H-Infinity Performance Limitations for Problems with Sensor Time Delays
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Motivated by ongoing research into automating radiotherapy, this thesis is concerned with linear feedback control and estimation problems where only a delayed output signal is measurable. Various discrete-time performance limitations are derived using tools from model-matching theory as well as the early $H_\infty$ literature. It is shown that there exist performance limitations for both one-degree-of-freedom control and estimation problems, but the nature of the limitations differs depending on whether the plant is stable or unstable. Some continuous-time performance limitations are also found, with more complete results in the case where the plant is unstable. Extensions of the various performance limitation to two-degree-of-freedom control are also studied.