Securing DSR against wormhole attacks in multirate ad hoc networks

A wormhole attack is one of the hardest problems to detect whereas it can be easily implanted in any type of wireless ad hoc network. A wormhole attack can easily be launched by the attacker without having knowledge of the network or compromising any legitimate nodes. Most existing solutions either require special hardware devices or make strong assumptions in order to detect wormhole attacks which limit the usability of these solutions. In this paper, we present a security enhancement to dynamic source routing (DSR) protocol against wormhole attacks for ad hoc networks which relies on calculation of round trip time (RTT). Our protocol secures DSR against a wormhole attack in ad hoc networks for multirate transmissions. We also consider the processing and queuing delays of each participating node in the calculation of RTTs between neighbors which to date has not been addressed in the existing literature. This work provides two test cases that show that not taking multirate transmission into consideration results in miss identifying a wormhole attack.     

Proportional and double imitation rules for spectrum access in cognitive radio networks

In this paper, we tackle the problem of opportunistic spectrum access in large-scale cognitive radio networks, where the unlicensed Secondary Users (SUs) access the frequency channels partially occupied by the licensed Primary Users (PUs). Each channel is characterized by an availability probability unknown to the SUs. We apply population game theory to model the spectrum access problem and develop distributed spectrum access policies based on imitation, a behavior rule widely applied in human societies consisting of imitating successful behaviors. We develop two imitation-based spectrum access policies based on the basic Proportional Imitation (PI) rule and the more advanced Double Imitation (DI) rule given that a SU can only imitate the other SUs operating on the same channel. A systematic theoretical analysis is presented for both policies on the induced imitation dynamics and the convergence properties of the proposed policies to the Nash equilibrium. Simple and natural, the proposed imitation-based spectrum access policies can be implemented distributedly based on solely local interactions and thus is especially suited in decentralized adaptive learning environments as cognitive radio networks.     

Contention-based forwarding with multi-hop connectivity awareness in vehicular ad-hoc networks

Recent vehicular routing proposals use real-time road traffic density estimates to dynamically select forwarding paths. Estimating the traffic density in vehicular ad hoc networks requires the transmission of additional dedicated messages increasing the communications load. These proposals are generally based on unicast sender-based forwarding schemes. The greedy nature of sender-based forwarding can result in the selection of forwarders with weak radio links that might compromise the end-to-end performance. To overcome these limitations, this paper presents TOPOCBF, a novel contention-based broadcast forwarding protocol that dynamically selects forwarding paths based on their capability to route packets between anchor points. Such capability is estimated by means of a multi-hop connectivity metric. The obtained results demonstrate that TOPOCBF can provide good packet delivery ratios while reducing the communications load compared to unicast sender-based forwarding schemes using road traffic density estimates.     

Improving fairness in IEEE 802.11 networks using MAC layer opportunistic retransmission

This paper introduces DAFMAC (Decode And Forward MAC), a scalable opportunistic cooperative retransmission enhancement for the IEEE 802.11 MAC protocol which operates without the need for additional explicit control signalling. Distributed opportunistic retransmission algorithms rely on selecting a single suitable relay without direct arbitration between nodes. Simulations show that DAFMAC offers a significant improvement in fairness for both throughput and jitter, giving multiple parallel data flows a more equal opportunity to utilise the channel. DAFMAC cooperative retransmissions are shown to reduce node energy consumption for a given throughput. Further, the DAFMAC relay selection algorithm is shown to scale very well in terms of complexity and memory requirements in comparison to other cooperative retransmission schemes.     

Evaluation of realtime people tracking for indoor environments using ubiquitous motion sensors and limited wireless network infrastructure

We present the development and evaluation of a realtime indoor localisation system for tracking people. Our aim was to track a person’s indoor position using dead-reckoning, while limiting position error without depending on extensive wireless network infrastructure. The Indoor People Tracker used wearable motion sensors, a floor-plan map and a limited wireless sensor network for proximity ranging. We evaluated how the position accuracy of the Indoor People Tracker was affected by floor-plan map features, wireless proximity range and motion information. The advantage of the Indoor People Tracker was found; it was able to achieve accurate position resolution with minimal error, while not depending on wireless proximity.     

