behaviors. It may decide to move in the wrong direction or take the longest route toward
a destination. Bad decisions may harm its source of energy. Malicious nodes may divert
traffic from the base station, drain energy of other nodes by producing fake information.
They may modify the collected data to cause the base station to make mis-informed deci-
sions. Such decisions are related t o errors in data collection or errors in data processing,
or shortly the quality of data collection and processing. The collection of undetected erro-
neous or incomplete data (due to data loss, misbehaviors, etc.) affects the quality of data
analysis and the decisions made by sensors. Another negative impact is caused by the
presence of data redundancy. Nodes that are densely deployed (20 nodes/m
3
[207]), and
sense the same property are expected to provide the same information. The transmission
of redundant data may waste energy. However, if data is filtered and redundancies are
detected, the communication overhead can be reduced and energy consumption can be
omitted. Fusion techniques were proposed to reduce the amount of data traffic, filter
noisy measurements, and make predictions about a monitored entity [163, 164]. However,
these techniques can lose much of the original structure in the data during compression,
aggregation or prediction. Therefore, they need to be convenient with the required quality
of data to prevent errors. For example, when sensor readings, from a number of sensors,
are aggregated into one value by taking the average over all these readings. This value is
used to represent each individual sensor reading. However, it deviates from the individual
sensor readings and thus introduces an error. Similarly, a loss of data may occur during
compression or predictions. In Chapter 2, we observe different data processing techniques
for WSNs, such as, data ag gregation, compression, prediction, anomaly detection. In the
following section, we present the motivation and contribution of our work.
1.4 Motivation and contributi on
WSNs are designed to sense, gather and transmit useful information to interested users
or applications. In some applications, sensor networks are expected to interact with the
physical world. They may resp ond to the sensed events by performing corresponding
actions and assist people in their life, such as in Wireless Sensors and Actuator Net-
works (WSANs). For example, in a fire handling system, the actuators can turn on the
water sprinklers upon receipt of a fire report [5]. Sensors can monitor and manipulate
the temperature and lighting in a smart office or the speed and direction of a mobile
robot [257]. To produce useful outcomes in a specific WSNs application, many sensors
collaborate in monitoring and gathering information. In patient monitoring system, sen-
sors can signal a possible health trouble, by gathering information from bloo d pressure,
glucose and other monitoring body sensors. An accurate data analysis and processing is
an important issue to increase the smartness and lifetime of nodes. However, data man-
agement (i.e collection, processing and communication) is not a trivial task, especially
for energy-limited sensor networks. The energy of a node is consumed in three aspects:
sensing, processing and communication. It has been mentioned in [192] that the amount
of energy consumed by the transceiver var ies a bout 15% to about 35% of the total energy.
Nonetheless, the maj ority of energy is consumed in radio communication rather than in
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阿利亚∙加达尔的博士论文,里尔第一大学,2011年
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Thèse d'Alia Ghaddar, Lille 1, 2011
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