Image Processing Reference
In-Depth Information
energy-efficient since sensor nodes have very limited energy supplies. To provide more
efficient dissemination of data, some sensors may process data streams, and provide
replication and caching.
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Distributed services layer
: It contains distributed services for supporting mobile sensor
applications. Distributed services coordinate with each other to perform decentralized
services. hese distributed servers may be replicated for higher availability, efficiency, and
robustness. We have identified two major services. he lookup service supports mobility,
instantiation, and reconiguration. he information service deals with aspects of collect-
ing data. This service allows vast quantities of data to be easily and reliably accessed,
manipulated, disseminated, and used in a customized fashion by applications.
On top of this architecture applications can be built using the sensor network and distributed ser-
vices. Communication in a sensor network is data-centric since the identity of the numerous sensor
nodes is not important, only the sensed data together with time and location information counts.
The three main functions of the nodes within a sensor network are directly related to this:
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Data discovery
: Several classes of sensors will be equipped in the network. Specialized
sensors can monitor climatic parameters (humidity, temperature, etc.), motion detec-
tion, vision sensors, and so on. A first step of data preprocessing can also be included
in this task.
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Data processing and aggregation
: This task is directly related to performing distributed
computations on the sensed data and also aggregating several observations into a single
one. he goal of this operation is the reduction of energy consumption. Data processing
influences it by the fact that the transmission of one (raw sensed) data packet is equivalent
to many thousands of computation cycles in the current architectures. Data aggregation
keeps the overall traffic low by inspecting the contents of the routed packets, and in gen-
eral, reducing the redundancy of the data in traffic by combining several similar packets
into a single one.
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Data dissemination
: his task includes the networking functionality comprising routing,
multicasting, broadcasting, addressing, etc.
The existing network scenarios contain both static and mobile nodes. In some cases, the static
nodes can be considered to form a back bone of the network and are more likely to be preferred in
certain distributed protocols. Both mobile and static nodes will have to perform data dissemination,
so the protocols should be designed to be invariant to node mobility. he particular hardware capa-
bilities of each kind of sensor node determine how the previously described tasks should be mapped
onto them (in principle all the nodes could provide all the previous functionality). During the initial-
ization phase of the network, the functionality of every node is decided based on both the hardware
configurations and the particular environmental conditions.
For a large sensor network to be able to function correctly, a tiered architecture is needed.
This means that nodes will have to organize themselves into clusters based on certain conditions.
The nodes in each cluster will elect a leader—the best fitted node to perform coordination inside the
cluster (this can be, for example, the node with the highest amount of energy or the node having the
most advanced hardware architecture or just a random node). The cluster leader is responsible for
schedulingthenodeoperations,managingtheresourcesandtheclusterstructure,andmaintaining
communication with the other clusters.
We can talk about several types of clusters that can coexist in a single network:
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Geographical clustering
: The basic mode of organizing the sensor network. The clusters
are built based on the geographical proximity. Neighboring nodes (nodes that are in
transmission range of each other) organize themselves into groups. This operation can
