Toward wireless Networked Control Systems: An experimental study on real-time communications in 802.11 WLANs

Networked control systems (NCSs) exploit a packet switching network to fulfill complex control tasks without cumbersome point-to-point wiring infrastructures. But their performances are greatly influenced by time-varying packet delays and losses due to the communication system. As a consequence, real time operating systems are usually employed at NCS nodes to timely serve events scheduled by control applications. So far NCS issues have been mainly investigated assuming a wired network infrastructure. Anyway the trend is toward wireless communications. For these reasons, this paper proposes a real-time communication architecture based on the leading wireless 802.11 technology and on the real-time networking framework RTnet. The QoS offered by the proposed system, in terms of packet loss ratio and end-to-end delay, has been experimentally evaluated by varying protocol parameters. Results show that a proper tuning of system parameters can ensure robust real-time wireless communications. Thus, the present work can be considered an important step toward the design of a wireless networked control system.