Qixin Wang

University of Illinois at Urbana-Champaign

 

Abstract:

As the industry is still migrating real-time industrial control
 systems from analog 4 ~ 20mA systems to digital wired fieldbuses, 
academia and research labs are already moving toward the next step.
 One direction is to develop wireless LAN for real-time industrial 
control (a.k.a. wireless fieldbus), so as to increase mobility, 
reduce cost, enhance flexibility, and promote safety 
(e.g., remote control of robots in hazardous areas). Another 
direction is to develop wired WAN backbone to interconnect 
wireless LANs for real-time industrial control. Wired WAN 
backbone provides higher reliability / robustness, larger 
data throughput, and legacy reuse.

 

However, both wireless LAN and wired WAN for real-time 
industrial control face new challenges. 

 

For wireless LAN, the top concern resides in communication
 reliability / robustness.  On the one hand, wireless 
communication by nature is less reliable / robust than
 wired communication due to large-scale path loss, multi-path, 
and Radio Frequency (RF) jamming. Industrial environments 
deteriorate the situation: heavy obstructions increase 
large-scale path loss and multi-path; Electro-Magnetic 
Interference (EMI) from electric motors, welding, and 
power cords persistently jam the wireless channel; and n
on-cooperative RF devices can be accidentally or 
macliciously turned on to create additional jamming. 
On the other hand, 
real-time requirements mendate wireless connections 
to work continuously even under adverse channel 
conditions; backoff based MAC is not allowed. 

 

For wired WAN backbone, the main challenge lies 
in the switch (a.k.a. router) design for efficient 
real-time packet forwarding. The success of such 
design largely depends on its backward compatibility 
with nowadays main stream switch designs, which,
 however, are not for real-time.

In this work, we try to address both challenges. 
For real-time wireless LAN, we compare various wireless c
ommunication paradigms and argue that by deploying 
largest processing gain (lowest data rate), DSSS-CDMA 
cell phone paradigm achieves much higher reliability / robustness
 than main stream alternatives.  For real-time wired WAN 
backbone, we propose a real-time switch design, which is
 not only compatible with, but even simpler than the main
 stream iSLIP switch design.