Browsing by Subject "Wireless sensor networks."

Now showing 1 - 8 of 8

Open Access
Bandwidth-aware and energy-efficient stream multicasting protocols for wireless multimedia sensor networks
(2010) Yargıçoğlu, Burcu
In recent years, the interest in wireless sensor networks has grown and resulted in the integration of low-power wireless technologies with cameras and microphones enabling video and audio transport through a sensor network besides transporting low-rate environmental measurement-data. These sensor networks are called wireless multimedia sensor networks (WMSN) and are still constrained in terms of battery, memory and achievable data rate. Hence, delivering multimedia content in such an environment has become a new research challenge. Depending on the application, content may need to be delivered to a single destination (unicast) or multiple destinations (multicast). In this work, we consider the problem of e ciently and e ectively delivering a multimedia stream to multiple destinations, i.e. the multimedia multicasting problem, in wireless sensor networks. Existing multicasting solutions for wireless sensor networks provide energy e ciency for low-bandwidth and delay-tolerant data. The aim of this work is to provide a framework that will enable multicasting of relatively highrate and long-durational multimedia streams while trying to meet the desired quality-of-service requirements. To provide the desired bandwidth to a multicast stream, our framework tries to discover, select and use multicasting paths that go through uncongested nodes and in this way have enough bandwidth, while also considering energy e ciency in the sensor network. As part of our framework, we propose a multicasting scheme, with both a centralized and distributed version, that can form energy-e cient multicast trees with enough bandwidth. We evaluated the performance of our proposed scheme via simulations and observed that our scheme can e ectively construct such multicast trees.
Open Access
A framework for the use of wireless sensor networks in forest fire detection and monitoring
(2010) Aslan, Yunus Emre
Wireless sensor networks have a broad range of applications in the category of environmental monitoring. In this thesis, we consider the problem of forest re detection and monitoring as a possible application area of wireless sensor networks. Forest res are one of the main causes of environmental degradation nowadays. The current surveillance systems for forest res lack in supporting real-time monitoring of every point of the region at all time and early detection of the re threats. Solutions using wireless sensor networks, on the other hand, can gather temperature and humidity values from all points of eld continuously, day and night, and, provide fresh and accurate data to the re ghter center quickly. However, sensor networks and nodes face serious obstacles like limited energy resources and high vulnerability to harsh environmental conditions, that have to be considered carefully. In our study, we propose a comprehensive framework for the use of wireless sensor networks for forest re detection and monitoring. Our framework includes proposals for the wireless sensor network architecture, clustering and communication protocols, and environment/season-aware activity-rate selection schemes to detect the re threat as early as possible and yet consider the energy consumption of the sensor nodes and the physical conditions that may hinder the activity of the network. We also implemented a simulator to validate and evaluate our proposed framework, which is using an external re simulator library. We did extensive simulation experiments and observed that our framework can provide fast reaction to forest res while also consuming energy e ciently.
Open Access
Multi-channel TDMA scheduling in wireless sensor networks
(2013) Uyanık, Özge
The Multiple Instance Learning (MIL) paradigm arises to be useful in many application domains, whereas it is particularly suitable for computer vision problems due to the difficulty of obtaining manual labeling. Multiple Instance Learning methods have large applicability to a variety of challenging learning problems in computer vision, including object recognition and detection, tracking, image classification, scene classification and more. As opposed to working with single instances as in standard supervised learning, Multiple Instance Learning operates over bags of instances. A bag is labeled as positive if it is known to contain at least one positive instance; otherwise it is labeled as negative. The overall learning task is to learn a model for some concept using a training set that is formed of bags. A vital component of using Multiple Instance Learning in computer vision is its design for abstracting the visual problem to multi-instance representation, which involves determining what the bag is and what are the instances in the bag. In this context, we consider three different computer vision problems and propose solutions for each of them via novel representations. The first problem is image retrieval and re-ranking; we propose a method that automatically constructs multiple candidate Multi-instance bags, which are likely to contain relevant images. The second problem we look into is recognizing actions from still images, where we extract several candidate object regions and approach the problem of identifying related objects from a weakly supervised point of view. Finally, we address the recognition of human interactions in videos within a MIL framework. In human interaction recognition, videos may be composed of frames of different activities, and the task is to identify the interaction in spite of irrelevant activities that are scattered through the video. To overcome this problem, we use the idea of Multiple Instance Learning to tackle irrelevant actions in the whole video sequence classification. Each of the outlined problems are tested on benchmark datasets of the problems and compared with the state-of-the-art. The experimental results verify the advantages of the proposed MIL approaches to these vision problems.
