Improvability of feedback systems

Introduces the notion of improvability and bottlenecks of feedback systems in the context of instrumentation cost. Specifically, a feedback system is improvable if its performance can be enhanced by reallocating sensor and actuator costs under budget constraints. We derive a criterion which determines when the system is improvable, using the LQG performance index. In addition, we introduce and analyze the notion of instrumentation bottleneck and provide a criterion for bottleneck identification. An important feature of the results derived is that both improvability and bottleneck indicators can be evaluated using online measurements in the feedback loop, without requiring precise knowledge of the plant data. Examples illustrating results are provided