Browsing by Subject "Ad hoc networks"
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Item Open Access Bluetooth or 802.15.4 technologies to optimise lifetime of wireless sensor networks: Numerical comparison under a common framework(IEEE, 2008-04) Buratti, C.; Körpeoğlu, İbrahim; Karasan, Ezhan; Verdone, R.This paper aims at comparing through simulations the network lifetime of a wireless sensor network using Bluetooth-enabled or IEEE802.15.4 compliant devices. The evaluation is performed under a common reference framework, namely the EMORANS scenario for wireless sensor networks. Since the two enabling technologies rely on different MAC paradigms, suitable definition of the performance metrics is needed, in order to make the comparison meaningful. Thus, the paper has also a methodological objective. In particular, three different definitions of network lifetime are introduced, and a comparison of performance obtained by applying the different definitions is provided. Then, the comparison between the two standards is introduced: it is shown that there are no orders of magnitude of difference in network lifetime when the two technologies are used and the choice of the technology depends on the application requirements.Item 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.Item Open Access Distributed construction and maintenance of bandwidth and energy efficient bluetooth scatternets(Institute of Electrical and Electronics Engineers, 2006-09) Tekkalmaz, M.; Sözer, H.; Korpeoglu, I.Bluetooth networks can be constructed as piconets or scatternets depending on the number of nodes in the network. Although piconet construction is a well-defined process specified in Bluetooth standards, scatternet formation policies and algorithms are not well specified. Among many solution proposals for this problem, only a few of them focus on efficient usage of bandwidth in the resulting scatternets. In this paper, we propose a distributed algorithm for the scatternet formation problem that dynamically constructs and maintains a scatternet based on estimated traffic flow rates between nodes. The algorithm is adaptive to changes and maintains a constructed scatternet for bandwidth-efficiency when nodes come and go or when traffic flow rates change. Based on simulations, the paper also presents the improvements in bandwidth-efficiency and reduction in energy consumption provided by the proposed algorithm.Item Open Access First large-scale information retrieval experiments on Turkish texts(ACM, 2006-08) Can, Fazlı; Koçberber, Seyit; Balcık, Erman; Kaynak, Cihan; Öcalan, H. Çağdaş; Vursavaş, Onur M.We present the results of the first large-scale Turkish information retrieval experiments performed on a TREC-like test collection. The test bed, which has been created for this study, contains 95.5 million words, 408,305 documents, 72 ad hoc queries and has a size of about 800MB. All documents come from the Turkish newspaper Milliyet. We implement and apply simple to sophisticated stemmers and various query-document matching fonctions and show that truncating words at a prefix length of 5 creates an effective retrieval environment in Turkish. However, a lemmatizer-based stemmer provides significantly better effectiveness over a variety of matching functions.Item Open Access Information retrieval on Turkish texts(John Wiley & Sons, Inc., 2008-02) Can, F.; Kocberber, S.; Balcik, E.; Kaynak, C.; Ocalan, H. C.; Vursavas, O. M.In this study, we investigate information retrieval (IR) on Turkish texts using a large-scale test collection that contains 408,305 documents and 72 ad hoc queries. We examine the effects of several stemming options and query-document matching functions on retrieval performance. We show that a simple word truncation approach, a word truncation approach that uses language-dependent corpus statistics, and an elaborate lemmatizer-based stemmer provide similar retrieval effectiveness in Turkish IR. We investigate the effects of a range of search conditions on the retrieval performance; these include scalability issues, query and document length effects, and the use of stop-word list in indexing. © 2007 Wiley Periodicals, Inc.Item Open Access Joint topology design with routing and power control in ad hoc networks(Bilkent University, 2003) Önal, AydoğanWe discuss the problem of designing an ad hoc network topology by jointly using power control and routing. A well-designed topology in ad hoc networks provides several advantages: increasing the capacity, decreasing the complexity and reducing the power consumption. We formulate the topology design problem as an Integer Linear Programming (ILP) model. An optimal topology is designed subject to interference and connectivity constraints with three different objective functions and two power control approaches. Common transmit power (COMPOW) and the adaptive power (ADPOW) are the two different power control techniques used in this thesis. The objectives of the models that are used in the topology design are maximizing the number of established links, using shortest path