Browsing by Subject "Sensor nodes"

Now showing 1 - 20 of 20

Open Access
Adaptive decision fusion based cooperative spectrum sensing for cognitive radio systems
(IEEE, 2011) Töreyin, B. U.; Yarkan, S.; Qaraqe, K. A.; Çetin, A. Enis
In this paper, an online Adaptive Decision Fusion (ADF) framework is proposed for the central spectrum awareness engine of a spectrum sensor network in Cognitive Radio (CR) systems. Online learning approaches are powerful tools for problems where drifts in concepts take place. Cooperative spectrum sensing in cognitive radio networks is such a problem where channel characteristics and utilization patterns change frequently. The importance of this problem stems from the requirement that secondary users must adjust their frequency utilization strategies in such a way that the communication performance of the primary users would not be degraded by any means. In the proposed framework, sensing values from several sensor nodes are fused together by weighted linear combination at the central spectrum awareness engine. The weights are updated on-line according to an active fusion method based on performing orthogonal projections onto convex sets describing power reading values from each sensor. The proposed adaptive fusion strategy for cooperative spectrum sensing can operate independent from the channel type between the primary user and secondary users. Results of simulations and experiments for the proposed method conducted in laboratory are also presented. © 2011 IEEE.
Open Access
An adaptive, energy-aware and distributed fault-tolerant topology-control algorithm for heterogeneous wireless sensor networks
(Elsevier BV, 2016) Deniz, F.; Bagci, H.; Korpeoglu, I.; Yazıcı A.
This paper introduces an adaptive, energy-aware and distributed fault-tolerant topology-control algorithm, namely the Adaptive Disjoint Path Vector (ADPV) algorithm, for heterogeneous wireless sensor networks. In this heterogeneous model, we have resource-rich supernodes as well as ordinary sensor nodes that are supposed to be connected to the supernodes. Unlike the static alternative Disjoint Path Vector (DPV) algorithm, the focus of ADPV is to secure supernode connectivity in the presence of node failures, and ADPV achieves this goal by dynamically adjusting the sensor nodes' transmission powers. The ADPV algorithm involves two phases: a single initialization phase, which occurs at the beginning, and restoration phases, which are invoked each time the network's supernode connectivity is broken. Restoration phases utilize alternative routes that are computed at the initialization phase by the help of a novel optimization based on the well-known set-packing problem. Through extensive simulations, we demonstrate that ADPV is superior in preserving supernode connectivity. In particular, ADPV achieves this goal up to a failure of 95% of the sensor nodes; while the performance of DPV is limited to 5%. In turn, by our adaptive algorithm, we obtain a two-fold increase in supernode-connected lifetimes compared to DPV algorithm.
Open Access
Balancing energy loads in wireless sensor networks through uniformly quantized energy levels-based clustering
(IEEE, 2010) Ali, Syed Amjad; Sevgi, Cüneyt; Kocyigit, A.
Clustering is considered a common and an effective method to prolong the lifetime of a wireless sensor network. This paper provides a new insight into the cluster formation process based on uniformly quantizing the residual energy of the sensor nodes. The unified simulation framework provided herein, not only aids to reveal an optimum number of clusters but also the required number of quantization levels to maximize the network's lifetime by improving energy load balancing for both homogeneous and heterogeneous sensor networks. The provided simulation results clearly show that the uniformly quantized energy level-based clustering provides improved load balancing and hence, a longer network lifetime than existing methods. © 2010 IEEE.
Open Access
Controlled sink mobility algorithms for wireless sensor networks
(Taylor and Francis Inc., 2014) Koç, M.; Korpeoglu I.
