Cryptography Reference
In-Depth Information
Data-transmission phase:
Once the ordinary nodes in the cluster have received the TDMA schedule, they are set
to begin their usual sensing operation and transmit data at their allocated time slot.
To minimize energy dissipation, the radio of each node is turned off until its allocated
time. Upon receiving data from all the non-cluster-head nodes, the cluster head can
preprocess the data and compress it before sending it to the sink node. In addition, to
prevent interference among the nodes, different CDMA codes can be used, and non-
cluster-head nodes can decide from the existing list of spreading codes. Subsequently,
the cluster heads can inform all the ordinary nodes to transmit using the new spreading
code, and they will filter all the messages received using this code.
Despite the fact that LEACH helps the sensors conserve energy in the system, the
cluster heads could expend a larger amount of energy when they are positioned farther
away from the sink node. In this model, each cluster head sends data directly to the
sink, thus presenting one of the main drawbacks with LEACH. A more pragmatic
approach is to allow multi-hop data transmission to the sink node through intermediate
cluster heads. Consequently, a cluster head does not need to consolidate the processed
data from other cluster heads; it only needs to forward the data to the nearest sink node.
In addition, this model does not consider the residual energy of the nodes in deciding
whether the node should be a cluster head.
7. 2 . 3 . 2 Cluster-Based Energy-Aware Routing
In general, WSN applications can be classified by their functionality (event-based sens-
ing, continuous sensing, and query-based sensing). An event-based sensing application
is based on a threshold value. If the sensing parameter value exceeds the threshold, the
sensing application in the node is initiated—for example, room temperature measure-
ment. As a result, the energy depletion of the entire sensor network system occurs at a
lower rate. For the continuous-sensing application, the nodes are required to continu-
ously sense their surroundings and can be required to transmit data to the sink on a
real-time basis (e.g., remote-sensing application). Therefore, such applications demand
the continuous sensing of data, which could result in rapid energy depletion of the sen-
sor nodes. In the event of a query-based sensing application, the sink node initiates a
query, requesting information from the nodes in a designated region. Upon receiving
the query, the sensing application of those designated nodes is activated, and subse-
quently, an aggregated response is sent to the sink node.
Another approach is a hierarchical, secure, cluster-based, energy-aware routing
(SCEAR) scheme (Mallanda et al. 2004). SCEAR proposes an energy-efficient solu-
tion by combining a noninteractive identity-based public key cryptography with a sym-
metric key-based encryption scheme (Maurer and Yacobi 1996; Boneh and Franklin
2001; Khalili et al. 2003). This protocol assumes the following:
• Each entity in the sensor network is static and the nodes are distributed in a
random fashion.
• There could be more than one sink node (resource-abundant device), which
could act as a gateway to the entire network.
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