routing strategy and minimizing the maximum traffic load over the most congested link by load balancing. Performance comparisons between two power control approaches with three different objectives in the topology design are achieved using numerical results on a sample network. Minimum end-to-end throughput, total throughput, total power consumption and the number of established links are used as the performance metrics. The numerical results show that selecting the optimal power for both power control approaches provides similar performance results. Therefore, simplicity of the COMPOW makes it more attractive than ADPOW in the topology design.Item Open Access A path-quality-aware peer-to-peer file sharing protocol for mobile ad-hoc networks: Wi-Share(IEEE, 2009-09) Karasabun, Efe; Ertemür, Doğuş; Sarıyıldız, Seyhun; Tekkalmaz, Metin; Körpeoğlu, İbrahimPeer-to-peer networks are rather well-studied and currently there are numerous systems based on peer-to-peer principles running on the Internet. On the other hand peer-to-peer networks for mobile ad-hoc networks have attracted attention only in the recent years. In this paper, we propose a novel peer-to-peer file sharing system particularly designed for mobile ad-hoc networks. The proposed system, namely Wi-Share, has both network and application layer aspects enabling efficient search and download of the shared files. Wi-Share uses reactive routing for the search operation combined with source discovery and uses the routing tables constructed during the search operation for the download operation. In order to increase the overall efficiency of the file sharing in the network, Wi-Share applies techniques to reduce the required traffic and to increase efficient parallelism of the download operation. These techniques include filtering search results, preferring the higher quality routing paths, using partitioned download scheme and allowing the nodes that have joined to the network recently to contribute to the ongoing downloads. Wi-Share is implemented to work on mobile computers and the results of several experiments are also presented in the paper. © 2009 IEEE.Item Open Access A peer-to-peer file search and download protocol for wireless ad-hoc networks(Elsevier BV, 2009-01) Sözer, H.; Tekkalmaz, M.; Korpeoglu, I.Deployment of traditional peer-to-peer file sharing systems on a wireless ad-hoc network introduces several challenges. Information and workload distribution as well as routing are major problems for members of a wireless ad-hoc network, which are only aware of their immediate neighborhood. In this paper, we propose a file sharing system that is able to answer location queries, and also discover and maintain the routing information that is used to transfer files from a source peer to another peer. We present a cross-layer design, where the lookup and routing functionality are unified. The system works according to peer-to-peer principles, distributes the location information of the shared files among the members of the network. The paper includes a sample scenario to make the operations of the system clearer. The performance of the system is evaluated using simulation results and analysis is provided for comparing our approach with a flooding-based, unstructured approach. © 2008 Elsevier B.V. All rights reserved.Item Open Access A performance comparison of zone-based multicast protocols for mobile ad hoc networks(IEEE, 2003) Zhang, Y.; Rangnekar, A.; Selçuk, Ali A.; Bicak, A.; Sidhu, D.With the current trend toward ubiquitous computing come wireless devices capable of forming the nodes of mobile ad hoc networks. Such networks typically rely on routing protocols in order to communicate messages from a source node to a destination node through a set of intermediary nodes. In a typical ad hoc environment, mobile nodes mostly work as a group and are involved in collaborative computing. Multicast communication is more effective in these scenarios. This paper presents the comparison of the performance of two zone-based multicast routing protocols. Shared-tree MZR is a shared tree variant of the Multicast Routing Protocol based on Zone Routing (MZR). We compare the two variants and analyze their performance under various network conditions. The test results show that Shared-tree MZR protocol performs well and has significantly low overhead in scenarios with multiple sources. ©2003 IEEE.Item Open Access PETAL: a fully distributed location service for wireless ad hoc networks(Academic Press, 2017) Ilkhechi, A. R.; Korpeoglu, I.; Güdükbay, Uğur; Ulusoy, ÖzgürLocation service is an essential prerequisite for mobile wireless ad hoc networks (MANETs) in which the underlying routing protocol leverages physical location information of sender and receiver nodes. Fulfillment of this requirement is challenging partly due to the mobility and unpredictability of nodes in MANETs. Moreover, scalability and location information availability under various circumstances are also substantial factors in designing an effective location service paradigm. By and large, utilizing centralized