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    Breadth-first search tree integrated vertex cover algorithms for link monitoring and routing in wireless sensor networks
    (Elsevier, 2021) Yigit, Yasin; Akram, Vahid Khalilpour; Dagdeviren, Orhan
    Wireless sensor networks (WSNs) are infrastructureless networks of tiny sensor motes which can sense from the environment and can transmit the sensed data through wireless communication. Generally, the transmission ranges of sensor nodes are limited and obstacles are present in the sensing area, so multi-hop communication by utilizing routing protocols is of utmost importance. Since the wireless transmission is prone to vulnerabilities such as eavesdropping and spoofing, monitoring the network traffic by secure points is a critical mission. In this paper, we propose breadth-first search tree (BFST) based vertex cover (VC) algorithms for routing and link monitoring in WSNs. BFST provides a shortest hop routing tree for WSNs and VC is a set of nodes for covering edges (communication links) of the network where it perfectly fits for network traffic monitoring. Unlike most existing algorithms which find minimal VC in a separate procedure, the proposed algorithms construct VC during the BFST establishment phase which leads to lower energy consumption for routing and link monitoring operations. We analyze the correctness proof of the algorithms along with the time, message, space, and bit complexities. We implement the proposed algorithms with their counterparts on a testbed of IRIS motes to evaluate their performances. We find through extensive evaluations from the IRIS testbed experiments and TinyOS simulations that the proposed algorithms find smaller VC sets with up to 3.1 times lower energy consumption than the existing distributed algorithms.
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    Evaluation of Fault Tolerant Link Monitoring Algorithms for Wireless Sensor Networks
    (Ieee, 2018) Yigit, Yasin; Dagdeviren, Orhan
    Wireless sensor networks are ad-hoc networks that operate with limited capacity and energy. in wireless sensor networks, it may be desirable to monitor the traffic on the network by checking the links for the security of the system. For such a scenario, the vertex cover problem, which is the well-known problem in the graph theory, can be used. The problem is covering of links on the graph by selecting the minimum number of nodes. Thus, all connections on the network can be controlled using as few devices as possible. Self-stabilizing algorithms are algorithms that stabilize the system without external intervention from a random initial state. At this point, the system guarantees a stabilization after a limited time against possible faults. in this study evaluation of vertex cover algorithms for fault tolerant link monitoring in wireless sensor network is made and it is shown that Kiniwa's algorithm performs better than the other algorithms.
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    Fault Tolerance Performance of Self-stabilizing Independent Set Algorithms on a Covering-Based Problem: The Case of Link Monitoring in WSNs
    (Ieee, 2018) Yigit, Yasin; Ileri, Can Umut; Dagdeviren, Orhan
    Vertex cover (VC) is one of the most fundamental graph-theoretical problems and has been widely used in wireless sensor networks (WSNs), particularly for the link monitoring problem. It is well known that a solution to the independent set problem (IS), which is another fundamental graph-theoretical problem, is complement of a VC. Self-stabilization is an important concept for designing fault tolerance systems. There have been many self-stabilizing VC and IS algorithms in the field. Even though a self-stabilizing IS algorithm can provide VC solutions, it does not give a theoretical guarantee on approximation ratio. In this work, we focus on practical fault tolerance performance of self-stabilizing IS algorithms in case of a vertex cover problem, particularly link monitoring in WSNs. We implement all existing self-stabilizing VC and IS algorithms and make simulations assuming a WSN in which nodes run synchronously. Results show that self-stabilizing IS algorithms in general are able to find better covers than VC algorithms, as they provide roughly 15% smaller solution sets. Furthermore, IS algorithms that run under distributed scheduler converges to a desired configuration in considerably less number of rounds than VC algorithms.