A wireless sensor network (WSN) consists of hundreds or thousands of sensor nodes organized in an ad hoc manner to achieve a predefined goal. Although WSNs have limitations in terms of memory and processors, the main constraint that makes WSNs different from traditional networks is the battery problem which limits the lifetime of a network. Different approaches are proposed in the literature for improving the network lifetime, including data aggregation, energy efficient routing schemes, and MAC protocols. Sink node mobility is also an effective approach for improving the network lifetime. In this paper, we investigate controlled sink node mobility and present a set of algorithms for deciding where and when to move a sink node to improve network lifetime. Moreover, we give a load-balanced topology construction algorithm as another component of our solution. We did extensive simulation experiments to evaluate the performance of the components of our mobility scheme and to compare our solution with static case and random movement strategy. The results show that our algorithms are effective in improving network lifetime and provide significantly better lifetime compared to static sink case and random movement strategy. © 2014 Metin Koç and Ibrahim Korpeoglu.
Open Access
A distributed and dynamic data gathering protocol for sensor networks
(IEEE, 2007-05) Tan, Hüseyin Özgür; Körpeoğlu, İbrahim; Stojmenović, I.
In this paper we propose a distributed, self organizing, robust and energy efficient data gathering algorithm for sensor networks operating in environments where all the sensor nodes are not in direct communication range of each other and data aggregation is used while routing. Proposed algorithm is based on local minimum spanning tree (LMST) structure, which nodes can construct from the position of their 1-hop neighbors. Reporting tree is constructed from the sink by allowing only edges of LMST to join the tree, plus possibly some direct links to the sink. Each node selects as parent the LMST neighbor so that the total energy cost of route to the sink is minimal. We also describe route maintenance protocols to respond to predicted sensor failures and addition of new sensors. Our simulation results show that our algorithm prolongs the network lifetime significantly compared to some alternative schemes. © 2007 IEEE.
Open Access
Distributed and location-based multicast routing algorithms for wireless sensor networks
(SpringerOpen, 2009-01) Korpeoglu, I.; Bagci, H.
Multicast routing protocols in wireless sensor networks are required for sending the same message to multiple different destinations. In this paper, we propose two different distributed algorithms for multicast routing in wireless sensor networks which make use of location information of sensor nodes. Our first algorithm groups the destination nodes according to their angular positions and forwards the multicast message toward each group in order to reduce the number of total branches in multicast tree which also reduces the number of messages transmitted. Our second algorithm calculates an Euclidean minimum spanning tree at the source node by using the positions of the destination nodes. The multicast message is forwarded to destination nodes according to the calculated MST. This helps in reducing the total energy consumed for delivering the message to all destinations by decreasing the number of total transmissions. Evaluation results show that the algorithms we propose are scalable and energy efficient, so they are good candidates to be used for multicasting in wireless sensor networks. Copyright © 2009 H. Bagci and I. Korpeoglu.
Open Access
Distributed bounding of feasible sets in cooperative wireless network positioning
(IEEE, 2013) Gholami, M. R.; Wymeersch, H.; Gezici, Sinan; Ström, E. G.
Locations of target nodes in cooperative wireless sensor networks can be confined to a number of feasible sets in certain situations, e.g., when the estimated distances between sensors are larger than the actual distances. Quantifying feasible sets is often challenging in cooperative positioning. In this letter, we propose an iterative technique to cooperatively outer approximate the feasible sets containing the locations of the target nodes. We first outer approximate a feasible set including a target node location by an ellipsoid. Then, we extend the ellipsoid with the measured distances between sensor nodes and obtain larger ellipsoids. The larger ellipsoids are used to determine the intersections containing other targets. Simulation results show that the proposed technique converges after a small number of iterations.
Open Access
A distributed positioning algorithm for cooperative active and passive sensors
(IEEE, 2010) Gholami, M.R.; Gezici, Sinan; Rydström, M.; Ström, E.G.
The problem of positioning a target node is studied for wireless sensor networks with cooperative active and passive sensors. Two-way time-of-arrival and time-difference-of-arrival measurements made by both active and passive nodes are used to estimate the position of the target node. A maximum likelihood estimator (MLE) can be employed to solve the problem. Due to the nonlinear nature of the cost function in the MLE, an iterative search might converge to local minima which often results in large estimation errors. To avoid this drawback, we instead formulate the problem of positioning as finding the intersection of a number of convex sets derived from measurements. To obtain this intersection, we apply the projection onto convex sets approach, which is robust and can be implemented in a distributed manner. Simulations are performed to compare the performance of the MLE and the proposed method. ©2010 IEEE.
