Sampling rate optimization for IEEE 802.11 wireless control systems

Design of wireless control systems has been extensively studied, which is one of the fundamental issues in cyber-physical systems. In this paper, we empirically investigate heterogeneous sampling rate assignment with a testbed when multiple physical systems are controlled through an IEEE 802.11 network. Among the critical design variables in wireless control systems, we focus on the sampling rates because they are always key control knobs regardless of network protocols. There has been little experimental research on heterogeneous sampling rate optimization for IEEE 802.11 wireless control systems, where the sampling rates of each control loop may have different values. We first formulate the co-design problem in an optimization framework with respect to the heterogeneous sampling rates by explicitly taking into account the relations of the sampling rates with the control cost, network energy consumption, and network delay. We further relax the problem as convex optimization, which is provably solved in polynomial time. Our empirical study ensures that the approximate solution is tightly close to the original optimum. To validate the proposed optimization framework, we build a disk-levitation tube testbed, which wirelessly controls the height of 20 disks at the same time. Our empirical study confirms that our optimization formulation is highly effective in practice.