Improving quality of control in networked control systems by co-design of sampling period and buffer size

The paper studies the control of networked control systems (NCS) with sensor-to-controller and controller-to-actuator time delays. The delays are bigger than one sample and random. By using of buffers, the original problem can be transformed into linear system with constant delay. The optimal size of the buffer is an open problem. Increase of the buffer length deteriorates the quality because of longer delay in the control loop. At the same time longer buffer decreases the probability of packet dropping and thus improves the quality. The idea is to make the system more robust by buffering and simultaneously adjusting the control loop sampling and actuation intervals. The paper presents this “co-design” approach and demonstrates it for LQ control problem of cart-pendulum model.