International Journal of Distributed Sensor Networks
2.1. Graph of Hybrid Two-Tier IWSANs. In order to facilitate
the following work, the communication relationship between
the actuators and sensors and among actuators themselves
over the hybrid two-tier IWSANs can be described by a graph
G. Assume that there are cells in a workshop. An actuator
(i.e., central air conditioning) and a group of temperature
sensors with wireless communication function are deployed
within every cell. At rst, we focus on the graph of actuator
network G
𝑎
{A,E} (i.e., a subgraph of G), where A =
{
1
,...,
𝑛
}is the set of actuators and
E =
𝑖
,
𝑙
|
𝑖
,
𝑙
∈A,
𝑙
∈N
𝑎
𝑖
,∀,∈
{
1,...,
}
()
is the edge set. N
𝑎
𝑖
is a set of the neighbor actuators of
𝑖
.
Each actuator is only allowed to communicate with neighbor
actuators over actuator network, that is, ∃(
𝑖
,
𝑙
)∈E,ifand
only if
𝑙
∈N
𝑎
𝑖
.
Consider that
𝑖
can communicate with a group of
intracell sensors (i.e., S
𝑖
={
1
𝑖
,...,
𝑚
𝑖
})oversensornetwork.
us, the overall graph G can be obtained via taking the
subgraph G
𝑎
and adding ×new vertices S,whereS =
1
∪
2
,...,∪
𝑛
corresponds to the set of all sensors. Dene
the edge set
E
O
=
𝑗
𝑖
,
𝑖
|
𝑖
∈A,
𝑗
𝑖
∈S
𝑖
,∀∈
{
1,...,
}
,
∀∈
{
1,...,
}
.
()
en, we obtain G ={A ∪S,E ∪E
O
}.
Remark 1. In this paper, E
O
represents the radioconnectivity
between actuators and their intracell sensors. However, E
represents not only the radio connectivity but also interactive
acting among neighboring actuators through some ventila-
tion pipes.
2.2. Modeling. Consider the above-mentioned temperature
control system, where the temperature is controlled in an
industrial workshop using hybrid two-tier IWSANs as pre-
sented in Figure . We focus on the following discrete-time
plant model:
𝑖,𝑘+1
=
𝑖
𝑖,𝑘
+
𝑖𝑖
𝑎
𝑖,𝑘
+
𝑎
𝑙
∈N
𝑎
𝑖
𝑖𝑙
𝑎
𝑙,𝑘
,
𝑖,𝑘
=
𝑖
𝑖,𝑘
,
()
where
𝑖,𝑘
, ∈ {1,...,}is the temperature state of th
celldomainofplantattime and is measured by a group
of intracell sensors, that is, S
𝑖
={
1
𝑖
,...,
𝑚
𝑖
},
𝑖,𝑘
=
[
1
𝑖,𝑘
,...,
𝑚
𝑖,𝑘
]
𝑇
is the generalized measurement value of
𝑖,𝑘
collected by S
𝑖
and can be sent to actuator
𝑖
,and
𝑎
𝑖,𝑘
and
𝑎
𝑙,𝑘
, ∈{1,...,}, are the input (output wind temperature)
corresponding to the acting applied to the state
𝑖,𝑘
by local
actuator
𝑖
and neighbor actuator
𝑙
,respectively.
Due to the unreliable wireless communication channels
and the interference from the harsh industrial environment,
it is necessary to take into account a more “realistic” plant
model. First, consider the unreliable wireless communica-
tion channels within actuator network. Let I.I.D Bernoulli
stochastic variable
𝑖𝑙,𝑘
with E{
𝑖𝑙,𝑘
}=
𝑖𝑙
indicate whether
data packet (including state information) from
𝑖
is received
(
𝑖𝑙,𝑘
=1)orlost(
𝑖𝑙,𝑘
=0)byneighbor
𝑙
∈N
𝑎
𝑖
.Apparently,
𝑖𝑖,𝑘
≡1,forall ∈ {1,...,}.Aeranyneighbor
𝑙
of
𝑖
obtains the state information of
𝑖
,itscontrolunitcan
compute an appropriate input to
𝑖
. erefore, when
𝑙
∈N
𝑎
𝑖
and
𝑖𝑙,𝑘
=1,
𝑖,𝑘
will be actuated cooperatively by local
actuator
𝑖
and its neighbor actuators {
𝑙
}.Forinstance,in
Figure ,exceptlocal
1
, cell domain can also receive the
other inputs sent from
2
,
3
,and
4
through some ventilation
pipes, respectively.
