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RT-WiFi: Real Time High-Speed
Communication Protocol for
Wireless Cyber-Physical Control
Applications
Authors: Y.Wei, Q.Leng, S.Han, K.Mok, W.Zhang, M.Tomizuka
Presenter: David Etim
Outline
• Introduction
• RT-Wi-Fi Design and Implementation
• Performance Evaluation
• Case Study
• Conclusion
• Future Work
Introduction
• Wireless control system with control loops
through wireless communication network
• Advantages:
– Enhanced Mobility
– Easier deployment
– Reduced maintenance cost
Wireless Control System Applications
• Industrial Process Control and Automation
• Healthcare
• Robotic Control
Robotic Control
Industrial Process
Control and Automation
Wireless Control System Requirements
• Sampling rate
• Reliability
• Real-time data delivery
– Bounded delay for estimating system state
RT-Wifi Design and Implementation
• Goals of RT-Wifi Design
– Real-time Data Delivery and High Sampling Rate
– Flexible Configuration
– Transparent System Design
Data Delivery and Sampling Rate
• Control applications rely on bounded latency
for estimating and controlling state of a
system
• High sampling rate supports increasing
number of sensors and actuators
– required to achieve good quality of control
Flexible Configuration
• Different control applications have different
requirements on data delivery
• Trade-offs: sampling rate, real-time data
delivery, co-existence to existing Wi-Fi
networks
• Control designer configures preferred
communication protocol
Transparent System Design
• Use commercial-off-the-shelf (COTS) Wi-Fi
network card
• Transparent to upper layer protocol stack and
underlying hardware
• Mesh networks can be easily built
TDMA on Wi-Fi
• TDMA: Time Division Multiple Access
• Divides channel into time slots, assign time slots to each station
• We can assign a simple TDMA time slots as following:
• Carrier sense and random backoff not needed. Each station knows when it can send next packet
Performance Evaluation
• Setup: UDP socket program installed in each
device
• Metrics: MAC layer latency, Packet loss ratio
• Environment: Interference free vs. Office
Integrate RT-WiFi with Smart Shoes
• Smart shoe is a human gait detecting device.
Air pressure sensors regularly sends data for
abnormal gait detection
• 2 shoes with 8 sensors generates 72 bytes of
data per sample
Simulation of a Wireless Control
System
• Traces of each sensor data packets are
collected after RT-WiFi integration with smart
shoes
• Simulation of controller is ran based on traces
to evaluate performance of wireless control
system.
• Simulation conducted with different controller
gains and reference frequencies
Simulation of a Wireless Control
System (continued)0
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Tracking Error (deg)
Emperical CDF
WiF
i
RT-W
iFi
Conclusion
• Design presented of RT-Wifi, a real-time
wireless communication protocol
• Provides high sampling rate up to 6 kHz and
real time data delivery
• Users adjust design trade-offs, including
sampling rate, real-time performance,
reliability, and compatibility to existing Wi-Fi
networks
Future Work
• Research on scheduling algorithms on
Network Manager
• Extend network topology to mesh structure
• Power saving in RT-Wifi
• Co-existence of multiple RT-Wifi networks