Egyptian Computer Science Journal (ISSN-1110-2586) Volume 41– Issue 1, January 2017 -1- Efficient Topology Extraction Technique for Wireless Sensor Networks Walaa Abdellatief, Osama Youness, Hatem Abdelkader , and Mohee Hadhoud Faculty of Computers and Information, Menoufia University, Egypt walaaali285@gmail.com, osama_youness@hotmail.com, hatem6803@yahoo.com, mmhadhoud@yahoo.com Abstract Wireless sensor networks have been widely used in many applications especially environmental monitoring. Thanks to the sensors small size and low cost, a large number of nodes can be easily deployed in hazardous areas by airplanes passing over it. Deploying the nodes using this random mechanism causes different node densities in different subregions of the area of interest. One of the challenges in such applications is the recognition of the topology structure after deployment. In this paper, we propose an efficient technique to help nodes to construct boundary cycles around each subregion of specified density-level. These cycles help in describing the layout the deployed network. The main contribution of this technique is the ability to work in sparse networks with the same efficiency as in dense networks. Evaluation of our proposed technique shows that it uses less average node degree in different simulation scenarios and achieves about 50% decrease in energy consumption than Heuristic Boundary Cycles Finding Technique. Keywords: Wireless Sensor Network, Random Deployment, Boundary Node, Interior Node, Transmission Range, Topology Extraction, Boundary Cycles. 1. Introduction Wireless Sensor Networks (WSNs) are networksof spatially distributed nodes called sensors. Sensors have good special characteristics which make WSNs differ from traditional wireless ad-hoc networks. These features allow it to be used in a wide range of discriminative applications. Sensor nodes are tiny ships called motes with a sensing, processing, and communication devices embedded on it. What make it different are its sensing capabilities. It enables them to monitor physical phenomenon in real environments such as, but not limited to, pressure, temperature, and moisture. Examples of WSN applications are: i) area monitoring where specific phenomenon has to be recognized such as air pollution[1, 2], forest fire detection [3, 4], disasters detection[5, 6], ii) health-care[7, 8],and iii) civil services [9, 10]. One of the challenges in WSNs is the used deployment method. According to the size of the application, one from two deployment methods can be used. The first one is planned deployment. It is used in small sized applications where a small number of sensors have to be deployed in the area of interest. The location of these sensors has to be studied and analyzed before deployment. This study helps in deciding the minimum number of sensors that is needed to satisfy the application requirements of coverage. The second deployment method is random deployment. It is used in large scale applications which especially serve in remote and