The key to realizing network security solutions based on location information is to obtain location information, which requires the help of positioning technology. "The application scenarios of physical fences are mostly indoors, so this article takes wireless sensor networks as an example to briefly describe the principles of indoor positioning technology.

　　In the wireless sensor network node location technology, sensor nodes are divided into beacon nodes and unknown nodes according to whether the node knows its own location. Beacon nodes account for a small proportion of network nodes and are reference points for unknown nodes to locate. Except for the beacon node, other sensor nodes are unknown nodes, and they calculate their own position according to a certain positioning algorithm through the position information of the beacon node.

　　According to whether the distance between actual nodes is measured in the positioning process, the positioning algorithm is divided into a distance-based (Range-based) positioning algorithm and a distance-independent (Range-free) positioning algorithm. The mainstream distance-based localization algorithms include maximum likelihood estimation method 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 a certain mathematical method to obtain its own position information.

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