Majid Iqbal Khan

Static vs. mobile sink

Over the last decade a large number of routing protocols has been designed for achieving energy efficiency in data collecting wireless sensor networks. The drawbacks of using a static sink are well known. It has been argued in the literature that a mobile sink may improve the energy dissipation compared to a static one. Some authors focus on minimizing Emax, the maximum energy dissipation of any single node in the network, while others aim at minimizing Ebar, the average energy dissipation over all nodes. In our paper we take a more holistic view, considering both Emax and Ebar. The main contribution of this paper is to provide a simulation-based analysis of the energy efficiency of WSNs with static and mobile sinks. The focus is on two important configuration parameters: mobility path of the sink and duty cycling value of the nodes. On the one hand, it is well known that in the case of a mobile sink with fixed trajectory the choice of the mobility path influences energy efficiency. On the other hand, in some types of applications sensor nodes spend a rather large fraction of their total lifetime in idle mode, and therefore higher energy efficiency can be achieved by using the concept of reduced duty cycles. In particular, we quantitatively analyze the influence of duty cycling and the mobility radius of the sink as well as their interrelationship in terms of energy consumption for a well-defined model scenario. The analysis starts from general load considerations and is refined into a geometrical model. This model is validated by simulations which are more realistic in terms of duty cycling than previous work. It is illustrated that over all possible configuration scenarios in terms of duty cycle and mobility radius of the sink the energy dissipation in the WSN can vary up to a factor of nine in terms of Emax and up to a factor of 17 in terms of Ebar. It turns out that in general the choice of the duty cycle value is more important for achieving energy efficiency than the choice of the mobility radius of the sink. Moreover, for small values of the duty cycle, a static sink turns out to be optimal in terms of both Emax and Ebar. For larger values of the duty cycle, a mobile sink has advantages over a static sink, especially in terms of Emax. These insights into the basic interrelationship between duty cycle value and mobility radius of a mobile sink are relevant for energy efficient operation of homogeneous WSNs beyond our model scenario.

Comparative study of trust and reputation systems for wireless sensor networks

Wireless sensor networks (WSNs) are emerging as useful technology for information extraction from the surrounding environment by using numerous small-sized sensor nodes that are mostly deployed in sensitive, unattended, and (sometimes) hostile territories. Traditional cryptographic approaches are widely used to provide security in WSN. However, because of unattended and insecure deployment, a sensor node may be physically captured by an adversary who may acquire the underlying secret keys, or a subset thereof, to access the critical data and/or other nodes present in the network. Moreover, a node may not properly operate because of insufficient resources or problems in the network link. In recent years, the basic ideas of trust and reputation have been applied to WSNs to monitor the changing behaviors of nodes in a network. Several trust and reputation monitoring (TRM) systems have been proposed, to integrate the concepts of trust in networks as an additional security measure, and various surveys are conducted on the aforementioned system. However, the existing surveys lack a comprehensive discussion on trust application specific to the WSNs. This survey attempts to provide a thorough understanding of trust and reputation as well as their applications in the context of WSNs. The survey discusses the components required to build a TRM and the trust computation phases explained with a study of various security attacks. The study investigates the recent advances in TRMs and includes a concise comparison of various TRMs. Finally, a discussion on open issues and challenges in the implementation of trust-based systems is also presented. Copyright

A survey on Green communications using Adaptive Link Rate

The Information and Communication Technology sector is considered to be a major consumer of energy and has become an active participant in Green House Gas emissions. Lots of efforts have been devoted to make network infrastructure and network protocols power-aware and green. Among these efforts, Adaptive Link Rate (ALR) is one of the most widely discussed approaches. This survey highlights the most recent ALR approaches with a brief taxonomy and the state of the art.

Congestion Avoidance and Energy Efficient Routing Protocol for Wireless Sensor Networks with aMobile Sink

Congestion severely affects the performance of a wireless sensor network in two aspects: increased data loss and reduced lifetime. This paper addresses these problems by introducing a mobile sink based routing scheme for congestion avoidance and energy efficient routing in wireless sensor networks. The proposed scheme utilizes the sink mobility and an in-network storage model that is used to set up mini-sinks along the mobility trajectory of the sink. Mini-sinks are responsible for collecting data from the sensor nodes located in their vicinity, thus avoiding data flow to a single data collection point, e.g., a static sink that is the major cause of congestion, data loss and reduced lifetime of the sensor network. Also, in the proposed scheme data only has to travel a limited number of hops to reach the nearest mini-sink which helps to improve the energy consumption of the sensor nodes. Through simulation we show the effectiveness of the given routing scheme in terms of congestion avoidance and increased lifetime of the wireless sensor network.

