Relationship between decentralized and centralized designs in mixed sensitivity problem

This paper concerns the decentralized design for a MIMO system. The decentralized design means the design of the combination of a pre-compensator and decentralized controllers. An advantage of this idea is that we can regard the decentralized controllers as SISO controllers, if the pre-compensator sufficiently decouples the plant. As a result, it is easy to comprehend the relationship between the controllers and specifications. However, it may occur that the structural restriction of the decentralized controllers results in a poorer performance than a centralized controller. This paper shows that the decentralized design proposed realizes a performance equal to the centralized one in the mixed sensitivity problem based on certain assumptions