Research On Node Localization Algorithm And Its Security In WSN

With the rapid development of wireless technology, wireless sensor networks can be widely used in various areas, such as, environmental monitoring, medical care, disaster prevention, inventory tracking, traffic monitoring, and military surveillance. A typical wireless sensor network is composed of nodes densely deployed in a field, which have a low-powered processor with a couple of onboard memory, a wireless transceiver, and some battery-powered sensors. Each sensor performs a sensing task for detecting specific events.There are some essential issues in wireless sensor networks, such as, localization, deployment, coverage, routing, location service, target tracking, and rescue. Localization is of the greatest importance among them because the location information is extremely useful for the others. Hence, it is the fundamental function to determine sensor nodes' own position and incident's location in wireless sensor networks. What's more, sensor node localization, as one of the supporting techniques, plays an extremely important role in wireless sensor networks. First, the node position information is required to make sure where the event happened; second, some system functions in WSN need to know where the node is; finally, quite a few wireless sensor network protocols have also made use of the node location information. As a result, with the continuous development of wireless sensor network, node localization technology has become a very challenging task, which will be applied in various requirements based on geographical position information.However, sensor node localization, as one of the supporting techniques, remains the most difficult challenge. Recently, the node localization problem has been a heavily researched topic, with many approaches proposed in the literature. However, since the problem of localization in WSNs is complicated, it is still difficult to deploy an existing localization solution practically and economically in application. When a specific WSN localization algorithm is designed, the thesis is according to the following principles:(1) Accurate. A location accuracy ranging from tens of centimeters to a couple of meters is of great importance for WSN (the required accuracy is application dependent).(2) Practical. WSN study has reached a critical point where real system evaluations are important. While theoretically interesting, schemes that have been evaluated only in simulations have little impact on the adoption of WSN technologies in the real world. (3) Inexpensive. The cost, represented by hardware cost and energy expenditure (both messages sent and time required for localization) can dramatically affect the suitability of a sensor network technology, to a particular problem. It is unrealistic to allow expensive hardware on cheap, unreliable devices.(4) Flexible. A localization system that is accurate, practical and inexpensive, but has strong assuptions, will have limited applicability. Our goal is to have a flexible, tailored to the deployment environment, localization scheme which ensures that each sensor node obtains its location information, with the highest accuracy possible.(5) Secure. Nodes in WSN are generally compromised and easy to be attacked. Sensor node localization, as one of the important supporting techniques, is much easier to be attacked, which will impact the whole network function. Therefore, it is extremely necessary to focus on the security problem on localization schemes.Taking into account the complex localization requirements in a realistic environment, according to the principles-accurate, practical, inexpensive, flexible, and secure, several localization solutions are proposed and evaluated. In light of the above principles, the contributions of the dissertation are the following:(1) RRDV-Hop:The defects of DV-Hop were analyzed, and then a new localization algorithm called RRDV-Hop was proposed, based on the regularly moving anchor node (RMAN) and RSSI assisting positioning, to improve the DV-Hop algorithm. The simulation results of the two algorithms were compared and analyzed respectively in the following respects, such as, average localization accuracy, cost and stability. Simulation results show that in the same network condition, compared with DV-Hop, RRDV-Hop achieves anchors' uniform distribution approximately, improves average positioning accuracy and keeps better stability in the randomly distributed network; meantime it also uses less anchor nodes, which reduces hardware cost of the network. Therefore, RRDV-Hop algorithm is much more competent in the randomly distributed wireless sensor networks.(2) LLA:We proposed a simple yet novel approach for mobile localization called LLA to mitigate the unavoidable TOA measurement errors, and evaluated its performance through prototype experiment. The algorithm was divided into three phases:(1) pre-ranging algorithm was proposed to initialize localization by employing TOA method; (2) refinement algorithm was designed to filter out bad nodes; (3) smallest circle covering algorithm was developed to deal with good nodes to complete the localization. Experimental results show that the presented approach efficiently eliminates the effects of the measurement bias and obtains a high accuracy of 2m, which can satisfy accuracy requirements for both outdoor and indoor localizations, as well as low complexity-the space complexity of LLA is O(n2) and the time complexity of LLA is O(n3), outperforming traditional trilateration. In other words, it is not at the expense of complexity to obtain higher precision for LLA, achieving the original design goals.(3) MASCL:Since LLA is not competent in indoor positioning system for such radioactive sources, a secure and cooperative approach called MASCL was proposed based on moving anchor nodes, adopting multi-robot cooperative location scheme. The new approach, developed from LLA, employed SWCAP protocol to ensure security and synchronization for pre-ranging, and refined the ranging results.(4) Application analysis for MASCL:The instance analysis for secure indoor localization system. Experimental results show that the localization error is mainly within 2m and the system security is ganranteed, achieving the original design goals.To sum up, all the above localization schemes have improved positioning accuracy, meantime reduced cost and complexity, taking into account security and flexibility, which obtains the original design goals.