Browsing by Subject "Sensor networks."

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Open Access
Active node determination for correlated data gathering in wireless sensor networks
(2009) Karasabun, Efe
In wireless sensor network applications where data gathered by different sensor nodes is correlated, not all sensor nodes need to be active for the wireless sensor network to be functional. However, the sensor nodes that are selected as active should form a connected wireless network in order to transmit the collected correlated data to the data gathering node. The problem of determining a set of active sensor nodes in a correlated data environment for a fully operational wireless sensor network can be formulated as an instance of the connected correlation-dominating set problem. In this work, our contribution is twofold; we propose an effective and runtime efficient iterative improvement heuristic to solve the active sensor node determination problem and a benefit function that aims to minimize the number of active sensor nodes while maximizing the residual energy levels of the selected active sensor nodes. Extensive simulations we performed show that the proposed approach can achieve a good performance in terms of both network lifetime and runtime efficiency.
Open Access
Active set partitioning scheme for extending the lifetime of large wireless sensor networks
(2010) Kalkan, Mustafa
Wireless Sensor Networks consist of spatially distributed and energy-constrained autonomous devices called sensors to cooperatively monitor physical or environmental conditions such as temperature, sound, vibration, pressure or pollutants at different locations. Because these sensor nodes have limited energy supply, energy efficiency is a critical design issue in wireless sensor networks. Having all the nodes simultaneously work in the active mode, results in an excessive energy consumption and packet collisions because of high node density in the network. In order to minimize energy consumption and extend network life-time, this thesis presents a centralized graph partitioning approach to organize the sensor nodes into a number of active sensor node sets such that each active set maintains the desired level of sensing coverage and forms a connected network to perform sensing and communication tasks successfully. We evaluate our proposed scheme via simulations under different network topologies and parameters in terms of network lifetime and run-time efficiency and observe approximately 50% improvement in the number of obtained active node sets when compared with different active node set selection mechanisms.
Open Access
Algorithms for sink mobility in wireless sensor networks to improve network lifetime
(2008) Koç, Metin
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 processor, the main constraint that makes WSNs different from traditional networks is the battery problem. Since sensor nodes are generally deployed to areas with harsh environmental conditions, replacing the exhausted batteries become practically impossible. This requires to use the energy very carefully in both node and network level. Different approaches are proposed in the literature for improving network lifetime, including data aggregation, energy efficient routing schemes and MAC protocols, etc. Main motivation for these approaches is to prolong the network lifetime without sacrificing service quality. Sink (data collection node) mobility is also one of the effective solutions in the literature for network lifetime improvement. In this thesis, we focus on the controlled sink mobility and present a set of algorithms for different parts of the problem, like sink sites determination, and movement decision parameters. Moreover, a load balanced topology construction algorithm is given as another component of network lifetime improvement. Experiment results are presented which compare the performance of different components of the mobility scheme with other approaches in the literature, and the whole sink mobility scheme with random movement and static sink cases. As a result, it is observed that our algorithms perform better than random movement and static cases for different scenarios.
Open Access
Connectivity and coverage preserving sleep scheduling mechanism with predictive coverage and multiple mode selections in wireless sensor networks
(2007) Bulut, Eyuphan
Open Access
Constructing energy efficient bluetooth scatternets for wireless sensor networks
(2004) Saginbekov, Sain
The improvements in the area of wireless communication and micro-sensor technology have made the deployment of thousands, even millions, of low cost and low power sensor nodes in a region of interest a reality. After deploying sensor nodes in a target region of interest, which can be inaccessible by people, people can collect useful data from the region remotely. The sensor nodes use wireless communication and can collaborate with each other. However, sensor nodes are battery powered and therefore they have limited energy and lifetime. This makes energy as the main resource problem in sensor networks. The design process for sensor networks has to consider energy constraints as the main factor to extend the lifetime of the network. The wireless technology used for communication among sensor nodes can affect the lifetime of the network, since different technologies have different energy consumption parameters. Bluetooth, being low power and low cost, is a good candidate for being the underlying wireless connectivity technology for sensor networks tailored for various applications. But in order to build a large network of Bluetooth-enabled sensor nodes, we have to first form a Bluetooth scatternet. The topology of the Bluetooth scatternet affects the routing scheme to be used over that topology to collect and route informaton from sensor nodes to a base station. And routing scheme, in turn, affects how much energy is consumed during transport of information. Therefore, it is important to build a Bluetooth scatternet wisely to reduce and balance the energy consumption, hence extend the lifetime of a sensor network. In this thesis work, we propose a new Bluetooth scatternet formation algorithm to be used in Bluetooth-based sensor networks. Our 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 (a Bluetooth constraint). We also propose a balancing algorithm over the degree constrained tree to balance the energy consumption of the nodes that are closer to the base station. The closer nodes are the nodes that will consume more energy in the network since all traffic has to be forwarded over these nodes. Our simulation results show that our proposed algorithm improves the lifetime of the network by trying to reduce the energy consumed during data transfer and also by balancing the load among the nodes.