Open Access
DSSP: A Dynamic Sleep Scheduling Protocol for prolonging the lifetime of wireless sensor networks
(IEEE, 2007-05) Bulut, Eyüphan; Körpeoğlu, İbrahim
This paper presents DSSP (Dynamic Sleep Scheduling Protocol), a centralized scheme for extending the lifetime of densely deployed wireless sensor networks by keeping only a necessary set of sensor nodes active. We present an algorithm for finding out which nodes should be put into sleep mode, and the algorithm preserves coverage and connectivity while trying to put as much nodes as possible into sleep mode. The algorithm is executed at the base station periodically. In this way, the network is reconfigured periodically, which also helps to a more even distribution of energy consumption load to sensor nodes. We evaluated our protocol via simulations and observed a significant increase in the lifetime, depending on the node density, while providing good coverage. © 2007 IEEE.
Open Access
An energy efficient scatternet formation algorithm for Bluetooth-based sensor networks
(IEEE, 2005-02) Saginbekov, Sain; Körpeoğlu, İbrahim
In this paper, we propose an energy-efficient scatternet formation algorithm for Bluetooth based sensor networks. The algorithm is based on first computing a shortest path tree from the base station to all sensor nodes and then solving the degree constraint problem so that the degree of each node in the network is not greater than seven, which is a Bluetooth constaint. In this way, less amount of energy is spent in each round of communication in the sensor network. The algorithm also tries to balance the load evenly on the high-energy consuming nodes which are the nodes that are close to the base station. In this way, the lifetime of the first dying node is also prolonged. We obtained promising results in the simulations. © 2005 IEEE.
Open Access
Improved position estimation using hybrid TW-TOA and TDOA in cooperative networks
(Institute of Electrical and Electronics Engineers, 2012-04-13) Gholami, M. R.; Gezici, Sinan; Ström, E. G.
This paper addresses the problem of positioning multiple target nodes in a cooperative wireless sensor network in the presence of unknown turn-around times. In this type of cooperative networks, two different reference sensors, namely, primary and secondary nodes, measure two-way time-of-arrival (TW-TOA) and time-difference-of-arrival (TDOA), respectively. Motivated by the role of secondary nodes, we extend the role of target nodes such that they can be considered as pseudo secondary nodes. By modeling turn-around times as nuisance parameters, we derive a maximum likelihood estimator (MLE) that poses a difficult global optimization problem due to its nonconvex objective function. To avoid drawbacks in solving the MLE, we linearize the measurements using two different techniques, namely, nonlinear processing and first-order Taylor series, and obtain linear models based on unknown parameters. The proposed linear estimator is implemented in three steps. In the first step, a coarse position estimate is obtained for each target node, and it is refined through steps two and three. To evaluate the performance of different methods, we derive the Cramér-Rao lower bound (CRLB). Simulation results show that the cooperation technique provides considerable improvements in positioning accuracy compared to the noncooperative scenario, especially for low signal-to-noise-ratios.
Open Access
On the analysis of expected distance between sensor nodes and the base station in randomly deployed WSNs
(Springer Verlag, 2014) Sevgi, C.; Ali, S.A.
In this study, we focus on the analytical derivation of the expected distance between all sensor nodes and the base station (i.e., E[dtoBS]) in a randomly deployed WSN. Although similar derivations appear in the related literature, to the best of our knowledge, our derivation, which assumes a particular scenario, has not been formulated before. In this specific scenario, the sensing field is a square-shaped region and the base station is located at some arbitrary distance to one of the edges of the square. Having the knowledge of E[dtoBS] value is important because E[dtoBS] provides a network designer with the opportunity to make a decision on whether it is energy-efficient to perform clustering for WSN applications that aim to pursue the clustered architectures. Similarly, a network designer might make use of this expected value during the process of deciding on the modes of communications (i.e., multi-hop or direct communication) after comparing it with the maximum transmission ranges of devices. Last but not least, the use of our derivation is not limited to WSN domain. It can be also exploited in any domain when there is a need for a probabilistic approach to find the average distance between any given number of points which are all assumed to be randomly and uniformly located in any square-shaped region and at a specific point outside this region. © Springer International Publishing Switzerland 2014.
