  Wireless networked control systems for the Industrial Internet of Things
(IIoT) require low latency communication techniques that are very reliable and
resilient. In this paper, we investigate a coding-free control method to
achieve ultra-low latency communications in single-controller-multi-plant
networked control systems for both slow and fast fading channels. We formulate
a power allocation problem to optimize the sum cost functions of multiple
plants, subject to the plant stabilization condition and the controller's power
limit. Although the optimization problem is a non-convex one, we derive a
closed-form solution, which indicates that the optimal power allocation policy
for stabilizing the plants with different channel conditions is reminiscent of
the channel-inversion policy. We numerically compare the performance of the
proposed coding-free control method and the conventional coding-based control
methods in terms of the control performance (i.e., the cost function) of a
plant, which shows that the coding-free method is superior in a practical range
of SNRs.