Open Access
A context aware approach for enhancing gesture recognition accuracy on handheld devices
(2010) Yıldırım, Hacı Mehmet
Input capabilities (e.g. joystick, keypad) of handheld devices allow users to interact with the user interface to access the information and mobile services. However, these input capabilities are very limited because of the mobile convenience. New input devices and interaction techniques are needed for handheld devices. Gestural interaction with accelerometer sensor is one of the newest interaction techniques on mobile computing. In this thesis, we introduce solutions that can be used for automatically enhancing the gesture recognition accuracy of accelerometer sensor, and as a standardized gesture library for gestural interaction on touch screen and accelerometer sensor. In this novel solution, we propose a framework that decides on suitable signal processing techniques for acceleration sensor data for a given context of the user. First system recognizes the context of the user using pattern recognition algorithm. Then, system automatically chooses signal ltering techniques for recognized context, and recognizes gestures. Gestures are also standardized for better usage. In this work, we also present several experiments which show the feasibility and e ectiveness of our automated gesture recognition enhancement system.
Open Access
Design, fabrication and characterization of surface plasmon resonance based MEMS displacement sensors
(2009) Güner, Hasan
Strong dependence of surface plasmon resonance (SPR) on coupling parameters offers new varieties of sensing mechanisms in nano and micro-scale engineering fields. In this study, design, fabrication and characterization of MEMS displacement sensors that utilize angular dependence of grating coupled SPR condition are explored. Several surface plasmon polariton (SPP) excitation mechanisms are reported in the academic literature. One of them which is quite adaptable to microelectromechanical systems is grating coupling scheme. In this scheme, thin metallized grating structures are particularly designed depending on the desired wavelength and the angle of incidence of the SPP excitation light. Geometric parameters like periodicity, surface profile, depth and duty cycle of the grooves and material parameters like dispersion and thickness of the top metal layer have to be chosen with care in order to reach sharp SPR curves in the reflected intensity spectra with respect to either wavelength or angle of incidence. As the first step, geometric and material parameters of SPR gratings are numerically optimized using rigorous coupled-wave analysis (RCWA). Angular quality factors on the order of tens are shown to be achievable. Various lithographic techniques (nanoimprint, electron beam and optical lithography) are used to nanofabricate those certainly defined gratings. It is observed that p-polarized reflected intensity measurements using spectroscopic ellipsometry are in quite good agreement with those numerically calculated. Spectroscopic scan measurements are also provided to show the polarization dependence of SPP excitation. All effort to obtain high angular Q-factor grating structures is aimed at enhancing the sensitivity of angular displacement detection scheme. In this scheme, angular position of the grating structure in the polarization plane is detected through the reflected intensity response of the photodetector. Dependence of sensitivity on excitation light source wavefront parameters and photodetector noise are analyzed. MEMS displacement sensor designs relying on the principle of angular displacement detection scheme are developed. Simply, SPR grating structures are transferred on conventional micromembranes. Two types of such particular designed micromembranes are introduced: corrugated microcantilevers (singly clamped) and corrugated microbridges (doubly clamped). They are fabricated through well-known surface micromachining processes in addition to SPR grating nanofabrication procedures. Mechanical resonance frequencies, flexural mode shapes and effective spring constants are analytically, numerically and experimentally obtained. In addition, a MEMS accelerometer design with plasmonic readout with nano-G noise floor is presented. An experimental configuration for micromechanical displacement sensing is investigated. According to the results of this work, novel arrayed sensors combining the sensitivities of plasmon resonance and micromembrane type sensors may provide unprecedented performance.
Open Access
E-sense : a wireless sensor network testbed and system for monitoring inbuilding environments
(2008) Berker, Berk
Wireless sensor networks consist of small, smart and battery-powered devices suitable for widespread deployment to monitor an environment by taking physical measurements. Wireless sensor nodes are deployed over an area in a random manner. They need to self-establish a wireless multi-hop network and routing paths from all sensor nodes to a central base station. In this thesis, we present our E-Sense system, a wireless sensor network testbed consisting of MICA2 sensor nodes which can be used to monitor an indoor environment like office buildings and homes. The testbed can be accessed through the Internet and provides a webbased interface to the sensor network. The users of the network can be located at any point in the Internet. Via the web based interface, the users can submit various types of queries to the sensor network and get the replies including the physical measurement results. The E-Sense system also includes a distributed and energy-aware routing protocol that we designed and implemented. The protocol aims efficient and balanced usage of energy in the sensor nodes to prolong the lifetime of the network. The routing protocol is based on a many-to-one routing tree where each node independently determines its next parent depending on the values of RSSI (Received Signal Strength Indicator). The protocol can also adjust the transmit power to further decrease the energy spent in each sensor node. The testbed will be useful for experimental studies at both application and network levels.
