\section{Introduction}
\label{ch1:sec:01}
%The wireless networking has received more attention and fast growth in the last decade.
-This last decade, wireless networking has became a major component of the global network infrastructure.
+In the last decade, wireless networking has became a major component of the global network infrastructure.
More precisely, the growing demand for the use of wireless applications and the continuous arrival of wireless devices such as portable computers, cellular phones, and personal digital assistants (PDAs) have led to develop different infrastructures of wireless networks. The wireless networks can be classified into two classes based on the network architecture~\cite{ref154,ref155}: Infrastructure-based networks that consist of a fixed network structure such as cellular networks and wireless local-area networks
(WLANs); and Infrastructureless networks that are constructed dynamically by the cooperation of the wireless nodes in the network, where each node is capable of sending packets and taking decisions based on the network status. Examples of such type of networks include mobile ad hoc networks and wireless sensor networks. Figure~\ref{WNT} shows the taxonomy of wireless networks.
\end{figure}
\begin{enumerate} [(I)]
-\item \textbf{Sensing Unit:} It consists of two main parts: sensors and Analog to Digital Converters (ADCs). It is responsible for sensing physical phenomena. The analog signal produced by a sensor is converted into digital data by ADC and then sent to the computation unit for further processing.
+\item \textbf{Sensing Unit:} It consists of two main parts: sensors and Analog to Digital Converters (ADCs). It is responsible for sensing physical phenomena. The analog signal produced by a sensor is converted into digital data by ADC, and then sent to the computation unit for further processing.
\item \textbf{Computation Unit:} The main purpose of this unit is to manage and manipulate the instructions that are related to sensing, communication, and self-organization. This allows the sensor node to cooperate with other sensor nodes in order to perform the allocated sensing tasks. It is composed of a processor chip, an active short-term memory for storing the sensed data, an internal flash memory for storing program instructions, and an internal timer.
\end{enumerate}
-Furthermore, additional components can be incorporated into wireless sensor node according to the application requirements, such as a localization system, a power generator, and a mobilizer~\cite{ref17,ref19}. These components are showed by the dashed boxes in figure~\ref{twsn}.
+Furthermore, additional components can be incorporated into wireless sensor node according to the application requirements, such as a localization system, a power generator, and a mobilizer~\cite{ref17,ref19}. These components are showed by the dashed boxes in figure~\ref{twsn}.
\begin{enumerate} [(I)]
\item \textbf{Localization System:} It is important that a sensor node is equipped with a location finding system because it is necessary for many WSN applications. It is required for routing algorithms and sensing coverage algorithms, which need information about the location of the wireless sensor nodes. Location finding system is composed of a Global Positioning System (GPS) or a discovery algorithm which provides information about the location of wireless sensor node using distributed computation \cite{ref232,ref233}.
-\item \textbf{Mobilizer:} The mobility function is sometimes needed in some applications, like move the wireless sensor node from one location to another so as to perform a certain task in WSN. Therefore it is necessary to equip the node with the mobilizer system for such applications. A high energy provision is needed to support mobility in wireless sensor node, and it should be supported efficiently. The movements are controlled by the mobility function in cooperation with the sensing unit and the computation unit.
+\item \textbf{Mobilizer:} The mobility function is sometimes needed in some applications, like health monitoring~\cite{ref27} and animal tracking~\cite{ref22}, to move the wireless sensor node from one location to another so as to perform a certain task in WSN. Therefore, it is necessary to equip the node with the mobilizer system for such applications. A high energy provision is needed to support mobility in wireless sensor node, and it should be supported efficiently. The movements are controlled by the mobility function in cooperation with the sensing unit and the computation unit.
-\item \textbf{Power Generator:} Several applications in WSNs need to operate for a long time. So it is essential to equip the wireless sensor node with additional power source in order to prolong the network lifetime. The better energy source to generate power in outdoor applications is a solar cell. Other power harvesting mechanisms~\cite{ref20,ref21} like thermal, motion, vibration, micro water flow, biological, pressure gradients, and electromagnetic radiation energy harvesting can be used to yield increasing power output.
+\item \textbf{Power Generator:} Several applications in WSNs need to operate for a long time. So, it is essential to equip the wireless sensor node with additional power source in order to prolong the network lifetime. The better energy source to generate power in outdoor applications is a solar cell. Other power harvesting mechanisms~\cite{ref20,ref21} like thermal, motion, vibration, micro water flow, biological, pressure gradients, and electromagnetic radiation energy harvesting can be used to yield increasing power output.
\end{enumerate}
\begin{figure}[h!]
\label{wsn}
\end{figure}
-%The TinyOS has been used as an operating system in wireless sensor node. It is developed by the university of California, Berkeley and designed to work on platforms with limited storage and processing power.
