This shows
that compared to our results, it is a low stress
since the delay is less than 0.5 second.
4.3. Data retrieval performance
In the following, RaWPG is evaluated in terms of response
delivery ratio and the average delay.
4.3.1. Response delivery ratio
Figure 6 shows the average delivery ratio of RaWPG. It
highlights that RaWPG ensures a response delivery ratio
upper to 90% in the precast concrete. As presented in (Mekki
et al., 2016c), RaWPG uses a link cost function which allows
choosing the most powerful node as next hop in the WSN.
Thus, the request and response
messages are forwarded
through a high quality of service path.
Fig. 6. Response delivery ratio of RaWPG.
4.3.2. Delay of data retrieval process
The delay is the elapsed time between the beginning of
request transmission and the reception of the response
message by the master node (i.e. the user). The simulation
results in Castalia show that RaWPG ensures a delay less
than 0.9 second for all the path length (min≈0.12s for TTL=1
and max≈0.81s for TTL=8). As shown in table 1,
the delay
constraint of data reading in the precast concrete must be less
than 5 second. This shows that compared to our results, it is
also a low stress since the delay is less than 0.9 second for all
the path length.
4.4. WSN lifetime estimation
In this section, the WSN lifetime inside the precast concrete
is estimated. The needed energy is estimated for each node to
“live” all the precast lifecycle (14 years). The energy
consumption of USEE and RaWPG was measured and
plotted in figure 7. Figure 7 shows the average energy
consumption of a node inside the concrete for different
number of storage and reading operations, respectively
performed using USEE and RaWPG. Using figure 7, the
trend line of USEE protocol could be calculated, it gives the
following equation:
y
= 0,00943782
x
+ 0,314038
(1)
As shown in table 1, the WSN
inside the concrete must
ensures at least x=11500 storage operations. Through
equation 1, each node should
be empowered with at least
y=109 Joules of energy capacity to execute this number of
operations.
In addition, the trend line of RaWPG protocol gives the
following equation:
y
= 0,009864048
x
(2)
As shown in table 1, the WSN inside the concrete must also
ensures at least x=11553 reading operations. Through
equation 2, each node should be empowered with at least
y=114 Joules of energy capacity to execute this number of
operations.
As conclusion, to execute all the storage and reading
operations during the precast concrete lifecycle, each node
must have at least a total energy of 223 Joules (109 Joules +
114 Joules). By adding the energy
required for the sensing
module and for the sleep mode, the
SensorCube
node
(voltage = 2.4 V) must be equipped with battery of 350 mAh
as shown in table 2, to ensure a WSN lifetime of over 14
years (this period corresponds to the duration of
BOL+MOL+EOL of precast concrete). However, battery
lifetime of WSN is actually limited to few years. As solution,
an energy scavenging module could be used for continuous
battery charging. Moreover, many
academic and industrial
researches, such as (Ongaro et al., 2012) (Merla et al., 2016)
(Zhang at al., 2016), work on increasing the battery lifetime.
Also, there is an early stage research regarding production of
sensors node without batteries, using similar technologies
applied to passive radio frequency identification (RFID)
chips without batteries (Vujic et al., 2012). In the future,
WSN technologies could improve the overall duration of
sensor nodes lifetime and thus it could reach 14 years without
charging or replacement of its battery.
Fig. 7. Consumed energy for different number of storage and
reading process for USEE and RaWPG, respectively.
Table 2.
SensorCube
lifetime vs. Battery capacity.
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