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ItemNonlinear Sampled-Data SystemsNesic, D ; Postoyan, R ; Baillieul, J ; Samad, T (Springer International Publishing, 2021)Sampled-data systems are control systems in which the feedback law is digitally implemented via a computer. They are prevalent nowadays due to the numerous advantages they offer compared to analog control. Nonlinear sampled-data systems arise in this context when either the plant model or the controller are nonlinear. While their linear counterpart is now a mature area, nonlinear sampled-data systems are much harder to deal with and, hence, much less understood. Their inherent complexity leads to a variety of methods for their modeling, analysis and design. A summary of these methods is presented in this article.
ItemInformation-theoretic privacy through chaos synchronization and optimal additive noiseMurguia, C ; Shames, I ; Farokhi, F ; Nešić, D ; Farokhi, F (Springer, 2020)We study the problem of maximizing privacy of data sets by adding random vectors generated via synchronized chaotics oscillators. In particular, we consider the setup where information about data sets, queries, is sent through public (unsecured) communication channels to a remote station. To hide private features (specific entries) within the data set, we corrupt the response to queries by adding random vectors.We send the distorted query (the sum of the requested query and the random vector) through the public channel. The distribution of the additive random vector is designed to minimize the mutual information (our privacy metric) between private entries of the data set and the distorted query. We cast the synthesis of this distribution as a convex program in the probabilities of the additive random vector. Once we have the optimal distribution, we propose an algorithm to generate pseudorandom realizations from this distribution using trajectories of a chaotic oscillator. At the other end of the channel, we have a second chaotic oscillator, which we use to generate realizations from the same distribution. Note that if we obtain the same realizations on both sides of the channel, we can simply subtract the realization from the distorted query to recover the requested query. To generate equal realizations, we need the two chaotic oscillators to be synchronized, i.e., we need them to generate exactly the same trajectories on both sides of the channel synchronously in time. We force the two chaotic oscillators into exponential synchronization using a driving signal. Simulations are presented to illustrate our results.
ItemSecure Networked Control Systems Design Using Semi-homomorphic EncryptionLin, Y ; Farokhi, F ; Shames, I ; Nešić, D ; Ferrari, RMG ; Teixeira, AMH (Springer, 2021-01-01)A secure and private nonlinear networked control systems (NCSs) design using semi-homomorphic encryption is studied. Static feedback controllers are used and network architectures are provided to enable control signal computation using encrypted signals directly. As a result, the security of the NCSs is further enhanced by preserving the privacy of information flowing through the whole network. Whereas in traditional encryption techniques, encrypted signals are decrypted before control computation and are encrypted again after computation for transmission. While this is highly desirable from privacy point of view, additional technical difficulties in the design and analysis of NCSs are induced compared to standard NCSs. In this chapter, we provide sufficient conditions on the encryption parameters that guarantee robust stability of the NCS in the presence of disturbances in a semi-global practical sense and discuss the trade-offs between the required computational resources, security guarantees, and the closed-loop performance. The proof technique is based on Lyapunov methods.