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

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:

Simulation of a Wireless Control

System (continued)0

24

68

1012

1416

0

0.2

0.4

0.6

0.8 1

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

Questions?