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lease-based publish/subscribe approach converges
to the ACK-based scheme. Finally, it is not clear
whether ACK-based collaboration is generally
executable on sensor networks with high node
densities and high failure rates. In that case, the
sensor network may be unable to manage the
amount of traffic associated to this collaboration
means. Even if this was possible, it significantly
stresses the already scarce energy resources and
reduces the throughput of the wireless network.
A sufficient performance further depends on
the size of the applied collaboration region, which
in turn highly depends on the density of nodes
and on the expected size of the phenomenon to be
sensed. A high density of nodes enables to down-
size the collaboration region to such extent that
a suitable average number of neighboring nodes
is still available. The customizable collaboration
region allows to fine-tune the collaboration process
to a certain extent but the degree of freedom in
this parameter is limited, too. If the collaboration
region is chosen too small the sensor nodes may
not share the respective collaboration regions
and hence, other nodes may not be available for
collaborative detection. In that case, the detec-
tion results converge down to those gathered by
the standard detection without collaboration but
require a message overhead for the subscriptions.
In the presented node deployment, a collaboration
region of 2.5 meters provided the best detection
accuracy. Further simulation results indicated a
proper average collaboration region to be smaller
than the expansion of the phenomenon. Aim-
ing at a proper ease of use for configuration of
collaboration by non-professional users, these
must be provided with restrictions indicating a
proper size of the collaboration region. The user
configuration assistant can help to ensure that the
following principles apply:
density of the sensor network, and transmis-
sion technology.
2. The maximum size of the collaboration re-
gion is the estimated size of the phenomenon.
If one or both restrictions cannot be guaran-
teed, the application of collaboration should be
omitted for cost-efficiency. In those cases, there
would either be no other device in the collabora-
tion region (collaboration region is smaller than
minimum) or events are most possibly not notified
because of sharing EDT node values with sensor
nodes outside the phenomenon (collaboration
region is larger than maximum). To summarize,
customized collaboration offers proper means
for WSNs to enhance the robustness of detection
in event-based applications. However, the user
is responsible for fine-tuning the collaboration
region to achieve a sufficient performance. As
we have already discussed, a user configuration
assistant based on an experts system should be
able to determine a proper size of the collaboration
region automatically by asking simple questions
about the phenomenon.
FUTURE RESEARCH DIRECTIONS
Future work should primarily focus on alternating
test and improvement of convenient configura-
tion means by participation of non-scientific test
persons. WSNs should be designed to support
all people in the world, who are predominantly
not scientists. There is currently a lot of ongoing
work in this research direction trying to visualize
configuration properties for WSNs. The first step
for ease of use could be to enable configuration
of WSNs by graphical tools. Besides, means
have to be found to create a kind of feedback
system for announcement of WSNs, their fea-
tures and properties and for reporting success of
configuration. Configuration of a priori unknown
WSNs requires establishment of request-response
features to enable interactions between the sensor
1. The minimum size of the collaboration region
is the mean distance between neighboring
sensor nodes, which is determined by the
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