Open Access
An optimal network dimensioning and initial energy assignment minimizing the monetary cost of a heterogeneous WSN
(IEEE, 2009) Sevgi, Cüneyt; Kocyigit, A.
In this paper, a novel method is proposed to dimension a randomly deployed heterogeneous Wireless Sensor Network (WSN) of minimum monetary cost satisfying minimum coverage and minimum lifetime requirements. We consider WSNs consisting of two different types of nodes clusterheads and ordinary sensor nodes, randomly deployed over a sensing field. All devices are assumed to be stationary and have identical sensing capabilities. However, the clusterheads are more energetic and powerful in terms of processing and communication capabilities compared to sensor nodes. For such a network, finding minimum cost WSN problem is not a trivial one, since the distribution of the mixture of two different types of devices and the batteries with different initial energies in each type of device primarily determine the monetary cost of a WSN. Therefore, we formulated an optimization problem to minimize the monetary cost of a WSN for given coverage and lifetime requirements. The proposed optimization problem is solved for a certain scenario and the solution is validated by computer simulations. © 2009 IEEE.
Open Access
Power-source-aware backbone routing in wireless sensor networks
(IEEE, 2010-11) Tekkalmaz, Metin; Körpeoğlu, İbrahim
Due to the limited energy-source and mostly unattended nature of the wireless sensor networks, efficient use of energy has a critical importance on the lifetime of the applications accomplished by such networks. Although in most of the cases sensor nodes are battery-powered, there are application scenarios in which battery- and mains-powered nodes coexist. In this paper, we present an approach and algorithms based on this approach that increase the lifetime of wireless sensor networks in such heterogeneous deployment cases. In the proposed approach, a backbone, which is composed of mains-powered nodes, sink, and battery-powered nodes if required, is constructed to relay the data packets. Simulation results show that, the proposed approach is able to increase the network lifetime up to more than a factor of two, compared to the case in which battery- and mains-powered nodes are not distinguished.
Open Access
Range based sensor node localization in the presence of unknown clock skews
(IEEE, 2013) Gholami, M.R.; Gezici, Sinan; Strom, E.G.
We deal with the positioning problem based on two-way time-of-arrival (TW-TOA) measurements in asynchronous wireless sensor networks. The optimal estimator for this problem poses a difficult global optimization problem. To avoid the drawbacks in solving the optimal estimator, we use approximations and derive linear models, which facilitate efficient solutions. In particular, we employ the least squares method and solve a general trust region subproblem to find a coarse estimate. To further refine the estimate, we linearize the measurements and obtain a linear model which can be solved using regularized least squares. Simulation results illustrate that the proposed approaches asymptotically attain the Cramér-Rao lower bound. © 2013 IEEE.
Open Access
Rule-based in-network processing in wireless sensor networks
(IEEE, 2009-07) Şanlı, Ö.; Körpeoğlu, İbrahim; Yazıcı, A.
Wireless sensor networks are application-specific networks, and usually a new network design is required for a new application. In event-driven wireless sensor network applications, the sink node of the network is generally concerned with the higher level information describing the events happening in the network, not the raw sensor data of individual sensor nodes. As the communication is a costly operation in wireless sensor networks, it is important to process the raw data triggering the events inside the network instead of bringing the raw data to the sink and processing it there. This helps reducing the total amount of packets transmitted and total energy consumed in the network. In this paper, we propose a new method that distributes the information processing into the sensor network for event-driven applications. We also describe an application scenario, healthcare monitoring application, that can benefit from our approach. © 2009 IEEE.
Open Access
Static positioning using UWB range measurements
(IEEE, 2010) Gholami, M.R.; Ström, E.G.; Sottile F.; Dardari, D.; Conti, A.; Gezici, Sinan; Rydström, M.; Spirito, M.A.
