@conference {
	title = {On Optimal Watermarking Schemes in Uncertain Gaussian Channels},
	author = {Cardenas, Alvaro A., Moustakides, George V., Baras, John S.},
	year = {2007},
	month = {09/2007},
	abstract = {This paper describes the analytical derivation of a new watermarking algorithm satisfying optimality properties when the distortion of the watermarked signal is caused by a Gaussian process. We also extend previous work under the same assumptions and obtain more general solutions.},
	address = {San Antonio, Texas},
	booktitle = {IEEE International Conference on Signal Processing ICIP 2007},
	pages = {pp. 449-452}
}
@conference {
	title = {Towards Optimal Design of Data Hiding Algorithms Against Nonparametric Adversary Models},
	author = {Cardenas, Alvaro A., Moustakides, George V., Baras, John S.},
	year = {2007},
	month = {03/2007},
	abstract = {This paper presents a novel zero-sum watermarking game between a detection algorithm and a data hiding adversary. Contrary to previous research, the detection algorithm and the adversary we consider are both nonparametric in a continuous signal space, and thus they have no externally imposed limitations on their allowed strategies except for some distortion constraints. We show that in this framework no deterministic detection algorithm is optimal. We then find optimal randomized detection algorithms for different distortion levels and introduce a new performance tradeoff between completeness and accuracy when a detection algorithm does not have enough evidence to make an accurate decision.},
	address = {Baltimore, Maryland},
	booktitle = {41st Annual Conference on Information Sciences and Systems},
	pages = {pp. 911-916}
}
@conference {
	title = {Detecting IEEE 802.11 MAC Layer Misbehavior in Ad Hoc Networks},
	author = {Radosavac, Svetlana., Cardenas, Alvaro A., Baras, John S., Moustakides, George V.},
	year = {2007},
	month = {01/2007},
	abstract = {Selfish behavior at the Medium Access (MAC) Layer can have devastating side effects on the performance of wireless networks, with effects similar to those of Denial of Service (DoS) attacks. In this paper we consider the problem of detection and prevention of node misbehavior at the MAC layer, focusing on the back-off manipulation by selfish nodes. We first propose an algorithm that ensures honest behavior of non-colluding participants. Furthermore, we analyze the problem of colluding selfish nodes, casting the problem within a minimax robust detection framework and providing an optimal detection rule for the worst-case attack scenarios. Finally, we evaluate the performance of single and colluding attackers in terms of detection delay. Although our approach is general and can be used with any probabilistic distributed MAC protocol, we focus our analysis on the IEEE 802.11 MAC.},
	booktitle = {Robust Strategies Against Individual and Colluding Attacker\&quot; Journal of Computer Security: Special Issue on Security of Ad Hoc and Sensor Networks},
	pages = {pp. 103-128}
}
@conference {
	title = {Multiple Sampling for Estimation on a Finite Horizon},
	author = {Rabi, Maben., Moustakides, George V., Baras, John S.},
	year = {2006},
	month = {12/2006},
	abstract = {We discuss some multiple sampling problems that arise in finite horizon real-time estimation when there is an upper limit on the number of allowable samples. Measuring estimation quality by the aggregate squared error, we compare the performances of the best deterministic, level-triggered and the optimal sampling schemes. We restrict the signal to be either a Wiener or an Ornstein-Uhlenbeck process. For the Wiener process, we provide closed form expressions and series expansions, whereas for the Ornstein Uhlenbeck process, procedures for numerical computation. Our results indicate that the best level-triggered sampling is almost optimal when the signal is stable.},
	address = {San Diego, CA},
	booktitle = {45th IEEE Conference on Decision and Control},
	pages = {pp. 1351-1357}
}
@conference {
	title = {Impact of Optimal MAC Layer Attacks on the Network Layer},
	author = {Radosavac, Svetlana., Baras, John S., Moustakides, George V.},
	year = {2006},
	month = {10/2006},
	abstract = {Node misbehavior in wireless ad hoc networks leads to sudden unpredictable changes in network topology, resulting in fluctuation of traffic load and capacity for already existing links. In this work we consider node misbehavior in the Medium Access Control (MAC) layer and its effects on the performance of the network layer. In order to capture uncertainty of the attacker{\textquoteright}s strategy as well as the unpredictable nature of the wireless medium, we quantify the optimal attack strategy by using the principle of minimum cross entropy. Following that, we apply the obtained results for analysis of the IEEE 802.11 DCF MAC protocol and investigate the effects of such optimal attacks on the network layer. Finally, we evaluate the robustness of two different routing protocols against the worst-case MAC layer attacks and justify the need for the MAC layer-based Intrusion Detection Systems (IDS).},
