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Halabian H.,Carleton University | Changiz R.,Carleton University | Yu F.R.,Carleton University | Lambadaris I.,Carleton University | Tang H.,Defense R and D Canada
Wireless Networks | Year: 2012

In this paper, we investigate the problem of optimal reliable relay selection in multiuser cooperative wireless networks in the presence of malicious relay nodes. A general discrete time queueing model for such networks is introduced which takes into account the dynamic variations of the channel state, the dynamic malicious behaviour of relay nodes as well as stochastic arrival of data packets into the system. The model consists of a set of mobile users, one destination node and a set of relay nodes which may be either mobile or fixed. The system uses the benefit of cooperative diversity by relaying in the decode and forward mode. We assume that each user either transmits its packets directly to the destination (direct mode) or transmits them with the cooperation of a selected relay node (cooperative mode). It is assumed that a centralized network controller manages the relay selection process in the system. At each time slot, a malicious relay node in the system may behave spitefully and refuse to cooperate with a user deliberately when it is selected to cooperate with that user. A malicious relay node usually acts stochastically to hide its malicious behaviour for longer time. In such a system, at each time slot the network controller should decide whether a user has to cooperate with any relay node or not and if so, which relay node must be selected for cooperation. First, we show that the malicious behaviour of relay nodes makes the stable throughput region shrink. Then, we propose a throughput optimal secure relay selection policy that can stabilize the system for all the arrival rate vectors strictly inside the network stability region. We show that the optimal policy is equivalent to finding the maximum weighted matching in a weighted bipartite graph at each time slot. Finally, we use simulations to compare the performance of the proposed policy with that of four other sub-optimal policies in terms of average queue occupancy (or queueing delay). © Springer Science+Business Media, LLC 2012. Source


Changiz R.,Carleton University | Halabian H.,Carleton University | Yu F.R.,Carleton University | Lambadaris I.,Carleton University | Tang H.,Defense R and D Canada
Proceedings - IEEE/IFIP International Conference on Embedded and Ubiquitous Computing, EUC 2010 | Year: 2010

Cooperative communication makes use of the broadcast nature of the wireless medium where adjacent nodes overhear the message transmitted by the source and assist in the transmission by relaying the overheard message to the destination. Although cooperative communication brings in significant benefits, it also raises serious security issues to wireless mobile networks. For example, there exists a possibility that a node refuses to cooperate when it is selected for cooperation or deliberately drop the received packets. In wireless mobile networks with cooperative communication, trust management is an important mechanism to monitor such networks for violations of security. In this paper, we propose a trust management method for wireless mobile networks with cooperative communications. Conventional Bayesian methodology is insufficient for the cooperative communication paradigm, as it is biased by the channel conditions and relay selection decision processes. Therefore, we modify the conventional trust management method by incorporating not only the relay selection policy but also the dynamic wireless channel conditions among the source, relays and destination. Simulation results are presented to show the effectiveness of the proposed scheme. © 2010 IEEE. Source


Li C.,Radiation Protection Bureau | Sadi B.,Radiation Protection Bureau | Wyatt H.,Chalk River Laboratories | Bugden M.,Chalk River Laboratories | And 3 more authors.
Radiation Protection Dosimetry | Year: 2010

Polonium-210 (210Po) is one of the most toxic radionuclides and was used as a poison in the Alexander Litvinenko case. In this study of the metabolism of 210Po in rats, volatile 210Po in excreta was measured, filling a knowledge gap of the previous studies. Five rats were intravenously administrated with 2 kBq and another five with 10 kBq of 210Po (citrate form). They were housed in a glass Metabowlw system for 4 d following the administration. Volatile 210Po from the excreta was collected in a trapping system filled with liquid scintillation cocktail and was measured by liquid scintillation counting. Results showed that the daily excretion of volatile 210Po by the rats is in a very small percentage (0.002-0.009 %) of the administered amounts. However, if the administered amount is large, the excretion of volatile 210Po can be significant. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org. Source


Bu S.,Carleton University | Yu F.R.,Carleton University | Liu P.X.,Carleton University | Tang H.,Defense R and D Canada
IEEE International Conference on Communications | Year: 2011

Continuous authentication is an important prevention-based approach to protect high security mobile ad-hoc networks (MANETs). On the other hand, intrusion detection systems (IDSs) are also important in MANETs to effectively identify malicious activities. Considering these two approaches jointly is effective in optimal security design taking into account system security requirements and resource constraints in MANETs. To obtain the optimal scheme of combining continuous authentication and IDSs in a distributed manner, we formulate the problem as a partially observable distributed stochastic system. We present structural results for this problem in order to decrease computational complexity, making our solution usable in large networks. The policies derived from structural results are easy to implement in practical MANETs. Simulation results are presented to show the performance of this method for the proposed scheme. © 2011 IEEE. Source


Bu S.,Carleton University | Yu F.R.,Carleton University | Liu X.P.,Carleton University | Tang H.,Defense R and D Canada
IEEE Transactions on Wireless Communications | Year: 2011

Continuous user authentication is an important prevention-based approach to protect high security mobile ad-hoc networks (MANETs). On the other hand, intrusion detection systems (IDSs) are also important in MANETs to effectively identify malicious activities. Considering these two approaches jointly is effective in optimal security design taking into account system security requirements and resource constraints in MANETs. To obtain the optimal scheme of combining continuous user authentication and IDSs in a distributed manner, we formulate the problem as a partially observable Markov decision process (POMDP) multi-armed bandit problem. We present a structural results method to solve the problem for a large network with a variety of nodes. The policies derived from structural results are easy to implement in practical MANETs. Simulation results are presented to show the effectiveness and the performance of the proposed scheme. © 2006 IEEE. Source

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