x lies within sensing radius r from p and x is visible from p, i.e., the segment px does not intersect any occluder. The goal is to compute a placement of the minimum number of sensors that cover P. We propose a landmarkbased approach for covering P. Suppose P has ς holes, and it can be covered by h sensors. Given a small parameter ε> 0, let λ: = λ(h, ε) = (h/ε) log ς. We prove that one can compute a set L of O(λ log λ log (1/ε)) landmarks so that if a set S of sensors covers L, then S covers at least (1 − ε)fraction of P. It is surprising that so few landmarks are needed, and that the number does not depend on the number of vertices in P. We then present efficient randomized algorithms, based on the greedy approach, that, with high probability, compute O ( ˜ hlog λ) sensor locations to cover L; here ˜ h ≤ h is the number sensors needed to cover L. We propose various extensions of our approach, including: (i) a weight function over P is given and S should cover at least (1−ε) of the weighted area of P, and (ii) each point of P is covered by at least t sensors, for a given parameter t ≥ 1. 1
Optimal Communications Systems and Network Design for Cargo Monitoring,” To appear
 in Proc. Tenth Workshop Mobile Computing Systems and Applications (HOTMOBILE
, 2009
"... In the United States there is an emerging trend to ship goods by rail directly from ports to inland intermodal traffic terminals. However, for this trend to succeed shippers must have “visibility ” into rail shipments. In this research we seek to provide visibility into shipments through optimal pla ..."
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Cited by 4 (4 self)
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In the United States there is an emerging trend to ship goods by rail directly from ports to inland intermodal traffic terminals. However, for this trend to succeed shippers must have “visibility ” into rail shipments. In this research we seek to provide visibility into shipments through optimal placement of sensor and communication technology. We formally define the notion of visibility and then highlight the objectives of our study. We also provide a generalized description of an optimization problem that has been developed to determine optimal sensor locations. Several problems must be solved to enable costeffective visibility into rail shipments. We break down these problems into tasks and discuss how they can be addressed. The expected result of the proposed research includes a model (or models) that predicts the system cost given an assignment of sensors to railbased containers. This model can be used to determine costeffective scenarios for deploying sensors to containers on a train, as well as the system tradeoffs.
Data Transmission and BaseStation Placement for Optimizing Network Lifetime
, 2010
"... We study the problem of transmitting data from a set of sensors to a basestation where the data is to be gathered. Each sensor continuously generates data and has to transmit it through the network (via other sensor nodes) to the base station. Considering the battery limitations of the sensors, our ..."
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Cited by 3 (1 self)
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We study the problem of transmitting data from a set of sensors to a basestation where the data is to be gathered. Each sensor continuously generates data and has to transmit it through the network (via other sensor nodes) to the base station. Considering the battery limitations of the sensors, our goal is to find an optimum location of the basestation and a corresponding data transmission scheme for routing the data from the sensors, such that the network is operating for the longest possible time. We focus mainly on tree networks for 2level trees, with at most 2 hops from sensor to the basestation. For such networks we give efficient algorithms for forwarding data from sensors to the basestation and for locating the basestation optimally for maximizing network lifetime. Further, we show that determining a transmission protocol for trees with 3 or more levels is NPhard. We demonstrate the effectiveness of our methods with experimental results on simulated data, comparing our 2level tree algorithm with methods based on linear programming.
Fundamental Results on Base Station Movement Problem for Sensor Networks
"... The benefits of using mobile base station to prolong sensor network lifetime have been well recognized. However, due to the complexity of the problem (timedependent network topology and traffic routing), theoretical performance limits and provably optimal algorithms remain difficult to develop. Th ..."
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The benefits of using mobile base station to prolong sensor network lifetime have been well recognized. However, due to the complexity of the problem (timedependent network topology and traffic routing), theoretical performance limits and provably optimal algorithms remain difficult to develop. This paper fills this important gap by contributing theoretical results regarding the optimal movement of a mobile base station. Our main result hinges upon two key intermediate results. In the first result, we show that a timedependent joint base station movement and flow routing problem can be transformed into a locationdependent problem. In the second result, we show that, for (1 − ε) optimality, the infinite possible locations for base station movement can be reduced to a finite set of locations via several constructive steps [i.e., discretization of energy cost through a geometric sequence, division of a disk into a finite number of subareas, and representation of each subarea with a fictitious cost point (FCP)]. Subsequently, for each FCP, we can obtain the best sojourn time for the base station (as well as the corresponding locationdependent flow routing) via a simple linear program. We prove that the proposed solution can guarantee the achieved network lifetime is at least (1 − ε) of the maximum network lifetime, where ε can be made arbitrarily small depending on required precision.
