Periodic, Strict, and Quasi-Invariance in Linear Systems
Gianfranco Cariolaro, Francesco De Pellegrini, V. Cellini · IEEE Transactions on Circuits and Systems II Analog and Digital Signal Processing · 2007
This brief deals with shift invariance in linear systems (LSs), using a group theoretical approach. The group approach is necessary to obtain general definitions, which can be applied to continuous-time, discrete-time, multirate and also multidimensional LSs. Thus, a unique definition is given for periodic invariance and strict invariance (SI) and also for quasi-invariance (QI), a new concept, intermediate between periodic and SI. The importance of QI relies upon the fact that it is comprehensive of practically all multirate LSs