Graceful degradation of the quality of control through data drop policy

Sharing a network link in a networked control system (NCS) may result in the network overload leading to the non respect of the specified periodicity of control system, this may cause an unpredictable performance degradation of the system. In this paper, we consider an overload management technique which selectively drops the data packets of the NCS to avoid network overload. The investigated problems are: how to design the controller under packet drops and how to distribute the packet drops in a packet delivery sequence so that the quality of control (QoC) is optimized. The paper first gives the optimal LQ-controller using the conventional technique to reduce the deterioration in QoC due to packet drops. Then, the paper proposes a methodology for deriving a distribution of the packet drops in the packet delivery sequence so that the QoC is optimal. Finally, an efficient algorithm is given to reduce the computation complexity of the proposed methodology. This proposal contributes to the co-design of the controller and the resource performance management process at the implementation level.