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\section{General Introduction}
-The enormous development in wireless networks and the emergence of fourth-generation technology led to the provision of various services to customers around the world that make of the Internet a more widely used everywhere. This kind of wireless networks may not be appropriate to be used in some sensitive areas that need to deploy a large number of wireless devices, which are capable of decide and communicate with each other in a distributed way so as to collect the sensed measurements from the physical dangerous environment directly such as volcanoes, nuclear reactors, forest fires, or military battles. So, another type of wireless networks has been emerged to cope with these challenges which is called wireless sensor network (WSN).
+The enormous development in wireless networks and the emergence of fourth and fifth-generation technology is led to provision of various services to customers around the world that make of the Internet a more widely used everywhere. This kind of wireless networks may not be appropriate to be used in some sensitive areas that need to deploy a large number of wireless devices, which are capable of decide and communicate with each other in a distributed way so as to collect the sensed measurements directly from the physical dangerous environment such as volcanoes, nuclear reactors, forest fires, or military battles. Therefore, another type of wireless networks has been emerged to cope with these challenges, which is called Wireless Sensor Network (WSN).
-It is a special case of the ad hoc wireless networks and it consists of a large number of wireless devices are called sensors, which are able to perform the communication, sensing, processing and storage with a limited capabilities. A WSN can be used by the human to monitor the physical phenomena remotely and without outside intervention. Inside a WSN, the wireless sensor nodes are self-contained units equipped with a radio transceiver, a microcontroller, a small memory, and a power source, usually a battery. These sensor nodes are cooperating together autonomously to perform the assigned tasks without the intervention or control from outside. The distributed self-organization and self-configuration capabilities of wireless sensor nodes make the distributed WSNs to enable myriad applications for monitoring, sensing and controlling the physical world.
+WSN is a special case of the ad hoc wireless networks and it consists of a large number of wireless cheap devices are called sensors, which are able to perform the communication, sensing, processing and storage with a limited capabilities. A WSN can be used by the human to monitor the physical phenomena remotely and without outside intervention. Inside a WSN, the wireless sensor nodes are self-contained units equipped with a radio transceiver, a microcontroller, a small memory, and a power source, usually a battery. These sensor nodes are cooperating together autonomously to perform the assigned tasks without the intervention or control from outside. The distributed self-organization and self-configuration capabilities of wireless sensor nodes make the distributed WSNs to enable myriad applications for monitoring, sensing, and controlling the physical world.
+
+The rapid advancement in Micro Electro-Mechanical Systems (MEMS), wireless communication hardware, digital electronics, and system-on-chip has given rise to use large networks of tiny sensors are becoming cheaper and more and more commercially available. The sensor nodes have several limitations, such as: power source, processing capability, bandwidth, uncertainty of sensed data, and the vulnerability of sensor nodes to physical world. These limitations have been tackled by many researchers during the last years, and consequently, many solutions have been proposed that take these constraints into account on the sensors. Sensor nodes are battery-powered with no means of recharging or replacing, usually due to environmental (hostile or unpractical environments) or cost reasons. Since the batteries are the most important limited resource inside the sensor nodes, therefore, it is desired that the WSNs are deployed with high densities so as to exploit the overlapping sensing regions of some sensor nodes to save energy by turning off some of them during the sensing phase to prolong the network lifetime.
+
+Since the network lifetime depends on sensor lifetime, the power depletion represents the most significant part during designing the WSN protocols because of the limited capacity of the sensor batteries. The major goal is to extend the network lifetime, taking into consideration the energy source limitations. Several energy-efficient approaches have been suggested so as to minimize the energy consumption and extend the network lifetime during monitoring a certain area by WSN. For example, one of the ways is to turn off the redundant sensors and put them in sleep mode to maintain the energy, whilst the active sensors perform the sensing coverage task during their life. Specifically, the energy-efficient protocols, which are proposed in this dissertation focuses on the area coverage problem in WSNs. The major goal of the area coverage problem is to ensure a maximum area coverage ratio for the entire sensing field of the WSN and for a longer time as possible. The area coverage problem is closely related to the performance of systems in many application, such as, monitoring the battlefield, target detection, tracking, personal protection, animal habit monitoring, and homeland security.
-The fast and continuous progress in Micro Electro-Mechanical Systems (MEMS), wireless communication hardware, digital electronics, and system-on-chip has given rise to the opportunity to use large networks of tiny sensors are becoming cheaper and more and more commercially available. There are several limitations on the sensor nodes such as power source, processing capability, bandwidth, uncertainty of sensed data, and the vulnerability of sensor nodes to physical world. These limitations have been tackled by many researchers during last years and many solutions have been proposed to handle these constraints on the sensors. Sensor nodes are battery-powered with no means of recharging or replacing, usually due to environmental (hostile or unpractical environments) or cost reasons. Since the batteries are the most important limited resource inside the sensor nodes, therefore, it is desired that the WSNs are deployed with high densities so as to exploit the overlapping sensing regions of some sensor nodes to save energy by turning off some of them during the sensing phase to prolong the network lifetime. Many energy-efficient mechanisms have been proposed so as to minimize the energy consumption during operating the WSN its monitoring task and to extend the network lifetime. Specifically, this dissertation focuses on the area coverage problem of in WSNs.
-The major goal of the area coverage problem is to ensure a maximum area coverage ratio for the entire sensing field of the WSN and for a longer time as possible. The area coverage problem is closely related to the performance of systems in many application, such as, monitoring the battlefield, target detection and tracking, personal protection, animal habit monitoring, and homeland security.
\section{Motivation of the Dissertation}
One of the fundamental challenges in Wireless Sensor Networks (WSNs) is the coverage preservation and the extension of the network lifetime continuously and effectively when monitoring a certain area (or region) of interest. Since sensor nodes have limited battery life; since it is impossible to replace batteries, especially in remote and hostile
