Sharif Digital Repository

The use of MANETs in many areas is rapidly spreading. Due to dynamic nature,and limited energy of this networks, they are vulnerable to some attacks including blackhole attack. Blackhole attack can disrupt the commiunication between hosts and cause denial of service. One of countermeasures to this attack which has been recently proposed is the ActiveTrust. ActiveTrust is a routing protocol which relys on malicious node detection using trust calculations; this scheme has been proposed for WSNs. In this work we adopt the ActiveTrust’s idea and try to apply it into MANETs. Then we simulate the resulting proposal in NS-3 and compare the results  

Recently, advances in the fabrication and integration of sensing, communication technologies and economical deployment of large scale sensor networks which are capable of large scale target tracking, become possible.therfore, the wireless sensor networks are a fast growing and marvelous research area that has attracted considerable research attention in the recent past. The creation of large-scale sensor networks interconnencting several hundered to a few thousand sensor nodes opens-up several wide range of application and technical challenges. Sensor nodes have been deployed to play significant roles in battlefield, disaster-prone area, traffic control, habitat monitoring and intruder... 

Given a set of obstacles as an arrangement of geometric shapes in the plane, we would like to find a path from the initial point s to the target point t that crosses the minimum number of obstacles. In other words, the goal is to determine the minimum number of obstacles that need to be removed to exist a collision-free path between s and t.On one hand, this problem can be used for measuring the strength of barrier coverage which is a fundamental concept in wireless sensor networks (WSNs), and on the other hand, it has been considered as a robot motion-planning problem. The objective of barrier coverage is to guarantee that any path from the start point to the target point, will intersect at... 

Let P be a set of points in the plane, each equipped with a directional antenna that can cover a sector of angle and range r. In the symmetric model of communication, two antennas u and v can communicate to each other, if and only if v lies in u’s coverage area and vice versa. In this paper, we introduce the concept of fault-tolerant spanners for directional antennas, which enables us to construct communication networks that retain their connectivity and spanning ratio even if a subset of antennas are removed from the network. We show how to orient the antennas with angle and range r to obtain a k-fault-tolerant spanner for any positive integer k. For ⩾ , we show that the range 13 for the... 

Recent advancements in wireless communications and also a tendency to use low cost, tiny, and autonomous high performance products have led to the emergence of wireless sensor networks (WSNs). As the main source of power in a sensor node is a limited and irreplaceable battery, energy is the main important issue. Data aggregation, as an in-network processing method, is a promised technique aiming to conserve energy by reducing the number of packet transmissions through the network. It is a key, yet time-consuming functionality in WSNS, where we hold packets in intermediate nodes to promote aggregation efficiency. However, the requirement of real-time communications is becoming more and more... 

Technology advances in the era of wireless communications leads to the birth of a very useful network called Wireless sensor Network which is very interesting for scientists and researchers. While these networks consist of tens to thousands of tiny sensor nodes, they consume their energy from none-rechargeable batteries. Reducing energy consumption and extend the life of network is the most challenging requirement for these kinds of networks; in some environments like military training which precision and sensitivity are critical, it might take at least K sensors to cover the whole area and these conditions leads to a vast data repetition in network and as a result energy exhaustions in... 

Wireless Sensor Networks (WSN) are wildly utilized in surveillance and controling applications, and because of their remote and standalone operation, lifetime and reliability of a typical WSN are two main concerns in these networks. One of the reliability threatening issues in a WSN is residual accessible energy for each node. Nowadays, energy harvesting systems are used in WSN nodes to catch environmental energy, and reduce the energy limitation. However, because of inherent uncertainty of energy harvesting systems, the networks that operate using environmental energy have new reliability issues. Different rate of energy harvesting, according to environmental conditions, is one of the most... 

In recent years, significant interest has been attracted towards using directional antennae in wireless and sensor networks due to it’s decreased energy consumption, increased security and decreased radio wave overlapping. Substituting omni-directional antennae with directional antennae should be performed in a way that not only guarantees connectivity, but also minimizes radius and latency in network nodes. The problem is not polynomially solvable in general and effort has been made in recent years to present approximation algorithms to solve this problem. The approximation algorithms have been made possible using unit disk
graphs, Euclidean minimum spanning trees, grouping of... 

Distinguishing characteristic of wireless sensor network is limited resources such as processing power, bandwidth, memory. Restrictions of sensor networks is impressive on the transfer of multimedia data such as video requiring high bandwidth and low latency. In wireless multimedia sensor networks, the probability of packet loss is high due to the high volume of multimedia data and limited bandwidth. Many congestion control protocols for wireless sensor networks have presented. Most of these protocols did not consider the multimedia content. Even some wireless sensor network congestion control protocols have worse result than a network which has no congestion control protocol in case of... 

As the applications of wireless sensor networks are expanding at an increasing rate, design of these networks so that they conform to the requirements of a specific application is considered to be a major challenge. Regarding to the specific application, network designers consider various suitable parameters to improve and then to enhance the efficiency of the network. Parameters included are such as area coverage, lifetime, reliability and etc which can significantly improve with the precise placement of nodes. Node localization problem in wireless sensor networks aiming at improvement of the performance parameters has been solved by different methods. In this thesis, in order to solve this... 