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    Movement Based Connectivity Restoration System for Wireless Sensor and Actor Networks
    (Ieee, 2018) Akram, Vahid Khalilpour; Yigit, Yasin; Dagdeviren, Orhan
    A k-connected wireless sensor and actor network (WSAN) has k independent paths to route between each node pair. Having high k value for a network is important in terms of fault tolerance and reliability. When a node in a network fails, k value can be kept constant by moving existing active nodes to desired locations. The aim of the k-connectivity restoration process is to maintain the current k value of the network at a constant value. in this study, a movement based restoration system is developed using IRIS nodes and Kobuki robots. The general architecture of the system is given, software and communication design are presented. The proposed system can be used as an infrastructure in various WSAN applications.
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    Performance Evaluation of Capacitated Vertex Cover Algorithms for Security Applications in Wireless Sensor Networks
    (Ieee, 2021) Yigit, Yasin; Dagdeviren, Zuleyha Akusta; Dagdeviren, Orhan; Challenger, Moharram
    Monitoring the links of wireless sensor networks (WSNs) is a very crucial operation to detect security attacks targeted to the legitimate nodes in internet of things. To achieve this, identifying the monitor nodes (secure points) among the nodes in a WSN and assigning their links are of utmost importance. Vertex cover is a popular problem in the areas of graph theory, approximation algorithms and optimization. Vertex coveris a set of nodes where an edge (link) is incident to at least one of nodes in this set. Hence, vertex cover can be used as the set of the monitor nodes. Capacitated vertex cover, which restricts the edge count that a node can cover, is a specialized version of the vertex cover problem. It provides energy-efficient link monitoring by restricting the link count. In this study, we evaluate capacitated vertex cover algorithms in terms of the cardinality of vertex cover, running time, and approximation ratio. To the best of our knowledge, this is the first evaluation in this manner. Firstly, we theoretically analyze the capacitated vertex cover algorithms, then implement these algorithms in SageMath language that is utilized for solving linear programming and mathematical problems. From our obtained extensive measurement results, we reveal that Naor 8-approximation algorithm performs best having the lowest approximation ratio with 1.13 by selecting 1.12 times fewer vertices in the feasible execution time, although its approximation ratio is worse than the others.
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    Self-Stabilizing Capacitated Vertex Cover Algorithms for Internet-of-Things-Enabled Wireless Sensor Networks
    (Mdpi, 2022) Yigit, Yasin; Dagdeviren, Orhan; Challenger, Moharram
    Wireless sensor networks (WSNs) achieving environmental sensing are fundamental communication layer technologies in the Internet of Things. Battery-powered sensor nodes may face many problems, such as battery drain and software problems. Therefore, the utilization of self-stabilization, which is one of the fault-tolerance techniques, brings the network back to its legitimate state when the topology is changed due to node leaves. In this technique, a scheduler decides on which nodes could execute their rules regarding spatial and temporal properties. A useful graph theoretical structure is the vertex cover that can be utilized in various WSN applications such as routing, clustering, replica placement and link monitoring. A capacitated vertex cover is the generalized version of the problem which restricts the number of edges covered by a vertex by applying a capacity constraint to limit the covered edge count. In this paper, we propose two self-stabilizing capacitated vertex cover algorithms for WSNs. To the best of our knowledge, these algorithms are the first attempts in this manner. The first algorithm is stabilized under an unfair distributed scheduler (that is, the scheduler which does not grant all enabled nodes to make their moves but guarantees the global progress of the system) at most O(n(2)) step, where n is the count of nodes. The second algorithm assumes 2-hop (degree 2) knowledge about the network and runs under the unfair scheduler, which subsumes the synchronous and distributed fair scheduler and stabilizes itself after O(n) moves in O(n) step, which is acceptable for most WSN setups. We theoretically analyze the algorithms to provide proof of correctness and their step complexities. Moreover, we provide simulation setups by applying IRIS sensor node parameters and compare our algorithms with their counterparts. The gathered measurements from the simulations revealed that the proposed algorithms are faster than their competitors, use less energy and offer better vertex cover solutions.