\section{Introduction}
\label{ch1:sec:01}
-The wireless networking has been receiving more attention and fast growth in the last decade. The growing demand for the use of wireless applications and emerging the wireless devices such as portable computers, cellular phones, and personal digital assistants (PDAs) have been led to develop different infrastructures of wireless networks. The wireless networks can be classified into two classes based on network architecture~\cite{ref154,ref155}: Infrastructure-based networks that consists of a fixed network structure such as cellular networks and wireless local-area networks
-(WLANs); and Infrastructureless networks that constructed dynamically by the cooperation of the wireless nodes in the network, where each node capable of sending the packets and taking the decision based on the network status. Examples for such type of networks include mobile ad hoc networks and wireless sensor networks. Figure~\ref{WNT} shows the taxonomy of wireless networks.
+The wireless networking has received more attention and fast growth in the last decade. The growing demand for the use of wireless applications and emerging the 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 constructed dynamically by the cooperation of the wireless nodes in the network, where each node capable of sending the packets and taking the decision 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.
\begin{figure}[h!]
\centering
\label{WNT}
\end{figure}
-In recent years, there is increasing interest in Wireless Sensor Networks (WSNs) by many researchers around the world. This extensive study on WSNs led to consider it as on of the most researched fields in the last decade. It represents a special case of the Ad Hoc networks. Recent advances in wireless networking, Micro-Electro-Mechanical Systems (MEMS), and embedded computing technologies, which have led to construct low-cost, small-sized, and low-power sensor nodes that can perform detection, computation, and data communication of surrounding environment. A WSN includes a large number of small, limited-power sensors that can sense, process, and transmit data over a wireless communication. They communicate with each other by using multi-hop wireless communications and cooperate together to monitor the area of interest, so that each measured data can be reported to a monitoring center called sink for further analysis~\cite{ref1,ref2}. The WSN receives the orders from the end user by means of sink to specify data aggregation, computation and deliver missions to wireless sensors, after that the sensed measurements can be received from the WSN by the sink~\cite{ref3}. The cooperation among the wireless sensor nodes in WSNs has been led to several advantages over the traditional wireless ad-hoc networks, like self-organization, rapid deployment, flexibility, and inherent intelligent-processing capability~\cite{ref5}.
+In recent years, there is increasing interest in Wireless Sensor Networks (WSNs) by many researchers around the world. WSNs are considered as one of the most researched fields in the last decade due to the extensive research in this discipline. It represents a special case of the Ad Hoc networks. Recent advances in wireless networking, Micro-Electro-Mechanical Systems (MEMS), and embedded computing technologies have led to construct low-cost, small-sized, and low-power sensor nodes. These sensor nodes can perform detection, computation, and data communication of surrounding environment. A WSN includes a large number of sensor nodes that can sense, process, and transmit data over a wireless communication. The sensor nodes communicate with each other by using multi-hop wireless communications and cooperate together to monitor the area of interest. The measured data is reported to a monitoring center called sink for further analysis~\cite{ref1,ref2}. The WSN receives the orders from the end user by means of the sink. These orders specify data aggregation, computation and delivery missions to wireless sensor nodes, after that the sensed measurements are received from the WSN by the sink~\cite{ref3}. The cooperation among the wireless sensor nodes in WSNs has been led to several advantages over the traditional wireless ad-hoc networks, like self-organization, rapid deployment, flexibility, and inherent intelligent-processing capability~\cite{ref5}.
\section{Wireless Sensor Network Architecture}
\label{ch1:sec:02}
-A typical WSN architecture consists of a set of a typical wireless sensor nodes, which are capable of sensing the physical phenomenon around it such as fire in the forest (see~figure~\ref{wsn}), and then send the sensed data to a controller node called a sink. One or more sink in WSN are responsible for collecting and processing the sensed data by the wireless sensors, and then send it through the Internet to the end user.
+A typical WSN architecture consists of a set of a typical wireless sensor nodes, which are capable of sensing the surrounded physical phenomenon such as fire in the forest (see~figure~\ref{wsn}), and then send the sensed data to a controller node called a sink. One or more sink in WSN are responsible for collecting and processing the received sensed data, and then send that data through the Internet to the end-user.
