Event-based Distributed Filtering Approach to Nonlinear Stochastic Systems over Sensor Networks 897
ences therein. It is still worth emphasizing that, when a
system with distributed sensors becomes highly modular
and complex, various noises or disturbances are likely to
be observed in distributed sensors. Therefore, it remains
a practical concern to design appropriate distributed fil-
tering approaches to maintain system stability and perfor-
mance.
Alongside the interest in desirable performance, it is the
concern for energy consumption of the individual sensor
node that has drawn more and more research attention.
Frequent signal transmissions can deplete sensor batter-
ies more easily and such is especially the case in net-
works with the periodic communication paradigm [15].
In contrast of sending information at time instants sepa-
rated by a constant interval, as is the essence of the de
facto strategy of time-triggering transmissions, the event-
based communication strategy is built with energy econ-
omy in mind and aims to reduce signal transmissions in
the network environment [16–18]. The general setting of
an event-triggering mechanism consists of an event detec-
tor unit and a sender unit. The detector unit monitors
a user-defined event-triggering condition and, on viola-
tion of this condition, instructs the sender unit to trans-
mit new measurements. The issue of uncertainties in
the stream of measurements was investigated in [19, 20].
In [19], A modified Rice fading channel was used to
model the situations of missing measurements, whereas
in [20] the missing measurements are modeled as a se-
ries of Bernoulli random variables. Additionally in [20],
the norm-bounded uncertainties was interpreted as distur-
bances within a bounded set. Moreover, considering the
distributed sensors used to exchange those meausrements,
it deserves to be mentioned that Liu et al. in [ 12] inves-
tigated the distributed filtering problem for linear time-
varying systems based on an event-triggered communica-
tion scheme over WSNs. Hu et al. [21] proposed an event-
triggered distributed state estimation scheme for linear
stochastic systems with randomly occurring uncertainties
and state-dependent noises over sensor networks. Ding et
al. [22] came up with a state estimation approach based on
event-triggered communication mechanism to the stochas-
tic systems with nonlinear stochastic process in a sensor
network. Another recent work in [23] investigated the
problem of designing event-driven distributed filters for
networked switched systems with network-induced trans-
mission delay to achieve finite-time boundedness. In view
of the stochastic nature of a wireless network, research on
stochastic system in relation to the networking arrange-
ment is still of great importance. And we feel that further
enrichment is possible for the above discussions on the
event-triggered filtering problem of the nonlinear stochas-
tic systems over WSNs.
Moreover, to represent nonlinearities in the real systems
Takagi-Sugeno (T-S) fuzzy models [24–26] have been
widely utilized in stochastic process or jumping param-
eters [27–30]. In a T-S fuzzy model, a series of simple lin-
ear subsystems weighted with the so-called membership
functions are utilized to approximate a nonlinear plant. As
a result, the analysis and the synthesis of the systems be-
comes trainable based on the control and filtering meth-
ods. Recently, Wu et al. designed an fuzzy filter approach
in [31] for the fault detection of fuzzy Itô stochastic sys-
tems. Wang et al. [32] discussed the event-triggered fuzzy
filtering problem of nonlinear physical plant. But both
plants were considered as a deterministic system with a
single sensor. Su et al. dealt with the distributed fuzzy
filter problem of discrete-time fuzzy systems with time-
varying delays over sensor networks. Therefore it can be
suggested that an integrated view of the above-mentioned
features would be of much value and provide some inter-
esting research. In this respect however, there seems to be
few works addressing this topic. And we intend to offer
results of our investigation in this paper.
Hence, in this work we are firstly concerned with the
formulation problems of the distributed filters and the non-
linear stochastic systems over the WSN. Then the prob-
lems of event-triggering and the distributed filtering are
considered. We intend to contribute the following results:
i) an event-driven distributed filtering stochastic system is
formulated including the fuzzy-model-based WSN, ii) a
multiple-event-triggered mechanism is designed based on
the distributed WSN, and iii) an event-based filtering ap-
proach with disk stability constraints is proposed for the
nonlinear stochastic systems. Subsequently, a simulation
example is provided to demonstrate the effectiveness of
the event-based distributed filtering methods.
The rest of the paper is structured as follows: Section
2 introduces the models of the stochastic plant with the
WSN, and the event-based filters are presented. Section 3
details the main results on the distributed filtering design
procedure. A simulation example is given in Section 4.
Section 5 concludes this paper.
Notation: N denotes the set of natural numbers.
ℓ
2
[0,∞) is the space of square-integrable vector func-
tions over [0, ∞). For a matrix X ∈ R
n×n
, “*” repre-
sents transposed elements in the symmetric positions;
“X
⊤
” the matrix transposition and “X
−1
” the inversion
of X. “I” and “0” are the identity and zero matrices re-
spectively with appropriate dimensions. X ◦ Y is used
here to denote element-wise multiplication for matri-
ces of suitable dimensions. X ⊗ Y stands for the Kro-
necker product of any dimensioned matrices X and Y .
∥e∥
E2
= E{
∑
∞
k=0
∥e(k)∥
2
} =
∑
∞
k=0
E{∥e(k)∥
2
}. If not ex-
plicitly stated, all matrices are assumed to have compatible
dimensions for algebraic operations.
2. PROBLEM FORMULATION
We adopt the following a-rule T-S fuzzy model based
on b fuzzy sets to approximate the nonlinear stochastic