An Efficient Data-Gathering Routing Protocol for Underwater Wireless Sensor Networks

Most applications of underwater wireless sensor networks (UWSNs) demand reliable data delivery over a longer period in an efficient and timely manner. However, the harsh and unpredictable underwater environment makes routing more challenging as compared to terrestrial WSNs. Most of the existing schemes deploy mobile sensors or a mobile sink (MS) to maximize data gathering. However, the relatively high deployment cost prevents their usage in most applications. Thus, this paper presents an autonomous underwater vehicle (AUV)-aided efficient data-gathering (AEDG) routing protocol for reliable data delivery in UWSNs. To prolong the network lifetime, AEDG employs an AUV for data collection from gateways and uses a shortest path tree (SPT) algorithm while associating sensor nodes with the gateways. The AEDG protocol also limits the number of associated nodes with the gateway nodes to minimize the network energy consumption and to prevent the gateways from overloading. Moreover, gateways are rotated with the passage of time to balance the energy consumption of the network. To prevent data loss, AEDG allows dynamic data collection at the AUV depending on the limited number of member nodes that are associated with each gateway. We also develop a sub-optimal elliptical trajectory of AUV by using a connected dominating set (CDS) to further facilitate network throughput maximization. The performance of the AEDG is validated via simulations, which demonstrate the effectiveness of AEDG in comparison to two existing UWSN routing protocols in terms of the selected performance metrics.

In-Network Storage Model for Data Persistence under Congestion in Wireless Sensor Network

Congestion in wireless sensor networks leads to the degradation of communication links that result in decreased throughput and waste of energy which is one of the scarcest resources of a sensor node. Various techniques have been proposed to cope with data congestion, such as data aggregation techniques, multi hop routing techniques and flow control techniques. Although these techniques help to avoid or control congestion, they do not address the issue of data persistency effectively. This paper presents an adaptive self configuring in-network storage model for data persistency in wireless sensor networks. The model is built on a clustered sensor field where we have utilized dense node deployment in the vicinity of the routing nodes to act as data buffers during congestion periods in order to avoid data loss. We show that the in-network storage model can be used in combination with congestion avoidance/control techniques to develop data persistent congestion avoidance/control strategies

A Comparative Performance Analysis of MANET Routing Protocols under Security Attacks

This paper comprehensively analyzes the impact of security attacks on the performance of both proactive (OLSR, DSDV) and reactive (AODV, DSR) MANETs routing protocols. The analysis is provided in terms of performance metrics, such as average end-to-end delay, packet delivery ratio, and normalized routing load. Simulations are setup in NS-2 and performance of these routing protocols is discussed under gray-hole and black-hole attacks. Our finding shows that these protocols are designed without considering security aspects, as result, performance of these protocols degrades significantly under attacks.

Adaptive Trust Threshold Strategy for Misbehaving Node Detection and Isolation

Due to dynamic network topology, distributed architecture and absence of a centralized authority, mobile ad hoc networks (MANETs) are vulnerable to various attacks from misbehaving nodes. To enhance security, various trust-based schemes have been proposed that augment traditional cryptography-based security schemes. However, most of them use static and predefined trust thresholds for node misbehavior detection, without taking into consideration the network conditions locally at each node. Using static thresholds for misbehavior detection may result in high false positives, low malicious node detection rate, and network partitioning. In this paper, we propose a novel Adaptive Trust Threshold (ATT) computation strategy, that adapts the trust threshold in the routing protocol according to network conditions such as rate of link changes, node degree and connectivity, and average neighborhood trustworthiness. We identify the topology factors that affect the trust threshold at each node, and leverage them to build a mathematical model for ATT computation. Our simulation results indicate that the ATT strategy achieves significant improvements in packet delivery ratio, reduction in false positives, and increase in detection rate as compared to traditional static threshold strategies.

MRI findings of bilateral posterior ischemic optic neuropathy in postcardiac transplant patient.

Introduction:Posterior ischemic optic neuropathy (PION) is a rare complication of prolonged surgical hypotension. It can occur in patients who have undergone nonocular surgery, particularly associated with significant blood loss, prolonged anesthesia time, and hypotension. Case Report:We report a 48-year-old female patient who developed postoperative visual loss after cardiac transplantation. Her operative course was marked by prolonged hypotension. The patient’s symptoms did not manifest until she was off sedatives. The initial ophthalmoscopic examination performed was normal. Magnetic resonance imaging confirmed the presence of restricted diffusion in both optic nerves consistent with bilateral PION. Conclusions:PION remains a difficult clinical diagnosis to prove. We report a magnetic resonance imaging–confirmed case of bilateral PION. Radiologic findings, especially diffusion-weighted images, can assist in the early identification of diffusion changes in ischemic optic nerves.

WSN-Based Fire Detection and Escape System with Multi-modal Feedback

Disasters do happen in our lives and we cannot avoid them but we can prepare ourselves so that when a disaster occurs, damage can be minimized. One such disaster can be the event of fire. In this paper, we have proposed a wireless sensor network based solution that can be used to detect fire, set-off a fire alarm and identify safe evacuation routes from the building. In order to accomplish this goal, we have designed a distributed algorithm for systematically deployed sensor nodes in a building. Then the obtained information about the safe evacuation routes is communicated to the occupants of the building using multimodal (visual + audio) feedback. In order to evaluate proposed system we have developed a simulation using Active Tcl and ns2. Front end of the simulation is designed using Active Tcl that can be used to sketch the blue-print of a building, place sensor nodes and set fire. At the back-end safe route identification algorithm is implemented in ns2 that is feed with the deployed network topology to identify safe routes for the occupants of the building.