Stability of sampled-data control systems with uncertain delays

Standard analysis and synthesis techniques for digital control systems assume that the total time-delay in the feedback loop is negligible or precisely known. This might not be the case in some applications. Such systems are quite common in industry, especially due to strong trends towards networking. Under certain circumstances the network-induced delays can be considered constant, and yet it might be very difficult to get an exact value of the time-delay. The delay then enters the description of the system as an uncertain parameter which is only known to be bounded by some extreme values. It is then possible to apply some convenient results of parametric robust control theory to test the stability of such systems. Polynomial description of SISO systems is considered. Possible extension to the more realistic case of varying delays is only outlined.