Experimental Results on the Effects of 802.11b WLAN on Networked Control System

Abstract

In this paper we expose theoretically and experimentally some of issues induced by wireless Ethernet when it is used to transmit plant state information to the controller, and control signals to the plant, in a closed-loop system. We also propose some compensation actions, and evaluate their performance in the experimental set up.

Practical issues in networked control systems

“…In other words, the system can tolerate the combined time-delay τ = τ pc + τ cp , and still converge to the origin. This of course, is more of an analysis result, but forms the basis of a predictive control action that was described by the authors in another paper [9].…”

“…Therefore, the control algorithms should be robust enough to handle such issues. While earlier research, [9] [5], [4], had clearly identified many of the problems discussed in this paper, we develop in this paper some experiments to also show some compensation approaches when a general purpose communication network is used. In order to focus on generic problems, we use standard operating systems and industrial hardware for data acquisition.…”

Leader-follower control with odometry error analysis

“…The virtual leader and the data collector computers are linked over a LAN, while the robots are connected over a wireless LAN (IEEE 802.11b). We chose User Datagram Protocol (UDP) as the transmission protocol, because TCP exhibits packet retention due to its "slow start" feature [38]. The desired trajectory is transmitted to the mobile agents, who re-transmit it along with their own state to the data collector ( Figure 15).…”

Cross-Layer Adaptive Feedback Scheduling of Wireless Control Systems

“…Wireless channels have adverse properties, such as path loss, multi-path fading, adjacent channel interference, Doppler shifts, and half-duplex operations [1]. While traditional wired networks usually have fixed communication capacity, the link capacity of wireless channels may vary significantly over time [5][6][7]. Because the operations of wireless transceivers are half-duplex, wireless systems cannot support non-destructive medium access control (MAC) protocols.…”

“…The area of WCSs is still in its infancy. The suitability of diverse wireless technologies for control applications has been studied through both simulations [12][13][14] and experiments [7,10,15]. A number of proposals on modifying established communication mechanisms for wireless networks to achieve real-time guarantees have been presented, e.g.…”