Sinem Coleri Ergen (joint with Yalcin Sadi) Wireless Networks Laboratory,

1. Optimal Power Control, Rate Adaptation and Scheduling for UWB-Based Wireless Networked Control Systems Sinem Coleri Ergen (joint with Yalcin Sadi) Wireless Networks Laboratory, Electrical and Electronics Engineering, Koc University

2. Outline • Motivation for UWB Based Wireless Networked Control Systems • System Model • Optimization Problem • Conclusion

3. Outline • Motivation for UWB Based Wireless Networked Control Systems • System Model • Optimization Problem • Conclusion

4. Wireless Networked Control Systems (WNCS) • Spatially distributed systems in which the communication between sensors, actuators and controllers occurs through a shared wireless medium

5. Wireless Networked Control Systems (WNCS) • Increasingly deployed to monitor and control Cyber-Physical Systems such as • mobile sensor networks • industrial control systems • smart grid • Benefits • ease of installation and maintenance • low complexity and cost • large flexibility • Requirements • Sensor data used in the real-time control • Very high reliability • Energy efficiency

6. UWB Based WNCS • UWB defined to be • Transmission for which emitted signal bandwidth exceeds lesser of 500MHz and 20% of the center frequency • UWB provides • Resistance to multi-path fading • Resistance to power loss due to lack of line of sight • Resistance to intentional/unintentional interference • UWB achieves robust performance at • High data rate and low transmit power • But short distance

7. UWB Based WNCS: Intra-Vehicular Wireless Sensor Networks • Today • Increases in number of sensors as electronic systems in vehicles are replacing purely mechanical and hydraulic systems causes weight, cost, complexity and reliability problems due to wiring • Advances in low power wireless networks and local computing • Intra-Vehicular Wireless Sensor Networks (IVWSN) Body Control Module sensor sensor sensor ECU ECU ECU sensor sensor sensor sensor sensor actuator sensor sensor

8. First IVWSN Example: Intelligent Tire • Active Safety Systems • Change the behavior of vehicle in pre-crash time or during the crash event to avoid the crash altogether • Examples: Anti-lock Braking System (ABS), Traction Control System (TCS), Electronic Stability Program (ESP), Active Suspension System • Requires accurate and fast estimation of vehicle dynamics variables • Forces, load transfer, actual tire-road friction, maximum tire-road friction available Enable a wide range of new applications • Intelligent Tire • More accurate estimation • Even identify road surface condition in real-time On-board sensors + indirect estimation S. C. Ergen, A. Sangiovanni-Vincentelli, X. Sun, R. Tebano, S. Alalusi, G. Audisio and M. Sabatini, “The Tire as an Intelligent Sensor”, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, vol.28, no.7, pp.941-955, July 2009.

9. Outline • Motivation for UWB Based Wireless Networked Control Systems • System Model • Optimization Problem • Simulation Results • Conclusion

10. Medium Access Control Layer: System Model • IVWSN contains • A certain number of controllers • A large number of sensor nodes • One controller selected as central controller • Responsible for synchronization and resource allocation Body Control Module sensor sensor sensor controller controller controller sensor sensor sensor sensor sensor actuator sensor sensor

11. Medium Access Control Layer: System Requirements • Packet generation period, transmission delay and reliability requirements: • Network Control Systems • sensor data -> real-time control of mechanical parts • Fixed determinism better than bounded determinism in control systems

12. Medium Access Control Layer: System Requirements • Adaptivity requirement • Nodes should be scheduled as uniformly as possible EDF Uniform

13. Medium Access Control Layer: System Requirements • Adaptivity requirement • Nodes should be scheduled as uniformly as possible 1 EDF Uniform

14. Medium Access Control Layer: System Requirements • Adaptivity requirement • Nodes should be scheduled as uniformly as possible 2 EDF Uniform

15. Medium Access Control Layer: System Requirements • Adaptivity requirement • Nodes should be scheduled as uniformly as possible 3 EDF Uniform

16. Medium Access Control Layer: System Model • given for each link l • Choose subframe length as for uniform allocation • Assume is an integer: Allocate every subframes • Uniform distribution minimize max subframe active time max active time=0.9ms EDF max active time=0.6ms ✓ Uniform

17. Outline • Motivation for UWB Based Wireless Networked Control Systems • System Model • Optimization Problem • Conclusion

18. Medium Access Control Layer: One Controller Maximum active time of subframes Periodic packet generation Delay requirement Energy requirement Maximum allowed power by UWB regulations Transmission time Transmission rate of UWB for no concurrent transmission case

19. Medium Access Control Layer: One Controller • Optimal power and rate allocation is independent of optimal scheduling • Optimal scheduling problem: Reduce the NP-hard Minimum Makespan Scheduling Problem on identical machines to our problem • Smallest Period into Shortest Subframe First (SSF) Scheduling • 2-approximation algorithm

20. Medium Access Control Layer: One Controller Simulations • Use intra-vehicle UWB channel model • Ten different random selection out of predetermined locations

21. Medium Access Control Layer: Multiple Controllers • How to exploit concurrent transmission to multiple controllers to decrease the maximum active time of subframes? • Allow concurrent transmission of sensors with the same packet generation period -> fixed length slot over all frame assignment What is the power, rate allocation and resulting length of time slot if they are combined? How to decide which nodes are combined?

22. Medium Access Control Layer: Multiple Controllers • Optimal power allocation for the concurrent transmission of n links: Geometric Programming Problem -> Power control needed in UWB Packet based networks • Which slots to combine? -> Mixed Integer Linear Programming problem • Propose Maximum Utility based Concurrency Allowance Scheduling Algorithm • Define utility of a set: decrease in transmission time when concurrent • In each iteration, add the node that maximized utility • Until no more node can be added to increase utility

23. Medium Access Control Layer: Multiple Controllers

24. Outline • Motivation for UWB Based Wireless Networked Control Systems • System Model • Optimization Problem • Conclusion

25. Conclusion • Wireless Networked Control Systems • Deployed to monitor Cyber-Physical Systems • Requirements for low delay, high reliability and robustness • UWB Based Wireless Networked Control Systems • Resistance to multi-path fading, power loss due to the lack of line-of-sight but short distance • Intra-Vehicular Wireless Sensor Networks • Optimization problem • Adaptivity requirement: Minimize maximum active of subframes • Tight interaction with vehicle control systems • Delay, energy and reliability requirements • One controller: 2-approximation algorithm • Multiple controllers: Utility based algorithm to decrease subframe length

26. Thank You! Sinem Coleri Ergen: sergen@ku.edu.tr Personal webpage: http://home.ku.edu.tr/~sergen Wireless Networks Laboratory: http://wnl.ku.edu.tr