or distributed location servers responsible for storing the location information of all, or a subset of participant mobile devices, is a method employed in a significant portion of location service schemes. However, from the fairness point of view, it is more suitable to employ a location service scheme that treats participant nodes fairly, without mandating an unlucky subset to undertake the responsibility of serving as location server(s). In this work, we propose a scalable and fully decentralized location service scheme (PETAL) in which the burden of location update and inquiry tasks is almost evenly distributed among the nodes, resulting in an improvement in resilience against individual node failures. PETAL does not require hashing which results in more complexity, it is resilient against swarm mobility pattern, it requires minimal periodic location update messages when nodes do not move, and finally it does not require too many parameter configurations on all nodes. Our simulation results reveal that PETAL performs efficiently, particularly in environments densely populated by wireless devices. © 2017 Elsevier LtdItem Open Access A survey on scheduling in IEEE 802.16 mesh mode(Institute of Electrical and Electronics Engineers, 2010) Kas, M.; Yargicoglu, B.; Korpeoglu, I.; Karasan, E.IEEE 802.16 standard (also known as WiMAX) defines the wireless broadband network technology which aims to solve the so called last mile problem via providing high bandwidth Internet even to the rural areas for which the cable deployment is very costly. The standard mainly focuses on the MAC and PHY layer issues, supporting two transmission modes: PMP (Point-to-Multipoint) and mesh modes. Mesh mode is an optional mode developed as an extension to PMP mode and it has the advantage of having an improving performance as more subscribers are added to the system using multi-hop routes. In 802.16 MAC protocol, mesh mode slot allocation and reservation mechanisms are left open which makes this topic a hot research area. Hence, the focus of this survey will mostly be on the mesh mode, and the proposed scheduling algorithms and performance evaluation methods. © 2010 IEEE.Item Open Access Topology design and scheduling in STDMA based wireless ad hoc networks(Bilkent University, 2003) Ergin, Sadettin AlpWith current advances in technology, wireless networks are increasing in popularity. Wireless networks allow users the freedom to travel from one location to another without interruption of their communication activities. Ad hoc networks, a subset of wireless networks, allow the formation of a wireless network without the need for a base station. Since no fixed infrastructure is involved in the communication, the nodes of ad hoc networks can communicate with each other or can relay data to other nodes. With this flexibility, wireless ad hoc networks have the ability to form a network anywhere, at any time, as long as two or more wireless users are willing to communicate. Managing ad hoc networks is a significantly more difficult task than managing wireline networks. The network requirements should be met by combined efforts of all the mobile nodes themselves. The nodes of ad hoc networks often operate under severe constraints, such as limited battery power, variable link quality and limited shared bandwidth. In this study, the topology design issue in ad hoc wireless networks is investigated. We employ hierarchical routing where the network topology is composed of clusters interconnected via a root node. Cluster-based topologies are suitable for military services, an important application area for ad hoc networks. The common power control technique (COMPOW) is used in this thesis where all nodes transmit at the same power level. Nodes employ the spatial TDMA (STDMA) scheme in order to access the channel. An important task is how to produce a minimum STDMA frame length, and this problem is known to be NP complete. We develop a heuristic algorithm for generating the minimum STDMA frame length. A new interference model for ad hoc networks is proposed which utilizes a hypergraph model. The relationship between the frame length, number of clusters and the transmit power level are investigated through numerical examples using a 15- node network.Item Open Access A zone-based shared-tree multicast protocol for mobile ad hoc networks(IEEE, 2003) Rangnekar, A.; Zhang, Y.; Selçuk, Ali A.; Bicak, A.; Devarapalli V.; Sidhu, D.This paper proposes a new multicast protocol for mobile ad hoc networks (MANETs). The proposed protocol, Shared-Tree MZR, is a shared tree variant of the Multicast Routing Protocol based on Zone Routing (MZR). The concept of zone-based multicast routing for mobile ad hoc networks was originally proposed in MZR. The new protocol utilizes the advantages of the shared-tree together with the advantages of the zone-based routing. The performance of the protocol is analyzed for various network conditions. The test results show that the new protocol performs well and has significantly low overhead in scenarios with multiple sources.