A novel dynamic model is proposed for the hysteresis in magnetostrictive actuators by coupling a Preisach operator to an ordinary di erential equation, and a parameter identiÿcation method is described. An e cient inversion algorithm for a class of Preisach operators with piecewise uniform density functions is then introduced, based upon which an inverse control scheme for the dynamic hysteresis model is presented. Finally the inversion error is quantiÿed and l1 control theory is applied to improve the robustness of inverse compensation. Simulation and experimental results based on a Terfenol-D actuator are provided. ?

Abstract-Within the realm of network security, we interpret the concept of trust as a relation among entities that participate in various protocols. Trust relations are based on evidence created by the previous interactions of entities within a protocol. In this work, we are focusing on the evaluation of trust evidence in ad hoc networks. Because of the dynamic nature of ad hoc networks, trust evidence may be uncertain and incomplete. Also, no preestablished infrastructure can be assumed. The evaluation process is modeled as a path problem on a directed graph, where nodes represent entities, and edges represent trust relations. We give intuitive requirements and discuss design issues for any trust evaluation algorithm. Using the theory of semirings, we show how two nodes can establish an indirect trust relation without previous direct interaction. We show that our semiring framework is flexible enough to express other trust models, most notably PGP's Web of Trust. Our scheme is shown to be robust in the presence of attackers.

Abstract-In this paper we solve a finite-horizon partially observed risk-sensitive stochastic optimal control problem for discrete-time nonlinear systems and obtain small noise and small risk limits. The small noise limit is interpreted as a deterministic partially observed dynamic game, and new insights into the optimal solution of such game problems are obtained. Both the risk-sensitive stochastic control problem and the deterministic dynamic game problem are solved using information states, dynamic programming, and associated separated policies. A certainty equivalence principle is also discussed. Our results have implications for the nonlinear robust stabilization problem. The small risk limit is a standard partially observed risk-neutral stochastic optimal control problem.

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In this paper we describe the design and implementation of ATEMU, a fine grained sensor network simulator. ATEMU is intended to bridge the gap between actual sensor network deployments and sensor network simulations. We adopt a hybrid strategy, where the operation of individual sensor nodes is emulated in an instruction by instruction manner, and their interactions with each other via wireless transmissions are simulated in a realistic manner. A unique feature of ATEMU is its ability to simulate a heterogeneous sensor network. Using ATEMU it is possible to not only accurately simulate the operation of different application on the MICA2 platform but also a complete sensor network where the sensor nodes themselves maybe based on different hardware platforms. In addition we also describe our implementation of XATDB, our front-end debugger/GUI for ATEMU. XATDB provides an excellent educational tool for people to start learning about the operation of sensor nodes and sensor networks, without requiring the purchase of actual sensor node hardware. The accuracy and emulation capabilities provided by ATEMU ensure that when and if actual hardware is used, the software will already have undergone rigorous testing and debugging on an accurate platform. This would provide the sensor network deployment community with a much more accurate estimate of the performance of various algorithms and protocols in realistic scenarios and platforms.

Abstract-Authentication is the process where claims of identity are verified. Most mechanisms of authentication (e.g., digital signatures and certificates) exist above the physical layer, though some (e.g., spread-spectrum communications) exist at the physical layer often with an additional cost in bandwidth. This paper introduces a general analysis and design framework for authentication at the physical layer where the authentication information is transmitted concurrently with the data. By superimposing a carefully designed secret modulation on the waveforms, authentication is added to the signal without requiring additional bandwidth, as do spread-spectrum methods. The authentication is designed to be stealthy to the uninformed user, robust to interference, and secure for identity verification. The tradeoffs between these three goals are identified and analyzed in block fading channels. The use of the authentication for channel estimation is also considered, and an improved bit-error rate is demonstrated for time-varying channels. Finally, simulation results are given that demonstrate the potential application of this authentication technique.

Avg. time to receive an answer (only successful requests are counted) while running freenet above different routing protocols. .. .. .. 4.5 Comparing Freenet and Gossiping on the diversity of evidence preserved. .

The pervasiveness of wireless devices and the architectural organization of wireless networks in distributed communities, where no notion of trust can be assumed, are the main reasons for the growing interest in the issue of compliance to protocol rules. Reliable and timely detection of deviation from legitimate protocol operation is recognized as a prerequisite for ensuring efficient and fair use of network resources and minimizing performance losses. Nevertheless, the random nature of protocol operation together with the inherent difficulty of monitoring in the open and highly volatile wireless medium poses significant challenges. In this paper, we consider the fundamental problem of detection of node misbehavior at the MAC layer. Starting from a model where the behavior of a node is observable, we cast the problem within a minimax robust detection framework, with the objective to provide a detection rule of optimum performance for the worst-case attack. The performance is measured in terms of required number of observations in order to derive a decision. This framework is meaningful for studying misbehavior because it captures the presence of uncertainty of attacks and concentrates on the attacks that are most significant in terms of incurred performance losses. It also refers to the case of an intelligent attacker that can adapt its policy to avoid being detected. Although the basic model does not include interference, we show that our ideas can be extended to the case where observations are hindered by interference due to concurrent transmissions. We also present some hints for the problem of notifying the rest of the network about a misbehavior event. Our work provides interesting insights and performance bounds and serves as a prelude to a future study that would capture more composite instances of the problem.