In recent years, wireless sensor networks (WSNs) have become one of the most interesting fields for research and have been realized in more and more application environments. Due to the constraints on low-cost sensor nodes such as limited size, power, processing and communication capabilities, developing applications for WSNs has always been a challenging issue.
Localization is one of the most fundamental works for WSNs, since many important WSN applications such as tracking, geographic routing and addressing require localization as one of the basic functions. A typical way to realize localization on sensor nodes is using GPS equipments. However, GPS bundles are pricey and power-demanding, and hence are not suitable for WSNs consisting of a large number of sensor nodes. For this sake, a lot of localization techniques for WSNs have been investigated based on the utilization of mobile beacons. A mobile beacon can know its position by using GPS equipments or by programming, and hence can assist sensor nodes for position estimation during its moving. The movement of beacons can be carried out by humans, aircrafts or robots.
In this thesis, we propose two new localization techniques for WSNs based on the received signal strength ratio (RSSR) at sensor nodes with the aid of two mobile beacons moving on parallel lines (called RSSR-PL) or moving on orthogonal lines (called RSSR-OL). The proposed RSSR techniques are efficient in power and memory usage and do not need additional hardware deployment. Simulation results show that they can provide satisfactory localization performance under several representative environments.

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