الفهرس 
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Abstract
Wireless Sensor Networks have received significant attention in recent years, motivated by advancements in wireless communications and electronics. These networks imposed numerous challenges due to their peculiarities, primarily limited energy resources, com¬putational capacities and memory to which sensors are typically subjected. These new constraints made energy-aware routing the goal of most published techniques. in addition, since the placement of nodes affects whether there exists sensors that could sense the environment and route to the gateway, then their placement is important.
This thesis presents an approach for studying the effect of increasing sensors’ density around the gateway, both at startup time and during network’s operation, on various performance metrics like network’s life time. The proposed approach consists of two parts. The first part proposes two approaches, R-U placement and gateway placement, for scattering sensors at setup time whereas the second part relocates the gateway dynamically towards nodes that are one-hop away from it.
R-U placement approach uses both R-random and uniform distributuionfor scattering sensors at deployment time. The R-random distribution is used to increase the sensors’ density around the gateway, whereas uniform distribution is used to uniformaly cover the whole area of interest. On the other hand, gateway placement approach chooses gateway’s position so that it is surrounded by the maximum possible number of neighbors. During network’s operation, gateway is relocated dynamically towards nodes that are one-hop away from it while giving more weight for nodes with higher number of neighbors.