Subsystem Monitored parameters T
Root Soil Soil temperature 15
Soil moisture 15
Canopy atmosphere Air temperature 15
Air humidity 15
Plant Leaf temperature 15
Shoot diametric growth 15
TAB LE I I
HARACTERISTICS OF EACH SUBSYSTEM COMPOSING THE VINEYARD.
The power consumption values for the adopted optimized
platform are those reported in Table I; besides, T
56 s and, consequently, d =6.7%, moreover, the deployed
batteries are C-type primary lithium batteries. Finally, the
applied communications protocol is described in III-B.
The whole system is still running unattended beginning
from the summer season; packets are collected by the master
node and their correct delivering is monitored by a speciﬁc
application hosted within the remote server ( logger) that
stores and processes data.
2) Experimental Results: First of all, it has been measured
the node’s energetic consumption by averaging it over the
whole network: it results to be equal to 1.44 mAh. On
the other hand, its estimated value, based on modeling the
network behavior as a FSM and considering the practical
power consumption values as in Table I, is equal to 1.15
mAh, pointing out a good agreement with the experimental
results. As a consequence, the node life time is greater than 7
months in the case of above mentioned battery adoption, that
allows the network to operate for a farming season without
maintenance, as it is claimed by the user requirements.
Then the packet delivery ratio (PDR), i.e., the ratio between
the number of data packets correctly received by the master
node and the number of sent packets, has been veriﬁed to
be equal to 0.948. It could be due to link failures or the
residual packet collisions rate, not correctly handled by the
STAR MAC protocol, as packets are retransmitted when the
receiver is the sleeping mode. This allow the WSN utilization
for accurate environmental monitoring and, implicitly, validate
the efﬁciency of the adopted communication protocol.
To the purpose of evaluate the Quality of Service (QoS)
of the cross-layer solution, it has been measured the average
number of hops needed to deliver a packet to its destination.
It has been made feasible by concatenating the identiﬁer of
intermediate nodes in a proper ﬁeld of the packet header. It
is equal to 2.83; this circumstance implies that almost all the
data packets are not subject to loops that involve at least 4
hops and the routing functionalities are preserved. Finally, the
measured mean delivery delay, that is the difference between
the packet delivering time and the instant of its ﬁrst sending,
results to be equal to 60.1 s, as the phase is randomly selected
with uniform distribution. This value represents a reasonable
latency for the considered application in which slow varying
phenomena are monitored.
This paper deals with the proposal of an efﬁcient cross-layer
communication protocol, allowing remarkable performance, in
terms of low power consumption and QoS, for a WSN oper-
ating in a critical scenario like outdoor environmental moni-
toring. At this aim an energy efﬁcient MAC protocol, namely
STAR MAC, has been proposed and properly integrated within
a routing scheme, minimizing the signaling overhead. The
performance of the overall multi-hop communication solution
has been evaluated, by implementing it on motes operating
in the operative scenario related to the EU Integrated Project
GoodFood. In particular, it has been also described a practical
implementation of the Pilot Site, in terms of adopted platforms
and architectures on which the testing procedure has been
performed. The experimental results highlighted a noticeable
performance as far as energetic consumption, the node life
time, the data delivering efﬁciency and latency are concerned.
This allows the application of the WSN under investigation to
the ﬁeld of environmental monitoring.
The authors would like to express their gratitude to Prof.
Gianfranco Manes for his fruitful comments and discus-
sions. A particular thank the members of the EU Integrated
Project FP6-IST-1-508774-IP ”GoodFood” WorkPackage 7 for
their supporting in this research.
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This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2006 proceedings.