-In those WSN architecture, the basic element is a typical wireless sensor node that composed of four major units~\cite{ref17,ref18}: sensing unit, computation unit, communication unit, and power unit. In addition, there are three optional units, which can be combined with the sensor node such as: localization system, mobilizer, and power generator. Figure~\ref{twsn} shows the components of a typical wireless sensor node~\cite{ref17}.
+In this WSN architecture, the basic element is a typical wireless sensor node that composed of four major units~\cite{ref17,ref18}: sensing, computation, communication, and power. In addition, there are three optional units, which can be combined with the sensor node such as localization system, mobilizer, and power generator. Figure~\ref{twsn} shows the components of a typical wireless sensor node~\cite{ref17}.
\begin{figure}[h!]
\centering
\end{figure}
\begin{enumerate} [(I)]
-\item \textbf{Sensing Unit:} consists of two main parts: sensors and analog to digital converters (ADCs). It is responsible of sensing the physical phenomena and produce the analog signals to the ADC so as to convert it to digital data, and sends it to the computation unit.
-\item \textbf{Computation Unit:} The main purpose of this unit is to manage and manipulate the instructions that related to sensing, communication, and self-organization, which make the sensor node cooperates 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.
-\item \textbf{Communication Unit:} It is responsible of all data transmission and reception of the sensor node that is performed by the transceiver circuitry. A transceiver circuit is composed of a mixer, frequency synthesizer, voltage-controlled oscillator (VCO), phase-locked loop (PLL), demodulator, and power amplifiers, all of which consume valuable power~\cite{ref19}.
-\item \textbf{Power Unit:} This unit represents the most significant part in wireless sensor node. It supplies the other units by the needed power.
+\item \textbf{Sensing Unit:} consists of two main parts: sensors and analog to digital converters (ADCs). It is responsible for sensing the physical phenomena. The analog signal produced by the sensors is converted into digital data by ADC. The resulted digital data is 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 related to sensing, communication, and self-organization. This allows to the sensor node cooperates 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.
+
+\item \textbf{Communication Unit:} It is responsible for all data transmission and reception of the sensor node that are performed by the transceiver circuitry. A transceiver circuit is composed of a mixer, frequency synthesizer, voltage-controlled oscillator (VCO), phase-locked loop (PLL), demodulator, and power amplifiers, all of which consume valuable power~\cite{ref19}.
+
+\item \textbf{Power Unit:} This unit represents the most significant part of wireless sensor node. It supplies the other units by the needed power.
\end{enumerate}
\begin{enumerate} [(I)]
-\item \textbf{Localization System:} It is important that the wireless sensor node is equipped with a location finding system because it is necessary for many WSN applications. It is required by routing algorithms and sensing coverage algorithms, which need information about the location of the wireless sensor nodes. The location finding system is composed of a Global Positioning System (GPS) or a discovery algorithm that executes a localization systems to provides information about the location of wireless sensor node using distributed computation.
+\item \textbf{Localization System:} It is important that the wireless 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. The location finding system is composed of a Global Positioning System (GPS) or a discovery algorithm that executes a localization system to provides information about the location of wireless sensor node using distributed computation.
-\item \textbf{Mobilizer:} The mobility function is sometimes needed in many applications to move the wireless sensor node from one location to another so as to perform a certain task in WSN, so it will be necessary that the wireless sensor node equipped with the mobilizer system for such applications. A high energy consumption is needed to support the mobility in wireless sensor node, and it should be supported efficiently. The movement of wireless sensor node is controlled by the mobility function with cooperation with the sensing unit and the computation unit .
+\item \textbf{Mobilizer:} The mobility function is sometimes needed in many applications to move the wireless sensor node from one location to another so as to perform a certain task in WSN. Therefore, it is necessary that the wireless sensor node equipped with the mobilizer system for such applications. A high energy consumption is needed to support the mobility in wireless sensor node, and it should be supported efficiently. The movement of wireless sensor node is controlled by the mobility function with cooperation with the sensing unit and the computation unit.
-\item \textbf{Power Generator:} Several WSN applications need to operate for a longer 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 the power for outdoor applications is a solar cells. An another power harvesting mechanisims~\cite{ref20,ref21} for thermal, motion, vibration, micro water flow, Biological, pressure gradients, and electromagnetic radiation energy harvesting can be used that yield increasing power output to extend the network lifetime.
