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Control over Wireless Communication Channel for Continuous-Time Systems. C. D. Charalambous ECE Department University of Cyprus, Nicosia, Cyprus. Also, School of Information Technology and Engineering, University of Ottawa, Ottawa Canada Stojan Denic and Alireza Farhadi

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Control over wireless communication channel for continuous time systems

Control over Wireless Communication Channel for Continuous-Time Systems

C. D. Charalambous

ECE Department

University of Cyprus, Nicosia, Cyprus.

Also,

School of Information Technology and Engineering,

University of Ottawa, Ottawa

Canada

Stojan Denic and Alireza Farhadi

School of Information Technology and Engineering,

University of Ottawa, Ottawa

Canada


Overview
Overview Continuous-Time Systems

  • Problem Formulation

  • Necessary Condition for Stabilizability

  • Optimal Encoding/Decoding Scheme for Observability

  • Optimal Controller, Sufficient Condition for Stabilizability


Problem formulation

Problem Formulation Continuous-Time Systems


Problem formulation1
Problem Formulation Continuous-Time Systems

  • Block diagram of control/communication system


Problem formulation2
Problem Formulation Continuous-Time Systems

  • Plant.

    where and are Borel measurable and bounded, and .

    Throughout, we assume that there exists a unique solution, such that , where


Problem formulation3
Problem Formulation Continuous-Time Systems

  • Channel. The communication Channel is an AWGN, flat fading, wireless channel given by

  • We assume for a fixed sample path


Problem formulation4
Problem Formulation Continuous-Time Systems

  • Bounded Asymptotic and Asymptotic Observability in the Mean Square Sense. Let .Then, the system is bounded asymptotically (resp. asymptotically) observable, in the mean square sense, if there exists encoder and decoder such that

  • Bounded Asymptotic and Asymptotic Stabilizability in the Mean Square Sense. The system is bounded asymptotically (resp. asymptotically) stabilizable, in the mean square sense, if there exists a controller, encoder and decoder, such that



Necessary condition for bounded asymptotic stabilizability
Necessary Condition for Bounded Asymptotic Stabilizability Continuous-Time Systems

  • Control/communication system


Necessary condition for bounded asymptotic stabilizability1
Necessary Condition for Bounded Asymptotic Stabilizability Continuous-Time Systems

  • Theorem. A necessary condition for the existence of a bounded asymptotic stabilizing controller is given by

    For the case of AWGN channel (e.g., ), the necessary condition is reduced to the following condition



Optimal encoding decoding scheme
Optimal Encoding/Decoding Scheme Continuous-Time Systems

  • Theorem. Suppose the transmitter and receiver are subject to the instantaneous power constraint

    ,Then the encoder that achieves the channel capacity, the optimal decoder, and the corresponding error covariance, are respectively given by


Necessary and sufficient condition for observability
Necessary and Sufficient Condition for Observability Continuous-Time Systems

  • Theorem. i) When , a sufficient condition for bounded asymptotic observability in the mean square sense is given by

    (1)

    while, a necessary condition for bounded asymptotic observability is given by

    (2)

    ii) When , (1) is a sufficient condition for asymptotic observability in the mean square sense, while, when , condition (2) is a necessary condition for asymptotic observability in the mean square sense.


Necessary and sufficient condition for observability1
Necessary and Sufficient Condition for Observability Continuous-Time Systems

  • Remark. In the special case of AWGN ( ), for which the channel capacity is , the conditions (1) and (2) are reduced to the following conditions, respectively.



Optimal controller
Optimal Controller

  • Problem. For a fixed sample path

    , the output feedback controller is chosen to minimizes the quadratic pay-off

  • Assumption. The noiseless analog of the plant is completely controllable or exponentially stable.


Optimal controller1
Optimal Controller

  • Solution. According to the classical separation theorem of estimation and control, the optimal controller that minimizes the pay-off subject to a flat fading AWGN channel and linear encoder is separated into a state estimator and a certainly equivalent controller given by


Optimal controller2
Optimal Controller

  • Corollary. For a fixed sample path of the channel, it follows that if the observer and regulator Ricatti equations have steady state solution and , respectively, the average criterion

    can be expressed in the alternative form

    where for the time-invariant case, it reduced to


Conditions for stabilizability
Conditions for Stabilizability

  • Proposition. Consider the time-invariant analog of plant and assume it is controllable or exponentially stable. Then, for a fixed sample path of the channel, we have the followings

    i) Assuming and as , by using the certainly equivalent controller, and as .

    ii) Assuming and as , by using the certainly equivalent controller, and

    as .


Sufficient condition for stabilizability
Sufficient Condition for Stabilizability

  • Theorem. Consider the time-invariant analog of plant and assume it is controllable or exponentially stable. Then, a sufficient condition for bounded asymptotic stabilizability and asymptotic stabilizability, in the mean square sense is given by

  • Remark. For the special case of AWGN channel, this condition is reduced to


Conclusion
Conclusion

  • For the class of scalar diffusion process controlled over AWGN flat fading channel, we built optimal encoder/decoder which achieves channel capacity and minimizes the mean square error.

  • Since the separation principle holds, the optimal encoder/decoder scheme and the certainly equivalent controller leads to the optimal strategy.

  • For the future work, it is interesting to build encoder which is independent of the decoder output. Also, it would be interesting to extend the results to the case when there is also AWGN flat fading communication link between the controller and the plant.


References
References

[1] C. D. Charalambous and Alireza Farhadi, Control of Continuous-Time Systems over Continuous-Time Wireless Channels, 2005 (preprint).

[2] C. D. Charalambous and Stojan Denic, “On the Channel Capacity of Wireless Fading Channels”, in Proceedings of the 41st IEEE Conference on Decision and Control, Las Vegas, December 2002.


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