Control Using Feedback over Wireless Ethernet and Bluetooth

This chapter is concerned with the general topic of control systems in which feedback information is transmitted over wireless communication channels as well as with some specific problems, challenges, and opportunities associated with implementing feedback control using Bluetooth and other current wireless networking technologies.

Networked control systems in which sensors, actuators, and other system components are interconnected using advanced wireless communications technologies (IEEE 802.11, IEEE 802.15.4, Bluetooth, etc.) present a number of unique advantages (e.g., the elimination of wiring, the possibility of self-organization of networks of heterogeneous devices, and the possibility of operation while all of the components are in motion relative to one another) as well as special challenges (rapid and unpredictable changes in communication channels, possible network congestion, packet loss, limited battery capacity, etc.). This chapter discusses the design and operation of networks of controlled devices using various networking technologies. While each of the approaches has its own advantages, our main focus will be on Bluetooth because of the support it provides for interoperability of heterogeneous devices. The primary focus of our discussion will be on the effectiveness of wireless networks in providing communications services in applications with hard real-time constraints. We have in mind systems which will fail to operate properly—perhaps in a catastrophic way—if data rates in network communications channels fall below certain critical thresholds. The issues raised by constraints on network data rates are illustrated by experiments performed with an inverted pendulum where the feedback loop is closed over a Bluetooth radio link.