+\item \textbf{Power Generator:} Several applications in WSNs need to operate for a longer 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 the power for outdoor applications is a solar cell. An another power harvesting mechanisms~\cite{ref20,ref21} for thermal, motion, vibration, micro water flow, Biological, pressure gradients, and electromagnetic radiation energy harvesting can be used to yield increasing power output to extend the network lifetime.
\end{enumerate}
\begin{figure}[h!]
\section{Types of Wireless Sensor Networks}
\label{ch1:sec:03}
-According to the physical phenomena for which the WSN is developed, several WSNs are deployed on the ground, underground and underwater, which suffer from different conditions and challenges. WSNs can be classified into six types, where five types of them presented in~\cite{ref4,ref5}. Figure~\ref{wsnt} gives an examples for WSNs types.
+According to the physical phenomena for which the WSN is developed, several WSNs are deployed on the ground, underground and underwater. These WSNs suffer from different conditions and challenges. WSNs can be classified into six types, where five types of them presented in~\cite{ref4,ref5}. Figure~\ref{wsnt} gives an example of WSNs types.
\begin{figure}[h!]
\centering
\includegraphics[scale=0.5]{Figures/ch1/typesWSN.pdf}
\begin{enumerate}[(I)]
\item \textbf{Terrestrial WSNs:}
-The wireless sensor nodes are deployed over the land constructing a network of hundreds to thousands of sensor devices. Several applications are used terrestrial WSNs such as physical environmental sensing and monitoring, industrial monitoring, and surface explorations. The main challenges in this type of WSNs are ensuring coverage and connectivity with removing redundancy, energy-efficient routing, data communication reduction, balancing energy consumption, energy-efficient data aggregation. The work in this dissertation concentrates on this type of WSNs. This dissertation focused on this type of WSNs.
+The wireless sensor nodes are deployed over the land constructing a network of hundreds to thousands of sensor devices. Several applications are used terrestrial WSNs such as physical environmental sensing and monitoring, industrial monitoring, and surface explorations. The main challenges in this type of WSNs are ensuring coverage and connectivity with removing redundancy, energy-efficient routing, data communication reduction, balancing energy consumption, energy-efficient data aggregation. This dissertation focuses on this type of WSNs.
\item \textbf{Underground WSNs:}
-The wireless sensor 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 so as to provide a robust wireless communication underground, where the risk to devices come from unsuitable underground conditions; replace or recharge the battery seems to be impossible; and the WSN deployment is high costly.
+The wireless sensor 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 so as to provides a robust wireless communication underground. The risk of devices comes from unsuitable underground conditions, replace or recharge the battery seems to be impossible, and the WSN deployment is expensive.
\item \textbf{Underwater WSNs:}
-A WSN is composed of a wireless sensor nodes deployed under the water such as the ocean~\cite{ref11,ref12}. There are many challenges should be faced in this type of WSN such as: the high cost of the underwater sensor devices; underwater wireless communication has 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 with various condition of the ocean environment; and the limited power of the wireless sensor node battery as well as it is impossible or difficult to replace or recharge it led to look for about energy efficient underwater wireless communication mechanisms. The main applications, which are used by underwater WSNs are seismic monitoring, disaster prevention monitoring, underwater robotics, pollution monitoring, equipment monitoring, and undersea surveillance and exploration.
+A WSN is composed of a wireless sensor nodes deployed in the water such as the ocean~\cite{ref11,ref12}. Many challenges should be faced in this type of WSN such as the high cost of the underwater sensor devices; underwater wireless communication has 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; and the limited power of the wireless sensor node battery as well as it is impossible or difficult to replace or recharge it that led to looking for about 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:}
-It consists of inexpensive wireless sensor devices supplied with CMOS cameras or microphones devices, deployed in a pre-guided way to ensure the coverage, where the multimedia WSN capable of retrieve the audio, vidio, and image contents from the physical environment~\cite{ref13,ref14,ref15}. The multimedia data such as images, videos, and sounds can be stored by these wireless sensor devices. The 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 the 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.
+It consists of inexpensive wireless sensor devices supplied with CMOS cameras or microphones devices. It is deployed in a pre-guided way to ensure the coverage, where the multimedia WSN capable of retrieving the audio, video, and image contents from the physical environment~\cite{ref13,ref14,ref15}. The multimedia data such as images, videos, and sounds can be stored by these wireless sensor devices. The 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 the 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.