Minimizing energy consumption is the most important concern in wireless sensor networks (WSNs). Cooperative multiple-input multiple-output (MIMO) and data aggregation are two promising techniques to conserve energy in network nodes by coordinating their transmissions through cooperative communications along with eliminating the inherent redundancy of raw data for transmissions. In this thesis, with the goal of reducing energy consumption, we present a dynamic clustering framework for combined used of cooperative MIMO and data aggregation in cluster-based WSNs. We derive a new and more general energy model for computing energy consumption of cooperative data aggregation in wireless sensor... 

Real-time asynchronous data fusion for high-speed phenomena is an important and challenging task in the sensor networks. Examples of data fusion applications in sensor networks are: managing the traffic of maneuvering airplanes and ground vehicles in airside areas of an airport, traffic management in streets and roads, Driver Assistance Systems, guidance of antiaircraft and antimissile missiles. In all the data fusion applications the estimation of the required variables is necessary.
In this research two methods are introduced for real-time asynchronous data fusion, especially for track-to-track fusion of high-speed phenomena in sensor networks. The effectiveness and usability of these... 

Wireless Sensor Networks have become widespread because of their flexibility, applicability and ability to precept data with high accuracy. However, the most limiting factor in their usage is the amount of available energy in nodes since energy depletion in a node means that it is dead, therefore many efforts have been done for optimum energy management in Wireless Sensor Networks. In many cases, the key solution to prolong the network lifetime is load balancing. In this way, all the nodes will die (approximately) together and the lifetime of network will be maximized. Load balancing can be implemented in all layers from physical layer to application. It should be noted that it is not always... 

Wireless Sensor Networks (WSNs) has been a research topic for more than a decade, and the range of potential applications has spanned beyond the military domain into commercial domains. A key feature of current WSN solutions is operation in unlicensed frequency bands, for instance, the worldwide available 2.4 GHz band. However, the same band is shared by other wireless applications, such as Wi-Fi and Bluetooth, as well as other proprietary technologies. There is evidence that unlicensed spectrum is becoming overcrowded, to solve this problem, concept of cognitive radio has been introduced.
A main challenge for routing in cognitive radio wireless sensor networks is the collaboration... 

Due to their specific characteristics such as huge data loads, heavy processes, various quality of service requirements (delay, jitter and reliability), multimedia streams have different necessities in comparison with normal data streams. The challenges of wireless sensor networks (process power, storage capacity and power limitations) add up to the challenges faced in WMSNs. In order to improve the quality of service in wireless multimedia sensor networks, attention must be paid to all the network layers. In this study improvement of quality of service is sought through the design of a protocol for the network layer of the wireless multimedia sensor network.
This protocol tries to... 

Due to the advances in wireless communications and electronics over the last few years, the development of networks of low-cost, low-power, and multifunctional sensors has received increasing attention. Most important constraints of this network are energy and bandwidth. Data aggregation is one of the effective approaches for reducing energy consumption in wireless sensor networks. Recent research on data collection reveals that, rather than reporting data through long, multi-hop and error-prone routes to a static sink using tree or cluster network structure, allowing and leveraging sink mobility is more promising for energy efficient data gathering. In this work we proposed an effective... 

Routing is one of the most challenging areas in wireless sensor networks because it has a significant impact on energy usage, transmit delay and network fault tolerance. In many situations, network nodes move around and it cause numerous challenges, namely changes in routing paths, failure in sending packets or maybe there is no end-to-end path. Opportunistic routing is one of the best solutions to these problems in mobile wireless sensor networks, thus it provides more efficient routing and less energy consumption in comparison with traditional routings.
In opportunistic routing, nodes try to utilize every opportunity to send their packets to sink. When two nodes are encountered, the... 

Wireless Sensor Networks (WSNs) attracted lots of researchers in recent years, these sensors are small and have limited computational resources and are not expensive in comparision with conventional sensors. These sensors can sense, measure, gathering information from environment and send them to user, they are typically characterized by limited communication capabilities due to tight energy and bandwidth constraints. As a result, WSNs have inspired a resurgence in research on decentralized algorithms, structure of these networks are variable and dynamic, sensors may deleted from the network or added to the network, so using models which don’t require precies specifications of environment is... 

Wireless sensor networks (WSNs) can be used in a variety of applications. The prime shortcoming of these networks is their energy constraint. The main energy consumer in a sensor node is its radio transmitter. Therefore data prediction is one of the most effective methods to reduce the data transmission rate. By data prediction, a large amount of energy is saved; which results in the longevity of the network life. Environmental variations almost have similar effects on different sensor sources in a sensor device. So, considering the correlation between different sources reduces the noise impact and increases data prediction accuracy. In this thesis, we use temporal and multisource... 

Today with growth of wireless communications and progress of small and cheap sensors which have capability of communication and calculation, wireless sensor networks are important and useful topic. But due to energy restrictions, efficient use of resources and increasing network lifetime, have been considered as key factors in network design. In this regard, using efficient multicast routing in energy consumption, for an efficient data transmission to specific number of nodes instead of all nodes code updates, information requests, task assignments and etc., is necessary.On the other hand these networks use unlicensed spectrum and suffer from collision due to congestion caused by other...