Wednesday , December 19 2018

A Control-aware QoS Adaptation Co-design Method for
Networked Control Systems

Octavian STEFAN, Toma-Leonida DRAGOMIR
Politehnica University Timisoara,
2 Piata Victoriei, Timisoara, 300006, Romania
octavian.stefan@upt.ro, toma.dragomir@upt.ro

Abstract: The current study proposes a control-aware Quality of Service adaptation co-design method for networked control systems. The novel networked control structure is based on a remotely placed Quality of Service adapter that continuously changes the network parameters using the Next Steps in Signaling protocol suite for end-to-end Quality of Service. The control system’s design is developed gradually and the system’s stability is assessed by considering the overall system as a switched linear one. Finally, the results are validated on a numerical example.

Keywords: Networked control systems, co-design control methods, switched linear systems.

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CITE THIS PAPER AS:
Octavian STEFAN, Toma-Leonida DRAGOMIR, A Control-aware QoS Adaptation Co-design Method for Networked Control Systems, Studies in Informatics and Control, ISSN 1220-1766, vol. 24 (1), pp. 33-42, 2015. https://doi.org/10.24846/v24i1y201504

  1. Introduction

Advances in digital communication technologies offered new possibilities for the development of telecontrol applications. Consequently, networked control systems (NCS) have gained an increasing amount of attention in the scientific community. Although NCS have several advantages ([11]), there are some network induced issues like time-varying delays, data loss, and limited data transfer capacity which can affect the system’s performance and stability ([24]). In order to overcome these issues, different control strategies are proposed in the specialized literature that can be divided in two categories: control over network solutions (e.g. gain scheduling ([15]), adaptive Smith predictor ([14]), optimal stochastic control ([18]), event based control ([12]), predictive control ([5]), communication disturbance observer ([17]) or robust control ([24])) and control of network solutions (e.g. end-to-end Quality of Service (QoS) ([8])). Although each category is proven to work in practice, best possible results are achieved when using co-design methods obtained by combining control solutions from both categories (best resource utilization) ([21]). Furthermore, when using a shared medium network to transport data for multiple NCS and other possible applications with an unknown traffic pattern, co-design methods are mandatory to assure the control objectives. According to [1], two types of co-design methods exist. The first one, referred to as “implementation-aware control law design”, presumes real-time continuous adaptation of the control parameters according to the ones of the network (e.g. continuous adaptation of the sample rate ([2]) or continuous adaptation of the controller gains ([22]) based on the values of the network time delays and packet loss number). The second one, named “control-aware QoS adaptation” presumes a real-time reallocation of network resources, by modifying the QoS parameters, in order to maintain the quality of control (e.g. dynamic bandwidth allocation in a Switched Ethernet Network ([9])).

Current paper proposes a new control-aware QoS adaptation co-design method for NCS using the Next Steps in Signaling (NSIS) protocol suite for end-to-end QoS. In addressing the control objective (tracking and stabilization) a networked control structure is considered, composed out of a local plant, a remotely placed controller and a network adaptation block. Based on the network parameters’ values, the network adaptation block performs a real-time continuous adaptation of the QoS parameters in order to assure the control objectives and to minimize the network resource utilization.

For the analysis stage, the study uses a switched linear system ([20]) as a network transmission model (NTM) – presented by the authors in [22] – that completely characterize network transmissions from an input-output perspective, taking into account time-varying delays, packet losses and irregular situations together with their handling strategy ([23]) that can occur when using unreliable networks and connectionless protocols.

The remainder of this paper is organized as follows. Section 2 describes the problem formulation. Section 3 presents the NTM. Section 4 presents the design methodology for the control structure. Section 5 analyses the system’s stability. Section 6 presents an illustrative example and Section 7 states some final conclusions.