	address = {Alexendria, VA},
	booktitle = {Fourth ACM Workshop on Security of Ad Hoc and Sensor Networks (SASN 2006)},
	pages = {pp. 135-145}
}
@conference {
	title = {Efficient Sampling for Keeping Track of an Ornstein-Uhlenbeck Process},
	author = {Rabi, Maben., Moustakides, George V., Baras, John S.},
	year = {2006},
	month = {06/2006},
	abstract = {We consider estimation and tracking problems in sensor networks with constraints in the hierarchy of inference making, on the sharing of data and inter-sensor communications. We identify as a typical representative for such problems tracking of a process when the number and type of measurements are constrained. As the simplest representative of such problems, which still encompasses all the key issues involved, we analyze efficient sampling schemes for tracking an Ornstein- Uhlenbeck process. We consider sampling based on time, based on amplitude (event-triggered sampling) and optimal sampling (optimal stopping). We obtain the best sampling rule in each case as the solution to a constrained optimization problem. We compare the performances of the various sampling schemes and show that the event-triggered sampling performs close to optimal. Implications and extensions are discussed.},
	address = {Anconia, Italy},
	booktitle = {14th Mediterranean Conference on Control and Automation},
	pages = {pp. 1-6}
}
@article {
	title = {Adaptive Sampling For Linear State Estimation},
	author = {Rabi, Maben., Moustakides, George V., Baras, John S.},
	year = {2012},
	month = {03/2012},
	abstract = {When a sensor has continuous measurements but sends occasional messages over a data network to a supervisor which estimates the state, the available packet rate fixes the achievable quality of state estimation. When such rate limits turn stringent, the sensor{\textquoteright}s messaging policy should be designed anew. What are good causal messaging policies? What should message packets contain? What is the lowest possible distortion in a causal estimate at the supervisor? Is Delta sampling better than periodic sampling? We answer these questions for a Markov state process under an idealized model of the network and the assumption of perfect state measurements at the sensor. If the state is a scalar or a vector of low dimension, then we can ignore sample quantization. If in addition, we can ignore jitter in the transmission delays over the network, then our search for efficient messaging policies simplifies. First, each message packet should contain the value of the state at that time. Thus a bound on the number of data packets becomes a bound on the number of state samples. Second, the remaining choice in messaging is entirely about the times when samples are taken. For a scalar, linear diffusion process, we study the problem of choosing the causal sampling times that will give the lowest aggregate squared error distortion. We stick to finite horizons and impose a hard upper bound N on the number of allowed samples. We cast the design as a problem of choosing an optimal sequence of stopping times. We reduce this to a nested sequence of problems, each asking for a single optimal stopping time. Under an unproven but natural assumption about the least-square estimate at the supervisor, each of these single stopping problems are of standard form. The optimal stopping times are random times when the estimation error exceeds designed envelopes. For the case where the state is a Brownian motion, we give analytically: the shape of the optimal sampling envelopes, the shape of the envelopes under optimal Delta sampling, and their performances. Surprisingly, we find that Delta sampling performs badly. Hence, when the rate constraint is a hard limit on the number of samples over a finite horizon, we should not use Delta sampling.},
	pages = {pp. 672-702},
	volume = {Volume 50},
	number = {No. 2},
	journal = {SIAM Journal on Control and Optimization}
}
@article {
	title = {An Analytic Framework for Modeling and Detecting Access Layer Misbehavior in Wireless Networks},
	author = {Radosavac, Svetlana., Moustakides, George V., Baras, John S., Koutsopoulos, Iordanis. },
	year = {2008},
	month = {07/2008},
	abstract = {The widespread deployment of wireless networks and hot spots that employ the IEEE 802.11 technology has forced network designers to put emphasis on the importance of ensuring efficient and fair use of network resources. In this work, we propose a novel framework for detection of intelligent adaptive adversaries in the IEEE 802.11 MAC by addressing the problem of detection of the worst-case scenario attacks. Utilizing the nature of this protocol we employ sequential detection methods for detecting greedy behavior and illustrate their performance for detection of least favorable attacks. By using robust statistics in our problem formulation, we attempt to utilize the precision given by parametric tests, while avoiding the specification of the adversarial distribution. This approach establishes the lowest performance bound of a given Intrusion Detection System (IDS) in terms of detection delay and is applicable in online detection systems where users who pay for their services want to obtain the information about the best and the worst case scenarios and performance bounds of the system. This framework is meaningful for studying misbehavior due to the fact that it does not focus on specific adversarial strategies and therefore is applicable to a wide class of adversarial strategies.},
