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 Industrial Process Control and Automation

Robotic Control Wireless Control System Requirements

• Sampling rate • Reliability • Real-time data delivery – Bounded delay for estimating system state Existing Technologies and RT-Wifi 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 Control System Overview using RT-WiFi Network System Architecture of RT-WiFi Performance Evaluation

• Setup: UDP socket program installed in each device • Metrics: MAC layer latency, Packet loss ratio • Environment: Interference free vs. Office Interference Free Environment Interference Free Environment Office Environment Office Environment Case Study

• Mobile Gait Rehabilitation System 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) • Root-mean-square (RMS) errors in simulations: Emperical CDF 0.2 0.4 0.6 0.8 0 1 0 Simulation of a Wireless Control System (continued) 2 4 TrackingError (deg) 6 8 10 12 14 RT-WiFi WiFi 16

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 Questions?