\item \textbf{Mobile WSNs:}
-A network composed of a mobile sensor nodes that can self-moving and reacting for the physical phenomena~\cite{ref16}. The mobile sensor node is self-organized and it is capable to replace its position autonomously. In addition, it is able to sense, process, and communicate with other mobile sensors. There are many challenges that should be faced in mobile WSNs such as: maintaining a sufficient sensing coverage
-and connectivity; the self-organization; the navigation and controlling mobile sensors; mobility management; processing and distributing in WSN; location determination with mobility; and minimizing the energy consumption especially during the movement. The mobile WSN applications are environment, habitat, and underwater monitoring; target tracking; military surveillance; and search and rescue. The mobile WSNs can provide a higher coverage ratio and connectivity compared with static sensors.
+A network composed of a mobile sensor nodes that can self-moving and reacting for the physical phenomena~\cite{ref16}. The mobile sensor node is self-organized and it is capable of replacing its position autonomously. In addition, it is able to sense, process, and communicate with other mobile sensors. Many challenges that should be faced in mobile WSNs such as: maintaining a sufficient sensing coverage and connectivity; the self-organization; the navigation and controlling mobile sensors; mobility management; processing and distributing in WSN; location determination with mobility; and minimizing the energy consumption especially during the movement. The mobile WSN applications are environment, habitat, and underwater monitoring; target tracking; military surveillance; and search and rescue. The mobile WSNs provide a higher coverage ratio and connectivity compared with static sensors.
\item \textbf{Flying WSNs:}
-A network consists of a low cost wireless sensor nodes, which are equipped with a Micro Aerial Vehicles (MAVs) that can fly autonomously or can be operated remotely without intervention of any human personnel~\cite{ref6,ref7}. The general objective of this type of WSN is to retrieve the information from some locations that it is difficult to access it. For example, establishing an ad hoc network connection between rescuers and disaster victims over airborne relays or surveying an area from the air. Flying WSN provides a remote sensing and wireless networking platforms that collect the data from local sensors or other sources, and send the collected information over airborne wireless relays to a ground station. Using Flying WSNs leads to new developments for both military and civilian applications due to their flexibility, versatility, easy installation and the operating low cost~\cite{ref8}. The applications are search and destroy operations, disaster monitoring, relay for ad hoc networks, wind estimation, managing wildfire, border surveillance, remote sensing and traffic monitoring. The main challenges are constructing a lightweight MAV capable of flight; the wireless communication; designing a software protocols to achieve semi-autonomous flight; and combining all the subsystems such as propulsion, flight control, and wireless networking into a flying WSN.
-
+A network consists of a low-cost wireless sensor nodes, which are equipped with a Micro Aerial Vehicles (MAVs). It can fly autonomously or can be operated remotely without intervention of any human personnel~\cite{ref6,ref7}. The general objective of this type of WSN is to retrieve the information from some inaccessible locations. For example, establishing an ad hoc network connection between rescuers and disaster victims over airborne relays or surveying an area from the air. Flying WSN provides a remote sensing and wireless networking platforms that collect the data from local sensors or other sources, and send the collected information over airborne wireless relays to a ground station. Using Flying WSNs have led to new developments for both military and civilian applications due to their flexibility, versatility, easy installation, and the operating low-cost \cite{ref8}. The applications are search and destroy operations, disaster monitoring, relay for ad hoc networks, wind estimation, managing wildfire, border surveillance, remote sensing, and traffic monitoring. The main challenges are constructing a lightweight MAV capable of flight; the wireless communication; designing a software protocols to achieve semi-autonomous flight; and combining all the subsystems such as propulsion, flight control, and wireless networking into a flying WSN.
\end{enumerate}
\section{Wireless Sensor Network Applications}
\label{ch1:sec:04}
-\indent The fast development in WSNs has been led to extensive study on different characteristics of it. However, the WSN is concentrated on various applications. In this section, we demonstrate a different academic and commercial applications. The WSN is composed of various types of sensors such as~\cite{ref17,ref19}: thermal, seismic, magnetic, visual, infrared, acoustic, and radar, which are capable of observing a different physical conditions such as: temperature, humidity, pressure, speed, direction, movement, light, soil makeup, noise levels, the presence or absence of certain kinds of objects, and mechanical stress levels on attached objects. Thus, a wide range of WSN applications can be classified into five classes~\cite{ref22}. Figure~\ref{WSNAP} shows classification of WSN applications.
