1,241,682 research outputs found
Value of Information in Feedback Control
In this article, we investigate the impact of information on networked
control systems, and illustrate how to quantify a fundamental property of
stochastic processes that can enrich our understanding about such systems. To
that end, we develop a theoretical framework for the joint design of an event
trigger and a controller in optimal event-triggered control. We cover two
distinct information patterns: perfect information and imperfect information.
In both cases, observations are available at the event trigger instantly, but
are transmitted to the controller sporadically with one-step delay. For each
information pattern, we characterize the optimal triggering policy and optimal
control policy such that the corresponding policy profile represents a Nash
equilibrium. Accordingly, we quantify the value of information
as the variation in the cost-to-go of the system given
an observation at time . Finally, we provide an algorithm for approximation
of the value of information, and synthesize a closed-form suboptimal triggering
policy with a performance guarantee that can readily be implemented
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Value of Information in Feedback Control: Quantification
Although transmission of a data packet containing sensory information in a networked control system improves the quality of regulation, it has indeed a price from the communication perspective. It is, therefore, rational that such a data packet be transmitted only if it is valuable in the sense of a cost-benefit analysis. Yet, the fact is that little is known so far about this valuation of information and its connection with traditional event-triggered communication. In the present article, we study this intrinsic property of networked control systems by formulating a rate-regulation trade-off between the packet rate and the regulation cost with an event trigger and a controller as two distributed decision makers, and show that the valuation of information is conceivable and quantifiable grounded on this trade-off. In particular, we characterize an equilibrium in the rate-regulation trade-off, and quantify the value of information VoIk there as the variation in a so-called value function with respect to a piece of sensory information that can be communicated to the controller at each time k. We prove that, for a multi-dimensional Gauss--Markov process, VoIk is a symmetric function of the discrepancy between the state estimates at the event trigger and the controller, and that a data packet containing sensory information at time k should be transmitted to the controller only if VoIk is nonnegative. Moreover, we discuss that VoIk can be computed with arbitrary accuracy, and that it can be approximated by a closed-form quadratic function with a performance guarantee
Lazy global feedbacks for quantized nonlinear event systems
We consider nonlinear event systems with quantized state information and
design a globally stabilizing controller from which only the minimal required
number of control value changes along the feedback trajectory to a given
initial condition is transmitted to the plant. In addition, we present a
non-optimal heuristic approach which might reduce the number of control value
changes and requires a lower computational effort. The constructions are
illustrated by two numerical examples
Information and flux in a feedback controlled Brownian ratchet
We study a feedback control version of the flashing Brownian ratchet, in
which the application of the flashing potential depends on the state of the
particles to be controlled. Taking the view that the ratchet acts as a
Maxwell's demon, we study the relationship that exists between the performance
of the demon as a rectifier of random motion and the amount of information
gathered by the demon through measurements. In the context of a simple
measurement model, we derive analytic expressions for the flux induced by the
feedback ratchet when acting on one particle and a few particles, and compare
these results with those obtained with its open-loop version, which operates
without information. Our main finding is that the flux in the feedback case has
an upper bound proportional to the square-root of the information. Our results
provide a quantitative analysis of the value of information in feedback
ratchets, as well as an effective description of imperfect or noisy feedback
ratchets that are relevant for experimental applications.Comment: LaTeX, 13 pages, 2 figure
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Value of Information in Feedback Control: Global Optimality
The rate-regulation tradeoff, defined between two objective functions, one penalizing the packet rate and one the regulation cost, can express the fundamental performance bound of networked control systems. However, the characterization of the set of globally optimal solutions in this tradeoff for multi-dimensional Gauss–Markov processes has been an open problem. In the present article, we characterize a policy profile that belongs to this set without imposing any restrictions on the information structure or the policy structure. We prove that such a policy profile consists of a symmetric threshold triggering policy based on the value of information and a certainty-equivalent control policy based on a non-Gaussian linear estimator. These policies are deterministic and can be designed separately. Besides, we provide a global optimality analysis for the value of information VoIk, a semantic metric that emerges from the rate-regulation tradeoff as the difference between the benefit and the cost of a data packet. We prove that it is globally optimal that a data packet containing sensory information at time k be transmitted to the controller only if VoIk becomes nonnegative. These results have important implications in the areas of communication and control
Tars: Timeliness-aware Adaptive Replica Selection for Key-Value Stores
In current large-scale distributed key-value stores, a single end-user
request may lead to key-value access across tens or hundreds of servers. The
tail latency of these key-value accesses is crucial to the user experience and
greatly impacts the revenue. To cut the tail latency, it is crucial for clients
to choose the fastest replica server as much as possible for the service of
each key-value access. Aware of the challenges on the time varying performance
across servers and the herd behaviors, an adaptive replica selection scheme C3
is proposed recently. In C3, feedback from individual servers is brought into
replica ranking to reflect the time-varying performance of servers, and the
distributed rate control and backpressure mechanism is invented. Despite of
C3's good performance, we reveal the timeliness issue of C3, which has large
impacts on both the replica ranking and the rate control, and propose the Tars
(timeliness-aware adaptive replica selection) scheme. Following the same
framework as C3, Tars improves the replica ranking by taking the timeliness of
the feedback information into consideration, as well as revises the rate
control of C3. Simulation results confirm that Tars outperforms C3.Comment: 10pages,submitted to ICDCS 201
Stability robustness improvement of direct eigenspace assignment based feedback systems using singular value sensitivities
A methodology to improve the stability robustness of feedback control systems designed using direct eigenspace assignment techniques is presented. The method consists of considering the sensitivity of the minimum singular value of the return difference transfer matrix at the plant input to small changes in the desired closed-loop eigenvalues and the specified elements of the desired closed-loop eigenvectors. Closed-form expressions for the gradient of the minimum return difference singular value with respect to desired closed-loop eigenvalue and eigenvector parameters are derived. Closed-form expressions for the gradients of the control feedback gains with respect to the specified eigenspace parameters are obtained as an intermediate step. The use of the gradient information to improve the guaranteed gain and phase margins in eigenspace assignment based designs is demonstrated by application to an advanced fighter aircraft
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