This paper studies discrete-time control systems subject to average data-rate limits. We focus on a situation where a noisy linear system has been designed assuming transparent feedback and, due to implementation constraints, a source-coding scheme (with unity signal transfer function) has to be deployed in the feedback path. For this situation, and by focusing on a class of source-coding schemes built around entropy coded dithered quantizers, we develop a framework to deal with average data-rate constraints in a tractable manner that combines ideas from both information and control theories. As an illustration of the uses of our framework, we apply it to study the interplay between stability and average data-rates in the considered architecture. It is shown that the proposed class of coding schemes can achieve mean square stability at average data-rates that are, at most, 1.254 bits per sample away from the absolute minimum rate for stability established by Nair and Evans. This rate penalty is compensated by the simplicity of our approach.
This note studies the performance of control systems subject to average data-rate limits. We focus on a situation where a noisy LTI system has been designed assuming transparent feedback and, due to implementation constraints, a source coding scheme (with unity signal transfer function) has to be deployed in the feedback path. For this situation, and by focusing on a specific source coding scheme, we give a closed-form upper bound on the minimal average data-rate that allows one to attain a given performance level. Instrumental to our main result is the explicit solution of a related (and previously unsolved) signalto-noise ratio minimization problem, subject to a closed loop performance constraint.
The successful operation of CDMA systems depend on the use of power control. This is needed to address the "near far" effect and to mitigate the effects of fading. Other factors also impact on the achievable performance of the power control loop including the fact that only the sign of the power increments are transmitted. The paper presents new methods and results to improve control with respect to the latter strongly non-linear effect. An adaptive control architecture, having three degrees of freedom, is therefore proposed for inner loop power control.
The three degrees of freedom are used to address errors resulting from (i) channel and interference variations, (ii) quantization of the power increments and (iii) saturation of the power increments.Simulations show that the proposed controller outperforms other related schemes. A major reason for this is the ability of the three degree of freedom controller to reduce the variation of the control signal to be quantized.
In this paper, performance limitations in the linear control of general linear discrete-time scalar systems are considered. The performance is measured with the 2-norm of an error function which, at the same time, ensures that the closed loop poles lie in a prescribed region. The deleterious effect of this constraint on a classical performance measurement is also quantified, in such a way, that the interplay between the size of the desired region and structural features of the plant is revealed.
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