+\indent The fast development in WSNs has been led to study their different characteristics extensively. However, the WSN is concentrated on various applications. In this section, we demonstrate a different academic and commercial applications. The WSN is composed of various types of sensors such as \cite{ref17,ref19}: thermal, seismic, magnetic, visual, infrared, acoustic, and radar. These sensors are capable of observing a different physical conditions such as: temperature, humidity, pressure, speed, direction, movement, light, soil makeup, noise levels, the presence or absence of certain kinds of objects, and mechanical stress levels on attached objects. Thus, a wide range of WSN applications can be classified into five classes~\cite{ref22}. Figure~\ref{WSNAP} shows classification of WSN applications.
\begin{figure}[h!]
\centering
\item \textbf{Coverage:} One of the fundamental challenges in WSNs is the coverage preservation and the extension of the network lifetime continuously and effectively when monitoring a certain area (or region) of interest. The major objective is to choose the minimum number of sensor nodes in order to monitor the target sensing field without affecting on the application requirements in executing its tasks as long time as possible.
-\item \textbf{Routing:} Represents one of the important problems in WSNs that needs to be solved efficiently. The limited resources of WSNs and the impacts of wireless communication led to a big challenge in ensuring energy-efficient routing. However, it is not enough to use the shortest path to route the packets among the sensor nodes toward the sink. It is necessary to design an energy-efficient routing protocol that considers the remaining energy of sensor node during taking the decision to route the packet to the next hop toward the destination. This participates in energy conservation and balancing among the sensor node in WSNs.
+\item \textbf{Routing:} Represents one of the important problems in WSNs that needs to be solved efficiently. The limited resources of WSNs and the impacts of wireless communication lead to a big challenge in ensuring energy-efficient routing. However, it is not enough to use the shortest path to route the packets among the sensor nodes toward the sink. It is necessary to design an energy-efficient routing protocol that considers the remaining energy of sensor node during taking the decision to route the packet to the next hop toward the destination. This participates in energy conservation and balancing among the sensor node in WSNs.
\item \textbf{Autonomous and Distributed Management:}
-Since the nature of many WSN applications need to be deployed in a remote or hostile environment, it is important that the wireless sensor nodes work in autonomous and distributed way to communicate and cooperate with other sensor nodes without human intervention because the maintenance or the repair may be difficult. The distributed management consumes less energy because it is based on only local information from the neighboring sensor nodes; on the other hand, it does not give the optimal solution, so the main challenge is how to apply the a distributed management in WSNs and in the same time ensuring an optimal or near optimal solution.
+Since the nature of many WSN applications need to be deployed in a remote or hostile environment, it is important that the wireless sensor nodes work in autonomous and distributed way to communicate and cooperate with other sensor nodes without human intervention because the maintenance or the repair may be difficult. The distributed management consumes less energy because it is based on only local information from the neighboring sensor nodes, moreover, it does not give the optimal solution. So the main challenge is how to apply the a distributed management in WSNs and in the same time ensuring an optimal or near optimal solution.
\item \textbf{Scalability:} Many physical phenomenons require to be deployed densely with a large number of sensor nodes for different reasons such as: the large sensed area, reliability requirement, or network lifetime prolongation. It is necessary that the proposed protocols in WSNs are scalable for these large number of sensor
nodes in order to achieve their tasks efficiently.
\begin{enumerate}[(a)]
\item Grouping the wireless sensor nodes into clusters is led to decrease the communication range within the cluster and therefore minimize the energy needed to communication among the nodes inside the cluster.
\item Minimizing the energy hungry operations such as collaboration and aggregation to the cluster head.
-\item Limiting the number of communications (transmitting and receiving) due to the fusion operation carried out by the cluster head.
+%\item Limiting the number of communications (transmitting and receiving) due to the fusion operation carried out by the cluster head.
\item The continuous changing of cluster head according to residual energy is led to balance the energy consumption among wireless sensor nodes inside the cluster.
\item Some nodes can be turned-off within the same cluster whilst the cluster head manage the responsibilities.
