Asian Journal of Control, Vol. 15, No. 4, pp. 1 6, July 2013
Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/asjc.391
–Brief Paper–
SOME PROPERTIES OF EXACT OBSERVABILITY OF LINEAR
STOCHASTIC SYSTEMS AND THEIR APPLICATIONS
Ting Hou, Weihai Zhang, and Hongji Ma
ABSTRACT
A new criterion is proposed for exact observability of linear stochastic
systems. As applications of this criterion, the effects of exact observability due
to state/output feedback are investigated. In addition, under the conditions of
stability and exact observability, we discuss the properties of a set defined by
the generalized Lyapunov equations (GLEs).
Key Words: Exact observability, state/output feedback, asymptotic mean
square stability, GLEs, convex cone.
I. INTRODUCTION
It is well-known that stability and observability
are essential concepts in modern control theory,
especially in system analysis and design. For linear
stochastic systems, several different interesting notions
of observability have appeared and a rich source of
references can be found in [1–6]. References [2] and
[4] have extended complete observability of determin-
istic linear systems to exact observability of Itˆo-type
stochastic systems. Exact observability has come into
current use in discussing the infinite horizon stochastic
linear quadratic (LQ) problems as well as the properties
Manuscript received March 29, 2010; revised October 29,
2010; accepted January 28, 2011.
T. Hou is with the College of Information and Electrical
Engineering and College of Science, Shandong University
of Science and Technology, Qingdao 266510, China (e-mail:
ht
math@sina.com).
W. Zhang (corresponding author) is with the College of
Information and Electrical Engineering, Shandong University
of Science and Technology, Qingdao 266510, China (e-mail:
w
hzhang@163.com).
H. Ma is with the College of Science, Shandong University
of Science and Technology, Qingdao 266510, China (e-mail:
mhj3027@sina.com).
This work was supported by the Key Project of Natural
Science Foundation of Shandong Province (Grant No.
ZR2009GZ001), the Specialized Research Fund for the
Doctoral Program of Higher Education of China (Grant No.
20103718110006) and the National Natural Science Founda-
tion of China (Grant No. 60874032).
of the related coupled algebraic Riccati equations
as done in [7]. A further step in the development
of this aspect is the establishment of its sufficient
and necessary condition by the spectrum technique,
which may be viewed as the generalized version of the
Popov-Belevitch-Hautus (PBH) criterion for complete
observability [2]. Our first objective in the present
paper is to contribute to presenting a new criterion for
the exact observability of linear stochastic systems. As
is known to all, for deterministic linear systems, the
observability of an open-loop system is not affected
by the output feedback, however, the observability of
open-loop and closed-loop state feedback systems is
unrelated. As applications of our obtained criterion,
we will generalize the previous classical results to
stochastic systems.
In the domain of stochastic stability and stabiliza-
tion of Itˆo differential systems, several authors have
been interested by these aspects for decades and some
extensive and elaborate results concerned with these
aspects have been derived since the fundamental works
[8, 9] appeared; See, e.g. [10–14] and the references
therein. We note that most of these works are concen-
trated on the investigation of mean square stabilization,
which has been playing a central role in many prob-
lems, such as infinite horizon stochastic optimal control
problems [10], robust and stochastic H
∞
problems
[15], etc. Similar to the deterministic system case,
some necessary and sufficient conditions on stabi-
lization of stochastic systems have been obtained in
terms of stochastic algebraic Riccati equations and
2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society
Asian Journal of Control, Vol. 14, No. 3, pp. 868–873, May 2012
Published online 28 April 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/asjc.391
© 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society