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
An inquiry into the metrics for evaluation of localization algorithms in wireless ad hoc and sensor networks
(2008) Aksu, Hidayet
In ad-hoc and sensor networks, the location of a sensor node making an observation is a vital piece of information to allow accurate data analysis. GPS is an established technology to enable precise position information. Yet, resource constraints and size issues prohibit its use in small sensor nodes that are designed to be cost efficient. Instead, most positions are estimated by a number of algorithms. Such estimates, inevitably introduce errors in the information collected from the field, and it is very important to determine the error in cases where they lead to inaccurate data analysis. After all, many components of the application rely on the reported locations including decision making processes. It is, therefore, vital to understand the impact of errors from the applications’ point of view. To date, the focus on location estimation was on individual accuracy of each sensor’s position in isolation to the complete network. In this thesis, we point out the problems with such an approach that does not consider the complete network topology and the relative positions of nodes in comparison to each other. We then describe the existing metrics, which are used in the literature, and also propose some novel metrics that can be used in this area of research. Furthermore, we run simulations to understand the behavior of the existing and proposed metrics. After having discussed the simulation results, we suggest a metric selection methodology that can be used for wireless sensor network applications.
Open Access
Location based multicast routing algorithms for wireless sensor networks
(2007) Bağcı, Hakkı
Multicast routing protocols in wireless sensor networks are required for sending the same message to multiple different destination nodes. Since most of the time it is not convenient to identify the sensors in a network by a unique id, using the location information to identify the nodes and sending messages to the target locations seems to be a better approach. In this thesis 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 sends a 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 target nodes. According to the calculated MST, multicast message is forwarded to destination nodes. This helps reducing the total energy consumed for delivering the message to all target nodes since it tries to minimize the number of transmissions. We compare these two algorithms with each other and also against another location based multicast routing protocol called PBM according to success ratio in delivery, number of total transmissions, traffic overhead and average end to end delay metrics. The results show that algorithms we propose are more scalable and energy efficient, so they are good candidates to be used for multicasting in wireless sensor networks.
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
Multi-sensor based ambient assisted living system
(2013) Yazar, Ahmet
An important goal of Ambient Assisted Living (AAL) research is to contribute to the quality of life of the elderly and handicapped people and help them to maintain an independent lifestyle with the use of sensors, signal processing and the available telecommunications infrastructure. From this perspective, detection of unusual human activities such as falling person detection has practical applications. In this thesis, a low-cost AAL system using vibration and passive infrared (PIR) sensors is proposed for falling person detection, human footstep detection, human motion detection, unusual inactivity detection, and indoor flooding detection applications. For the vibration sensor signal processing, various frequency analysis methods which consist of the discrete Fourier transform (DFT), mel-frequency cepstral coefficients (MFCC), discrete wavelet transform (DWT) with different filter-banks, dual-tree complex wavelet transform (DT-CWT), and single-tree complex wavelet transform (ST-CWT) are compared to each other to obtain the best possible classification result in our dataset. Adaptive-threshold based Markov model (MM) classifier is preferred for the human footstep detection. Vibration sensor based falling person detection system employs Euclidean distance and support vector machine (SVM) classifiers and these classifiers are compared to each other. PIR sensors are also used for falling person detection and this system employs two PIR sensors. To achieve the most reliable system, a multi-sensor based falling person detection system which employs one vibration and two PIR sensors is developed. PIR sensor based system has also the capability of detecting uncontrolled flames and this system is integrated to the overall system. The proposed AAL system works in real-time on a standard personal computer or chipKIT Uno32 microprocessors without computers. A network is setup for the communication of the Uno32 boards which are connected to different sensors. The main processor gives final decisions and emergency alarms are transmitted to outside of the smart home using the auto-dial alarm system via telephone lines. The resulting AAL system is a low-cost and privacy-friendly system thanks to the types of sensors used.
