Fig. 2From: Detection of an unknown radio transmitter using an enhanced K-nearest neighbor algorithm based on virtual reference point and RSSD informationProcess of the RSSD-VRKNN positioning system. Off-line phase: RSSD-based fingerprint database is established. On-line phase: when the URT enters the positioning area, real-time RSSD is obtained and matched with the RSSD in the databaseBack to article page