For a concise derivation, according to the zero-input
strategy in the literature [], we can write
𝑎
𝑖,𝑘
=
𝑖,𝑘
,
𝑎
𝑙,𝑘
=
𝑙,𝑘
,
()
where
𝑖,𝑘
and
𝑙,𝑘
are the desired control laws computed by
embedded control units of
𝑖
and
𝑙
,respectively.
Secondly,weusetheGilbert-Elliottmodeltosimulate
the unreliable wireless channels within sensor network. At
time , the stochastic variable
𝑖,𝑘
is used to describe the
packet loss model
0
𝑖,𝑘
and the packet arrival model
1
𝑖,𝑘
of
communication channel from S
𝑖
to
𝑖
,forall∈{1,...,},
where
𝛼
𝑖,𝑘
{
𝑖,𝑘
=}, =0,1.Tocapturethetemporal
correlation of channel variation,
𝑖,𝑘
can be modeled as a
two-state Markovian chain with the initial model probability
vector
𝑖,0
and the transition probability matrix (TPM) Ξ
𝑖
as
𝑖,0
=
0
𝑖,0
1
𝑖,0
, ()
Ξ
𝑖
=
00
𝑖
01
𝑖
10
𝑖
11
𝑖
, ()
where
𝛼
𝑖,0
Pr{
𝛼
𝑖,0
} ( = 0,1) is the initial model
probability,
𝛼𝛽
𝑖
Pr{
𝛽
𝑖,𝑘
|
𝛼
𝑖,𝑘−1
} (, = 0,1) is the
transition probability of switching from model
𝛼
𝑖,𝑘−1
to model
𝛽
𝑖,𝑘
,and
00
𝑖
,
11
𝑖
,
01
𝑖
=1−
00
𝑖
,and
10
𝑖
=1−
11
𝑖
are
called packet remaining loss rate, packet remaining arrival
rate, packet recovery rate, and packet failure rate, respectively.
Apparently, Ξ
𝑖
, the TPM, is characterized by the
00
𝑖
and
11
𝑖
.
When aggregating all states at time into the
𝑘
=
[
𝑇
1,𝑘
,...,
𝑇
𝑛,𝑘
]
𝑇
and considering packet losses, noises, and
(), the above plant model () can be written in vector form
as
𝑘+1
=
𝑘
+
𝑘
𝑘
+
𝑘
,
𝑘
=
𝑘
𝑘
+]
𝑘
,
()
where
𝑘
∈ R
𝑛
,
𝑘
∈ R
𝑛
,
𝑘
∈ R
𝑛𝑚
,
𝑘
∈ R
𝑛
, ]
𝑘
∈ R
𝑛𝑚
,
𝑘
and ]
𝑘
are mutually uncorrelated Gaussian, white, and zero-
mean noises with covariance >0and covariance >0,
respectively, =diag(
1
,...,
𝑛
), (
𝑘
)∈R
𝑛×𝑛
,
𝑖𝑙
(
𝑖𝑙,𝑘
)=
0if
𝑙
∉N
𝑎
𝑖
or
𝑖𝑙,𝑘
=0,and(
𝑘
)=diag(
1
(
𝑘
),...,
𝑛
(
𝑘
))
with
𝑖
(
𝑘
)=[
1
𝑖
(
𝑖,𝑘
),...,
𝑚
𝑖
(
𝑖,𝑘
)]
𝑇
.
In this paper, the main objective is to control temperature
within every cell domain to a required set value. For the