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issue and requires novel approaches since maintaining any kind of infrastructure
under these circumstances is impossible. Several approaches considering this topic
will be further discussed.
6.4.1
Data Transmission Strategies in WSN with Mobile
Sensor Nodes
Two approaches where data dissemination is based on history are initially dis-
cussed. Then, a more efficient solution for adaptive data dissemination considering
mobility is presented. The last part explains how a cooperative communications can
be utilized for efficient messages delivery in a mobile scenario.
A simple and efficient data delivery scheme for special kind of a mobile WSN,
called DFT-MSN (Delay-Fault Tolerant Mobile Sensor Network), based on delivery
probability and fault tolerance is given in [ 43 ]. DFT-MSN has several unique char-
acteristics such as sensor mobility, loose connectivity, fault tolerability, delay toler-
ability, and buffer limit. In the protocol, the decision on when and where to transmit
data messages is based on the delivery probability, and the decision which messages
to transmit or drop is based on the fault tolerance. The fault tolerance of a message
is defined to be the probability that at least one copy of the message is delivered to
the sink by other sensors in the network, or according to the hop count of the mes-
sage. When a message is generated, its fault tolerance is initialized to be zero, so
the messages with a smaller fault tolerance are considered more important and are
transmitted with a higher priority (by sorting the messages in the queue with an
increasing order of their fault tolerance based on their hop count).
A data transmission decision is made based on the delivery probability. At
first, the nodes learn their neighbors' delivery probabilities and available buffer
spaces via simple handshaking messages. Then, the message is sent to a set of
neighbors with higher delivery probabilities. At the same time, the total delivery
probability of the considered message is controlled, just enough to reach a pre-
defined threshold, in order to reduce unnecessary transmission overhead. The
message transmission scheme is equivalent to direct transmission when the net-
work is just deployed; as the delivery probability is gradually updated with non-
zero values, multi-hop transmission will take place. Two data delivery schemes
are further proposed, the Replication-Based Efficient Data Delivery Scheme
( RED ) and the Message Fault Tolerance-Based Adaptive Data Delivery Scheme ( FA D )
[ 44 ]. The RED scheme utilizes the erasure coding technology in order to achieve
the desired data delivery ratio with minimum overhead. It consists of two key
components for data transmission and message management. The former makes
the decision on when and where to transmit data messages according to the deliv-
ery probability. The latter decides the optimal erasure coding parameters (includ-
ing the number of data blocks and the needed redundancy) based on its current
delivery probability. The FAD scheme employs the message fault tolerance, which
indicates the importance of the messages.
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