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

Outline

Motivation for UWB Based Wireless Networked Control Systems System Model Optimization Problem Conclusion

Outline

Motivation for UWB Based Wireless Networked Control Systems System Model Optimization Problem Conclusion

Wireless Networked Control Systems (WNCS)

Spatially distributed systems in which the communication between sensors, actuators and controllers occurs through a shared wireless medium

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

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

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)

sensorsensor

ECUECU

sensorsensor actuatoractuator sensorsensor

ECUECUECUECU

Body Control Module

Body Control Module

sensorsensor sensorsensor

sensorsensor

sensorsensor

sensorsensorsensorsensorsensorsensor

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

On-board sensors + indirect estimation

Intelligent Tire

•More accurate estimation

•Even identify road surface condition in real-time

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.

Enable a wide range of new applications

First IVWSN Example: Intelligent Tire

Outline

Motivation for UWB Based Wireless Networked Control Systems System Model Optimization Problem Simulation Results Conclusion

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

sensorsensor

controllercontroller

sensorsensor actuatoractuator sensorsensor

controllercontrollercontrollercontroller

Body Control Module

Body Control Module

sensorsensor sensorsensor

sensorsensor

sensorsensor

sensorsensorsensorsensorsensorsensor

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

Medium Access Control Layer: System Requirements

Adaptivity requirement Nodes should be scheduled as uniformly as possible

EDF

Uniform

Medium Access Control Layer: System Requirements

Adaptivity requirement Nodes should be scheduled as uniformly as possible

EDF Uniform

1

Medium Access Control Layer: System Requirements

Adaptivity requirement Nodes should be scheduled as uniformly as possible

2

EDF Uniform

Medium Access Control Layer: System Requirements

Adaptivity requirement Nodes should be scheduled as uniformly as possible

3

EDF Uniform

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

EDF

Uniform

max active time=0.9ms

max active time=0.6ms

✓

Outline

Motivation for UWB Based Wireless Networked Control Systems System Model Optimization Problem Conclusion

Medium Access Control Layer: One Controller

Transmission rate of UWB for no concurrent transmission case

Transmission time

Maximum allowed power by UWB regulations

Energy requirement

Delay requirement

Periodic packet generation

Maximum active time of subframes

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

Medium Access Control Layer: One Controller Simulations

Use intra-vehicle UWB channel model Ten different random selection out of

predetermined locations

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?

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

Medium Access Control Layer: Multiple Controllers

Outline

Motivation for UWB Based Wireless Networked Control Systems System Model Optimization Problem Conclusion

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

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