Open Access
Power efficient data gathering and aggregation in wireless sensor networks
(2004) Tan, Hüseyin Özgür
Recent developments in processor, memory and radio technology have enabled wireless micro-sensor networks which are deployed to collect useful information from an area of interest. The sensed data must be gathered and transmitted to a base station where it is further processed for end-user queries. Since the network consists of low-cost nodes with limited battery power, power efficient methods must be employed for data gathering and aggregation in order to achieve long network lifetimes. In an environment where each of the sensor nodes has data to send to a base station in a round of communication, it is important to minimize the total energy consumed by the system in a round so that the system lifetime is maximized. A near optimal data gathering and routing scheme can be achieved in terms of network lifetime, while minimizing the total energy per round with the use of data fusion and aggregation techniques, if power consumption per node can be balanced as well. So far, different routing protocols have been proposed to maximize the lifetime of a sensor network. In this thesis, we propose two new protocols PEDAP (Power Efficient Data gathering and Aggregation Protocol) and PEDAP-PA (PEDAPPower Aware), which are minimum spanning tree based routing schemes, where one of them is the power-aware version of the other. Our simulation results show that our protocols perform well both in systems where base station is far away from and where it is in the center of the field.
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
Real-time routing with priority scheduling and power adjustment in wireless sensor networks
(2008) Çelikkaya, Emine Büşra
Many wireless sensor network applications require real-time communication, and real-time applications require packets to reach destination on time. However, applications may send packets with different priorities and hence delay bounds for packets may vary significantly. Therefore packet differentiation in the network is essential for meeting the deadline requirements. We propose a routing protocol that supports real-time communication by utilizing transmit power adjustment in order to meet the deadline of urgent packets and use energy efficiently. Our protocol also provides packet scheduling and gives precedence to urgent packets. We have conducted experiments on our sensor network testbed to observe the effects of transmit power on end-to-end delay. As expected, increasing transmit power increases the range and link quality, and reduces the number of hops to reach destination. Therefore adjusting transmit power has a great effect on delivery time and can reduce the end-to-end delay. Our protocol, Real-time Routing with Priority Scheduling and Power Adjustment, uses different levels of transmit power for packets with different priorities. It sends urgent packets with maximum power to minimize end-to-end delay and lower priority packets with reduced power to save energy and balance the load on nodes. Simulation results show that our routing protocol increases the deadline meet ratio of packets and reduces the transmit energy spent per packet when compared to routing protocols that use fixed transmit power. Additionally, results indicate that our approach lessens the interference on sensor nodes that are caused by other transmissions and helps balancing the load on the nodes.
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
Sleep scheduling for energy conservation in wireless sensor networks with partial coverage
(2006) Yardibi, Tarık
Wireless sensor networks, which consist of many sensor devices communicating with each other in order to sense the environment, is an emerging field in the area of wireless networking. The primary objective in these wireless networks is the efficiency of energy consumption. Since these networks consist of a large number of sensors, allowing some of the nodes to sleep intermittently can greatly increase the network lifetime. Furthermore, some applications do not require 100% coverage of the network field and allowing the coverage to drop below 100%, i.e., partial coverage, can further increase the network lifetime. A sleep scheduling algorithm must be distributed, simple, scalable and energy efficient. In this thesis, the problem of designing such an algorithm which extends network lifetime while maintaining a target level of partial coverage is investigated. An algorithm called Distributed Adaptive Sleep Scheduling Algorithm (DASSA) which does not require location information is proposed. The performance of DASSA is compared with an integer linear programming (ILP) based optimum sleep scheduling algorithm, an oblivious algorithm and with an existing algorithm in the literature. DASSA attains network lifetimes up to 89% of the optimum solution, and it achieves significantly longer lifetimes compared with the other two algorithms. Furthermore, the minimum number of sensors that should be deployed in order to satisfy a given partial coverage target with a certain probability while maintaining connectivity is computed and an ILP formulation is presented for finding the minimum number of sensors that should be activated within the set of deployed sensors.
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
Wireless radio frequency sensors for structural health monitoring
(2011) Ertuğrul, Hatice
Structural health monitoring (SHM) is fundamentally important in civil engineering. Sensing transient changes in strain build-up of a construction is essential for determining and assessing mechanical health of its structure. To date different types of strain sensors have been reported to monitor strain. However, it is technically challenging to design and operate a strain sensor at a reduced complexity and cost, while also achieving strain assessment in plastic deformation. In this study, to address this challenge, we propose a new class of wireless radio frequency (RF) strain sensors based on metamaterial-inspired architectures that allow for real-time SHM including the plastic deformation of steel rods. Such a capability is vitally critical especially in geographical locations where earthquakes frequently occur. To enable telemetric strain sensing for SHM, we developed cost-effective, easy-to-make, passive RF sensors composed of comb-like split ring resonators, each with a cut between the two halves making the splits and a wire jumper on one end making the ring. By externally applying loads on standard steel rods, which are used in buildings, we demonstrated that the frequency shift in S11 changes with the gap width and the applied load, and that the displacement on the steel rods can be monitored telemetrically. Our results indicate that these wireless sensors hold great promise for real-time remote SHM.