\end{enumerate}
\subsection{Battery Repletion:}
-\indent In the last years, extensive researches have been focused on energy harvesting and wireless charging techniques. These solutions represent alternate energy sources to recharge wireless sensor batteries without human intervention and instead of depending on the limited power supplied by a typical batteries~\cite{ref91,ref59}.
+\indent In the last years, extensive researches have been focused on energy harvesting and wireless charging techniques. These solutions represent alternate energy sources to recharge wireless sensor batteries without human intervention~\cite{ref91,ref59}.
\subsubsection{Energy Harvesting:} In energy harvesting, several sources of environmental energy have been developed so as to enable the wireless sensors to acquire energy from the surrounding environment like solar, wind energy, vibration based energy harvesting, radio signals for scavenging RF power, Thermoelectric generators, and shoe-mounted piezoelectric generator to power artificial organs~\cite{ref59}.
\label{ch1:sec:07}
\indent The limited resources in WSNs have been addressed, and one of the main challenges in WSNs is the limited power resource. For this reason, extensive researches have been proposed in order to prolong the network lifetime by means of designing and implementing energy-efficient protocols. The reason for these large number of proposed protocols to maximize the network lifetime is the difficulty and sometime impossibility to replace or recharge the batteries of wireless sensor nodes especially in the large WSN and hostile environment.
-\indent The authors have defined the network lifetime in different contexts and use it as a metric to evaluate the performance of their protocols. Based on the previous proposed works in prolonging the network lifetime, Various definitions are exist for the lifetime of a sensor network~\cite{ref92,ref93} such as:~\textbf{(i)} is the time spent by WSN until the death of the first wireless sensor node ( or cluster head ) in the network due to its energy depletion.~\textbf{(ii)} is the time spent by WSN and has at least a specific set $\beta$ of alive sensor nodes in WSN.~\textbf{(iii)} is the time spent by WSN until the death of all wireless sensor nodes in WSN because they have been depleted their energy.~\textbf{(iv)} for k-coverage is the time spent by WSN in covering the area of interest by at least $k$ sensor nodes.~\textbf{(v)} for 100 $\%$ coverage is the time spent by WSN in covering each target or the whole area by at least one sensor node.~\textbf{(vi)} for $\alpha$-coverage: the total time by which at least $\alpha$ part of the sensing field is covered by at least one node; or is the time spent by WSN until the coverage ratio becomes less than a predetermined threshold $\alpha$.~\textbf{(vii)} the working time spent by the system before either the coverage ratio or delivery ratio become less than a predetermined threshold.~\textbf{(viii)} the number of the successful data gathering trips.~\textbf{(ix)} the number of sent packets.~\textbf{(x)} the percentage of wireless sensor nodes that have a route to the sink.~\textbf{(xi)} the prediction of the total period of time during which the probability of ensuring the connectivity and k-coverage concurrently is at least $\alpha$.~\textbf{(xii)} the time spent by WSN until loosing the connectivity or the coverage.~\textbf{(xiii)} the time spent by WSN until acceptable event detection ratio is not acceptable in the network.~\textbf{(xiv)} the time spent by WSN and the application requirement has been met.
+\indent The authors have defined the network lifetime in different contexts and use it as a metric to evaluate the performance of their protocols. Based on the previous proposed works in prolonging the network lifetime, Various definitions are exist for the lifetime of a sensor network~\cite{ref92,ref93} such as:
+%~\textbf{(i)}
+\begin{enumerate} [i.]
+
+\item The time spent by WSN until the death of the first wireless sensor node ( or cluster head ) in the network due to its energy depletion~\cite{ref162,ref163}.
+\item The time spent by WSN and has at least a specific set $\beta$ of alive sensor nodes in WSN~\cite{ref164,ref165}.
+\item The time spent by WSN until the death of all wireless sensor nodes in WSN because they have been depleted their energy~\cite{ref166}.
+\item For k-coverage, is the time spent by WSN in covering the area of interest by at least $k$ sensor nodes~\cite{DESK}.
+\item For 100 $\%$ coverage is the time spent by WSN in covering each target or the whole area by at least one sensor node~\cite{ref167}.
+\item For $\alpha$-coverage: the total time by which at least $\alpha$ part of the sensing field is covered by at least one node~\cite{ref168}; or is the time spent by WSN until the coverage ratio becomes less than a predetermined threshold $\alpha$~\cite{ref169}.
