The key to realize the network security solution based on location information is to obtain location information, which requires the help of location technology. "The application scenarios of physical fence are mostly indoor, so this paper takes wireless sensor network as an example to briefly describe the principle of indoor positioning technology.

　　In the node location technology of wireless sensor networks, sensor nodes are divided into beacon nodes and unknown nodes according to whether the node knows its own position. Beacon nodes account for a small proportion of network nodes, and are the reference points for unknown node positioning. In addition to beacon nodes, other sensor nodes are unknown nodes. They calculate their own positions according to certain positioning algorithms based on the location information of beacon nodes.

　　According to whether the distance between actual nodes is measured in the localization process, the localization algorithm is divided into range based localization algorithm and range free localization algorithm. The mainstream range based localization algorithms include maximum likelihood estimation and circular localization algorithm. Their principle is that the unknown node obtains the actual distance from the beacon node by measuring the received signal strength (RSS), and then uses certain mathematical methods to obtain its own location information.

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