+The sensor node use software layer that logically locates between the node's hardware and the application called, An operating system (OS)~\cite{ref18}. OS enables the applications to interact with hardware resources, to schedule and prioritize tasks, memory management, power management, file management, networking, and to arbitrate between contending applications and services that attempt to reserve resources. The TinyOS has been used as an operating system in wireless sensor node. It is developed by the university of California, Berkeley and designed to work on platforms with limited storage and processing power.
\section{Types of Wireless Sensor Networks}
Nodes are deployed over caves, mines, or underground and communicate through soil~\cite{ref9,ref10}. The most important applications in underground WSNs are structural monitoring, agriculture monitoring, landscape management, underground environment monitoring of soil, water or mineral and military border monitoring. The essential challenges of underground WSNs are the high levels of attenuation and signal loss in communication. Therefore, it needs a certain type of devices able to provide a robust wireless underground communication. The risk on these devices comes from unsuitable underground conditions, replacing or recharging the battery seems to be impossible, and the WSN deployment is expensive.
\item \textbf{Underwater WSNs:}
-Such a WSN is composed of nodes deployed in the water such as the ocean~\cite{ref11,ref12}. Many challenges must be faced in this type of WSN such as the high cost of the underwater sensor devices; underwater wireless communication with limited bandwidth, high latency, signal fading, and long propagation delay problems; sparse deployment in which the wireless sensors should be able to self-organized to adapt to various condition of the ocean environment; the limited power of the node battery, and the difficulty to replace or recharge it. These challenges led to look for energy efficient underwater wireless communication mechanisms. The main underwater WSNs applications are seismic monitoring, disaster prevention monitoring, underwater robotics, pollution monitoring, equipment monitoring, and undersea surveillance and exploration.
+This type of WSNs is composed of wireless sensor nodes deployed in the water such as the ocean~\cite{ref11,ref12}. Many challenges must be faced in this type of WSN such as the high cost of the underwater sensor devices; underwater wireless communication with limited bandwidth, high latency, signal fading, and long propagation delay problems; sparse deployment in which the wireless sensors should be able to self-organized to adapt to various condition of the ocean environment; the limited power of the node battery, and the difficulty to replace or recharge it. These challenges led to look for energy efficient underwater wireless communication mechanisms. The main underwater WSNs applications are seismic monitoring, disaster prevention monitoring, underwater robotics, pollution monitoring, equipment monitoring, and undersea surveillance and exploration.
\item \textbf{Multimedia WSNs:}
They consist of inexpensive wireless sensor nodes supplied with CMOS (Complementary Metal-Oxide-Silicon) cameras or microphones devices. The nodes are deployed in a pre-guided way to ensure the coverage. Multimedia WSN is capable of retrieving and storing audio, video, and image contents from the physical environment~\cite{ref13,ref14,ref15}. Multimedia WSN contributed in improving some existing WSN applications such as tracking and monitoring. The main challenges in multimedia WSN include: the processing, filtering, and compressing of multimedia data; the requested bandwidth and high energy consumption; Quality-of-Service provisioning is very difficult because of the link capacity and delays; it should combine different wireless techniques; energy-efficient cross-layer design; it needs flexible architecture to support various applications; and the deployment is based on the multimedia devices coverage.
\begin{enumerate}[(I)]
-\item \textbf{Health-care Applications:} There is an increasing interest and extensive research in this domain. Two types of health-care systems are recognized~\cite{ref22}: vital status monitoring and remote health-care surveillance. In vital status monitoring applications, sick persons are wearing the sensors in order to oversee their health and to allow medical staff to monitor and control the patient's status expeditiously. The most general used vital signs are ECG, pulse oximetry, body temperature, heart rate, and blood pressure~\cite{ref27}. These applications include mass-casualty disaster monitoring, vital sign monitoring in hospitals, and sudden fall or epilepsy seizure detection. On the other hand, remote health-care surveillance refers to health services that do not require continuous existence of health care. These applications include elderly monitoring, providing support to a physically impaired person, gather clinically relevant information for rehabilitation supervision~\cite{ref28}, location tracking, and medication intake monitoring~\cite{ref27}.
+\item \textbf{Health-care Applications:} There is an increasing interest and extensive research in this domain. Two types of health-care systems are recognized~\cite{ref22}: vital status monitoring and remote health-care surveillance. In vital status monitoring applications, sick persons are wearing the sensors in order to oversee their health state and to allow medical staff to monitor and control the patient's status expeditiously. The most general used vital signs are ECG, pulse oximetry, body temperature, heart rate, and blood pressure~\cite{ref27}. These applications include mass-casualty disaster monitoring, vital sign monitoring in hospitals, and sudden fall or epilepsy seizure detection. On the other hand, remote health-care surveillance refers to health services that do not require continuous existence of health care. These applications include elderly monitoring, providing support to a physically impaired person, gather clinically relevant information for rehabilitation supervision~\cite{ref28}, location tracking, and medication intake monitoring~\cite{ref27}.