Open Access
Performance analysis of the carrier-sense multiple access protocol for future generation wireless networks
(2013) Köseoğlu, Mehmet
Variants of the carrier-sense multiple access (CSMA) protocol has been employed in many communications protocols such as the IEEE 802.11 and Ethernet standards. CSMA based medium access control (MAC) mechanisms have been recently proposed for other communications scenarios such as sensor networks and acoustical underwater networks. Despite its widespread use, the performance of the CSMA protocol is not well-studied from the perspective of these newly encountered networking scenarios. We here investigate the performance of the CSMA protocol from the point of three different aspects: throughput in networks with large propagation delay, short-term fairness for delay sensitive applications in large networks and energy efficiency-throughput trade-off in networks with battery operated devices. Firstly, we investigate the performance of the CSMA protocol for channels with large propagation delay. Such channels are recently encountered in underwater acoustic networks and in terrestrial wireless networks covering larger areas. However, a mathematical model of CSMA performance in such networks is not known. We propose a semi-Markov model for a 2-node CSMA channel and then extend this model for arbitrary number of users. Using this model, we obtain the optimum symmetric probing rate that achieves the maximum network throughput as a function of the average propagation delay, ¯d, and the number of nodes sharing the channel, N. The proposed model predicts that the total capacity decreases with ¯d −1 as N goes to infinity when all nodes probe the channel at the optimum rate. The optimum probing rate for each node decreases with 1/N and the total optimum probing rate decreases faster than ¯d −1 as N goes to infinity. Secondly, we investigate whether the short-term fairness of a large CSMA network degrades with the network size and density. Our results suggest that (a) the throughput region that can be achieved within the acceptable limits of shortterm fairness reduces as the number of contending neighboring nodes increases for random regular conflict graphs, (b) short-term fair capacity weakly depends on the network size for a random regular conflict graph but a stronger dependence is observed for a grid topology. We also present related results from the statistical physics literature on long-range correlations in large systems and point out the relation between these results and short-term fairness of CSMA systems. Thirdly, we investigate the energy efficiency of a CSMA network proposing a model for the energy consumption of a node as a function of its throughput. We show that operating the CSMA network at a very high or at a very low throughput is energy inefficient because of increasing carrier-sensing and sleeping costs, respectively. Achieving a balance between these two opposite operating regimes, we derive the energy-optimum carrier-sensing rate and the energy-optimum throughput which maximize the number of transmitted bits for a given energy budget. For the single-hop case, we show that the energy-optimum total throughput increases as the number of nodes sharing the channel increases. For the multi-hop case, we show that the energy-optimum throughput decreases as the degree of the conflict graph of the network increases. For both cases, the energy-optimum throughput reduces as the power required for carrier-sensing increases. The energy-optimum throughput is also shown to be substantially lower than the maximum throughput and the gap increases as the degree of the conflict graph increases for multi-hop networks.
Open Access
Power-source-aware adaptive routing in wireless sensor networks
(2013) Tekkalmaz, Metin
A wireless sensor network (WSN) is a collection of sensor nodes distributed over an area of interest to accomplish a certain task by monitoring environmental and physical conditions and sending the collected data to a special node called sink. Most studies on WSNs consider nodes to be powered with irreplaceable batteries, which limits network lifetime. There are, however, perpetual power source alternatives as well, including mains electricity and energy harvesting mechanisms, which can be utilized by at least some portion of the sensor nodes to further prolong the network lifetime. Our aim here is to increase the lifetime of such WSNs with heterogeneous power sources by centralized or distributed routing algorithms that distinguish battery- and mains-powered nodes in routing, so that energy consuming tasks are carried out mostly by mains-powered nodes. We first propose a framework for a class of routing algorithms, which forms and uses a backbone topology consisting of all mains-powered nodes, including the sinks, and possibly some battery-powered nodes, to route data packets. We propose and evaluate a set of centralized algorithms based on this framework, and our simulation results show that our algorithms can increase network lifetime by up to more than a factor of two. We also propose a fully distributed power-source-aware backbone-based routing algorithm (PSABR) that favors mains-powered nodes as relay nodes. We validate and evaluate our distributed algorithm with extensive ns-2 simulations and our results show that the proposed distributed algorithm can enhance network lifetime significantly with a low control messaging overhead. Besides wireless technology independent routing solutions, we also propose a technology specific power-source-aware routing solution (PSAR) for sensor and ad hoc networks which use 802.15.4/ZigBee as the wireless technology. Our solution is fully distributed, tree-based, and traffic-adaptive. It utilizes some protocol specific properties of ZigBee, such as distributed and hierarchical address assignment, to eliminate battery-powered nodes on the routing paths as much as possible. To validate and evaluate our ZigBee-specific algorithm, we first implemented ZigBee extensions to ns-2 simulator and then implemented and simulated our protocol in this extended ns-2 environment. Our results show that the proposed algorithm operates efficiently and can increase network lifetime without increasing the path lengths significantly, compared to the default ZigBee routing algorithm.
