RSSI of RF radio signals can be used to locate the position of a target device. There are two distinct approaches to achieve positioning using RSSI i.e, Map based and Model based. RF fingerprinting belongs to Map Based technique.
In Fingerprinting technique, the area of interest (building, home, hospital)is evenly divided in to a number of reference points. The target node whose location is to be determined, transmits uplink messages to the anchor nodes(Gateways) from these reference points. A minimum of 3 gateways are required to achieve good accuracy. Each gateway would receive the packet with different RSSI because distance to the reference point from each gateway would be different. And thus a table would be created that stores the RSSI values against reference points for each gateway. This is known in Offline phase and table is called a Map.
In online phase, the unknown target can be located anywhere inside the area of interest in real time using this look up table (map). Although it gives a rough estimation of position of the target node but people have used Machine learning techniques to achieve better results and accuracy(1-3m for zigbee). But the problem here is the time required to make fingerprinting, collecting RSSI at reference points.
Since 2nd generation gateways arent available yet (i guess),this could be an alternate to be used inside the buildings for location tracking applications.
Please share your thoughts.