+\item The working time spent by the system before either the coverage ratio or delivery ratio become less than a predetermined threshold~\cite{ref170}.
+\item The number of the successful data gathering trips~\cite{ref173}.
+\item The number of sent packets~\cite{ref174}.
+\item The percentage of wireless sensor nodes that have a route to the sink~\cite{ref170}.
+\item The prediction of the total period of time during which the probability of ensuring the connectivity and k-coverage concurrently is at least $\alpha$~\cite{ref175}.
+\item The time spent by WSN until loosing the connectivity or the coverage~\cite{ref171}.
+\item The time spent by WSN until acceptable event detection ratio is not acceptable in the network~\cite{ref166}.
+\item The time during which the application requirement is satisfied~\cite{ref172}.
+\end{enumerate}
\indent According to the above definitions for network lifetime, there is no universal definition reflects the requirements of each application and the effects of the environment. In real WSN, the network lifetime reflects a set of a particular circumstances of the environment. Accordingly, the current definitions are applicable for the WSNs that meet a particular conditions. However, many more parameters, which are affecting on the network lifetime of WSN such as~\cite{ref92}: heterogeneity, node mobility, topology changes, application characteristics, quality of service, and completeness.
\section{Coverage in Wireless Sensor Networks }
\label{ch1:sec:8}
-%\indent Energy efficiency is a crucial issue in wireless sensor networks since sensory consumption, in order to maximize the network lifetime, represents the major difficulty when designing WSNs. As a consequence, one of the scientific research challenges in WSNs, which has been addressed by a large amount of literature during the last few years, is the design of energy efficient approaches for coverage and connectivity~\cite{ref94,ref101}.
-Coverage reflects how well a sensor field is monitored. On the one hand, we want to monitor the area of
-interest in the most efficient way~\cite{ref95}. On the other hand, we want to
-use few energy as possible. Sensor nodes are battery-powered with no
+%\indent Energy efficiency is a crucial issue in wireless sensor networks since sensory consumption, in order to maximize the network lifetime, represents the major difficulty when designing WSNs. As a consequence,
+
+One of the scientific research challenges in WSNs, which has been addressed by a large amount of literature during the last few years, is the design of energy efficient approaches for coverage and connectivity~\cite{ref94,ref101}. Coverage reflects how well a sensor field is monitored. On the one hand, we want to monitor the area of interest in the most efficient way~\cite{ref95}. On the other hand, we want to use few energy as possible. Sensor nodes are battery-powered with no
mean of recharging or replacing, usually due to environmental (hostile or
unpractical environments) or cost reasons. Therefore, it is desired that the
WSNs are deployed with high densities so as to exploit the overlapping sensing
\item \textbf{The Probabilistic Sensing Model}
-In reality, the event detection by sensor node is imprecise; therefore, the coverage $C_{xy}$ requires to be represented in probabilistic manner. The probabilistic sensing model is more practical, which can be used as an extension for the binary disc sensing model. The equation \ref{eq2-ch1} shows the probabilistic sensing model that expresses the coverage $C_{xy}$ of the point P by sensor node $s_i$.
+In reality, the event detection by sensor node is imprecise; therefore, the coverage $C_{xy}$ requires to be represented in probabilistic manner. The probabilistic sensing model is more practical, which can be used as an extension for the binary disc sensing model. The equation \ref{eq2-ch1} shows the probabilistic sensing model that expresses the coverage $C_{xy}$ of the point P by sensor node $s_i$ as follow
\begin{equation}
C_{xy}\left(s_i \right) = \left \{
\section{Design Issues for Coverage Problems:}
\label{ch1:sec:11}
-\indent Several design issues that should be considered in order to produce a solutions for the coverage problems in WSNs. These design issues can be classified into~\cite{ref103}:
+\indent Several design issues should be considered in order to produce solutions for the coverage problems in WSNs. These design issues can be classified into~\cite{ref103}:
\begin{enumerate}[(i)]
\item $\textbf{Coverage Type}$ refers to determining what is it exactly that you are trying to cover. Typically, it may be required to monitor a whole area, observe a set of targets, or look for a breach among a barrier.