REFERENCES

  1. AUBRUN, C., D. SIMON, Y.-Q. SONG, Ed., Co-design Approaches for Dependable Networked Control Systems, Wiley, 2010.
  1. Bai, J., E. P. Elisi, F. Qiu, Y. Xue, X. D. Koutsoukos, Optimal Cross-Layer Design of Sampling Rate Adaptation and Network Scheduling for Wireless Networked Control Systems, IEEE/ACM Third International Conference on Cyber-Physical Systems (ICCPS), Beijing, 2012, pp. 107-116.
  2. BOYD, S., L. EL GHAOUI, E. FERON, V. BALAKRISHNAN, Linear Matrix Inequalities in System and Control Theory, SIAM, 1994.
  3. Carmo, M., B. Carvalho, J. S. Silva, E. Monteiro, P. Simões, M. Curado, F. Boavida, NSIS-based Quality of Service and Resource Allocation in Ethernet Networks, Proceedings of the 4th International Conference on Wired/Wireless Internet Communications, Bern, 2006.
  4. Caruntu, C. F., C. Lazar, Networked Predictive Control for Time-varying Delay Compensation with an Application to Automotive Mechatronic Systems, Journal of Control Engineering and Applied Informatics, vol. 13, no. 4, 2011, pp. 19-25.
  5. Cloosterman, M. B. G., L. Hetel, N. van de Wouw, W. P. M. H. Heemels, J. Daafouz, H. Nijmeijer, Controller Synthesis for Networked Control Systems, Automatica, vol. 46, 2010, pp. 1584-1594.
  6. Daafouz, J., P. Riedinger, C. Iung, Stability Analysis and Control Synthesis for Switched Systems, IEEE Transactions on Automatic Control, vol. 47, no. 11, 2002, pp. 1883-1887.
  7. DE MORAES, R. A. R, F. VASQUES, A Quality-of-Service (QoS) Based Approach for the Communication Support in Network-based Control Systems: an On-going Project, 11th IFAC Symposium on Information Control Problems in Manufacturing, Salvador, 2004.
  8. Diouri, I., J. Georges, E. Rondeau, Accommodation of Delays for NCS using Classification of Service, International Conference on Networking, Sensing and Control, London, 2007, pp. 410-415.
  9. Grant, M., S. Boyd, CVX: Matlab Software for Disciplined Convex Programming, version 1.21., 2011, http://cvxr.com/cvx.
  10. Hespanha, J. P., P. Naghshtabrizi, Y. Xu, A survey of Recent Results in Networked Control Systems, Proceedings IEEE, vol. 95, no. 1, 2007, pp. 138-162.
  11. Hu, W., G. Liu, D. Rees, Event-Driven Network Predictive Control, IEEE Transactions on Industrial Electronics, vol. 59, no. 3, 2011, pp. 905-913.
  12. KAPPLER, C., X. FU, B. SCHLOER, A QoS Model for Signaling IntServ Controlled-Load Service with NSIS, Internet draft, work in progress, 2011, https://tools.ietf.org/html/draft-kappler-nsis-qosmodel-controlledload-14.
  13. Lai, C.-L., P.-L. Hsu, Design the Remote Control System With the Time-Delay Estimator and the Adaptive Smith Predictor, IEEE Transactions on Industrial Informatics, vol. 6, no. 1, 2010, pp. 73-80.
  14. Li, H., Z. Sun, M.-Y. Chow, F. Sun, Gain-Scheduling-Based State Feedback Integral Control of Networked Control Systems, IEEE Transactions on Industrial Electronics, vol. 58, no. 6, 2011, pp. 2465-2472.
  15. Luenberger, D. G., An Introduction to Observers, IEEE Trans. on Automatic Control, vol. 16, no. 6, 1971, pp. 596-602.
  16. Natori, K., T. Tsuji, K. Ohnishi, A. Hace, K. Jezernik, Time-Delay Compensation by Communication Disturbance Observer for Bilateral Teleoperation under Time-varying Delay, IEEE Transactions on Industrial Electronics, vol. 57, no. 3, 2010, pp. 1050-1062.
  17. Nilsson, J., Real-time Control Systems with Delay, Ph.D. Thesis, Lund Institute of Technology, Lund, 1998.
  18. NS-2 network simulation software, 2014, http://www.isi.edu/nsnam/ns/.
  19. SOGA, T., N. OTSUKA, Stabilizability Conditions for Switched Linear Systems with Constant Input via Switched Observer, Studies in Informatics and Control, vol. 22, no. 1, 2013, pp. 7-14.
  20. Song, Y.-Q., Networked Control Systems: From Independent Designs of the Network QoS and the Control to the Co-design, 8th IFAC International Conference on Fieldbuses and Networks in Industrial and Embedded Systems, Ansan, 2009, pp. 155-162.
  21. Stefan, O., A. Codrean, T.-L. Dragomir, A Network Control Structure with a Switched PD Delay Compensator and a Nonlinear Network Model, American Control Conference, Washington, 2013, pp. 758-764.
  22. Stefan, O., A. Codrean, T.-L. Dragomir, A Nonlinear State Space Model of Network Transmissions in a Network Control System, Journal of Control Engineering and Applied Informatics, vol. 13, no. 4, 2011, pp. 58-63.
  23. Tipsuwan, Y., M. Y. Chow, Control Methodologies in Networked Control Systems, Control Engineering Practice, vol. 11, 2003, pp. 1099-1111.
  24. Xiaoming, F., H. Schulzrinne, A. Bader, D. Hogrefe, C. Kappler, G. Karagiannis, H. Tschofenig, S. Van den Bosch, NSIS: A New Extensible IP Signaling Protocol Suite, IEEE Communications Magazine, vol. 43, no. 10, 2005, pp. 133-141.