Open Access
Routing and scheduling approaches for energy-efficient data gathering in wireless sensor networks
(2011) Tan, Hüseyin Özgür
A wireless sensor network consists of nodes which are capable of sensing an environment and wirelessly communicating with each other to gather the sensed data to a central location. Besides the advantages for many applications, having very limited irreplaceable energy resources is an important shortcoming of the wireless sensor networks. In this thesis, we present effective routing and node scheduling solutions to improve network lifetime in wireless sensor networks for data gathering applications. Towards this goal, we first investigate the network lifetime problem by developing a theoretical model which assumes perfect data aggregation and power-control capability for the nodes; and we derive an upper-bound on the functional lifetime of a sensor network. Then we propose a routing protocol to improve network lifetime close to this upper-bound on some certain conditions. Our proposed routing protocol, called L-PEDAP, is based on constructing localized, self-organizing, robust and power-aware data aggregation trees. We also propose a node scheduling protocol that can work with our routing protocol together to improve network lifetime further. Our node scheduling protocol, called PENS, keeps an optimal number of nodes active to achieve minimum energy consumption in a round, and puts the remaining nodes into sleep mode for a while. Under some conditions, the optimum number can be greater than the minimum number of nodes required to cover an area. We also derive the conditions under which keeping more nodes alive can be more energy efficient. The extensive simulation experiments we performed to evaluate our PEDAP and PENS protocols show that they can be effective methods to improve wireless sensor network lifetime for data gathering applications where nodes have power-control capability and where perfect data aggregation can be used.
Open Access
Tree-based channel assignment schemes for multi-channel wireless sensor networks
(2012) Terzi, Çağlar
A lot of sensor node platforms used for establishing wireless sensor networks (WSNs) can support multiple radio channels for wireless communication. Therefore, rather than using a radio single channel and sharing it for the whole network, multiple channels can be utilized in a sensor network simultaneously to decrease the overall interference in the network, which may help increasing the aggregate throughout in the network and decrease packet collisions and delay. This requires, however, appropriate channel assignment schemes to be used for assigning channels to the nodes for multi-channel communication in the network. Since, data generated by sensor nodes are usually carried to one or more sinks in the network using routing trees, tree-based channel assignment schemes are a natural approach for assigning channels in a WSN. We present two fast tree-based channel assignment schemes (called BUCA and NCCA) for multi-channel WSNs. We also propose a new network interference metric that is used in our algorithms while making decisions. We evaluate our proposed schemes by extensive simulation experiments and compare them with another well-known tree-based protocol from the literature. The results show that our proposed algorithms can provide better performance, up to 40% performance increase in some cases, compared to the other method. We also discuss in which cases the performance improvement can be achieved.
Open Access
Using spread spectrum coded pings in active sonar technology
(2014) Kumru, Yasin
Performance of coded signals in active Sound Navigation and Ranging (SONAR) technology is studied in this work. In this work, the possibility of having covertness and environment friendliness in SONAR systems is investigated. Spread spectrum ping signal is considered to achieve low probability of detection and interception, while maintaining good performance. Direct Sequence Spread Spectrum (DSSS) coded transmitted signals having a sequence type of maximal with lengths from 7 chips to 127 chips and tone burst pulse having single length as a reference signal are used as spread spectrum ping signal. The length of the tone burst pulse can not be increased indefinitely because of the multipath propagation. The problem of detection and localization of the targets and the cross correlation properties of the maximal length sequences are investigated as well. The Signal to Noise Ratio (SNR) and Signal to Interference and Distortion ratio (SINAD) are important parameters in detection and localization of the targets. It is found that as the number of chip length increases, the SNR and SINAD increase but the improvement of the SINAD is comparatively less because of the cross correlation properties of the maximal length sequences.