Image Processing Reference
In-Depth Information
LiandRus[]proposeanotherdifusiontechniquecalledrate-baseddifusionalgorithm.he
diffusion algorithm has two types: synchronous and asynchronous. The synchronous diffusion
algorithm performs the following steps:
. Do the following with some given frequency
.
for
each sensor
n
i
in the network
do
. Exchange clock times with
n
′
i
s
neighbors
.
for
each neighbor
n
j
do
. Let the time difference between
n
i
and
n
j
be
t
i
−
t
j
. Change
n
′
i
s
time to
t
i
−
r
ij
(
t
i
−
t
j
)
The synchronous method allows the sensor nodes to exchange their clock values and adjust them by
r
ij
is the time difference between nodes
n
i
and
n
j
.
The diffusion rate is greater than zero and can be chosen randomly provided that the
(
t
i
−
t
j
)
,where
r
ij
is the diffusion rate and
(
t
i
−
t
j
)
i
r
ij
≤
. If
∑
j
≠
nodes
n
i
and
n
j
are not neighbors, then the diffusion rate is equal to zero.
The synchronous version of the rate-based diffusion algorithm requires all nodes to perform tasks
in a set order. To relax such constraint, the asynchronous version of the rate-based difusion algorithm
is executed as follows:
.
for
each node
n
i
with uniform probability
do
. Ask its neighbors the clock readings (read values from
n
i
and its neighbors)
. Average the readings (compute)
. Sendbacktotheneighborsthenewvalue(writevaluesto
n
i
and its neighbors)
As with TDP, the Rate-based Difusion Algorithm is lightweight but cannot provide tunable services.
Macii and Petri [] propose another adaptive-rate time synchronization technique called ARSP.
ARSP is based on the simple response method that adaptively adjust the calibration intervals of mea-
surement instruments based on the last calibration []. [].The objective of ARSP is to assure that the
probability of having time offsets larger than ε
max
at the end of
k
th synchronization is smaller than
P
T
,where
P
T
is the desired end-of-period synchronization probability.
First, the nodes in the network elects a synchronization master. he synchronization master broad-
casts a synchronization packet, and all nodes that receive the packet measure the arrival time,
−
̂
T
ik
.
Afterwards, a reference master is elected. The arrival time of the synchronization packet measured
by the reference master is
̂
̂
T
mk
.heelectedreferencemastersends
T
mk
to all nodes, where they will
̂
∣
̂
−
̂
compare
is greater
than the allowed maximum error ε
max
, then the node will set probability
p
ik
to ; otherwise,
p
ik
is
set to .
After all the nodes calculate
p
ik
, they send it to the reference master, where it calculates the
probability
P
k
as follows:
T
mk
to the arrival time of the synchronization packet. If the difference
T
ik
T
mk
∣
M
i
m
p
ik
=
∑
=
,
i
≠
P
k
(.)
M
−
where
M
is the number of sensor nodes that the reference master is connected to
k
represents
k
th synchronization
Afterward, the reference master calculates the next synchronization interval
I
k
according to the
+
following:
I
k
(
+
a
)
P
k
≥
P
T
I
k
={
(.)
+
I
k
(
−
b
)
P
k
<
P
T
