Browsing by Subject "Wireless LANs."

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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
Double binary turbo codes analysis and decoder implementation
(2008) Yılmaz, Özlem
Classical Turbo Code presented in 1993 by Berrau et al. received great attention due to its near Shannon Limit decoding performance. Double Binary Circular Turbo Code is an improvement on Classical Turbo Code and widely used in today’s communication standards, such as IEEE 802.16 (WIMAX) and DVBRSC. Compared to Classical Turbo Codes, DB-CTC has better error-correcting capability but more computational complexity for the decoder scheme. In this work, various methods, offered to decrease the computational complexity and memory requirements of DB-CTC decoder in the literature, are analyzed to find the optimum solution for the FPGA implementation of the decoder. IEEE 802.16 standard is taken into account for all simulations presented in this work and different simulations are performed according to the specifications given in the standard. An efficient DB-CTC decoder is implemented on an FPGA board and compared with other implementations in the literature.
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
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
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
A system level simulation study of WiMAX
(2010) Başçiftçi, Yüksel Ozan
In this thesis, we implement a WiMAX system level simulator compliant with the evaluation methodology document published by the IEEE 802.16m Task Group. We study the PHY abstraction of polar codes and integrate polar codes into the simulator. We compare the system level performances of polar code and convolutional turbo code (CTC) and observe that CTC outperforms polar code. On the simulator, we study the downlink (DL) performance of WiMAX under various configurations such as scheduling methods, subchannelization methods, and frequency reuse models. We study there types of scheduling methods, namely round robin (RR) scheduling, proportional fair (PF) scheduling, and maximum sum rate (MSR) scheduling. We observe that MSR scheduling has the best throughput performance but does not support the users far from the base station. We study three frequency reuse models, namely 1×3×1, 1×3×3, and 3×3×1. We observe that 1 ×3×1 reuse model has the best throughput performance and maximum spectral efficiency is obtained in 1 × 3 × 3 reuse model. We study two subchannelization methods, namely PUSC and band AMC. We observe that in low mobility cases, band AMC outperforms PUSC and in high mobility cases, PUSC is better than band AMC.
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.