\item \textbf{ Environment and agriculture Applications}
\indent Several WSNs applications have been developed for precision agriculture, cattle monitoring, and environmental monitoring.
\indent Precision agriculture refers to the science of using innovative and modern technologies to improve the crop production. WSNs are the main technology for developing precision agriculture~\cite{ref29}. This technology contributes to increasing the agricultural yields, improving quality, and reducing costs whilst decreasing the damaging impact on the environment. The wireless sensors are distributed over the target field so as to monitor the main parameters such as soil moisture, atmospheric temperature, and create a decision support system \cite{ref22}.
-%The wireless sensors can be used in agricultural services like Irrigation, fertilization, pest control, animal and pastures monitoring, horticulture (e.g., greenhouse and viticulture)~\cite{ref30}.
-\indent Various WSN applications can be used in agricultural services and environmental monitoring like Irrigation, fertilization, pest control, animal and pastures monitoring, horticulture (e.g., greenhouse and viticulture), coastline erosion, air quality monitoring, safe drinking water, and contamination control~\cite{ref30,ref22}
+The wireless sensors can be used in agricultural services like Irrigation, fertilization, pest control, animal and pastures monitoring, horticulture (e.g., greenhouse and viticulture)~\cite{ref30}. For instance, in cattle monitoring applications, the WSN is used to livestock control and monitoring such as virtual fencing for extensive grazing systems, animal behavior study, health monitoring, to detect disease breakouts, to localize them, and to control end-product quality (meat, milk).
-\indent In cattle monitoring applications, the WSN is used to livestock control and monitoring such as virtual fencing for extensive grazing systems, animal behavior study, health monitoring, to detect disease breakouts, to localize them, and to control end-product quality (meat, milk).
+\indent Various WSN applications for environmental monitoring have been used in coastline erosion, air quality monitoring, safe drinking water, and contamination control~\cite{ref30,ref22}.
+
+%\indent In cattle monitoring applications, the WSN is used to livestock control and monitoring such as virtual fencing for extensive grazing systems, animal behavior study, health monitoring, to detect disease breakouts, to localize them, and to control end-product quality (meat, milk).
\item $\textbf{Coverage Ratio}$ is the percentage of the sensing field that fulfills the coverage degree of the application. If all the points in the sensing field are covered, the coverage ratio is $100\%$ and it can be called a complete coverage. Otherwise, it is said as partial coverage.
-\item $\textbf{Network Connectivity}$ is to ensure the existence of a path from any sensor node in WSN to the sink. A connected WSN ensures the sending of the sending the sensed data from one sensor node to another sensor node directly toward the sink.
+\item $\textbf{Network Connectivity}$ ensures the existence of a path from any sensor node in WSN to the sink. A connected WSN ensures the sending of the sending the sensed data from one sensor node to another sensor node directly toward the sink.
%It is necessary to consider the communication range of wireless sensor node is at least twice that of the sensing range ($R_c \geqslant 2R_s$) so as to imply connectivity among the sensor nodes during covering the sensing field~\cite{ref108}.
+Activity based Scheduling schedules the activation and deactivation of sensor nodes during the network lifetime.
-\item $\textbf{Activity based Scheduling}$ is to schedule the activation and deactivation of sensor nodes during the network lifetime. The basic objective is to decide which sensors are in what states (active or sleeping mode) and for how long, so that the application coverage requirement can be guaranteed and the network lifetime can be prolonged. Various centralized, distributed, and localized approaches have been proposed for activity scheduling. In distributed algorithms, each node in the network autonomously makes decisions on whether to turn on or turn off itself, using only local neighbor information. In centralized algorithms, a central controller (a node or base station) informs every sensor of the time intervals to be activated.
+\item $\textbf{Activity based Scheduling}$ schedules the activation and deactivation of sensor nodes during the network lifetime. The basic objective is to decide which sensors are in what states (active or sleeping mode) and for how long, so that the application coverage requirement can be guaranteed and the network lifetime can be prolonged. Various centralized, distributed, and localized approaches have been proposed for activity scheduling. In distributed algorithms, each node in the network autonomously makes decisions on whether to turn on or turn off itself, using only local neighbor information. In centralized algorithms, a central controller (a node or base station) informs every sensor of the time intervals to be activated.
This dissertation deals with activity based scheduling to ensure the best coverage.
\end{enumerate}