Joint base station placement and faulttolerant routing in wireless sensor networks
 in Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE
, 2009
"... Abstract—Fault tolerance techniques have been widely used in wireless sensor networks. Base station placement to maximize the network lifetime has also been well studied. However, limited research has been done on the joint base station placement and faulttolerant routing problem. To fill this void ..."
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Abstract—Fault tolerance techniques have been widely used in wireless sensor networks. Base station placement to maximize the network lifetime has also been well studied. However, limited research has been done on the joint base station placement and faulttolerant routing problem. To fill this void, we study this problem and present a fully polynomial time approximation scheme in this paper. Our scheme can compute a (1 − ε)approximation with a running time bounded by a polynomial in 1/ε and the input size of the instance. Despite our solution is presented for the model where the base station can be placed anywhere, however it can be easily extended to cases where forbidden areas are present or candidate locations for the base station are given. To the best of our knowledge, this paper is the first theoretical result on this problem. I.
Polygon Guarding with Orientation
, 2014
"... The art gallery problem is a classical sensor placement problem that asks for the minimum number of guards required to ensure that every point in the environment is visible from a guard. The standard formulation for the art gallery problem does not handle selfocclusions. For instance, even though ..."
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The art gallery problem is a classical sensor placement problem that asks for the minimum number of guards required to ensure that every point in the environment is visible from a guard. The standard formulation for the art gallery problem does not handle selfocclusions. For instance, even though each point of the environment is seen from a camera, it is not guaranteed that the face of person will be visible. Obtaining a good view from all orientations is seen as an important requirement for many visual tracking applications. With this as motivation, we study the polygon guarding problem with orientation. Our objective is to place the fewest number of cameras such that each point is visible from a set of cameras, and the point lies in the convex hull of the cameras. This condition, referred to as △guarding, ensures the entire perimeter of convex object moving in the environment will be visible from at least one camera, in spite of selfocclusion. Our contributions in this paper are twofold: we first prove that for △guarding the complete interior of a simple polygon with n vertices, at least Ω ( √ n) guards are necessary. In light of this large requirement, we study a more practical scenario, where the goal is to △guard a set of line segments connecting points on the boundary of the polygon. This is motivated by applications where a person or object of interest can only move along certain paths in the polygon. For this version of the problem, we present a constant factor approximation algorithm – one of the few such results for art gallery problems.
Sensor Placement and Selection for Bearing Sensors with Bounded Uncertainty
"... We study the problem of placing sensors so as to accurately estimate the location of a target in a given environment. We focus on bearing sensors (such as cameras, microphone arrays) which are commonly used for target localization. We seek to discover and exploit the geometric structure associated w ..."
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We study the problem of placing sensors so as to accurately estimate the location of a target in a given environment. We focus on bearing sensors (such as cameras, microphone arrays) which are commonly used for target localization. We seek to discover and exploit the geometric structure associated with both the sensing model and the estimation process in order to obtain sensor placement schemes with performance guarantees. We use a geometric model to represent the sensing uncertainty: Each measurement yields an unbounded 2D wedge with angular width 2α around the measurement (α is an input parameter representing the maximum sensing noise). The wedge is guaranteed to contain the true location of the target. The target is localized by intersecting the wedges obtained from all sensors. The quality of the placement is given by the area or diameter of the intersection in the worstcase (i.e. regardless of the target’s location). We study the bicriteria optimization problem of placing a small number of sensors while guaranteeing a worstcase bound on the estimation error. Our main result is a constantfactor approximation for this problem: Let U ∗ D and UA ∗ be the diameter and area uncertainty achieved by an optimal algorithm using n ∗ sensors. We show that at most 9n ∗ sensors placed on a triangular grid has diameter uncertainty of at most 5.88U ∗ D and area uncertainty of at most 7.76U ∗ π π A, when the sensing noise 0 < 2α ≤ 2