	pages = {pp. 19.1 - 19.28},
	volume = {Vol. 11},
	number = {Issue 4, Article 19},
	journal = {ACM Transactions on Information and System Security}
}
@article {
	title = {Detecting IEEE 802.11 MAC Layer Misbehavior in Ad Hoc Networks: Robust Strategies Against Individual and Colluding Attackers},
	author = {Radosavac, Svetlana., Cardenas, Alvaro A., Baras, John S., Moustakides, George V.},
	year = {2007},
	month = {01/2007},
	abstract = {Selfish behavior at the Medium Access (MAC) Layer can have devastating side effects on the performance of wireless networks, with effects similar to those of Denial of Service (DoS) attacks. In this paper we consider the problem of detection and prevention of node misbehavior at the MAC layer, focusing on the back-off manipulation by selfish nodes. We first propose an algorithm that ensures honest behavior of non-colluding participants. Furthermore, we analyze the problem of colluding selfish nodes, casting the problem within a minimax robust detection framework and providing an optimal detection rule for the worst-case attack scenarios. Finally, we evaluate the performance of single and colluding attackers in terms of detection delay. Although our approach is general and can be used with any probabilistic distributed MAC protocol, we focus our analysis on the IEEE 802.11 MAC.},
	pages = {pp.  103-128},
	volume = {Vol. 15},
	number = {No. 1},
	journal = {Journal of Computer Security: Special Issue on Security of Ad Hoc and Sensor Networks}
}
@techreport {
	title = {Efficient Sampling for Keeping Track of an Ornstein-Uhlenbeck Process},
	author = {Rabi, Maben., Moustakides, George V.},
	year = {2006},
	month = {01/2006},
	abstract = {We consider estimation and tracking problems in sensor networks with constraints in the hierarchy of inference making, on the sharing of data and inter-sensor communications. We identify as a typical representative for such problems tracking of a process when the number and type of measurements in constrained. As the simplest representative of such problems, which still encompasses all the key issues involved we analyze efficient sampling schemes for tracking an Ornstein-Uhlenbeck process. We considered sampling based on time, based on amplitude (event-triggered sampling) and optimal sampling (optimal stopping). We obtained the solution in each case as a constrained optimization problem. We compare the performance of the various sampling schemes and show that the event-triggered sampling performs close to optimal. Implications and extensions are discussed.},
	number = {Number: ISR TR 2006-3}
}
@techreport {
	title = {Detection of Greedy Individual and Colluding MAC Layer Attackers},
	author = {Radosavac, Svetlana., Cardenas, Alvaro A., Moustakides, George V.},
	year = {2006},
	month = {01/2006},
	abstract = {Selfish behavior at the Medium Access (MAC) Layer can have devastating side effects on the performance of wireless networks, with effects similar to those of Denial of Service (DoS) attacks. In this paper we consider the problem of detection and prevention of node misbehavior at the MAC layer, focusing on the back-off manipulation by selfish nodes. We propose an algorithm that ensures honest behavior of non-colluding participants. Furthermore, we analyze the problem of colluding selfish nodes, casting the problem within a minimax robust detection framework, providing a detection rule of optimum performance for the worst-case attack. Finally, we compare the effects of colluding attackers with a single attacker in terms of the detection delay. Although our approach is general and can serve as a guideline for the design of any probabilistic distributed MAC protocol, we focus our analysis on the IEEE 802.11 MAC.},
	number = {Number: ISR TR 2006-8}
}
@techreport {
	title = {Multiple Sampling for Estimation on a Finite Horizon},
	author = {Rabi, Maben., Moustakides, George V.},
	year = {2006},
	month = {01/2006},
	abstract = {We discuss some multiple sampling problems that arise in real-time estimation problems with limits on the number of samples. The quality of estimation is measured by an aggregate squared error over a finite horizon. We compare the performances of the best detereministic, level-triggered and the optimal sampling schemes. We restrict the signal to be either a Wiener process or an Ornstein-Uhlenbeck process. For the Wiener process, we provide closed form expressions and series expansions. For the Ornstein Uhlenbeck process, we provide procedures for numerical computation. Our results show that level-triggered sampling is almost optimal when the signal is stable.},
	number = {Number: ISR TR 2006-7}
}
