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: [email protected]
Personal webpage: http://home.ku.edu.tr/~sergen
Wireless Networks Laboratory: http://wnl.ku.edu.tr