  To efficiently support the real-time control applications, networked control
systems operating with ultra-reliable and low-latency communications (URLLCs)
become fundamental technology for future Internet of things (IoT). However, the
design of control, sensing and communications is generally isolated at present.
In this paper, we propose the joint optimization of control cost and energy
consumption for a centralized wireless networked control system. Specifically,
with the ``sensing-then-control'' protocol, we first develop an optimization
framework which jointly takes control, sensing and communications into account.
In this framework, we derive the spectral efficiency, linear quadratic
regulator cost and energy consumption. Then, a novel performance metric called
the \textit{energy-to-control efficiency} is proposed for the IoT control
system. In addition, we optimize the energy-to-control efficiency while
guaranteeing the requirements of URLLCs, thereupon a general and complex
max-min joint optimization problem is formulated for the IoT control system. To
optimally solve the formulated problem by reasonable complexity, we propose two
radio resource allocation algorithms. Finally, simulation results show that our
proposed algorithms can significantly improve the energy-to-control efficiency
for the IoT control system with URLLCs.
