Improving Performance of Networked Control Systems by Using Adaptive Buffering

The performance of networked control systems is strongly affected by time-varying transmission delays. A traditional solution to this problem consists of storing arriving packets in a buffer which smooths delay jitter at the cost of an increased constant delay. The size of the buffer is based on either a long-term or worst case analysis of network behavior leading to poor performance when the instantaneous network behavior is different. To overcome this problem, this paper proposes the following: 1) to adapt the buffer size according to the actual delay variation; 2) to resize buffer content by using cubic spline smoothing which also reduces the signal noise; and 3) to use a Smith predictor at the controller side. Simulation results show that the adaptive buffering strategy reduces delay and packet loss probability while the spline smoothing process improves control performance even in case of constant-size buffers.