  Real-time end-to-end task scheduling in networked control systems (NCSs)
requires the joint consideration of both network and computing resources to
guarantee the desired quality of service (QoS). This paper introduces a new
model for composite resource scheduling (CRS) in real-time networked control
systems, which considers a strict execution order of sensing, computing, and
actuating segments based on the control loop of the target NCS. We prove that
the general CRS problem is NP-hard and study two special cases of the CRS
problem. The first case restricts the computing and actuating segments to have
unit-size execution time while the second case assumes that both sensing and
actuating segments have unit-size execution time. We propose an optimal
algorithm to solve the first case by checking the intervals with 100% network
resource utilization and modify the deadlines of the tasks within those
intervals to prune the search. For the second case, we propose another optimal
algorithm based on a novel backtracking strategy to check the time intervals
with the network resource utilization larger than 100% and modify the timing
parameters of tasks based on these intervals. For the general case, we design a
greedy strategy to modify the timing parameters of both network segments and
computing segments within the time intervals that have network and computing
resource utilization larger than 100%, respectively. The correctness and
effectiveness of the proposed algorithms are verified through extensive
experiments.