The performance of several existing and partly new algorithms for positioning of sensor node based on distance estimate is compared when the distance estimates are obtained from a measurement campaign. The distance estimates are based on time-of-arrival measurements done by ultrawideband devices in an indoor office environment. Two different positioning techniques are compared: statistical and geometrical. In statistical category, distributed weighted-multidimensional scaling (dwMDS), least squares, and sum product algorithm are evaluated and in geometrical technique projections approach and outer approximation (OA) method are investigated. No method shows the best performance in all cases, while in many situations, sum product algorithm, dwMDS, nonlinear least square, projection approach, OA, and weighted least square work well. Copyright © The authors.
Open Access
Tree-based channel assignment schemes for multi-channel wireless sensor networks
(John Wiley & Sons Ltd., 2016) Terzi, C.; Korpeoglu, I.
Many sensor node platforms used for establishing wireless sensor networks (WSNs) can support multiple radio channels for wireless communication. Therefore, rather than using a single radio channel for whole network, multiple channels can be utilized in a sensor network simultaneously to decrease overall network interference, which may help increase the aggregate network throughput and decrease packet collisions and delays. This method, however, requires appropriate schemes to be used for assigning channels to nodes for multi-channel communication in the network. Because data generated by sensor nodes are usually delivered to the sink node using routing trees, a tree-based channel assignment scheme is a natural approach for assigning channels in a WSN. We present two fast tree-based channel assignment schemes (called bottom up channel assignment and neighbor count-based channel assignment) for multi-channel WSNs. We also propose a new interference metric that is used by our algorithms in making decisions. We validated and evaluated our proposed schemes via extensive simulation experiments. Our simulation results show that our algorithms can decrease interference in a network, thereby increasing performance, and that our algorithms are good alternatives for static channel assignment in WSNs.
Open Access
Upper bounds on position error of a single location estimate in wireless sensor networks
(Hindawi Publishing Corporation, 2014) Gholami, M. R.; Ström, E. G.; Wymeersch, H.; Gezici, Sinan
This paper studies upper bounds on the position error for a single estimate of an unknown target node position based on distance estimates in wireless sensor networks. In this study, we investigate a number of approaches to confine the target node position to bounded sets for different scenarios. Firstly, if at least one distance estimate error is positive, we derive a simple, but potentially loose upper bound, which is always valid. In addition assuming that the probability density of measurement noise is nonzero for positive values and a sufficiently large number of distance estimates are available, we propose an upper bound, which is valid with high probability. Secondly, if a reasonable lower bound on negative measurement errors is known a priori, we manipulate the distance estimates to obtain a new set with positive measurement errors. In general, we formulate bounds as nonconvex optimization problems. To solve the problems, we employ a relaxation technique and obtain semidefinite programs. We also propose a simple approach to find the bounds in closed forms. Simulation results show reasonable tightness for different bounds in various situations.
Open Access
A Wi-Fi cluster based wireless sensor network application and deployment for wildfire detection
(Hindawi Publishing Corporation, 2014) Ulucinar, A.R.; Korpeoglu I.; Cetin, A.E.
We introduce the wireless sensor network (WSN) data harvesting application we developed for wildfire detection and the experiments we have performed. The sensor nodes are equipped with temperature and relative humidity sensors. They are organized into clusters and they communicate with the cluster heads using 802.15.4/ZigBee wireless links. The cluster heads report the harvested data to the control center using 802.11/Wi-Fi links. We introduce the hardware and the software architecture of our deployment near Rhodiapolis, an ancient city raising on the outskirts of Kumluca county of Antalya, Turkey. We detail our technical insights into the deployment based on the real-world data collected from the site. We also propose a temperature-based fire detection algorithm and we evaluate its performance by performing experiments in our deployment site and also in our university. We observed that our WSN application can reliably report temperature data to the center quickly and our algorithms can detect fire events in an acceptable time frame with no or very few false positives. © 2014 Alper Rifat Ulucinar et al.