Improved concentration and separation of particles in a 3D dielectrophoretic chip integrating focusing, aligning and trapping

This article presents a dielectrophoresis (DEP)-based microfluidic device with the three-dimensional (3D) microelectrode configuration for concentrating and separating particles in a continuous throughflow. The 3D electrode structure, where microelectrode array are patterned on both the top and bottom surfaces of the microchannel, is composed of three units: focusing, aligning and trapping. As particles flowing through the microfluidic channel, they are firstly focused and aligned by the funnel-shaped and parallel electrode array, respectively, before being captured at the trapping unit due to negative DEP force. For a mixture of two particle populations of different sizes or dielectric properties, with a careful selection of suspending medium and applied field, the population exhibits stronger negative DEP manipulated by the microelectrode array and, therefore, separated from the other population which is easily carried away toward the outlet due to hydrodynamic force. The functionality of the proposed microdevice was verified by concentrating different-sized polystyrene (PS) microparticles and yeast cells dynamically flowing in the microchannel. Moreover, separation based on size and dielectric properties was achieved by sorting PS microparticles, and isolating 5 μm PS particles from yeast cells, respectively. The performance of the proposed micro-concentrator and separator was also studied, including the threshold voltage at which particles begin to be trapped, variation of cell-trapping efficiency with respect to the applied voltage and flow rate, and the efficiency of separation experiments. The proposed microdevice has various advantages, including multi-functionality, improved manipulation efficiency and throughput, easy fabrication and operation, etc., which shows a great potential for biological, chemical and medical applications.     

A novel method to construct 3D electrodes at the sidewall of microfluidic channel

We report a simple, low-cost and novel method for constructing three-dimensional (3D) microelectrodes in microfluidic system by utilizing low melting point metal alloy. Three-dimensional electrodes have unique properties in application of cell lysis, electro-osmosis, electroporation and dielectrophoresis. The fabrication process involves conventional photolithography and sputtering techniques to fabricate planar electrodes, positioning bismuth (Bi) alloy microspheres at the sidewall of PDMS channel, plasma bonding and low temperature annealing to improve electrical connection between metal microspheres and planar electrodes. Compared to other fabrication methods for 3D electrodes, the presented one does not require rigorous experimental conditions, cumbersome processes and expensive equipments. Numerical analysis on electric field distribution with different electrode configurations was presented to verify the unique field distribution of arc-shaped electrodes. The application of 3D electrode configuration with high-conductive alloy microspheres was confirmed by particle manipulation based on dielectrophoresis. The proposed technique offers alternatives to construct 3D electrodes from 2D electrodes. More importantly, the simplicity of the fabrication process provides easy ways to fabricate electrodes fast with arc-shaped geometry at the sidewall of microchannel.     

Fast intrusion detection based on a non-negative matrix factorization model

In this paper, we present an efficient fast anomaly intrusion detection model incorporating a large amount of data from various data sources. A novel method based on non-negative matrix factorization (NMF) is presented to profile program and user behaviors of a computer system. A large amount of high-dimensional data is collected in our experiments and divided into smaller data blocks by a specific scheme. The system call data is divided into blocks by processes, while command data is divided into consecutive blocks with a fixed length. The frequencies of individual elements in each block of data are computed and placed column by column as data vectors to construct a matrix representation. NMF is employed to reduce the high-dimensional data vectors and anomaly detection can be realized as a very simple classifier in low dimensions. Experimental results show that the model presented in this paper is promising in terms of detection accuracy, computation efficiency and implementation for fast intrusion detection.     

Acclimatization model of an aerobic bioreactor for the treatment of toxic wastewater

This work proposes a mathematical model for the acclimatization process of a bioreactor treating toxic wastewater. Experimental data was used to identify the changing kinetic parameters of the model as acclimatization progresses. It was found that only one key parameter, the specific biomass growth rate function, changed during the acclimatization process. Therefore, an acclimatization model was proposed to explain the changes of this parameter.     

Chevrel Phase Mo6T8 (T = S,Se) as Electrodes for Advanced Energy Storage

With the large‐scale applications of electric vehicles in recent years, future batteries are required to be higher in power and possess higher energy densities, be more environmental friendly, and have longer cycling life, lower cost, and greater safety than current batteries. Therefore, to develop alternative electrode materials for advanced batteries is an important research direction. Recently, the Chevrel phase Mo₆T₈ (T = S, Se) has attracted increasing attention as electrode candidate for advanced batteries, including monovalent (e.g., lithium and sodium) and multivalent (e.g., magnesium, zinc and aluminum) ion batteries. Benefiting from its unique open crystal structure, the Chevrel phase Mo₆T₈ cannot only ensure rapid ion transport, but also retain the structure stability during electrochemical reactions. Although the history of the research on Mo₆T₈ as electrodes for advanced batteries is short, there has been significant progress on the design and fabrication of Mo₆T₈ for various advanced batteries as above mentioned. An overview of the recent progress on Mo₆T₈ electrodes applied in advanced batteries is provided, including synthesis methods and diverse structures for Mo₆T₈, and electrochemical mechanism and performance of Mo₆T₈. Additionally, a briefly conclusion on the significant progress, obvious drawbacks, emerging challenges and some perspectives on the research of Mo₆T₈ for advanced batteries in the near future is provided.