| This dissertation studies the limitations of Networked Controlled Systems (NCS) caused by the presence of a finite capacity channel in the feedback loop.;First, we analyze the stabilization issue for an NCS that uses a Delta-Modulator scheme within the encoder/decoder structures. We also analyze the packet-loss issue, and determine a maximum allowable number of consecutive bits lost while keeping closed-loop stability. We then design a compensation scheme for regaining equimemory between the encoder and decoder after a bit is lost in a network without acknowledgment signals. We finally present a compensation scheme that ensures stability after a pre-determined number of bits is lost.;Second, we extend results from packet-based control theory and present sufficient conditions on the rate of a packet network to guarantee asymptotic stabilizability of unstable discrete-time linear invariant (DLTI) systems with less inputs than states. We use a truncation-based encoder/decoder scheme and two types of NCS are considered in the absence of communication delays, then for one of the two NCS types, the case of a constant time delay is discussed. We also propose a new encoder/decoder scheme that is more complex than the truncation-based one, but that requires a lower stabilization rate.;Third, we obtain information theoretical conditions for tracking in DLTI control systems. The mutual information rate between the feedback signal and the reference input signal is used to quantify information about the reference signal that is available for feedback. This mutual information rate must be maximized in order to improve the tracking performance; however, the associated rate is shown to be upper bounded by a quantity that depends on the unstable eigenvalues of the plant and on the channel capacity. We also find a lower bound on the expected squared tracking error in terms of the entropy of a random reference signal.;Finally, we analyze the counterintuitive case where non-minimum zeros increase the mutual information rate between the feedback and reference signals. This analysis indicates that mutual information rate is an imperfect metric for specifying the performance for a DLTI tracking system. We also obtain a frequency interpretation of the tradeoffs that exist when tracking and disturbance rejection are required simultaneously and we obtain guidelines to satisfy the requirements on the controller in order to achieve good tracking and disturbance rejection. |
