# Movable Platform-Based Topology Detection for a Geographic Routing Wireless Sensor Network
## 1 Introduction  
With the rapid development of WSN technologies and protocols, WSN has been applied to many scenarios, such as environmental monitoring, earthquake detection, indoor positioning and battlefield monitoring. Such a large-scale deployment and application of wireless sensors has inevitably attracted more attention on the monitoring, maintenance and efficiency evaluation of networks, especially for large-scale networks. Topology, as the working structure to observe WSN, is the most instinctive form in troubleshooting and is of great significance to WSN management and safety. Therefore, the recovery of WSN topology has become a hot research topic [1], in terms of both network management and non-cooperative network detection. However, the channel conflict and link instability between WSN nodes have posted a challenge to the network monitoring and diagnosis. Moreover, the topological relation among network nodes is always changing dynamically, or is established temporarily, due to limited computing capacity, memory and power of network nodes, as well as the lack of network system structure and protocol standards [2]. At present, WSN monitoring system [3] determines network topology mainly by tracking the transport path of data packets within the network. There are two types of monitoring systems: active monitoring systems and passivemonitoring systems. The active monitoring system acquires network operation information from sensor node installation and monitoring modules. Although its monitoring data are accurate and it requires no extra monitoring system, monitoring data packets occupies bandwidth, power and information transport capacity of the network itself, and lengthens the transport time delay of data packets. Passive monitoring systems require deploying WSN as the monitoring network outside the network and the network in need of monitoring is named as the target network. The monitoring network captures and analyzes the data packets of the target network without consuming any resource of the target network. Besides, failure of the target network will not affect the operation of the monitoring network. Since the WSN faces the application scenarios, and the network layer and application layer do not form a unified protocol or mainstream protocols, either the active monitoring system or passive detection system can be designed and developed only according to the specific network, which sets limits on the universality of the monitoring system to third-party networks. Moreover, the active detection system requires adding monitoring modules to each node, while the passive monitoring method requires designing and setting up an extra monitoring network of the same scale for the target network. Because of their complicated process and increased cost, both of the recovery methods cannot be applied on a large scale [4]. As described above, our paper brings forth a method to recover the topology of WSN based on a movable platform, which can recover the topology of a relatively large scale WSN by using location-based routing protocol efficiently. In the WSN using a location-based routing protocol, nodes select routing nodes according to the geological position of neighbor nodes, and the network topology is consistent with the selected node-routing. Hence, the cost parameters for the targeted network to select routing nodes are calculated according to the connection of part of the nodes, and then the topology of the whole network is calculated on the basis of cost parameters.