A modest CSMA for control over wireless

In a feedback control system where a controller tries to control the behavior of a plant, when observing the histories of the control data and sensed data between them, we can estimate their importance thus priority; current (control or sensed) data with larger differences from previous data are more important so they should be given higher priorities, because the large differences mean that the controller is given a new setpoint or the plant is in a transient and instable state. In this paper, we propose a “modest” carrier sense multiple access (CSMA) for feedback control systems sharing a common wireless channel. The modest CSMA simply adjusts its back-off interval for packet transmission according to the difference between successive data; if the difference is smaller, it sets the back-off interval to a larger value so as to give its own packet a lower priority, in other words, to give other systems more chances to access the channel, on the other hand, if the difference is larger, it sets the backoff interval to a smaller value so as to quickly get a chance to access the channel. Computer simulation results show that the modest CSMA, which is purely distributed though, can achieve a comparable control performance to a conventional centralized time division multiple access (TDMA).