-\item $\textbf{Deployment Method}$ refers to the way by which the wireless sensor nodes are deployed over the target sensing field in order to build the wireless sensor network. Generally, the sensor nodes can be placed either deterministically or randomly in the target sensing field so as to construct the wireless sensor network~\cite{ref107}. The method of placement the sensor nodes can be selected based on the type of sensors, application, and the environment. In the deterministic placing, the deployment can be achieved in case of small number of sensor nodes and in friendly environment, whilst for a large number of sensor nodes or where the area of interest is inaccessible or hostile, a random placing is the choice. The sensor network can be either dense or sparse. The dense deployment is preferred when the robust security is important or when it is required that the area is covered by more than one sensor node. On the other hand, the sparse deployment is used when the dense deployment is expensive or when the maximum coverage is performed by a less number of sensor nodes.
+\item $\textbf{Deployment Method}$ refers to the way by which the wireless sensor nodes are deployed over the target sensing field in order to build the wireless sensor network. Generally, the sensor nodes can be placed either deterministically or randomly in the target sensing field so as to construct the wireless sensor network~\cite{ref107}. The method of placement the sensor nodes can be selected based on the type of sensors, application, and the environment. In the deterministic placing, the deployment can be achieved in case of small number of sensor nodes and in friendly environment, whilst for a large number of sensor nodes or where the area of interest is inaccessible or hostile, a random placing is the choice. The sensor network can be either dense or sparse. The dense deployment is preferable when it is necessary to provide a security robustness in WSNs. On the other hand, the sparse deployment is used when the dense deployment is expensive or when the maximum coverage is performed by a less number of sensor nodes.
\item $\textbf{Coverage Degree}$ refers to how many sensor nodes are required to cover a target or an area. This K-coverage mean the point in the sensing field is covered by at least K sensor nodes. Some applications need a high reliability to achieve their tasks, therefore, the sensing field is deployed densely so as to perform a K-coverage for this field. The simple coverage problem consists of a coverage degree equal to one (i.e., K=1), where every point in the sensing field is covered by at least one sensor.
\section{Conclusion}
\label{ch1:sec:10}
-\indent In this chapter, an overview about the wireless sensor networks have been presented that represent our focus in this dissertation. The structure of the the typical wireless sensor network and the main components of the sensor nodes have been demonstrated. Several types of wireless sensor networks are described. Various fields of applications covering a wide spectrum for a WSNs have been presented, including health, home, environmental, military, and industrial applications. As demonstrated, since sensor nodes have limited battery life; since it is impossible to replace batteries, especially in remote and hostile environments; the limited power of a battery represents the critical challenge in WSNs. The main challenges in WSNs have been explained; on the other hand, the energy efficient solutions have been proposed in order to handle these challenges through energy conservation to prolong the network lifetime. Many energy efficient mechanisms have been illustrated, which are aimed to reduce the energy consumption by the different units of the wireless sensor nodes in WSNs. The definition of the network lifetime has been presented and in different contexts. The problem of the coverage is explained, where constructing energy efficient coverage protocols one of the main scientific research challenges in WSNs. This chapter highlights the main design issues for the coverage problems that need to be considered during designing a coverage protocol for WSNs. In addition, the energy consumption Modeling have been demonstrated.
+\indent In this chapter, an overview about the wireless sensor networks have presented that represent our focus in this dissertation. The structure of the typical wireless sensor network and the main components of the sensor nodes have been demonstrated. Several types of wireless sensor networks are described. Various fields of applications covering a wide spectrum for a WSNs have been presented, including health, home, environmental, military, and industrial applications. As demonstrated, since sensor nodes have limited battery life; since it is impossible to replace batteries, especially in remote and hostile environments; the limited power of a battery represents the critical challenge in WSNs. The main challenges in WSNs have explained; on the other hand, the energy efficient solutions have proposed in order to handle these challenges through energy conservation to prolong the network lifetime. Many energy efficient mechanisms have been illustrated, which are aimed to reduce the energy consumption by the different units of the wireless sensor nodes in WSNs. The definition of the network lifetime has been presented and in different contexts. The problem of the coverage is explained, where constructing energy efficient coverage protocols one of the main scientific research challenges in WSNs. This chapter highlights the main design issues for the coverage problems that need to be considered during designing a coverage protocol for WSNs. In addition, the energy consumption Modeling have been demonstrated.
