Multivariable Sensitivity Reduction and Decentralized Control

A plant P(s) is represented by an N×N matrix of frequency responses. It is shown that if P^-1(s) is analytic in Re(s) ¿ 0, P(s) approaches diagonal dominance at high frequencies, and P(s) satisfies an attenuation condition at high frequencies, then it is possible to make sensitivity arbitrarily small without violating a global sensitivity bound by means of a diagonal feedback. The result is then interpreted as a condition for the existence of a wide-band decentralized control.